Kohler's 16hp engine cylinder headInformation about Cylinder Heads for Single Cylinder Kohler Engines

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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 (6¼hp), K160 (6.6hp), K161 (7hp) and K181/M8 (8hp) 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 so it's perfectly flat to prevent a blown or leaking head gasket. OEM Kohler part # 41 755 25-S.

Kohler made five different cylinder heads for the 10hp, 12hp and 14hp K-series and Magnum engines through the years -

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 (10hp) 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 This particular head was originally made for and came on the very early K241 (10hp) engines. It'll also work on the K301 (12hp) engines and the early K321 (14hp) engines with a 1-1/8" exhaust valve. But being the newer 14hp 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 12 or 14hp engine, Premium, race gas, E-85 or methanol fuels must be used, or the engine will overheat and wear out too soon. The compression ratio is 7:1 when used on a 10hp and 8.6:1 when used on a 12hp. If this head was used on a 14hp, it would yield a 9:1 compression ratio. And LP heads did not come on nor will they fit the 16hp (K341) engines. This head requires 2" long bolts.

Number on this head is 235461. Cub Cadet part # is IH-385303-R1. No longer available from Kohler or new from any other source.

NOTE: This particular head was originally designed many years ago ONLY for the 10hp (K-241) 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 10hp, 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 an engine, about all you can do is look for a good used one because they're no longer available from Kohler or any other source. They haven't been made since the early 1960s. They were discontinued when the 12hp engine came into production, because these engines require a lower compression head. So if you need an LP head, remember, they came only on the very early 10hp engines equipped with the starter/generator and no indention on the side of the block for the upper mount gear starter. And if you can't find a head like this for a reasonable price, what you could do is find someone to re-cast an aluminum head just like this one. But you'll first need a good head to use as a mold.

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 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 10hp and 12hp engines, before the 14hp 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 rpms.

Unlike the LP head, the depression area places the majority of the expanding gases over the piston instead over of the valves, which produces more engine power. The spark plug is centered in the combustion chamber. It was lowered in compression and was made for both the 10hp and 12hp engines, but would not work on the 14hp engine because of its' larger exhaust valve (it was manufactured before the 14hp engine appeared) unless reduce the size of the exhaust valve on a 14hp to a 1.125" (same as a 10 & 12hp) 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 10hp and 6.6:1 when used on a 12hp. If this head was used on a14hp (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" long bolts (OEM Kohler part # 236546-S; number on head is 235461, but not an LP head), and the later ones require 1-1/2" long bolts (OEM Kohler part # 236675-S). Also, the reason Kohler redesigned the head with the low bosses for shorter head bolts is so more air flow can past over the head bolts to better efficiently cool the other parts of the head.

The Third Generation Head -

The third head manufactured by Kohler has a low compression (depressed) D-shaped combustion chamber. The spark plug is centered in the combustion chamber. It'll work on the 10hp, 12hp and 14hp engines because the exhaust valve area was made bigger. (It was manufactured when the 14hp engine first appeared.) The compression ratio is 5:1 when used on a 10hp, 6.1:1 when used on a 12hp, and 6.6:1 when used on a 14hp. This head requires 1-1/2" long 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 10hp, 12hp and 14hp 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:

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 10hp, 12hp and 14hp 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 10hp "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 12 and 14hp 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 (16hp) Cylinder Head -

The 16hp (K341) head that's manufactured by Kohler is in a class 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" long bolts. And there are no "LP" type 16hp cylinder heads. OEM Kohler part # 45 015 09-S.

Compression ratios for factory stock Kohler engines are as follows:
K90 (3.6hp), K91 (4hp) ? K141 (6¼hp) - 5.93:1 K160/K161 (7hp) - 6.2:1
K181/M8 (8hp) - 6.8:1 K241/M10 (10hp) - 5:1, 5.4:1 or 7.1:1 (depending which head is used) K301/M12 (12hp) - 6.1:1, 6.6:1 or 8.6:1 (depending which head is used)
K321/M14 (14hp) - 6.6:1, 7:1 or 9:1 (depending which head is used) K341/M16 (16hp) - 7.4:1 K361 (18hp OHV) - 9.2:1

Kohler Cylinder Head Identification and Cub Cadet Applications:

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 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 of the spark plug will also help to increase power. 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.

If you're pulling in class where the rules read that you must use 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 prominent/raised gasket mating surface ridge. To guarantee that the head is absolutely parallel, this must be performed on a milling machine with a flycutter and not on a sanding disc or belt sander. Use a sanding disc or wide belt sander only if the head is warped. Resurface the head until it's perfectly flat. If the sanding disc or belt is worn uneven (from multiple sandings), the head won't resurface perfectly flat.

Milling of the head (remove the raised ridge that mates with the head gasket) will increase the compression ratio about 3/4 of a point. And depending on engine size, this will add about 1-3 more horsepower. The engine will have a "snappier" response when the throttle is opened suddenly. 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 need to be done. In most cases with a stock-lift cam, there should be adequate clearance once the 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. To learn what else can be done to a stock engine to increase it's power output, click here.

Milling of a cylinder head is performed with a flycutter and the head clamped in a milling machine vise that's fastened to the table of a milling machine. First, securely clamp the head with the fins upward in the vise and use a couple of parallels to insure that the head is exactly at a 90° angle with the spindle. Then remove just enough metal from the fins with the flycutter so they are all even. Next, flip the head over in the vise and mill (or cut) the gasket mating area until the desired amount of metal is removed (so many thousands of an inch) or until the flycutter starts to touch the flat area above the piston.

Reusing OEM Head Gaskets -

A used OEM metal-shielded head gasket can be reused if it is in good condition (not bent or burned-out). To reuse it, clean it with a wire wheel and then coat it evenly with ordinary aluminum spray paint. Then reinstall the gasket and torque the head bolts to specs. Normal operating engine combustion heat will melt the aluminum paint, and if the block and head are perfectly flat, it will form an absolutely perfect seal.

And did you know that aluminum paint was first applied on used head gaskets to reassemble engines that was in the American WW2 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.

For pulling competition 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, then a head gasket isn't really necessary. Just apply a thin layer of either VersaChem - Mega Copper Silicone or Permatex® Ultra Copper® Maximum Temperature RTV Silicone Gasket Maker. These products have fine-ground soft copper particles for heat transfer and the silicone is to seal in the combustion. Engine heat has very little effect on silicone sealant. These products work equally. I don't think one works better than the other. 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.

Use modeling clay, such as Play-Doh, to measure the clearances between the valves and the head. Apply motor oil on each valve and in the head (valve cavities) to prevent the clay from sticking to either surface. Fasten the head with the head gasket to the block and then crank the engine over slowly by hand one full revolution so the valves can compress the clay. Remove the head and use the depth gauge on a dial or digital caliper to carefully measure the thickness of the clay. There needs to be a minimum of .100" clearance between the valves and the head.

On some [dirty] blocks, to prevent a blown head gasket, besides resurfacing the head(s), due to dirt/debris in the threads for the head bolts, the threads may need to be cleaned out with the appropriate size tap (5/16-18 NC for the Kohler K141, K161, and K181/M8 engines; and 3/8-NC for the Kohler K241/M10, K301/M12, K321/M14, K341/M16 and K361 engines) to get the head bolts to fully compress the head and gasket when torqued to specs. 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.

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. And always torque the head bolts in the correct sequence to proper specs.

The causes of "burn-out" on an aluminum cylinder head on virtually any 4-cycle small gas engine are:

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Cylinder Head Work -
  • Resurface air-cooled small engine cylinder head to remove warpage. $7.00 labor, plus return shipping & handling.
  • Bead-blast (thoroughly clean) and resurface air-cooled small engine cylinder head. $15.00 labor, plus return shipping & handling.
  • Mill cylinder head approximately .050". Remove prominent/raised gasket mating surface from head to increase compression ratio for the 10-16hp flathead, K-series or Magnum single cylinder engines only. $25.00 labor each, plus return shipping & handling. Click photo to the right for a larger view. NOTE: Seal the head gasket with Permatex® Ultra Copper® Maximum Temperature RTV Silicone Gasket Maker or Copper SPRAY-A-GASKET Hi Temp Adhesive Sealant to prevent a blown or leaking head gasket. Because engine heat has very little effect on silicone sealant.
  • Repair stripped 14mm spark plug threads. No need to purchase another cylinder head. $5.00 - $20.00 each (depending on size of hole and type of head) for parts and labor, plus return shipping & handling.
  • Mill out exhaust valve cavity in LP and 2nd generation cylinder head to clear the larger 1-3/8" exhaust valve. $25.00 labor each, plus return shipping & handling.
Cylinder head gasket for Kohler flathead engine models K90 (3.6hp), K91 (4hp). Approximately .050" compressed thickness. Doesn't need to be retorqued once hot. Included in complete engine rebuild gasket set. Kohler part # 220124-S.
  • Aftermarket. $8.00 each, plus shipping & handling.
  • OEM Kohler part. $9.10 each, plus shipping & handling.
Cylinder head gasket for Kohler K-series and Magnum flathead engine models K141 (6¼hp), K160 (6.6hp), K161 (7hp) and K181/M8 (8hp). Approximately .050" compressed thickness. Doesn't need to be retorqued once hot. Included in complete engine rebuild gasket set. Kohler part # 41 041 10-S.
  • Aftermarket. $6.50 each, plus shipping & handling.
  • OEM Kohler part. $9.10 each, plus shipping & handling.
Cylinder head gasket for Kohler K-series and Magnum flathead engine models K241/M10 (10hp), K301/M12 (12hp) and K321/M14 (14hp). Approximately .050" compressed thickness. Doesn't need to be retorqued once hot. Included in complete engine rebuild gasket set. Kohler part # 47 041 15-S.
  • Aftermarket. $6.00 each, plus shipping & handling.
  • OEM Kohler part. $14.75 each, plus shipping & handling.
Cylinder head gasket for Kohler K-series and Magnum flathead engine models K341/M16 (16hp). Approximately .050" compressed thickness. Doesn't need to be retorqued once hot. Included in complete engine rebuild gasket set. Kohler part # 45 041 17-S.
  • Aftermarket. $10.50 each, plus shipping & handling.
  • OEM Kohler part. $14.80 each, plus shipping & handling.
Cylinder head gasket for Kohler K-series engine model K361 (18hp OHV). Approximately .050" compressed thickness. Doesn't need to be retorqued once hot. Included in complete engine rebuild gasket set. Kohler part # 45 052 02-S.
  • OEM Kohler part only. $21.50 each, plus shipping & handling.
Cylinder Head Gasket for Tecumseh engine models VH80, HH80, VH100 and HH100. Approximately .050" compressed thickness. Doesn't need to be retorqued once hot. OEM Tecumseh part # 32000B.
  • $7.00 each, plus shipping & handling.
Cylinder head gasket for Kohler KT-series and Magnum twin cylinder flathead engine models MV16, KT17, KT17II, KT19, KT19II, M18, MV18, M20 and MV20. Approximately .050" compressed thickness. Doesn't need to be retorqued once hot. Included in complete engine rebuild gasket set. Kohler part # 52 041 20-S.
  • Aftermarket. $9.50 each, plus shipping & handling.
  • OEM Kohler part. $19.00 each, plus shipping & handling.
Cylinder head gasket for Kohler twin cylinder flathead engine models K482, K532 and K582. Approximately .050" compressed thickness. Doesn't need to be retorqued once hot. Included in complete engine rebuild gasket set below Ê. Kohler part # 48 041 13-S.
  • Aftermarket. $7.00 each, plus shipping & handling.
  • OEM Kohler part. $8.40 each, plus shipping & handling.
Refurbished OEM Cylinder Heads. These have been cleaned and resurfaced, with good fins and good spark plug threads.
Cylinder head for Kohler K-series engine models K90 (3.6hp), K91 (4hp). OEM Kohler part # 220541-S.
  • Used. Refurbished and in excellent condition. $50.00 each, plus shipping & handling. (When available.)
  • New head. (Soon to be discontinued from Kohler.) $94.60 each, plus shipping & handling.
Cylinder head for Kohler K-series and Magnum engine models K141 (6¼hp), K160 (6.6hp), K161 (7hp) and K181/M8 (8hp).
  • Used. Refurbished and in excellent condition. Cylinder head only. OEM Kohler part # 41 015 09-S. Head alone; Discontinued from Kohler. $50.00 each, plus shipping & handling. (When available.)
  • New cylinder head kit. Includes: cylinder head (41 755 25-S); 5/16" grade 5 hex nut; Sems screw 1/4-20 x 5/8 (X-132-5-S); Stud (52 072 15-S). OEM Kohler part # 41 755 25-S. $135.75 per kit, plus shipping & handling.
1st generation "LP" head for Kohler K-series and Magnum engine models K241/M10 (10hp), K301/M12 (12hp) and early K231 (14hp) with small diameter (1-1/8") exhaust valve. This is the most sought-after high compression "LP" head. Number embossed in head is 235461. Cub Cadet part # IH-385303-R1. No longer available from Kohler or new from any other source.
  • Used. Refurbished and in excellent condition. Requires 2" bolts. $160.00 each, plus shipping & handling. (When available.)
2nd generation head for Kohler K-series and Magnum engine models K241/M10 (10hp), K301/M12 (12hp) and early K231 (14hp) with small diameter (1-1/8") exhaust valve. These have a small, heart-shaped combustion chamber w/centered spark plug. Next best thing to the LP head.
  • Used. Refurbished and in excellent condition. Requires either 1-1/2" or 2" bolts. $50.00 each, plus shipping & handling. (When available.)
  • New head. OEM Kohler part # 236546-S. Number embossed in head is 235461, but this is not an LP head. Requires 2" bolts. $184.00 each, plus shipping & handling.
  • New head. OEM Kohler part # 236675-S. Requires 1-1/2" bolts. $176.00 each, plus shipping & handling.
3rd generation head for Kohler K-series and Magnum engine models K241/M10 (10hp), K301/M12 (12hp) and K231/M14 (14hp). These have a larger combustion chamber for the large 1-3/8" 14hp exhaust valve w/centered spark plug.
  • Used. Refurbished and in excellent condition. Requires 1-1/2" or 2" bolts. $50.00 each, plus shipping & handling. (When available.)
  • New head. OEM Kohler part # 237827-S. Requires 1-1/2" bolts. $169.00 each, plus shipping & handling.
  • New head. OEM Kohler part # 237829-S. Requires 2" bolts. $171.00 each, plus shipping & handling.
Newest style head for Kohler K-series and Magnum engine models K241/M10 (10hp), K301/M12 (12hp) and all K231/M14 (14hp). These have a larger combustion chamber for the large 1-3/8" 14hp exhaust valve w/offset spark plug. These particular heads lessens the chance of plug fouling from cold starting and helps produce more power by retaining majority of heat in one area.
  • Used. Refurbished and in excellent condition. Requires 1-1/2" bolts.$75.00 each, plus shipping & handling. (When available.)
  • New head. OEM Kohler part # 237670-S (K-series). Requires 1-1/2" bolts. $175.00 each, plus shipping & handling.
  • New head. OEM Kohler part # 47 015 05-S (M10 Magnum). Requires 1-1/2" bolts. $108.00 each, plus shipping & handling.
  • New head. OEM Kohler part # 47 015 06-S (M12/M14 Magnum). Requires 1-1/2" bolts. $108.00 each, plus shipping & handling.
Head for Kohler K-series and Magnum engine models K341/M16 (16hp). Each requires 1-1/2" bolts. OEM Kohler part # 45 015 09-S.
  • Used. Refurbished and in excellent condition. $120.00 each, plus shipping & handling. (When available.)
  • New. $193.45 each, plus shipping & handling.
Cylinder Heads for Kohler KT-series and Magnum Twin Cylinder Flathead Engines.
  • Stock head for model MV16. OEM Kohler part # 52 015 10-S.
    • Used. Refurbished and in excellent condition. $25.00 each, plus shipping & handling. (When available.)
    • New. $110.00 each, plus shipping & handling.
  • Stock head for models KT17, KT17II, KT19, KT19II, M18, MV18, M20 and MV20. OEM Kohler part # 52 015 08-S.
    • Used. Refurbished and in excellent condition. $30.00 each, plus shipping & handling. (When available.)
    • New. $140.50 each, plus shipping & handling.
Cylinder Head Bolts and Flat Washers for Cylinder Heads Above - Note: The length of any bolt do not include the head itself. All bolts are measured from under the head to the end of the threads.

For Kohler engine models K141 (6¼hp), K160 (6.6hp), K161 (7hp) and K181/M8 (8hp). 5/16" diameter x 1-1/2" long. Kohler part #'s 41 086 02-S (bolt), 220534-S (washer).

  • Aftermarket. High quality grade 8 bolts and washers. $10.50 per set of 7 each, plus shipping & handling.
  • OEM Kohler parts. $49.35 per set of 7 each, plus shipping & handling.

For Kohler engine models K241/M10 (10hp), K301/M12 (12hp) and K321/M14 (14hp). 3/8" diameter. NOTE: Bolt length is determined by type of cylinder head used. Head with short bolt holes requires 1-1/2" long bolts, and head with tall bolt holes requires 2-1/2" long bolts.

  • 1-1/2" long. Aftermarket. High quality grade 8 bolts and washers. Kohler part # 270158 (bolt; discontinued from Kohler), 270889-S (washer). $13.50 per set of 9 each, plus shipping & handling.
  • 2-1/2" long. Aftermarket. High quality grade 8 bolts and washers. Kohler part # 235175-S (bolt), 270889-S (washer). $13.50 per set of 9 each, plus shipping & handling.
  • 2-1/2" long. OEM Kohler parts. $88.00 per set of 9 each, plus shipping & handling.

For Kohler engine models K341/M16 (16hp). 3/8" diameter. Replaces Kohler part #'s 270158 (bolt; discontinued from Kohler), 270889-S (washer).

  • 1-1/2" long. Aftermarket. High quality grade 8 bolts and washers. $15.00 per set of 10 each, plus shipping & handling.
Head Stud Kit for OEM or Billet Cylinder Heads. For High-Performance/High RPM Use Only. NOTE: Studs provide even torque pressure for better head gasket sealing. Plus, they help maintain cylinder wall stability for better ring seal to lessen the loss of compression. They do not help the performance of an engine running around 4,000 rpms whatsoever.
  • For Kohler engine models K241/M10 (10hp), K301/M12 (12hp) and K321/M14 (14hp). Kit includes (9) 3/8" diameter x 1-1/2" or 2-1/2" long heat-treated studs, grade 8 nuts and grade 8 flat washers. NOTE: stud length is determined by the type of cylinder head. The head with the short bolt holes use the 1-1/2" studs, and the head with the tall bolt holes use the 2-1/2" studs. $20.00 per set, plus shipping & handling.
  • For Kohler engine models K341/M16 (16hp). Kit includes (10) 3/8" diameter x 2" long heat-treated studs, grade 8 nuts and grade 8 flat washers. $22.50 per set, plus shipping & handling.

Billet Aluminum Cylinder Head from Midwest Super CubIf 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 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 won't 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 Make a New Spark Plug Hole -

Spark Plug Thread Hole Chaser and Spark Plug Hole TapWhen making a new hole and cutting threads for the spark plug, use a 1/2" drill bit (for 14mm threads) to bore the hole and 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 360° 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 clean carbon deposits and renew damaged threads.

Repairing Stripped 14mm Spark Plug Holes -

If 14mm spark plug threads are stripped-out in a cylinder head, a Heli-Coil stainless steel thread insert or a solid steel thread insert can be installed. The solid insert should be installed with high strength liquid threadlocker (usually fully cured in 24 hours at room temperature), so the insert will not come out when removing the spark plug. The Heli-Coil insert doesn't require threadlocker because it expands against the threads, keeping it intact with the head. A Heli-Coil thread repair kit or a solid thread insert repair kit can be acquired on eBay, at a local hardware or auto parts store, or machine shop/steel supply company. Or a machine shop can install an insert for a few dollars. For cleanliness and to prevent metal cuttings from getting into the combustion chamber which will cause severe engine damage and wear, the cylinder head must be removed before installing the thread insert! By the way - a stainless steel thread insert is absolutely, without a doubt, much stronger than aluminum threads.

If a stripped 14mm spark plug threaded hole is too large for the thread repair inserts as mentioned above È, or if a smaller (14mm) spark plug is to be used (such as for a Wisconsin engine), the hole can be repaired or converted to smaller threads with a mild steel 1/2" NPT Allen pipe plug. Here's how to do it:

  1. If necessary, use a 23/32" drill bit to enlarge the hole for the spark plug hole.
  2. Use a 1/2" NPT tap to cut threads in the hole perpendicular to the head. USE CAUTION! Don't get carried away the first time! Meaning don't cut the threads too big or the pipe plug will set too deep in the hole! The tap should go about 3/4's in the hole, which should allow the plug to set midway in the hole when tightened. Just cut a little bit, then install the plug to check the depth. Remove the plug and cut a little more if necessary.
  3. Install the pipe plug in the head with high strength liquid threadlocker and tighten securely.
  4. Use a 1/2" drill bit to bore the center of the pipe plug perpendicular to the head. This is best performed with the head firmly clamped on the table of a vertical milling machine.
  5. For the spark plug to seat (seal) against the plug, reface (mill) the pipe plug on both ends so it'll be flush with the outside of the head and inside of the combustion chamber. This is best performed by using a small diameter end mill with the cylinder head firmly clamped on the table of a vertical milling machine.
  6. Cut new threads in the pipe plug perpendicular to the head with a 14mm x 1.25 pitch spark plug tap for the spark plug. To accurately start the thread-cutting process, this is best performed with the cylinder head firmly clamped on the table of a vertical milling machine, and slowly rotate the spindle by hand to start the threads in the hole.
  7. Chamfer or bevel the threaded hole (inside and out) with a chamfering bit or larger drill bit to remove any sharp edges.
  8. The spark plug can now be installed.

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...

  1. Strip the engine down to the bare block.
  2. Fasten the billet cylinder head and head gasket on the block with a couple of bolts.
  3. Run a 5/16" diameter steel rod that has a sharp point on one end into each valve guide from inside the block with the pointed end toward the head.
  4. Using a small hammer, lightly tap on the end of the rod so a small impression (punch mark) will be created on the head. These punch marks are the location for the center of the valve heads.
  5. Using a machinists' inside divider caliper, scribe a circle (radius) around each punch mark the same diameter as the valve heads, plus approximately .100" for side clearance.
  6. Now the cylinder head can be machined for the valve cavities and combustion chamber.

How to check for proper valve clearance between the valves and cylinder head...

  1. For the 10-16hp engines, set the valves at their respective clearances. (See above È.) Adjustment is made with a flat feeler gauge and with the lifter held in place with a slender 1/2" open-end wrench and turning the adjuster screw in the lifter with a 7/16" open-end wrench. Make sure the lifters are on the base circle of the cam lobes, too.
  2. Place a small amount of modeling clay, such as Play-Doh, on each valve head and under the head in each valve cavity. (Place some oil on each valve and valve cavity to keep the clay from sticking to either.)
  3. Place the head and gasket on the engine and tighten down a couple of head bolts.
  4. Rotate the crankshaft slowly by hand 360°. If it stops rotating, do not force it, because damage may occur to the camshaft. Remove the head and see if one of the valves made contact with the head.
  5. If the crankshaft rotates freely after 360°, remove the head and use the depth gauge on a dial or digital caliper to determine the thickness of the clay. The clay should have a minimum thickness of about .070".
  6. Remove metal from inside head (valve cavities) as necessary to gain proper clearance.
  7. Clearance around the valves should be the same as above the valves (valve shrouding).
  8. Repeat steps 2 through 6 to gain proper valve to head clearance. 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.

INFORMATION!

USE CAUTION BEFORE INSTALLING A BILLET HEAD!

If you're popping the piston out of the cylinder beyond the thickness of the [compressed] head gasket, and the head isn't cut out for piston clearance (there should be a minimum of .030" clearance between the piston and head), this could (or more likely, will) cause the piston to hit the head. When this happens, the upper half of the bearing insert will become flattened, and this will cause the connecting rod to run loose on the crank journal. And when this happens, the engine will knock, the rod bolts will stretch and the rod and/or bolts will eventually break. These series of events are a common problem when using a billet head. So always check the clearance between the piston and head before using a billet head. And make sure that there is at least .075" clearance between the spark plug tip and the exhaust valve when the valve is at its highest lift point, and .075" clearance between the intake valve and head! By the way - on the late model cylinder heads that some single cylinder Kohler engines use have the spark plug located directly over the exhaust valve. They did this to gain more power by maintaining the heat in a certain area and to keep incoming raw fuel from fouling the spark plug.

É Below is a drawing and picture of a custom designed combustion chamber in a billet head. ÊCustom Designed Combustion Chamber by Vogel Manufacturing Company

Picture by Vogel Manufacturing Company

É Torque the head bolts in the following order in the drawings below. Ê
ALWAYS torque head bolts in a cross-pattern sequence so the head won't become warped!

NOTE: If the torque value(s) are shown only in inch pounds (in. lb.), and the only tool you have is a torque wrench that shows in foot pounds (ft. lb.), you can convert inch pounds into foot pounds by dividing the torque value by 12. Example: if the value is shown in 420 in. lb., then divide 420 by 12 = 35 ft. lb.

When replacing the head bolts, always use grade 8 bolts or heat-treated steel studs with grade 8 nuts. Because stainless steel bolts have the same strength as grade 5 bolts. Which means if stainless steel or grade 5 bolts are used, the threads may stretch over time, causing a compression leak and/or a warped head.

How to Repair A Loose Valve Seat and Worn or Loose Valve Guides in the K361 18hp OHV Cylinder Head -

The Kohler engine model K361 18hp single cylinder cast iron block OHV 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:

  1. Acquire a quality bronze valve seat insert with the outside diameter slightly larger than the counterbore of the old seat, but the same approximate inside diameter so the original size valve can be reused. FYI - Bronze is highly recommended because it grips aluminum better than any steel valve seat. Plus, bronze is harder than cast iron.
  2. With the head set up in a valve seat machine or on the table of a milling machine with the right kind of tooling, cut into the head to remove the old seat.
  3. Bore the counterbore for the new seat .005" smaller than the outside diameter of the new seat and machine the depth of the counterbore the same height as the new seat. The .005" interference fit is the standard for a perfect press fit regarding a valve seat insert.
  4. Chamfer or bevel the lower outer edge of the new seat in a small metal lathe for easier installation into the counterbore.
  5. Apply high strength liquid threadlocker on the circumference of the seat and/or in the counterbore.
  6. Press or drive the new seat perpendicular into the counterbore until it bottoms out.
  7. The seat angle is then cut or ground to match the angle on the valve face and be perpendicular with the centerline of the valve guide.
  8. NOTE - If a small "stress crack" forms between the valves after the seat is installed, this will hurt absolutely nothing because the crack only goes down about half the depth of the installed seat. And besides, the engine is not water-cooled.

About Installing Bigger Valves in the K361 (18hp) OHV 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 rpms. 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 flat belt or large disc sander until perfectly flat again, 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.

Removing 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 NC tap to clean the threads. If you feel this is too much for you, you can take your engine to a machine shop and have them do this for you.

How to make your own modeling clay (Play-Doh):
2-1/2 Cups All Purpose Flour
1/2 Cup Salt
1 Tablespoon Cream of Tartar or Alum
3 Tablespoons Vegetable Oil
2 Cups Water
Directions: 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

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