Information
about Cylinder Heads for Single Cylinder Kohler Engines
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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head was originally made for and came on the very early K241 (10hp) engines.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 -
Compression ratios for factory stock Kohler engines are as follows:
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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 check the piston and valve clearances. The
valves need a minimum safety margin of .100" each.
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 -
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 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.
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 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.
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 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.
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 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.
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 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.
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 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.
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 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.
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 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.
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| 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.
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Cylinder head
for Kohler K-series and Magnum engine models K141 (6¼hp), K160 (6.6hp),
K161 (7hp) and K181/M8 (8hp).
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 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.
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 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.
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 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.
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 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.
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 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.
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 Cylinder Heads
for Kohler KT-series and Magnum Twin Cylinder Flathead Engines.
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 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).
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.
For Kohler engine models K341/M16 (16hp). 3/8" diameter. Replaces Kohler part #'s 270158 (bolt; discontinued from Kohler), 270889-S (washer).
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 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.
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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 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, 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:
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...
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.
How to check for proper valve clearance between the valves and cylinder head...
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".
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.
Ê
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:
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.
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
(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.
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Brian
Miller.
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.
Resurface air-cooled small engine
cylinder head to remove warpage. $7.00 labor, plus return shipping
& handling.