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Important Information About Small Engine Flywheels

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A-1 Miller's Fully Computerized Stuska Water Brake Dynamometer (Engine Dyno) Service!

For performance testing engines up to 200hp at speeds up to 12,000 RPM. The only engine dyno service in Missouri for Kohler pulling engines! As soon as we have this dyno set up and fully operational in our shop, every competition pulling engine that we build will be dyno-tested, fine-tuned and adjusted on our Stuska water brake dynamometer with data logger before it leaves our shop to make sure it is producing maximum horsepower and torque, or customers can rent dyno time and make adjustments or changes to their engines and print-out the results. Proposed Engine Dyno Rental Fee: $50.00 per hour run time. No setup fee for Cub Cadet engines with a 3- or 6-pin/stud clutch driver. An adapter may need to be needed or fabricated for other makes and models of engines. As soon as this service is available, it will be posted here. - Brian Miller

First of all, the Kohler K-series K241 (10hp), K301 (12hp), K321 (14hp), K341 (16hp) flathead engines, and the K361 (18hp OHV single cylinder) engine flywheels will all interchange, because the tapers and keyway widths are the same. The only difference is the type of starter and ignition system used. Some engines with a rope starter have magneto ignition and a 9-1/2" flywheel with no ring gear; other engines with a starter/generator and battery ignition, use either a 8" or 9-1/2" flywheel with no gear ring; some early engines with magneto ignition have a 9-1/2" flywheel with no ring gear; while most later K-series engines have battery ignition, and a 9-1/2" ring gear flywheel with internal magnets for an alternator charging system. Also, all Kohler Magnum 10-16hp single cylinder flathead engines use the same flywheel. The Kohler KT-series twin cylinder flathead engine models KT17, KT17II, KT19, KT19II and KT21 (which is a snowmobile engine) use the same flywheel. And the Kohler Magnum twin cylinder flathead engine models M18 and M20 use the same flywheel.

Four types of flywheels were used on the 10hp-16hp K-series Kohler engines. They are as follows:

  1. From 1960 to 1973, many of the 10hp and 12hp engines came with an 8" diameter flywheel. The engine had battery-powered ignition, and a starter/generator provided the cranking source to start the engine and then it produced the power source to recharge the battery and power any electrical accessories. These were popular with the narrow- and wide-frame (with solid-mounted engine) IH Cub Cadets.
  2. Very few of the early 10hp and 12hp engines came with a 9-1/2" diameter flywheel with an unmachined edge for a starter ring gear, and there's no way to install a ring gear. These engines had a magneto ignition system. There's two magnets attached to inside the flywheel, the ignition coil is fastened on a stator to the bearing plate and a rope was used on a large notched pulley that's attached to the flywheel to crank the engine. There is no battery and no charging system involved. These were used on self-contained, stand-alone engine units, such as truck-mounted air compressors, generator/welders, water pumps, etc., and they were popular with the U.S. Military because there was no recoil starter and very few ignition parts to give trouble. Certain ignition coils are no longer available from Kohler for these engines.
  3. Another 9-1/2" diameter flywheel with an unmachined edge for a starter ring gear was also used on very few of the early 10hp and 12hp engines. There's no magnets inside the flywheel and no [magneto] stator. The engine had battery-powered ignition, and a starter/generator provided the cranking source to start the engine and then it produced the power source to recharge the battery and power any electrical accessories. These are popular with certain models of Case garden tractors.
  4. In 1974, the 10hp through 16hp engines came with a 9-1/2" diameter flywheel with a machined edge for a starter ring gear and a ring of magnets on the inside. The engine had battery-powered ignition, and a small, gear type starter motor cranks the engine to start it and an alternator charging system produced the power source to recharge the battery and power any electrical accessories. These were popular with the wide-frame "Quiet Line" IH-built Cub Cadets and certain spread-frame MTD-built Cub Cadets.

And the K-series and Magnum flywheels have the same overall dimensions. The only difference is, the K-series flywheel has integrated fins (fan blades) and the Magnum flywheel use a bolt-on plastic fan blade unit, and it has an integrated magnet for the solid state ignition. The starter ring gear will also interchange between the two flywheels. As a matter of fact, the same ring gear fits the 10-16hp K-series and Magnum single cylinder engines, and the KT-series and Magnum twin cylinder engines.

FYI - A cast flywheel with a broken fin (fan blade) will run out of balance. To put it back in balance, simply break off the fin (fan blade) directly across from the broken one with a hammer. Try to make sure that one broken fin (fan blade) matches the height of the other to maintain the balance. The flywheel will still be safe to use, and the remaining intact fins will produce plenty of fresh air to adequately cool the engine.

The Safe and Correct Way to Remove a Small Engine Flywheel -

To remove the flywheel from a Kohler (or virtually any) small engine, remember, the retaining nut or bolt have right-hand threads. Remove the flywheel with a quality-made automotive harmonic balancer/vibration damper puller tool (Lisle Corporation makes a quality puller) that have fine threads and with a quality-made 1/2" impact wrench (with a large capacity [minimum 30 gallon] air compressor reservoir tank) to literally "pop" the flywheel off the crankshaft taper. Be sure the puller bolt is centered on the crankshaft, too. Avoid using an low-quality imported puller because it might move sideways when under pressure and break off the stud or bend the bolt. Use the protective cap that's supplied with the puller to prevent from damaging the threads on the end of the crankshaft. Apply grease or motor oil on the threads of the center threaded shaft to increase the pulling torque. The puller tool requires either two 5/16" or two 3/8" diameter grade 8 coarse thread bolts with a thick flat washer under each bolt head so the head won't pull through the puller's slots. And use bolts that's long enough so the threads can penetrate the entire length of the threaded holes in the flywheel to prevent the threads from being pulled out. Use a tap to clean the threads in the flywheel if necessary. And although some flywheels are stubborn to remove, just remember, it'll eventually come off. It's not made on the crankshaft!

Personally, I use a quality-made 1/2" impact wrench running off of 150 psi of pressure with a 60 gallon air compressor tank and a Lisle harmonic balancer puller with grade 8 bolts w/flat washers threaded deep into the flywheel threads to remove Kohler flywheels. I ain't never had one that was so stubborn it took a lot of effort to remove. My set up pops them off every time with very little effort! You can hear the air wrench when it gets under a severe strain, it starts to slow down and then POW, the flywheel pops loose.

On most aluminum block engines, such as Briggs & Stratton, Tecumseh, etc., a flywheel knock-off tool can be used to remove the flywheel. You can get a knock-off tool at virtually any place that sells small engine parts, and they come in 4 different sizes: 1/2" hole for older B&S engines, 7/16-20 UNF, 1/2-20 UNF and 5/8-18 UNF.

To use the knock-off tool, for an older B&S engine with the crankshaft that has a long unthreaded shaft that protrudes into the starter clutch, the tool is placed on the end of the shaft, and for all other engines with a threaded stud on the end of the crankshaft, the tool is threaded onto the stud. A crowbar or prybar is wedged under the flywheel against the engine block to provide extra leverage (and to prevent breaking the rod journal on the crankshaft if it's cast iron or bending the crankshaft if it's steel), then a 2-3 lb. hammer is used to sharply strike the tool perpendicular to literally "pop" the flywheel free from the crankshaft taper. To prevent from damaging the threads in the tool and on the crankshaft stud, always thread the tool all the way on the stud, and then back it off 1/2 turn. And don't strike the knock-off tool at an angle, or the stud on the crankshaft could get bent or break off!

But on flywheels with no threaded holes to use the automotive harmonic balancer/vibration damper puller tool, a knock-off tool of the correct thread size with a pry bar wedged under the flywheel and a 2-3 lb. hammer can be used to remove the flywheel. Be sure to strike the tool perpendicular, too!

IMPORTANT! The Incorrect and Dangerous Way To Remove A Small Engine Flywheel -

Most Kohler crankshafts are made of somewhat brittle cast iron material. So NEVER hit or strike the end of the crankshaft with a big hammer to remove a flywheel! And DO NOT attempt to use a wrecking bar (crowbar) to "pry" the flywheel off the crankshaft! Also, never use a large [2 or 3 jaw] outside gear puller to remove a flywheel. Doing any of these could break or crack the crankshaft and/or possibly crack the flywheel or break it in half. AND DEFINITELY DO NOT USE A KNOCK-OFF TOOL WITH A BIG HAMMER ON A KOHLER CRANKSHAFT WITH THE 5/8" STUD TO REMOVE THE FLYWHEEL! Being the crank is made entirely of cast iron, the stub will likely to break off!

A true story: One of my customers brought his walk-behind rotary lawn mower with a 3.5hp Tecumseh engine (model LAV35) to me just to have the flywheel removed. When I had the mower on my work table to remove the flywheel, I noticed that the flywheel was wobbly but still tight on the crankshaft, then I found the crankshaft was broken in two at the connecting rod journal. I thought this was odd , so I called my customer to tell him about this, and he said his neighbor tried to "pop" the flywheel off [by hitting the threaded end of the crankshaft] with the mower on the ground standing with a 10 lb. sledge hammer!

About Crankshafts Breaking at High RPM -

A stock crankshaft should be fine as long as the engine isn't over-revved for a long period of time, which could cause it to go into harmonic vibrations, which would cause it to break in two. But if precision spin-balanced, a cast or billet steel crankshaft should survive as high as 7,000 RPM for a long time if they've been precision-balanced to the connecting rod and piston assembly. Some cast cranks break, and steel crankshafts are prone to breaking, too. When they do break, it's usually due to: being in an engine that broke the connecting rod and the rotating assembly came to a "sudden stop", and the flywheel kept wanting to spin, but cracked the crank instead; an out of balance flywheel (even CNC-machined steel flywheels should be precision spin-balanced, too); and/or an out of balance starter pulley on the PTO end (which should also be precision-balanced). An out of balanced flywheel or pulley will cause the crankshaft to flex a few thousands of an inch at high RPM. When they flex, this causes metal fatigue, which creates a microscopic crack next to the rod journal, and they eventually break. Kind of like bending a piece of wire back and forth by hand, until it eventually breaks. I heard that the Magnum crankshafts are tougher than the old K-series cranks when precision-balanced. And when a crankshaft breaks at high RPM, it can also break a cast cam or bend a billet steel cam, which could crack the engine block at the cam pin on the flywheel side.

Always Use a Steel Flywheel on a Pulling Tractor Engine That Turns Above 4,000 RPMs!

The smaller (8") steel flywheels requires that a billet pulley be installed on the PTO end of the crankshaft and a starter cart w/V-belt be used to crank the engine to start it. (Which can be a major inconvenience if you have no assistance.) And the bigger (9") steel flywheels will accept a ring gear and can be used with a gear starter fastened on the side of the engine block. (Which I think is much more convenient.) Also, the heavier (31 lb.) 9" flywheel is more suitable for stock engines that turn around 4,000 RPMs, and the lighter (19 lb.) 9" steel flywheel is ideal for engines that run at wide open throttle.

Most of the time a heavier-than-stock, custom-made, machined steel flywheel will add more "grunt" or more torque to an engine when pulling. In our experience, a light-weight flywheel will cause an engine to lose power toward the end of a pull. Light-weight flywheels are actually made for high speed racing applications, such as for drag racing or race cars. A lightweight flywheel works great for circle track racing because they allow the engine to accelerate quicker and regain the RPM after coming out of the turns. A heavy flywheel will "bog" an engine down and make it sluggish upon acceleration.

Pulling tractors on the other hand need ground speed (momentum) to do well in a pull, with the use of a heavier-than-stock flywheel. Once a heavy flywheel is spinning, it's hard to stop it or slow it down. A heavy flywheel may somewhat cause a [stock] engine to rev up slower, but once it's revved up, and because of the greater momentum force or increase of weight in the rotating mass, it'll "hold" the RPM longer, allowing a tractor to pull the sled right out the gate.

Remember, there's only two things to be gained by using a heavy steel flywheel; 1: the safety of steel versus cast iron, and 2: the increase in rotating mass with use of a heavier-than-stock flywheel. This means that a heavy flywheel will help an engine to produce more torque at higher RPM, which is very important for a pulling engine. A heavy flywheel (heavier-than-stock) will, without a doubt, will add more lugging power to an engine. That's why they're used on the large farm tractors. By the way - the average 9-1/2" diameter OEM (Original Equipment Manufacturer) cast iron flywheel for the single cylinder 10-16hp Kohler K-series engines with the starter ring gear and full integrated fins (fan blades) weighs 23-24 lbs.

By the way - covering a shiny (new) billet steel flywheel with clear gloss enamel acrylic coating will help identify it visually as made of steel. Otherwise, if it's covered with colored paint, it'll be somewhat difficult to tell right away rather if it's a factory cast iron or steel flywheel. The enamel coating will also help protect the steel flywheel from rusting over time. (I think a nicely painted pulling engine looks good with a shiny [clear coated] steel flywheel.) Actually, the best way to determine if an engine has either a cast iron or steel flywheel (if they look the same) is to tap it with a small hammer or wrench. Cast iron will make a "clunk" sound, and steel will have a high pitch ring to it.

Here's the dimensions if you want to fabricate a 9-1/2" diameter steel flywheel for the 10-18hp single cylinder Kohler engine:

If the above dimensions are somewhat confusing, then perhaps it's best to acquire a Kohler flywheel and take the measurements off of it.

By the way - the flywheel for the 10, 12, 14, 16hp flatheads and the 18hp OHV single cylinder Kohler K-series and Magnum engines will interchange. They all have the same taper in the center, and most of them have two or four tapped holes for accessories, and for using an automotive harmonic balancer/vibration damper puller tool to remove the flywheel from the crankshaft.

And adding a heavy pulley on the PTO end of the crankshaft would help add torque to the engine at high RPM. But if/when the engine bogs down upon launch at the starting line or several feet from the starting line, it may be hard to get it to rev back up due to the extra spinning weight. So you gain one thing, but may lose another.


Before installing the flywheel on a crankshaft, always use a clean cloth (white in color, to see the dirt) to remove any dirt, oil or debris from the crankshaft taper and most importantly, inside the flywheel taper. Use cleaning solvent (paint thinner) or brake cleaner because these leave no oily residue when they dry. And use emery cloth to remove any light rust. Clean both tapers thoroughly. This is very important because there must be direct metal-to-metal contact between the two tapers for a secure bonding of the parts. Because the flywheel must keep up with the rapid acceleration (or driving force) of the piston via the crankshaft. Do not use anti-seize for easy removal of the flywheel later! With a heavier steel flywheel (20 lb. and heavier) high strength liquid threadlocker (Red Loctite, Permatex or equivalent) should be applied inside the flywheel taper or on the crankshaft taper to prevent the flywheel from slipping on the crankshaft. Thorough cleaning of the tapers should still be performed even with the use of the threadlocker. If the threadlocker is used, an acetylene torch will be required to soften the threadlocker in order to remove the flywheel. If the flywheel needs to be removed later, use a quality gear puller and an air impact wrench or some muscle. Any oil, dirt or debris trapped in the tapers, or even anti-seize, will, without a doubt, allow the flywheel to slip or rock back and forth on the crankshaft, in which will shear the key, wallow out both keyways and possibly crack or break the flywheel and/or crankshaft. Dirt/oil on the tapers is the main reason why most custom-made billet steel high-performance crankshafts break. And if the flywheel use a Cub Cadet or billet aluminum clutch hub adapter, be sure to install the [1-3/8" o.d.] thick flat washer under the retaining nut or bolt and then torque the nut or bolt to the proper specs.

NOTE: As long as the rotating clutch components are trued-up in a metal lathe to minimize vibrations, and the wide, thick washer is used inside the hub to secure the hub to the flywheel, and the flywheel retaining nut or bolt properly torqued, the OEM (Original Equipment Manufacturer) cast aluminum clutch hub have been proven to hold up to a wide open throttle pulling engine.

Torquing the Flywheel Nut or Bolt - Top of Page

Personally, I use an air impact wrench to lightly snug the flywheel nut or bolt against the flywheel, then I finish torquing it with a torque wrench. The flywheel won't rotate with an air wrench either.

But if an air wrench isn't available, and if the flywheel has a starter ring gear, clamp Vise Grips on the edge of the ring gear, allow it to bump against the bolt boss on the bearing plate and then the flywheel nut or bolt can be torqued to specs. But if the flywheel doesn't have a ring gear, clamp the Vise Grips on the PTO end of the crankshaft, install a long bolt in one of the bolt holes on the PTO side of the block, and allow the Vise Grips to bump against the bolt to torque the flywheel nut or bolt.

With the tapers clean, and when the flywheel nut or bolt is tightened or torqued to specs, the "squeezing" action of the flywheel taper actually "grips" it to the crankshaft, guaranteeing positive metal to metal contact, with no slip whatsoever. Torque the 15/16" nut at 65 ft. lb., and the 3/8" bolt at 40 ft. lb., but do not overtorque it! (As with an air impact wrench.) And Kohler's flywheel [castle] nut is self tightening. Therefore, a lock washer isn't necessary. But sometimes the nut will wear and tend to loosen over time. When this happens, the flywheel could loosen, and the keyway in both the flywheel and crankshaft will become damaged beyond repair. Therefore, a new all metal self locking nut is required for a professional repair. But use a split lock washer on the bolt. And use a grade 8 bolt, nothing less.

IMPORTANT! A cast iron flywheel with a crack in it, even a small crack, should never be used on any engine!

Oil, grease, dirt on the crankshaft and/or flywheel tapers or even an overtorqued nut or bolt could cause the center in a cast iron flywheel to crack in the keyway or the threaded stud of the crankshaft to break off. Cast iron flywheels always crack at the weakest point, which is at the keyway. If the crack is welded, and when the flywheel is installed on the crankshaft, and the nut or bolt is torqued to specs, the taper would still split next to the weld. But steel flywheels don't crack (or break).

A crack in a flywheel will cause an engine to vibrate severely, plus it'll be noisy. (It'll make a "clunk, clunk" sound at idle.) The crack will get worse over time, causing the flywheel to split in half at high RPM. If this happens, the two halves could cause severe bodily injury or possibly death if they were to become airborne and strike an innocent bystander.

The only valuable part on a cast iron flywheel with a crack in the keyway would be the starter ring gear. It can be installed on a [good] cast flywheel or a steel flywheel. Cast iron flywheels that's in good condition works great up to 4,000 RPM. (The factory setting of maximum RPM for virtually all small gas engines, including all of Kohler engines is 3,600.) Above 4,000 RPM, a steel flywheel is highly recommended for safety.

To minimize damage to the keyways, do not use a steel flywheel key. A heat-treated hardened key would be even a worse thing to use. An soft aluminum (4041 hardness) key works best. To keep a keyway in a cast flywheel from splitting, it's best to use soft aluminum key. The reason for this is if the connecting rod breaks resulting in instant crankshaft lockup, the soft key will prevent damage to the flywheel and crankshaft. The aluminum key will shear in two, allowing the flywheel to slip on the crankshaft, preventing damage to either the flywheel or crankshaft. A steel key will cause a cast iron flywheel to crack or break, or if a flywheel loosens on the crankshaft, it'll wallow out the keyways. But if an aluminum V-belt starter pulley with ignition timing degree marks is installed on the PTO end of the crankshaft, there's really no need to install a flywheel key. The only reason most small engines use a flywheel key is to time the ignition, and not to prevent the flywheel from slipping on the crankshaft.

Removing the Majority of the Integrated Fins (Fan Blades) from the Flywheel to Reduce Drag on Engine and Boost Horsepower -

One sure way to increase the power output of a 4,000 RPM stock pulling engine is to reduce the amount of [air] drag that the flywheel fins (fan blades) cause. To do this, the majority (about 3/4) of the fins (fan blades) will need to be removed from the flywheel. For competition pulling, the flywheel will still provide plenty of fresh air to sufficiently cool the engine. This shouldn't be done for an engine that's used for general yard work because the engine could run hotter than normal, causing premature wear.

And due to the cast iron material, this shouldn't be done on an engine that runs at higher RPM or at wide open throttle. The flywheel could explode, causing serious injury or possible death to a bystander.

How to Remove the Integrated Fins (Fan Blades) -

A 14" chop saw, like the one that most automotive muffler shops use, can be used to remove the majority of the fins (fan blades) from the flywheel. To cut the flywheel fins (fan blades) off with a chop saw...

  1. First of all, wear eye protection or safety glasses and a dust and particle mask or surgical face mask to keep from breathing in the cast iron and cutting wheel dust particles. (If you don't wear a mask, you may wish you did.)
  2. Position the flywheel in alignment with the cutting wheel, firmly hold the flywheel with one hand and carefully bring the cutting wheel down even with the outside taper in the flywheel. Cut a few fins (fan blades), then rotate the flywheel, and keep doing this until all the fins (fan blades) are removed. Try to keep all the fins (fan blades) even and in alignment, too.
  3. Now chuck the flywheel in a large metal lathe to true up the fan blades so they'll all be the same height. (This requires less effort to rebalance.) If one has access to a large CNC machine, this would work better, the blades would all be the same height and the cutting process would be much safer.
  4. To spin-balance the flywheel, a 1-1/2" diameter x approximately 24 mild steel rod machined with a precision-machined taper to match the angle of the taper in the flywheel, and a threaded bolt hole in the end to retain the flywheel will need to be fabricated for chucking the flywheel in the metal lathe. This shaft is also used to spin-balance the flywheel afterwards.

Then without a doubt (and using common sense), any flywheel with the majority of the fan blades removed should definitely be dynamically precision spin-balanced using an automotive crankshaft/flywheel balancing machine. The same machine for balancing the crankshaft to the connecting rod/piston assembly can be used to balance flywheels, too. The flywheel should be balanced to within 1/10th of an ounce (0.1 lb.) or 1 gram. For an example of how much 1/10th of an ounce is, a dime (10¢) weighs exactly 1/10th of an ounce (or 2 grams).

NEVER use an automotive tire bubble balancer to balance a flywheel! Also, make sure the flywheel has all the internal magnets intact (for the charging system) or remove the magnets altogether if using no charging system. And do not spin a cast flywheel (on the engine) no faster than 4,000 RPM! Or better yet, install a billet steel flywheel and an electric fan to cool the engine.

Below are the results of a cast iron Kohler flywheel with a crack in the keyway and/or when spun well above 4,000 RPM (wide open throttle) Ê

The photos below are the results of a 9-1/2" diameter cast iron Kohler flywheel when it was spun at wide open throttle in a garden pulling tractor. This was a very serious accident that could have been a life-threatening tragedy. Remember: a well-constructed and precision-balanced steel flywheel is cheap compared to hospital bills, rehabilitation or funeral costs and not to mention the seemingly never-ending lawsuits!

The guy (name withheld) had just recently bought the Pro Stock motor. He already had the clutch setup on the flathead kohler twin he was running. According to what a friend of his told me (that also has a Pro tractor) the guy called him and asked would it be ok just to start the motor so he could hear it run. He was told not to turn it over 3,000 RPM. There is no question the guy knew he needed a steel flywheel and safety shields on the tractor before pulling it. I am confident those measures would have been on it before he pulled it the first time. There "was" someone standing by the tractor - the guy that owns it. He was working the throttle standing right in-line with the cast iron flywheel. You can see what it did to the air filter. Apparently it hit the carburetor and filter on its way to hitting him. It wasn't his leg that got the brunt of the piece of flywheel!

He just got too eager to find out what he had purchased and made a bad decision. It's an injury that will be with him the rest of his life. The point of putting these pictures on this site is so other pullers would not make the same mistake. I'm confident he is embarrassed by his actions...but he didn't have to share those pictures, ya know. I admire him for sharing these photos, and he's still suffering from the accident. - Story by Ron Ethridge

Also, check out this video: Farmall 1206 Breaks in Half when flywheel Explodes - YouTube (

IMPORTANT! It's highly recommended that all flywheels, despite the material it's made of, be dynamically spin-balanced on a precision balancing machine. The same machine to balance a crankshaft can be used to balance a flywheel, too. And never use an automotive tire "bubble balancer" to balance a flywheel! They are NOT precision!
Various High Quality Small Gas Engine Tachometers -
  • Veethree 0-4000 RPM Back-lit Panel Mount Tachometer. This analog tachometer is made to be dash-mounted in a garden tractor.
  • Tachometer Proximity Sensor. This digital tachometer setup is also made to be dash-mounted in a garden tractor. It works like much like crank trigger ignition, with a single steel detector screw in a rotating disc on the crankshaft.
  • Strandix Wireless Tachometer. This handheld analog non-contact tachometer works great for checking/setting the RPM on various small engines in the shop, and/or for checking/setting the RPM [tech] on stock governored engines at pulling events.
  • Dawson Tools DAM110B. This handheld digital non-contact tachometer also works great for checking/setting the RPM on various small engines in the shop, and/or for checking/setting the RPM [tech] on stock governored engines at pulling events.

Shielding of the Flywheel is Important!

I remember years ago, I was reading a club's rules, and it stated that all tractors must have a steel flywheel, and it must be shielded 360º with minimum 1/4" thick steel. I asked one of the pullers of the club, "why shield a steel flywheel? It's not going to break." And he told me: "There's a possibility that the end of the crankshaft could break off."

Actually, it's not rare that this kind of thing happens. It's happened to various pullers. The end of a crankshaft, despite if it's steel or cast iron, can break off next to the flywheel. It's a slight possibility. But then again, it could happen. Like the old saying goes: "A bad apple will spoil the bunch." And remember Murphy's Law? Must be prepared for the unexpected. So need to shield them flywheels folks, before a catastrophe happens.

If you need any of the parts or services listed below Ê, please contact A-1 Miller's Performance Enterprises | 1501 W. Old Plank Rd. | Columbia, MO 65203-9136 USA | Phone: 1-573-256-0313 (shop) | 1-573-881-7229 (cell). Please call Monday-Friday (except Holidays), 9am to 5pm, Central time zone. If no answer, please try again later. (When speaking with Brian, please be patient because I stutter.) A-1 Miller's shop is open to the public from 9am to 5pm, including weekends (except Holidays). Please call before coming so I'll be here waiting for your arrival. Fax: 1-573-449-7347. E-mail: Directions to our shop | 1501 West Old Plank Road, Columbia, MO - Google Maps or Map of 1501 West Old Plank Road, Columbia, MO by MapQuest. NOTE: To place an order, please call either number above or send an email with a list and description of the parts or services you need. Because as of right now, my websites are not set up to accept orders online.
Used 9-1/2" diameter genuine OEM cast iron Kohler K-series flywheel for 10hp-16hp K-series flathead and 18hp OHV engines. These flywheels are for battery ignition only, not magneto ignition. They're in excellent condition and unaltered. No crack in the keyway, no broken or missing fan blades and no cracked or missing internal magnets for charging system (if used for yard use). These flywheels are for stock tractors only; not to be turned above 4,000 RPM!
  • Flywheel with ring gear and internal charging magnets. $125.00 each, plus shipping and handling.
  • Flywheel without ring gear (install your own ring gear) and with or without internal charging magnets. $85.00 each, plus shipping and handling.
  • Flywheel without ring gear (install your own ring gear) and majority of fan blades removed and precision balanced and with or without internal charging magnets. $115.00 each, plus shipping and handling. (Click on picture to the right for a larger view.)
  • Flywheel with ring gear and majority of fan blades removed and precision balanced and with or without internal charging magnets. $135.00 each, plus shipping and handling. (Click picture below for a larger view.)
  • Used ring gear. $25.00 each, plus shipping & handling.
  • Your flywheel - remove majority of fan blades and precision rebalance. $85.00 labor, return shipping extra. Includes cutting most of the integrated fan blades off, chuck it in our lathe to true up the fan blades so they're all even and then balancing it.
Reconditioned OEM Kohler Crankshafts - [When available.]

Available for Kohler engine models K241/M10 (10hp), K301/M12 (12hp), K321/M14 (14hp), K341/M16 (16hp) or K361 (18hp OHV). These cast iron cranks are genuine Kohler, used and in excellent condition. They have either a 1" or 1-1/8" diameter x 3-1/2 PTO shaft w/1/4" wide keyway. They have good gear teeth and may have a worn or unworn connecting rod journal in either STD size or undersize. Which can be reground to .010", .020" or .030" undersize. Although .030" is rare, it's still very safe to use. FYI - To be honest, these are old, used crankshafts. So if you need one with an unworn STD size rod journal, you'll probably have a better chance of winning the lottery than finding a used Kohler K-series or Magnum single cylinder crankshaft with an unworn STD size journal. And if you're going to use a pulley, clutch, etc., on the PTO end, then I will need to know the exact dimensions of the PTO end on your crankshaft so I can match it to one that I may have in stock. For accuracy, measure the length from the oil seal shoulder out. If you have the engine's original model and specification numbers, go to (requires Internet Explorer), to find the correct part number for the crankshaft, then find the dimensions and specifications of the crankshaft is here: CRANKSHAFT REFERENCE MANUAL. (Requires Adobe Acrobat Reader and use Google Chrome web browser for a faster download of web sites with large files.) Shipping weight: 12 lbs.

  • K241/M10 (10hp) $100.00 each, plus shipping & handling. (When available.)
  • K301/M12 (12hp) $125.00 each, plus shipping & handling. (When available.)
  • K321/M14 (14hp), K341/M16 (16hp) and K361 (18hp OHV) $150.00 each, plus shipping & handling. (When available.)
  • NOTE: Once installed and in use, there is no warranty or guarantee of any kind on any crankshaft purchase!
Precision, Dynamic Flywheel and Crankshaft Spin-Balancing Service. To balance the rotating assembly, the crankshaft, piston/rings, pin, clips, connecting rod and bearing inserts (if applicable) are all required. The flywheel is balanced separately.
  • Balance (cast or steel) flywheel for Kohler 10-16hp cast iron block engine. $60.00 labor, plus return shipping & handling.
  • Balance flywheel for other make and model of engine. I will need to make a spindle with a tapered end/bolt hole to match the taper in the flywheel to spin the flywheel. $85.00 labor, plus return shipping & handling.
  • Balance single cylinder cast OEM Kohler crankshaft. $150.00 for welded weight plate and labor, plus return shipping & handling.
  • NOTE: Usually, a steel plate (of various thicknesses) is welded on the side of one of the counterweights of the crankshaft to balance it. But on various non-OEM cast Kohler crankshafts where there's no room for the plate, holes would need to be drilled crossways through the counterweights, and plugs of tungsten steel will need to be welded in the holes. To do this, the price will be around $400.00 each, plus return shipping & handling.

IMPORTANT - When sending your flywheel and/or rotating assembly to me for balancing, package everything securely so the items won't get damaged in shipping and please include a note in the box with your name, mailing address, phone number (in case I have any questions) and a description of what you want done. When shipping heavy parts, it's best to put a slightly smaller box inside a larger box, to double the strength and integrity of the package. Because some "gorillas" that work for certain delivery services don't care. And when the work is completed, I'll either call or email you an invoice with the total including shipping & handling.

  • Regrind Crankshaft Journal - $50.00 per journal. On a twin cylinder crankshaft, $100.00 total, plus return shipping & handling. Note: The 10hp-16hp and the 18hp OHV single cylinder Kohler crankshafts can be ground as far as .030" and still be safe to use with a matching undersized bearing insert installed in the rod. And all crankshafts, rather if they're automotive or small engine, are checked for straightness before grinding. If they're bent or twisted, sometimes they can be straightened.
  • On the 7hp and 8hp Kohler and other makes of engines, if the crankshaft is worn beyond .010" and needs to be reground again, the journal can be reground to .020" and then the connecting rod can be resized so it'll fit the smaller undersize journal. I do this sometimes on engines when a .020" undersize rod isn't available. This hurts nothing and it lasts as long as an ordinary STD rod and crank journal. Price for doing this is $75.00, plus return shipping & handling. I will need your crankshaft and connecting rod.
  • Repair a broken off stud in crankshaft on flywheel end: $20.00. I drill and cut threads for a hardened 3/8" or 5/8" diameter bolt in the end of the crankshaft to secure the flywheel. And a steel bolt is much stronger than a cast iron stud. Because cast iron is brittle and steel is flexible.
  • Drill and cut 7/16-30 UNF threads in the PTO end of the crankshaft for a retaining washer and bolt. $20.00.
Flywheel Retaining NutAll-Metal Self-Locking Flywheel Retaining Nuts for threaded stud on end of of early K-series and all steel crankshafts. Each torque at 65 ft. lbs. IMPORTANT: For proper torque, apply thin coat of oil on threads of crankshaft before installing nut.
  • For 5/8" diameter stud (5/8-18 UNF). $1.50 each, plus shipping & handling.
  • For 3/4" diameter stud (3/4-16 UNF). $1.75 each, plus shipping & handling.
Flywheel retaining bolts for threaded hole in end of later K-series and all Magnum crankshafts. Each are grade 8, 1-1/2. IMPORTANT: For proper torque, apply thin coat of oil on threads of bolt or inside hole before installing.
  • 3/8" diameter, fine thread (3/8-24 UNF). (Torque at 40 ft. lb.) .50¢ each, plus shipping & handling.
  • 5/8" diameter, fine thread (5/8-16 UNF). (Torque at 65 ft. lb.) $1.00 each, plus shipping & handling.
Steel Rectangular Flywheel Key for early Kohler K-series engine models K241, K301, K321 with the 8" diameter flywheel. Dimensions: 3/16" wide x 1/4" tall x 1-3/8 length. OEM Kohler part # X-366-1-S.
  • Used. $1.00 each, plus shipping & handling. (When available.)
  • New. $2.50 each, plus shipping & handling.

Aluminum Rectangular Flywheel Key for Kohler K-series engine models K141, K160, K161, K181, K241, K301, K321, K341, K361 and Magnum M8. Made of 6061 alloy; medium-grade hardness aluminum. Dimensions: 3/16" square x 1-3/8" length. Replaces Kohler part # X-366-1-S.

  • $5.00 each, plus shipping & handling.

Steel Square Flywheel Key for Kohler K-series engine models K141, K160, K161, K181, K241, K301, K321, K341, K361 and Magnum M8. Dimensions: 3/16" square x 1-3/8 length.

  • High quality aftermarket. $1.00 each, plus shipping & handling.
  • OEM Kohler part # X-286-17-S. $1.70 each, plus shipping & handling.

Aluminum Square Flywheel Key for Kohler K-series engine models K141, K160, K161, K181, K241, K301, K321, K341, K361 and Magnum M8. Made of 6061 alloy; medium-grade hardness aluminum. Dimensions: 3/16" square x 1-3/8 length. Replaces Kohler part # X-286-17-S.

  • $5.00 each, plus shipping & handling.

Steel Woodruff Flywheel Key for early Kohler engine models K160, K161, K181 and later 10-16hp K-series and all Magnum engines. 3/16" wide x 1.

  • High quality aftermarket. $1.00 each, plus shipping & handling.
  • OEM Kohler part # X-46-3-S. $1.85 each, plus shipping & handling.
Flat washer for retaining flywheel or aluminum clutch hub to flywheelFlywheel / Aluminum Hub Retaining Washers. A thick, wide washer is a must to secure flywheel and prevent clutch/driveshaft aluminum hub adapter breakage! Each made of steel and measures 1-1/4" o.d. x approximately 1/4" thick.
  • Washer w/13/32" hole. Must be used with aluminum hub that has a 3/8" hole.
    • A-1 Miller part. $3.00 each, plus shipping & handling.
    • OEM Kohler part # 12 468 03-S. $3.40 each, plus shipping & handling.
  • Washer w/5/8" hole. To be used with aluminum hub that has a 5/8" hole. A-1 Miller part. (Discontinued from Kohler.) Replaces Kohler part # X-25-104. $3.50 each, plus shipping & handling.
  • Washer w/3/4" hole. To be used with aluminum hub that has a 3/4" hole. A-1 Miller part. (Discontinued from Kohler.) Replaces Kohler part # X-25-71. $3.50 each, plus shipping & handling.
Steel Adapter Step-Washer for installing Cub Cadet cast aluminum clutch hub with 5/8" center hole to Kohler Magnum crankshaft with a 3/8" bolt. A must to center hub and prevent hub breakage! NOTE: As long as the rotating clutch components are trued-up in a metal lathe to minimize vibrations, and the wide, thick washer is used inside the hub to secure the hub to the flywheel, and the flywheel retaining nut or bolt properly torqued, the OEM cast aluminum clutch hub is capable of holding up to a wide open throttle pulling engine.
  • $12.00 each, plus shipping & handling.
1/4" Steel Dowel Pin for aluminum clutch hub. 3/4. Secures above hub to flywheel to prevent slippage.
  • $1.00 each, plus shipping.

Cooling the Engine with an Electric Fan -

Using a steel flywheel with no fan blades will, without a doubt, allow any engine to operate at a much higher temperature. If you're burning methanol fuel and full synthetic motor oil, they'll help keep the engine somewhat cool, but the engine will still run hot from lack of a cooling system. Excessive heat will cause an engine to lose power and eventually "wear out." Therefore, installing an electric fan to cool the engine, especially between pull-offs, wouldn't be a bad idea. Pulling tractors that have a smaller engine (8hp or 10hp) usually don't go very fast down the track will really benefit from an electric cooling fan. Acquire a quality fan that can handle a lot of vibration, and mount it securely!

The most popular durable and compact cooling fans that works great for a single- or twin-cylinder pulling engine is the Attwood Turbo Blower (model 3000; 3" or 4000; 4"), Rule In-Line Blower (model 240) or In Line Bilge Blower. These fans can be securely mounted on the [Cub Cadet] clutch cover or between the grille and PTO end of the engine and aimed toward the exhaust area of the engine, because that's the hottest part of any engine. Also, the fan shouldn't be used to cool the engine when pulling. The vibrations from the engine could damage the brushes in the fan motor, which might render the fan useless. The fan should only be used for cooling with the engine off just before a pull-off or between classes, when there isn't enough time for the engine to naturally air-cool. These fans are available on eBay and from other places. Return to a previous page or paragraph.

Because this fan draws power from the battery, which could weaken the spark for the engine, use an electric only to cool the engine after a pull, while driving the tractor around, or between pull-offs. And if the cooling fins on the engine block are clean and free of debris, if the throttle shaft isn't worn in the carburetor, if the ignition timing is set at 20 degrees BTDC, and if there's plenty of air blowing over the engine, then it should operate at a cool temperature.

To swap a starter ring gear from one flywheel to another, first of all, Kohler don't sell just the ring gear by itself. You will need to acquire a used flywheel with a good ring gear on it.

  1. To remove the ring gear from a flywheel, it's not necessary to heat it. Instead, place the flywheel face up on a steel top work table or bench, then use a brass drift and 2-3 lb. hammer to remove the ring gear. Gently tap equally around the entire gear to avoid warping or bending it. It should eventually fall off.
  2. To install the ring gear on a flywheel, position the flywheel face down, and place the ring gear on the flywheel with the beveled edge of the gear teeth facing upward. This allows the starter gear teeth to engage more easily without causing damage to the teeth.
  3. Use an oxy-acetylene torch to heat the ring gear 360º to expand the steel so it'll install on the flywheel. This should only take a few minutes. Once the gear drops in place, it'll have a loose fit until it cools. Allow it to air-cool. Do not cool it with water. Once cooled, it'll have a tight, secure fit. NEVER attempt to install a [cold] ring gear onto the flywheel with a hammer! Doing this will bend it badly out of shape and ruin it for use.
  4. Go here for a video of this process: How to swap or flip a ring gear off a flywheel - YouTube.

By the way - the same flywheel ring gear fits the Kohler K-series and Magnum 7hp through 18hp OHV single cylinder engines and the Kohler aluminum block/cast iron cylinders twin cylinder engines. The flywheel itself on the 7 and 8hp engine is different. It's taper that fits on the crankshaft is smaller.

How to Widen the Frame Rails on a Narrow Frame Cub Cadet for Use of a Large Flywheel with a Gear Starter - (Updated 7/24/15)

The larger 9-1/2" diameter flywheel with a starter ring gear, larger K-series bearing plate and K-series flywheel housing can be installed on any 10-18hp Kohler engine for use with the gear starter, as long as there's an indention in the block just above the starter motor's mounting holes (when using the upper-mount type starter). (The small flywheel is 8" in diameter.) If the engine is being installed in a narrow frame Cub Cadet (models 70, 71, 72, 73, 100, 102, 104, 106, 122, 124 and 126), the frame rails must be widened to accept the larger flywheel, bearing plate and flywheel housing. No charging system is required or recommended for a pulling tractor because it'll rob horsepower and add unnecessary weight and extra wiring. Read below for information on how to convert a narrow frame Cub Cadet.

If you want to do away with the old, heavy, battery draining, power-robbing starter/generator on a narrow frame Cub Cadet and install a lightweight gear starter along with the larger 9-1/2" diameter geared flywheel on a Kohler engine, you'll have to widen the frame rails. To do this, with the engine removed, cut a slot halfway down into the frame where the front of the flywheel shroud sits. For the rear cut, measure 17" back from the front of the frame (to where the metal bends for the clutch cover), and then make the cut there. Then using a large pipe wrench or very large Crescent wrench (I found either of these work great), bend or spread the frame rails outward 11" from the front of the frame. Use a (large) flywheel shroud as a gauge to determine how wide the rails will need to be. This will eliminate having to put the engine in and take it out again. Spread the frame 5" forward (towards front of tractor) from where the slot was cut. Check to see that the frame rails are bent upward from spreading out the metal. (Hold a straight edge tool under each frame rail to check for straightness.) If the widening process was performed correctly, then they shouldn't be bent. If they are bent, they will need to be straightened so the driveshaft/clutch will be in correct alignment with the engine. It'll be best to securely weld two full-length 1/4" thick x 1-1/2" wide steel pieces under each frame rail to reduce the chance of bending. Then securely weld a 1/8" thickness mild steel gusset plate (angle reinforcement brace) into each wedge/cut) opening. A Magnum flywheel housing and bearing plate would require a lot more widening of the frame rails to install in a narrow frame Cub Cadet.

Widening the frame rails as mentioned above and then properly welding in the gussets (reinforcement angle braces) shouldn't weaken it. But make sure that the frame is in fact straight before welding in the gussets. Because sometimes it can bend during the process of widening the frame. To prevent the frame from bending overtime when doing ground-pounding wheelies, weld in the gussets on both the inside and outside of the frame. Put down a good bead of weld, too. If the frame is bent, only slightly, this will interfere with the operation and proper alignment of the clutch and driveshaft. The Cub Cadet model 147 is the only narrow frame tractor that came from the factory with widened places in the frame for the large flywheel. This is also the last narrow frame Cub Cadet manufactured before the wide frame models were produced. There's no need to widen the frame rails on a wide frame Cub Cadet (models 86, 108, 128, 800, 1000 and 1200), because the large flywheel and gear starter will clear the rails.

The parts needed to convert a 10-16hp Kohler K-series engine with a starter/generator into a gear starter are as follows:

To install a gear starter on a 10-16hp Kohler engine in a narrow frame Cub Cadet...

  1. The engine will need to be removed.
  2. The frame rails will need to be cut and widened (enough to clear the [9-1/2"] flywheel shroud), and a couple of gusset plates will need to be welded in for strength.
  3. Install the large diameter bearing plate, (9-1/2") flywheel with a starter ring gear and flywheel shroud on the engine.
  4. A gear starter motor will need to be bolted on the side of the engine block. The block will need to have an indention for the starter.
  5. Then there's the wiring, starter solenoid and push-button starter switch that needs to be installed.

But if you prefer to use the starter/generator when pulling, remember this: the generator part requires less than 1hp of engine power to charge a fully drained battery. Therefore, if you were to install an OFF/ON toggle switch to turn off the field windings in the starter/generator, this will prevent it from charging the battery. Which will allow the engine to produce more power.

After installing the flywheel shroud and if the hub adapter, flywheel or starter cup screen rubs part of the shroud on one side. This means the big hole in the shroud is out-of-alignment with the centerline of the crankshaft. It needs to be tweaked to put it in alignment. Sometimes I have the same problem with my customer's engines. To fix it, install all the mounting bolts in the shroud, but leave them loose, then place a soft 2x4 board against the shroud, and then hit the board with a big hammer or heavy rubber hammer to force the shroud over until it's centered with the screen. This is the only way I know how to fix it. I don't know how they get out of alignment in the first place, unless it came that way from the factory and haven't been noticed before. Heck, when rebuilding and/or reassembling an engine, you tend to notice a lot of new things about it. It's kind of like painting your own house on the outside. The owner don't notice maybe a cracked window, loose siding, etc., until they get up-close with it.

Installing a 10-16hp Single Cylinder Kohler Magnum Engine in an Older Cub Cadet Garden Tractor -

With the flanges on a Kohler Magnum engine model M10, M12, M14 or M16 block cut off and with a narrow Cub Cadet oil pan installed, the Magnum will install in a spread-frame Cub Cadet with little to no modifications. But it won't fit in a narrow- or wide-frame Cub Cadet, because the Magnum flywheel shroud and bearing plate are too wide to fit between the frame rails, even when the frame rails on a narrow frame Cub Cadet are widened. Therefore, a large flywheel shroud, bearing plate and upper mount gear starter from an older 10-16hp Kohler K-series engine will need to be installed on the Magnum engine and then the Magnum should install in a narrow- or wide-frame Cub Cadet with little to no modifications.

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