Information
about the Cylinder Head on Single Cylinder Kohler Engines
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The cylinder head on Kohler
engine models K141, K161 and K181 (6.6hp, 7hp and 8hp) are all identical.
There are no difference.
Kohler made four different cylinder heads over the years (excluding the 16hp head):
This cylinder head was manufactured
by Kohler during the very early 1960s. 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originally made for and came on the very early 10hp (K241) engines. It'll
also work on the 12hp (K301) engines and the 14hp engines, but being the
newer 14hp engines have a larger exhaust valve, the area around the exhaust
valve in the head will need to be machined out or reduce the size of the
exhaust valve in the block to a 1.125" (same as a 10hp & 12hp exhaust
valves) This can be accomplished by installing a valve seat insert in the
block for the smaller 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 mounting bolts.
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 your 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 a junior high student who's taking shop class to re-cast an aluminum head just like this one for a few bucks. But you'll first need a good head to use as a mold.
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 rpms. Unlike the LP head,
the depression area places the majority of the expanding gases over the piston
instead 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." 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. This head requires 2" long mounting bolts. By the way
- Kohler no longer makes this type of head either. If you want to use one
of these, look around for a good used one. They came on the early 10hp and
12hp engines.
Also, the reason Kohler redesigned the head with the low bosses for the head bolts is so more air flow can get past the bosses to better efficiently cool the other parts of the 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 the 14hp engines because the exhaust valve area was made larger.
(It was manufactured when the 14hp engine 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 mounting 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.
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:
- It prevents cold-starting incoming raw fuel from fouling the spark plug.
- It helps to produce more engine power and torque by retaining the majority of the combustion heat in one area.
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.
 The 16hp (K341) head that's
manufactured by Kohler are in a class all by themselves. They have the depression
and D-shaped combustion chamber. The early ones have the spark plug located
in the center of the combustion chamber, and the newer ones have it located
directly over the exhaust valve. The compression ratio is 7.4:1. It requires
1-1/2" long mounting bolts. And there are no "LP" type 16hp cylinder heads. |
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| If need any of the services below, please contact me, Brian
Miller, at A-1 Miller's Small Engine & Specialty
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1-573-875-4033). Please call any day between 12 noon and 8:00 p.m. Central
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Cylinder Head Work -
|
||||
| Used cylinder heads for 10-16hp Kohler K-series and Magnum engines. These have been cleaned and resurfaced, with good spark plug threads. (When available.) | ||||
| Head for 7hp & 8hp engines. $30.00 each, plus shipping.
High compression "LP" head. $150.00 each, plus shipping.  |
High compression head for 10, 12 & 14hp engines with small exhaust
valve. $50.00 each, plus shipping. |
Head with centered spark plug hole for 10, 12 & 14hp engines having
large or small exhaust valve. $40.00 each, plus shipping. |
Head with offset spark plug hole for 10, 12 & 14hp engines having
large or small exhaust valve. Prevents plug fouling from cold starting.
$40.00 each, plus shipping. |
Head for 16hp engines. $60.00 each, plus shipping. |
 Head Stud
Kit for OEM or billet (with counter-sunk holes) cylinder heads. Studs
maintain an even torque pressure around the head gasket for better sealing
and they maintain cylinder wall stability.
|
||||
the
OHV 18hp K361 Kohler or Tecumseh OHV engines. (Install oversize o.d. valve
seat so the OEM valve can still be reused.): $40.00 each for parts
and labor, plus return shipping.
The causes of burn-out on an aluminum cylinder head on virtually any small gas engine are:
- Too lean of fuel mixture, especially if using a Walbro carburetor above 3,200 rpms.
- Over-advanced ignition timing.
- A combination of the two above.
If you're pulling in class where the rules state 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 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. Use a flat
sanding disc only if the head is warped. If it is warped, have
it
resurfaced on a flat sanding
disc or belt sander until it's 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, resulting in about
1-3 more horsepower. Reworking the
valves so they'll clear the head may also need to be done. In most cases,
there should be adequate clearance once the head is shaved. Always check
the clearance when the valves are at full lift before "shaving" 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 or "shaving" of a cylinder head (remove the raised ridge that mates with the head gasket) 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.
All of the newest 10hp, 12hp and 14hp cylinder heads will interchange. 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 higher compression combustion chamber and shouldn't be used on the 12 and 14hp engines, except for pulling purposes only using methanol fuel. The reason for this is because the compression will be so high, the engine will run too hot for gas, and severe damage to the engine may result. The 16hp head is in a class by itself. Compression ratios for factory stock engines are as follows: 8hp - 6.8:1; 10hp - 5.4:1, 12hp is 6.6:1; 14hp - 7.1:1 and the 16hp engines are 7.3:1. There was an early 10hp head that produced a higher compression ratio (6:1), but it didn't flow as well above 4,000 rpm as the later 12hp/14hp head does. For pulling applications, use the later model 12hp/14hp head, even on a 10hp engine. There won't be any drop in power in the 10hp engine because of the improved combustion chamber design in the head.
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.
The ideal location of the spark plug in the cylinder head is in the area between the piston and exhaust valve. The reason for it being close to the exhaust valve is because when heat is maintained in one particular area in any given combustion chamber, the increase in power will be much greater. Fuel within a combustion chamber will "find" or locate the main heat source. When the majority of the heat is maintained in a certain area, the fuel will burn more thoroughly, allowing the engine to produce more power at any rpm. If the plug is positioned in the center of the combustion chamber, the incoming fuel could splash against the plug tip and cause the engine to misfire or run erratic at high speed, especially when burning methanol. And the plug could easily become fouled when burning gas.
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.
When
making a new hole for the spark plug, use the proper size drill bit (1/2"
for 14mm threads) to bore the hole and then use a 14mm size x 1.25 pitch
spark plug threading tap to cut the threads. If the spark plug hole is drilled
crooked or the threads are cut crooked, the spark plug won't seat properly
and loss of compression will result. You can get a spark plug tap at a local
hardware store or machine shop/steel supply company. Don't use a spark plug
thread hole chaser tap to cut new threads. They're made to clean and renew
damaged threads. Click HERE
to learn the correct way of cutting threads.
If by chance the threads are either stripped out or ruined, a
Heli-Coil stainless steel 14mm size x 1.25 pitch spark
plug thread insert can be installed. You can get a Heli-Coil thread repair
kit at virtually any auto parts store or have a machine shop install an insert
for a few dollars. For cleanliness and to prevent premature engine wear,
the cylinder head must be removed! By the way - stainless steel thread inserts
is absolutely, without a doubt stronger than any aluminum threads.
- If necessary, enlarge the spark plug hole with a 23/32" drill bit.
- Cut threads SQUARELY in the hole with a 1/2" NPT tap. Click HERE to learn how to do this correctly. Don't cut the threads too big or the pipe plug will set too deep in the hole!
- Install the pipe plug with Loctite® Threadlocker Red and tighten securely.
- Drill the center of the pipe plug SQUARELY with a 1/2" drill bit.
- Mill the plug on both sides so it'll be flush with the rest of the head.
- Cut threads SQUARELY with a 14mm x 1.25 pitch tap for the spark plug (click HERE to learn how to do this correctly), and then chamfer the edges of the hole.
Or as the last resort, the stripped hole can also be welded up with aluminum welding, then re-machined for installation of a spark plug. And remove the head from the engine before doing any machine work on the head, to prevent metal shavings from getting into the combustion chamber.
How to locate where to cut in the cylinder head for the valves...
- Strip the engine down to the bare block.
- Fasten the cylinder head and gasket on the block with a couple of bolts.
- 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.
- Using a hammer, 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.
-
Using
a machinists' caliper, divider or protractor, draw a circle (radius) around
each punch mark the same diameter as the valve heads, plus approximately
.100" for clearance.
- Now you can machine the cylinder head for the valve cavities and combustion chamber.
How to check for proper valve clearance between the valves and cylinder head:
- Install the valves and set clearance for both valves at .010".
- Place a small amount of modeling clay 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.)
- Place the head and gasket on the engine and tighten down a couple of head bolts.
- Rotate the engine slowly by hand 360º. If it stops rotating, do not force it! (Because a valve may get bent.) Remove the head and see if one of the valves is hitting the head.
- If the engine does rotate freely, and after rotating it 360º, remove the head and use the depth gauge on a dial caliper to check to see how much the clay has flattened out.
- Remove metal from inside head (valve cavities) as necessary to gain proper clearance.
- Clearance around the valves should be the same as above the valves (valve shrouding).
- Repeat steps 2 through 6 to gain proper valve to head clearance. Return to previous paragraph È
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
The above drawing and picture are by
Vogel Manufacturing Company
(http://www.vogelmanufacturing.com).
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 head bolts, always use grade 8 bolts. Because stainless steel bolts have the same strength as grade 5 bolts. Which means the threads may stretch over time, causing a leak or a warped head. But grade 8 won't stretch.
For billet head blanks and possible machining of the combustion chamber, contact Lakota Racing (http://www.lakotaracing.com), Nichols Performance (http://nicholsperformance-online.com) or Vogel Manufacturing Company (http://www.vogelmanufacturing.com).
Reusing OEM Head Gaskets -
Most used OEM metal-shielded head gasket can be reused if it is in good condition (not bent or burned-out). They can be cleaned on a wire wheel and coated 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!
Another thing that works great
to reseal old head gaskets or when the head is fastened directly to the block
is Permatex® Ultra Copper® Maximum Temperature RTV Silicone Gasket
Maker or Copper SPRAY-A-GASKET Hi Temp Adhesive Sealant. Because engine heat
has no effect on silicone sealer. And did you know that aluminum paint was
first used on used head gaskets that was on the American WW2 fighter planes
to reassemble the engines? It was used because at the time there was a shortage
of new head gaskets. This is part of the reason why Americans don't speak
German and Japanese now. 
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 È
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