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Where Science and Common Sense Come Together for Better Engine
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Identification of Kohler K-series and Magnum Single Cylinder Engine Cylinder Heads -
The cylinder head used on Kohler engine models K141, K160, K161 and K181/M8 was introduced in 1952, and are all identical. There is no difference. These heads shouldn't be milled because the valves are already close to the head when the valves are at full lift. All that can be done is resurface it on a wide flat belt sander or large diameter flat sanding disc to remove warpage and restore flatness, and to prevent a blown or leaking head gasket. If one don't have their own belt/disc sander, most automotive machine shops and carpenters have one. Do the repair job right the first time and it won't have to be done again later. OEM Kohler part # 41 755 25-S.
The First Generation Head -
This cylinder head was manufactured by Kohler from the early 1960s until 1971 and was available only on engine model K241 before engine serial number 3184999. It has a heart-shaped and wedge-contoured combustion chamber and is now known as the high compression, "LP head." The spark plug is centered in the combustion chamber. This particular head was originally made for and came on the very early K241 engines. It'll also work on the Magnum engine model M10, K301/M12 engines and the early K321/M14 engines with a 1-1/8" exhaust valve. But being the later K321 engines have a larger exhaust valve (1-3/8"), the exhaust area in the head would need to be machined out for use with the bigger exhaust valve. And because of its high compression ratios, if this head is used on a K301 or K321 engine, Premium, race gas, E-85 or methanol fuels must be used, or the engine will overheat and wear out prematurely. The compression ratio is 7:1 when used on a K241/M10 and 8.6:1 when used on a K301/M12. If this head was used on a K321/M14, it would yield a 9:1 compression ratio. And LP heads did not come on nor will they fit the K341 engines. This head requires 2-1/4" length bolts with no mounting bracket(s) under the bolt, and 2-1/2" length bolts with [gas tank] mounting bracket or other bracket(s) under the bolt. And due to early technology and design of the combustion chamber, the majority of the expanding gases or combustion pressure is placed over the valves instead of the piston, resulting in lower engine performance. The number embossed on this head is 235461. Cub Cadet part # is IH-385303-R1. It is no longer available from Kohler or new from any other source.
This Kohler cylinder head with the numbers 235461 embossed in it is designed for the K241, K301 and early K321 engines with the small (1-1/8") exhaust valve. To use this head on a newer K321 engine with the larger (1-3/8") exhaust valve, the valve shrouding area in the head will need to be milled out for adequate clearance.
NOTE: This particular head was originally designed many years ago ONLY for the K241 engine because these engines have low compression due to their small bore and short stroke. The only reason anyone would put one of these heads on a bigger engine today is to attempt to get more power out of it. Also, people found that the LP head worked better than a newer low compression head on an engine burning liquefied petroleum (propane) gas. LP gas is a high octane fuel (about 110-115 octane). Therefore, it burns more thoroughly and produces more power in a high compression engine. That's why these heads are known today as the "LP head." Also, the LP head, when used on any size engine including the K241, have been known to cause detonation (pinging) nowadays even with 93 octane Premium gas. That's why Kohler stopped making them. They replaced them with the "dished" head. Ê However, high octane race gas, E-85 or methanol fuels can be safely used with the LP head.
If you want to use an LP head on your engine, the genuine OEM Kohler LP head is no longer available from Kohler or any other source. They haven't been made since the early 1960s. They were discontinued when the K301 engine came into production, because this engine requires a lower compression head. So if you need an LP head, remember, they came only on the very early K241 engines equipped with the starter/generator and no indention on the side of the block for the upper mount gear starter. But if you can't find an LP head at all or for a reasonable price, what you could do is cast an aluminum head just like the LP head. An LP head can be CNC-machined from billet aluminum, but if you prefer a head that's close to the genuine product, first, you'll need a good LP head to use as a mold or pattern. For more information on this subject and a how-to video, click here: Melting Cans With The Mini Metal Foundry - YouTube.
The Second Generation Head -
The second type of head manufactured by Kohler has a heart-shaped and a depression area in the combustion chamber. It has improved technology over the earlier LP head. Kohler engine engineers made the depression area for a special reason and it helps engines to produce more torque and horsepower than the LP head at any RPM. This head was installed on Kohler's K241 and K301 engines, before the K321 engine went into production. It's a good head. It flows good and with increased compression. The "hump" directs the incoming air/fuel toward the piston at higher RPM.
Unlike the sought-after, but misunderstood LP head, the depression area places the majority of the expanding gases or combustion pressure over the piston instead over of the valves, which produces more engine power and torque. The spark plug is centered in the combustion chamber. It was lowered in compression and was made for both the K241 and K301 engines, but would not work on the K321/M14 engine because of its' larger exhaust valve (it was manufactured before the K321 engine went into production) unless reduce the size of the exhaust valve on a K321 to a 1.125" (same as a K241 and K301) This can be accomplished by installing a valve seat insert in the block for the smaller valve. By the way - this type of head is not officially a "high compression head" because it has a depression in the combustion chamber. It is however, 'slightly higher' in compression than the newer style heads, but it's not a "high compression" or even an "LP head," but the next best to it. The compression ratio is 5.4:1 when used on a K241 and 6.6:1 when used on a K301. If this head was used on a K321 (the exhaust circumference area would need to be machined larger), it would yield a 7:1 compression ratio. By the way - Kohler no longer makes this type of head either.
These early heads require 2-1/4" length bolts with no mounting brackets or plates under the bolt head, and 2-1/2" length bolts with [gas tank] mounting bracket or other brackets/plates under the bolt head. The reason Kohler redesigned the head with the low bosses for shorter head bolts is so more air can flow over the head bolts instead of around them to better efficiently cool the head.
The Third Generation Head -
The third head manufactured by Kohler has a low compression (depressed) D-shaped combustion chamber. And unlike the sought-after, but misunderstood LP head, the depression area places the majority of the expanding gases or combustion pressure over the piston instead over of the valves, which produces more engine power and torque. The spark plug is centered in the combustion chamber. It'll work on the K241/M10, K301/M12 and K321/M14 engines because the exhaust valve area was made bigger. (It was manufactured when the K321 engine went into production.) The compression ratio is 5:1 when used on a K241/M10, 6.1:1 when used on a K301/M12, and 6.6:1 when used on a K321/M14. This head requires 1-1/2" length bolts. The reason Kohler lowered the bolt hole bosses is to allow more air to flow over the fins for better cooling of the engine. By the way - Kohler no longer makes this type of head either. If you want to use one of these, look for a good used one. They came on the later model K241, K301 and K321 engines. OEM Kohler part # 237827-S.
The Fourth Generation and Newest Style Head -
The newest style head manufactured by Kohler is much like the previous one, but has the spark plug located directly over the exhaust valve. There are two reasons why Kohler did this:
Again, unlike the sought-after, but misunderstood LP head, the depression area places the majority of the expanding gases or combustion pressure over the piston instead over of the valves, which produces more engine power and torque. The compression ratios and mounting bolt lengths are the same as the previous head. By the way - these type of heads are available from Kohler and are the newest ones made. They come on Magnum engines, too.
By the way - the Chevrolet V8 performance racing cylinder heads have the spark plug tip moved toward the exhaust valve for improved performance. It works. The plugs are angled so the tip is closer to the exhaust valve, and so the porcelain part will clear the exhaust header pipes. There's no reason to angle the spark plug in a Kohler head.
NOTE: The fourth generation head will interchange on the K241/M10, K301/M12 and K321/M14 engines. It doesn't matter about the spark plug location, except for pulling purposes. For pulling, it's best to have the spark plug directly over the exhaust valve. The only exception is the very early K241 "LP" head. It has a smaller combustion chamber which will allow the engine to have a higher compression ratio, and shouldn't be used on the K301/M12 and K321/M14 engines for general yard work. It should be used for pulling purposes only using high octane gas, E-85 or methanol fuel. The reason for this is because the compression will be so high, the engine will run too hot for low octane gas, and severe damage to the engine may result.
The K341/M16 Cylinder Head -
The K341 cylinder head is in a class all by itself. It has the depression and D-shaped combustion chamber. They have the spark plug located directly over the exhaust valve. The compression ratio is 7.4:1. It requires 1-1/2" length bolts. And there are no "LP" type K341 cylinder heads. And ALL K341/M16 cylinder heads have the spark plug located over the exhaust valve. No exceptions. OEM Kohler part # 45 015 09-S. The head too, has the spark plug located directly over the exhaust valve. And there are two reasons why Kohler did this:
Kohler Cylinder Head Identification and Cub Cadet Applications:
Kohler K-series engine model K241. OEM Kohler part # 235461, Cub Cadet part # IH-385303-R1. LP head; discontinued from Kohler. Originally came on the 1965 and earlier Cub Cadet model 100, and other makes and models of garden tractors and small engine equipment. Requires 2-1/4" length bolts (Kohler part # 271077 - Discontinued from Kohler) with no mounting bracket(s) under the bolt head, and 2-1/2" length bolts (Kohler part # 235175-S) with [gas tank] mounting bracket or other mounting brackets/plates under the bolt head.
Kohler K-series engine model K241. OEM Kohler part #'s 236546-S. Either head originally came on various Cub Cadet models 100, 102, 104, 105, 106, 107, 108, 109 or 1000, and other makes and models of garden tractors and small engine equipment. This head is no longer available from Kohler. Requires 2-1/4" length bolts (Kohler part # 271077 - Discontinued from Kohler) with no mounting bracket(s) under the bolt head, and 2-1/2" length bolts (Kohler part # 235175-S) with [gas tank] mounting bracket or other mounting brackets/plates under the bolt head.
Kohler K-series engine models K301 and K321. OEM Kohler part #'s 237670-S (Discontinued from Kohler; or 237827-S. Either head originally came on various Cub Cadet models 122, 123, 124, 125, 126, 127, 128, 129, 147, 149, 680, 1200, 1250, 1282 or 1450, and other makes and models of garden tractors and small engine equipment. Both heads require 1-1/2" length bolts, w/centered spark plug).
Kohler K-series engine model K341 (including M16 Magnum engine). OEM Kohler part # 45 015 09-S. Originally came on Cub Cadet models 169 and 1650, and other makes and models of garden tractors and small engine equipment. Requires 1-1/2" length bolts (OEM Kohler part # 25 086 115-S), w/offset spark plug hole.
Kohler Magnum engine model M10. OEM Kohler part #'s 237670, 47 015 05-S. Originally came on Cub Cadet model 1050. Requires 1-1/2" length bolts (OEM Kohler part # 25 086 115-S), w/offset spark plug hole.
Kohler Magnum engine models M12 and M14. OEM Kohler part # 47 015 06-S. (Discontinued from Kohler; Requires 1-1/2" length bolts (OEM Kohler part # 25 086 115-S), w/offset spark plug hole.)
Compression ratios for factory stock Kohler K-series and Magnum engine models are as follows:
A good head for a Stock pulling tractor with the engine running around 4,000 RPM would be the one with the spark plug located in the center of the combustion chamber. And the best head to use for a high RPM pulling tractor would be the one with the spark plug located over the exhaust valve.
Did you know that installing two spark plugs per cylinder doesn't help to increase the power output of an engine whatsoever? Simply because one plug will be running hot (exhaust side) and the other will be cool (intake side). Engine power is generated from the heat source, because heat is how an engine produces power. When the spark plug in the cylinder head is located over (flathead) or close to (OHV) the exhaust valve, this maintains the majority of the heat in the combustion chamber in one area. When heat is maintained in one particular area in any given combustion chamber, the increase in power will be much greater, especially at high RPM. Burning fuel within a combustion chamber will "find" or locate the main heat source. The fuel will burn more thoroughly, allowing the engine to produce more power at any RPM. If the plug is located in the center of the combustion chamber, the incoming fuel could splash against the plug's tip and cause the engine to misfire or run erratic at high speed, especially when burning methanol fuel. And the plug could easily become fouled when burning gas, especially when the engine is cold. So it's best to install just one spark plug positioned over the exhaust valve with the plug gap set at .060". Because a .060" gap will simulate having two spark plugs. Use of a high-performance coil will help produce a stronger spark, too. Indexing the spark plug will also help to increase power and torque. This is when the open gap faces the center of the piston. It helps in a more thorough combustion of the fuel so the engine will produce more power at high RPM. Indexing washers is used to index a spark plug. They're a copper washer of certain thicknesses that's placed on the threads of the plug. Indexing of the spark plug helps to increase the power on a high-performance engine that operates at high RPM. It doesn't help much on a stock engine or at low RPM.
Grind away any sharp edges (after milling head, milling out combustion chamber and/or factory casting flash) within the combustion chamber, and polish the entire combustion chamber, including around the valves and top of the piston, to a high luster (smooth as glass, if possible) to help increase power and torque, especially at higher RPM or at wide open throttle. Removing sharp edges prevents hot spots, which can cause detonation and/or pre-ignite the incoming fuel, and polishing reflects heat and prevents the majority of it from being absorbed into the metals. Go here for more information on this subject.
If you're pulling in class where the rules state that the engine must have a stock OEM cylinder head, stock valve lift and stock diameter valves, and you want to get a little more power out of your engine, what can be done is "shave" or mill the head. This is when approximately .050" of metal is removed from the raised gasket mating surface. The milling process of the head must be performed with a fly cutter with the head securely clamped in a milling machine vise fastened on the table of a vertical milling machine. To guarantee that the gasket mating surface is absolutely parallel to the height of the fins, before actually milling the head, the fins must first be milled [in the vise on the table of the milling machine] until they are all the same height. Then flip the head over and the milling process can be performed. Failure to do this could cause the gasket area be milled crooked and not parallel to the fins, resulting in a lop-sided head. Then if necessary, use a wide flat belt sander or large diameter flat sanding disc to smooth the gasket surface. And do not use a belt sander or sanding disc to mill a head. Use it only to resurface a cylinder head to remove warpage and restore flatness. If the sanding material on the belt sander or sanding disc is worn uneven (from multiple sandings), the head will not resurface perfectly flat and/or may have skip marks. If one don't have their own belt/disc sander, most automotive machine shops and carpenters have one. Remember - do the repair job right the first time and it won't have to be done again later. Click here to learn how to resurface a warped cylinder head at home with sandpaper.
Be sure to check the valve clearance before milling a head! If a lot of metal is removed from the head, then milling of the valve cavity to clear the head may also need to be done. In most cases with a stock-lift cam, there should be adequate clearance once a stock OEM head is milled. Always check the clearance with the valves at full lift before milling a head! To learn how to do this, scroll down or click here.
Milling of the head will increase the compression ratio about 3/4 of a point. And depending on engine size, this will definitely, without a doubt, add about 1-3 more horsepower and more torque. The engine will have a "snappier" response when the throttle is opened suddenly, and if the engine is in good running condition, it will literally "pull you back in the seat" of a garden tractor when the engine is quickly accelerated. To learn what else can be done to a stock engine to increase it's power output, click here.
Reusing Metal-Shielded Head Gaskets -
A used metal-shielded head gasket can be reused if it is in good condition and not bent, distorted or burned-out. To reuse it, clean it thoroughly with a spinning wire wheel, then coat it evenly with ordinary aluminum or silver color spray paint (available at Walmart or virtually any hardware store), reinstall the gasket, and tighten the head bolts or nuts (with studs) to the correct torque specs. Normal operating engine combustion heat will melt the aluminum/silver paint, creating an absolutely perfect seal. And if a new, metal-shielded head gasket has light surface rust from sitting in storage, the rust can be removed with a spinning wire wheel, and then the gasket can be coated with the same aluminum or silver color spray paint. It'll still be a usable gasket, only with a much better appearance (and sealing quality). This will not work with heavily-rusted head gaskets. And did you know that aluminum paint was first applied on used head gaskets to reassemble engines that was in the American World War 2 fighter planes? Aluminum paint was used because at the time there was a shortage of new head gaskets. This is part of the reason why most Americans don't speak German or Japanese today. (Hitler said he was going to dance on the White House steps. Fortunately, that did not happen.)
And for general yard work, to lessen the chance of a blown or leaking head gasket, seal the head gasket with either VersaChem - Mega Copper Silicone, Permatex® Ultra Copper® Maximum Temperature RTV Silicone Gasket Maker or Copper SPRAY-A-GASKET Hi Temp Adhesive Sealant. Apply it on both sides of the head gasket or cylinder head and engine block. These products work equally, and have fine-ground soft copper particles for heat transfer and the silicone is to seal in the combustion pressure. I don't think one works better than the other. Also, combustion chamber heat has very little effect on silicone rubber. It can withstand heat up to 2,500º Fahrenheit.
If an engine has a leaking head gasket, then this means either the head bolts are loose or the cylinder head is warped and needs to be resurfaced on a wide flat belt sander or large diameter flat sanding disc to remove warpage and restore flatness. If one don't have their own belt/disc sander, most automotive machine shops and carpenters have one. Do the repair job right the first time and it won't have to be done again later. And if the head is perfectly flat and if the head bolts or studs w/nuts are torqued to specs, most head gaskets alone will seal with no problems. But if you want a guarantee that the gasket will seal well, apply a thin layer of either VersaChem - Mega Copper Silicone, Permatex® Ultra Copper® Maximum Temperature RTV Silicone Gasket Maker or Copper SPRAY-A-GASKET Hi Temp Adhesive Sealant on each side of the head gasket or on the cylinder head and engine block, then torque the bolts or studs w/nuts to factory specs.
For competition pulling only: If the deck (top) of the engine block and cylinder head gasket surface are perfectly flat, and if the valves have adequate head clearance at full lift, and if the piston doesn't come flush with the top of the block, or if the head is milled for a pop-out piston, then a head gasket isn't really necessary. Just use the copper silicone as described above È. When using copper/silicone only as a head to block sealant, it'll be like using a dried "liquid" copper head gasket. The absence of a head gasket will prevent the head from warping when the head bolts or nuts with studs are torqued to specs. The head and block will have positive metal to metal contact with the silicone filling in any imperfections between the two metals. The copper particles will transfer the heat. But if the piston pops out of the cylinder, the clearance between the piston and head will need to have a safety margin of minimum .030" due to rod stretch and crankshaft flex at very high RPM. And yes, when precision-balanced, even a cast iron crankshaft will flex a few thousands of an inch at high RPM without breaking. The clearances over each valve when at full lift will need to be checked, too.
For dirty or rusted engine blocks, to prevent a blown or leaking head gasket, besides resurfacing the head(s) and cleaning the deck of the block, due to dirt/debris that gets accumulated in the threads for the head bolts, the threads may need to be cleaned out with the appropriate size tap (5/16-18 UNC (coarse thread) for Kohler engine models K141, K161/K160, and K181/M8 engines; and 3/8-16 UNC (coarse thread) for Kohler engine models K241/M10, K301/M12, K321/M14, K341/M16 and K361 engines) to get the head to fully compress the gasket when the bolts are torqued to specs. It's best to use a TAPER hand tap. A TAPER tap cleans threads more thoroughly [than a PLUG tap] and is less likely to break off in the block when in use. Then a PLUG tap can be used to clean the threads deeper. Be sure the threads on the bolts are clean, too. And to obtain the proper torque, apply clean motor oil on the threads before installing and torquing the bolts to specs. This should be done with any engine, lawn & garden, farm, heavy equipment or automotive.
Removing a Broken-Off Tap - A threading tap that has broken off in an engine block or metal casting can be very difficult to remove. About all I can tell you is to either take your block to a reputable machine shop to have the tap removed, or go here and try to do it yourself: https://www.google.com/?gws_rd=ssl#q=removing+broken+tap+from+hole. Actually, it's best to use a TAPER hand tap to cut new threads and clean out existing threads. If used correctly, a TAPER tap is less likely to break off. Click here to learn how to cut new threads, the professional way.
And OEM Kohler head bolts don't need to be retorqued again after the engine gets hot. Also, as long as there's plenty of metal on the hex head (due to being rusted away), they can be reused many times. The OEM Kohler head bolts are actually harder than hardware store grade 8 bolts and the threads don't stretch on them whatsoever. Personally, I always try to reuse Kohler head bolts on my engine builds whenever possible.
To repair broken-off head bolt(s)...
The Causes of "Burn-Out" with an OEM Aluminum Cylinder Head used Virtually on any 4-Cycle Small Gas Engine Are:
If you're planning to use a big cam with a lot of valve lift than a stock head can handle, then it's time to install a machined billet aluminum cylinder head. A billet head is just some 6061 or 7071 [hard material] aluminum that's had the combustion chamber and valve cavities machined out on a vertical milling machine. Stock heads do well in some cases, but in a high-performance situation, more power and better flow can be had with a specially designed combustion chamber. Billet heads don't necessarily provide a higher compression ratio, they're just made of thicker metal to allow more room for the valves to open more. That's why most professional engine builders prefer to make a head from thicker metal and create a specially designed combustion chamber that's more efficient than a factory head.
When a billet head is purchased new, they are just a flat piece of thick aluminum. Before the combustion chamber is machined out, the bolt holes drilled and the spark plug hole drilled and tapped, no previous machining should have been done to it.
After machining the combustion chamber and valve cavities, hand-sand it with 80 grit emery cloth. Make it as smooth as possible. The smoother, the better.
A thick billet head will not warp like the thinner factory OEM ones sometimes do. Therefore, the head gasket won't blow out. Billet heads are either 1" thick for an average lift cam (up to .500" lift) or 1-1/4" or slightly thicker for a higher lift cam (more than .500" lift). Thicker material must be used with a high lift cam so there'll be enough metal for the spark plug threads and to prevent the metal from cracking or blowing out under full throttle/high-compression. When choosing the thickness of a billet head, consider the thickness of the head gasket material when it's compressed, tip of the valve head(s) if they're above the deck, cam lift and of course clearance over the valves. After considering this four items, remember that the threads for the spark plug will need at least 3/8" thickness.
And billet cylinder heads don't stay cool because most of them have no fins machined in the head and most steel flywheels have no cooling fins. Besides, most pulling tractors don't run long enough to do any serious overheating and when they burn methanol fuel, the methanol will help cool the combustion chamber as the engine runs.
How to Remove Carbon Deposits from the Combustion Chamber in a Cylinder Head - (added 11/6/16)
Use a narrow, steel blade putty knife (with a stiff blade) or paint scraper to remove the carbon deposits from the combustion chamber (and from around the valves and from the top of the piston). Be sure the putty knife or scraper has a sharp edge, too. Don't worry about scratching the surface of the combustion chamber either. The tiny scratches will cause no problems. If the putty knife or scraper can't easily remove the carbon, soak the head in plain water at room temperature for a few days. This will soften the carbon and then it should be a lot easier to remove.
How to Make a New Spark Plug Hole -
When making a new hole and cutting threads for the spark plug, use a 1/2" drill bit (for 14mm threads) to bore the hole, then use a 14mm x 1.25 pitch spark plug tap to cut the threads. Be sure to drill the hole and cut the threads perpendicular to the head! If the hole is drilled crooked or the threads are cut crooked, the spark plug won't seat (seal) a full 360º and loss of compression will result. A spark plug tap can be acquired on eBay, at a local hardware store or machine shop/steel supply company. Don't use a spark plug thread hole chaser to cut new threads. They're made to remove carbon deposits and/or renew damaged threads.
Repairing Stripped 14mm Spark Plug Holes -
If 14mm spark plug threads are stripped-out in a cylinder head, a stainless steel Heli-Coil thread repair insert or a special-made mild steel solid thread repair insert can be installed. For cleanliness and to prevent metal cuttings from entering the combustion chamber, which will cause severe engine damage and wear, the cylinder head must be removed before installing the insert! By the way - a mild steel or stainless steel thread insert is absolutely, without a doubt, much stronger than any aluminum threads. To install the solid thread insert...
The Heli-Coil insert doesn't require threadlocker because its "spring-like" action expands outward against the threads in the head, keeping it intact with the head.
Or contact a-1 Miller's Performance Enterprises if you are not able to repair stripped spark plug threads.
If a stripped 14mm spark plug threaded hole is too large for the thread repair insert as mentioned above È, and/or if an attempt was made to repair a stripped spark plug hole with a thread insert that was inadvertently installed not perpendicular with the head (crooked or cocked), or if a smaller (14mm) spark plug threads is to be used in a head originally with an 18mm spark plug hole (such as a Wisconsin engine), the hole can be repaired correctly or converted to smaller 14mm threads with a 1/2" NPT mild steel Allen pipe plug. Here's how to do it: An innovative concept by Brian Miller, because nobody else advertise this type of repair.
As the last resort, stripped threads in an aluminum head can be welded up with aluminum welding, refaced (milled flush), then drilled and tapped for installation of the spark plug.
How to locate where to machine the cylinder head for the valves...
Directions: Thoroughly mix flour, salt and cream of tartar or alum. Boil liquids together. Pour in dry ingredients and stir together. Knead and add flour as needed. [Return To Previous Paragraph] È
When machining the valve cavities in an OEM stock head or in a billet head when installing a cam with more valve lift, use the following clearances:
FYI - I've milled several stock heads as much as 1/8" and they did well at the pulls. However, using methanol on a cool day could blow the combustion chamber out on a stock head that's been excessively milled for valve clearance. I've had this happen on my 12hp Super-Stock pulling tractor once. I was going down the track, engine running excellent, then all of a sudden "PUFF!" went the head.
Below Ê is a drawing and picture of a custom designed combustion chamber in a billet head. Ê
How to Repair A Loose Valve Seat and Worn or Loose Valve Guides in the K361 Cylinder Head -
The Kohler engine model K361 cylinder head is notorious for one or both valve seats and/or one or both valve guides becoming loose. What causes a seat to loosen is the aluminum was molded around the steel seats with a "tongue and groove" design to secure the seat in place. Due to normal (or perhaps excessive) engine heat, sometimes the two metals (aluminum head and steel seat) will separate from each other, allowing the seat to loosen. And the reason the guides loosen is because the hole they're pressed into is very short. In other words, there's not much metal (in the head) to secure them in place 100%.
First of all, before attempting to repair a loose seat, if the valve guide for the seat in question is worn (inside) or loose in it's bore, it will need to be repaired first.
How to Repair a Loose Valve Seat:
About Installing Bigger Valves in the K361 Engine Cylinder Head -
On the K361's cylinder head, the stock valve head diameters are: intake - 1.438"; exhaust - 1.400". The exhaust valve is already plenty big enough, even for high RPM. But there's not that much room in the combustion chamber to install a bigger intake valve because a bigger seat would need to be installed first. The outside diameter of the seat is always larger than the diameter of the valve head. The biggest intake valve that can be installed would be about 1.5", which really wouldn't give the engine that much more performance. For more noticeable performance, the intake valve needs to be about 20% bigger than the exhaust valve, which would make it 1.68". And this is way too big for the K361 head.
If an OHV aluminum block engine blows smoke out the exhaust upon start up then quits smoking, and/or oil is forced out the oil fill tube, this is likely the signs of a warped cylinder head, which results in a blown head gasket. The problem is caused by normal engine heat from the first time the engine is ran. To fix this, remove the head, resurface it on a wide sanding belt or large diameter disc sander to remove warpage and restore flatness, install a new head gasket, torque the head bolts to specs in the correct sequence, and readjust the valve clearances. It shouldn't warp again. If one don't have their own belt/disc sander, most automotive machine shops and carpenters have one. Do the repair job right the first time and it won't have to be done again later.
How to Remove a Broken Head Bolt -
Use a "centering drill," which is a stubby drill bit that creates a hole exactly in the center of a stud. Then use a 5/16" carbide-tip drill bit to drill the broken stud out, and then use a 3/8-16 UNC (coarse thread) tap to clean the threads. If you feel this is too much for you, you can take your engine to a reputable machine shop and have them do this for you.
To place an order, please call the number below Ê or send an email with your name, complete and correct postal address and phone number and so I can figure the total with shipping cost and USPS Tracking. For payment options for parts ordered or services performed, or to make a donation to my websites, I accept cash (in person), USPS Postal Money Orders, cashier's checks, business checks, MasterCard, VISA, Discover, American Express (please add 2.5% to the total for the credit/debit card processor's surcharge), Western Union Money Transfer, MoneyGram Money Transfers or Popmoney. (If a part for a specific purpose is special ordered, your debit/credit card may be charged for the full amount or as a deposit right after your order is placed; please do not send your debit/credit card information in email!) Or you can pay me through PayPal. (My PayPal account name is my email address. And be sure to mention in PayPal a description of what the payment is for.) If sending a money order, please include a note in the envelope with your name, complete and correct postal address, phone number and a description of what the payment is for. My mailing address and phone number are below Ê . I'll make a note of your order, and I may have to order some of the parts, which should take a few days to come in, but I will send the parts to you as soon as I have everything in stock after I receive your payment.
IMPORTANT - When sending your part(s) to me for rebuilding or repair, package everything securely so the item(s) 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 the clumsy "gorillas" or incompetent and uncaring workers that work for certain delivery services mishandle the heavy packages and don't care. And when the work is completed, I'll either call or email you an invoice with the total including shipping & handling.
To figure the shipping cost, I weigh the package with the parts, then I go online to the USPS Postage Rate Calculator website. I type in the weight, my zip code and your zip code, then it shows me the prices for various ways to ship the package. I always choose US Postal Service because I believe that's the most fastest, economical and reliable method.
Shipping: (United States and it's territories)
We Ship to Canada and Worldwide
To make a payment to me through PayPal, go to PayPal's secure website ( https://www.paypal.com/ ) and click on Send and Request -> Pay for goods or services. Type in my email address, or copy and paste this: email@example.com, the amount and follow the directions. Be sure to mention in PayPal a description of what the payment is for. After you've finished, PayPal will send me an email notifying me that you have made a payment to me for the product(s) or services and amount entered. Then I go to their website and direct PayPal to deposit the money in my bank account. And I will send the parts to you as soon as I receive your payment. But I may have to order some of the parts if they're not in stock, which should take a few days. In that case, I will send you the parts as soon as they come in. PayPal protects your financial privacy and security. With PayPal, privacy is built in. It's a way for you to pay without exposing their financial information.
Coming Soon - Detailed Illustrated Plans on How to Construct a Professional Pull-Back Garden Tractor Pulling Sled, and a Motorized/Self-Propelled Garden Tractor Pulling Sled. FYI - My professionally-built motorized/self-propelled pulling sled, Track Master (click the picture to the right to see a larger image of my sled), is the only one I've ever built and I got it right the first time, with very few changes that had to be made to it. I guess I'm just one of those kind of guys that knows what he's doing. Pullers really like pulling my sled, too. They say it's the best sled they've ever pulled. (Not bragging, just stating the truth.) By the way - Track Master sled is engineered so well (by Brian Miller), that other sled builders/owners have copied my well thought-out and proven design. Anyway, I have lots of work to do in my shop and I work on the sled plans in my spare time. As soon as my plans with an inventory list of parts to use are perfected, I'll post the update in my websites. Remember - Perfection takes time. If it's worth having, it's worth waiting for. Also, I plan to acquire a bigger shop and I may build high quality garden tractor pulling sleds in the future to offer for sale. Please call me at 573-256-0313 (shop) or 573-881-7229 (cell), or email me at firstname.lastname@example.org or email@example.com if you're interested. - Brian Miller
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