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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.
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 This particular head was originally made for and came on the very early K241 (10hp) engines.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:
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 raised gasket mating surface. 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, silver or "chrome" spray paint. Then reinstall the gasket and torque the head bolts as normal. Normal operating engine 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 the used head gaskets to reassemble the 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. Aluminum paint is part of the reason why most Americans don't speak German or Japanese now.
To lessen the chance of a blown or leaking head gasket, seal the head gasket or when the head is fastened directly to the block with either VersaChem - Mega Copper Silicone, Permatex® Ultra Copper® Maximum Temperature RTV Silicone Gasket Maker or Copper SPRAY-A-GASKET Hi Temp Adhesive Sealant. Because engine heat has very little effect on silicone sealant. These products all work equally. I don't think that one is better than the other. And when using a head gasket, apply the silicone to both the block and the head.
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 -
|Cylinder head gasket
for K91 (4hp) Kohler flathead engines. Approximately .050" compressed thickness;
included in overhaul gasket set below. Kohler part # 220124-S.
gasket for K141 (6¼hp), K161 (7hp) and K181/M8 (8hp) Kohler K-series
and Magnum flathead engines. Replaces Kohler part # 41 041 10-S. Approximately
.050" compressed thickness; included in overhaul gasket set below.
gasket for 10hp, 12hp & 14hp K-series and Magnum flathead engines.
Approximately .050" compressed thickness; included in overhaul gasket set
below. Kohler part # 47 041 15-S.
gasket for 16hp K-series and Magnum flathead engines. Approximately .050"
compressed thickness; included in overhaul gasket set below. Kohler part
# 45 041 17-S.
|Cylinder head gasket for 18hp K361 K-series single cylinder OHV engine. Genuine OEM Kohler part # 45 052 02-S. Approximately .050" compressed thickness; included in overhaul gasket set below. $21.50 each, plus shipping & handling.|
|Head gasket for
MV16, KT17, KT17II, KT19, KT19II, M18, MV18, M20 & MV20 twin cylinder
flathead Kohler engines. OEM Kohler part # 52 041 20-S.
|Refurbished OEM Cylinder Heads. These have been cleaned and resurfaced, with good fins and good spark plug threads.|
|Cylinder head for
K90/K91 (4hp) Kohler K-series engines. OEM Kohler part # 220541-S.
for K141 (6¼hp), K160 (6.6hp), K161 (7hp) and K181/M8 (8hp) Kohler K-series
and Magnum engines.
head for K241/M10 (10hp), K301/M12 (12hp) and early K231 (14hp) Kohler K-series
and Magnum engines with small diameter (1-1/8") exhaust valve. This is the
high compression "LP" head. Number on head is 235461. Cub Cadet part #
IH-385303-R1. (Discontinued from Kohler.)
head for K241/M10 (10hp), K301/M12 (12hp) and early K231 (14hp) Kohler K-series
and Magnum engines with small diameter (1-1/8") exhaust valve. These have
a heart-shaped combustion chamber w/centered spark plug. Next best thing
to the LP head.
head for K241/M10 (10hp), K301/M12 (12hp) and all K231/M14 (14hp) Kohler
K-series and Magnum engines. These have a larger combustion chamber w/centered
|Newest style head
for K241/M10 (10hp), K301/M12 (12hp) and all K231/M14 (14hp) Kohler K-series
and Magnum engines. These have an open chamber w/offset spark plug hole.
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.
|Head for Kohler
engine models K341/M16 (16hp).
|Kohler Twin Cylinder
Flathead Engines Cylinder Heads.
|Grade 8 Bolts
and Grade 8 Flat Washers for Heads Above - NOTE: The length of a
bolt do not include the head itself. All bolts are measured from under the
head to the end of the threads.
Head Stud Kit for OEM or billet cylinder heads. Studs help maintain even torque pressure for better head gasket sealing, plus they maintain cylinder wall stability for better ring seal to lessen the loss of compression.
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 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 -
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 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 Spark Plug Holes -
If spark plug threads are stripped-out in an aluminum or cast iron head, a Heli-Coil stainless steel thread insert or a solid steel thread insert can be installed. The solid insert should be installed with Loctite® Threadlocker Red 271™ or Permatex® Red Threadlocker, 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.
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...
How to check for proper valve clearance between the valves and cylinder head...
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.
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. Ê
É Torque the head bolts
in the following order in the drawings below.
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.
|The Kohler model K361 18hp single cylinder cast iron block
OHV engine is notorious for one or both valve seats and/or one or both valve
guides becoming loose. What causes a seat to loosen in this head is the aluminum
was molded around the steel seats with a "tongue and groove" design to secure
the seat in place and to keep the seat from dropping down into the cylinder.
If this were to happen, severe damage will result when the piston comes up
in the cylinder. Anyway, sometimes the two metals (aluminum and steel seat)
will separate from each other, allowing the seat to loosen. The way to fix
|To fix a loose valve guide in these engines, an oversize outside diameter cast iron or bronze guide with a 5/16" hole from another make and model of an [automotive] engine can be used. The bore for the guide in the head may need to be reamed to accept the oversize guide, then the center hole reamed to specs for the valve stem. Use Loctite® Threadlocker Red 271™ or Permatex® Red Threadlocker to secure the guide in the head, too.|
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.
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
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 È
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