The Differences Between the Older Kohler K-series and the Newer Kohler Magnum Engines

P The Magnum engines replaced the older K-series in later years. The Magnum engines are basically the same engine as the K-series. The main differences are, besides the sheet metal that covers the block, the Magnum has solid state electronic ignition, a fixed main jet (Walbro) carburetor and the starter fastens to the bearing plate instead of the engine block. And there are no provisions for using ignition points. Most of the external and all the internal parts are interchangeable, and most aftermarket (high-performance) parts are interchangeable with either engine. And if you're looking for some yellow paint to paint your Cub Cadet with, try your local farm and home supply store. They usually have International Harvester Yellow. It closely matches the color of Cub Cadet yellow.

Why Aluminum Block Engines (except V-Twins) Don't Work Well for Pulling Competition

An aluminum engine block will "bend and twist" or flex a few thousands of an inch when hot and under pulling stress. Therefore, they'll lose valuable compression because the valves become unseated and the piston rings lose partial contact against the cylinder wall. Not to mention the main bearings are also put into a bind under the stress of pulling. Cast iron engine blocks on the other hand hold their shape a lot better when hot and under stress. Aluminum engines work best for conditions that doesn't place them in a lot of stress. Such as ATVs, racing go-karts, racing lawn mowers, etc. Because there's fresh air moving over the engine, keeping the metal cool, and the block isn't being strained by the vehicle pulling a heavy load. That's why cast iron Kohler engines work best for competitive pulling. Because cast iron is able to "hold its shape," handle high operating temperatures, severe stress, high compression and very high rpms (above 4,000 rpm). This is why riding mowers, lawn tractors, lawn and garden tractors all have aluminum block engines. And most garden tractors have a cast iron engine block. In addition, on the cast iron block single cylinder Briggs and Stratton and Tecumseh engines, the valve stems are parallel to the cylinder. This means that the valve heads set further away from the piston. And in the cast iron block single cylinder Kohler engines, the valve heads are set closer to the piston (valve stems are angled). Therefore, the other engines can't build up as much compression as the Kohler engines can. Plus, they can't flow as much air in and out of the combustion chamber at high rpms, like the Kohler engines can.

How To Determine If An Engine Needs To Be Rebuilt

Before the engine is removed from the tractor and disassembled, first, remove the cylinder head and observe the top of the piston. If it's covered with carbon, then the piston rings are in good condition. But if some of the carbon is washed away and there's oil present, this means that the rings are worn and the piston and rings need replacing, or maybe the cylinder needs to be rebored for installation of an oversized piston and rings assembly. Now move to the valves. With the piston at TDC on the compression stroke (both valves fully closed), spray some WD-40 around each valve head and then use compressed air to blow through the exhaust and intake ports. Wrap a rag around the air nozzle and place it against the port so full air pressure will be against the valve. If bubbles form around the valves when applying the air pressure, this means that the valves are leaking and a professional valve job is required. To remove the engine from a typical IH Cub Cadet, first disconnect the battery negative terminal and disconnect all the wiring from the engine and fuel line if the gas tank is separate from the engine. Then remove the PTO clutch engaging linkage, remove the engine mounting bolts, then slide the engine forward so it'll clear the clutch disc or driveshaft, then lift the engine out of the tractor. Now remove the oil pan and connecting rod cap. Observe the rod cap for scoring or burning. Replace or repair it if necessary. Also, the crankshaft journal may be worn and if it is, it will need to be reground to the next undersize. And have the crank journal mic'd (precision measured with a micrometer) to determine if it's excessively worn. If it is worn, it can be reground to .010" and a .010" undersize connecting rod can be used or you can have your old rod bored for installation of .010" bearing inserts. But if it needs to be reground to .020" or .030", the rod will need to be bored for installation of matching bearing inserts. The only OEM rods available without a bearing are STD and .010" undersize. If the cylinder wall is badly scored or tapered, have it bored to the next oversize. The only pistons available for a stock engine are STD, .010", .020" and .030". If the cylinder is worn beyond for installation for a .030" piston/rings assembly, it will need to be sleeved for installation of a STD size piston/rings assembly. But if building an engine for more power, don't have the cylinder bored to a maximum of .030" if it doesn't need it. Because a .030" overbore won't necessarily give an engine more power. Having a longer crankshaft stroke increases the power.

Don't Be A Slob When Rebuilding An Engine!

Always be professional whenever you rebuild an engine! Before assembling a fresh engine, always take the time to provide a neat and absolutely clean work environment. Make sure that your repair table or bench is sturdy enough to support the weight of a fully assembled cast iron bock Kohler engine. And make sure that your tools, shop towels, engine parts and hands are clean, too. Don't allow any dust or dirt to enter the work area, including the engine block and it's internal parts. If necessary, place the engine parts on a large, clean cloth or cardboard to help keep them clean and organized until they're ready to be installed. The reason everything should be kept as clean as possible is because even the smallest bit of dirt inside an engine will "grind away" at the internal parts when the engine is in operation, causing unnecessary and expensive wear. You can also use an automotive engine stand to rebuild a Kohler engine. Just use the two starter bolt holes on the side of the block to mount your engine to the stand. You can completely disassemble and reassemble the entire engine, except for the starter, and you can get at everything on the outside and inside of the engine with no problems. To "basically" overhaul or rebuild an engine that burns a lot of oil, all that needs to be done on a Kohler engine is remove the oil pan and cylinder head, disconnect the connecting rod from the crankshaft and then drive the piston and rod out of the block with a long wooden stick and a medium size hammer. Inspect the entire piston and cylinder wall for wear. If no wear is evident, then install a new set of rings on the piston (thoroughly clean the parts first though) and reinstall the piston in the block as described. But to do a professional and complete rebuild, read the rest of the information in this web page and linked pages

Important Information About Kohler Crankshafts

Crankshafts, rather being made of steel or cast iron, and despite how well-balanced the rotating parts are in a pulling engine, suffer a lot of vibration at very high rpms in a single cylinder engine. Therefore, if possible, before purchasing a used crankshaft, it's best to look it over for hairline cracks with a strong magnifying glass or better yet, a microscope. And as I always say about buying anything off of eBay: BUYER BEWARE! So ask for a money-back guarantee, or you may have nothing but a piece of scrap metal on your hands.

Identifying Kohler Crankshafts - To identify the 10, 12, 14 and 16hp Kohler crankshafts, the 10hp cranks have a shorter stroke than the other cranks. You can compare a 10hp crank to a 12, 14 or 16hp crank by placing them side by side, and with the counter weights down, looking at the bottom part of the rod journal, the journal on the 10hp will be closer to the main journals. (3/8" of difference in stroke.) The 12hp crankshaft is different from the 14 and 16hp cranks because the counter weights are machined off for the lighter-weight 12hp piston assembly. NOTE: Some 10hp cranks also have the counter weights machined off like the 12hp does, but some don't. And the 14hp and 16hp cranks are identical in weight and appearance. Some may have a few more holes drilled into the counter weights, but that's the only difference.

How to Remove Only the Crankshaft from a Kohler Engine

Remove the flywheel and anything that's on the PTO end of the crankshaft. Remove the cylinder head. Remove the oil pan. Remove the piston/connecting rod assembly from the engine block. Remove the bearing plate. Finally, being very gentle, bump the PTO end of the crankshaft with a large brass head hammer or a large hammer and wooden block to remove it from the engine block. And if an engine originally came with balance gears, there's no need to reinstall them. They serve very little purpose.

Here's Something Important To Keep In Mind About A Reground Crankshaft Journal

When a crankshaft journal (crank pin) wears, they will most likely become "egg shaped" or create a "flat spot." Therefore, when regrinding a journal, and if a standard size journal is not worn past .005" on the low side or the "flat spot," then the crank grinder person can regrind it "centered" to the next undersize, which is .010", or if he gives it an extra .001" of additional oil clearance, it'll have a .011" undersize journal and the crankshaft will retain it's original stroke. But if a standard size journal is worn .006" or more, then the crank grinder can "cheat" and regrind the journal to the next undersize by offsetting the journal .006" or more in the lathe and regrind it to .010". By doing this, and depending on the amount of wear the journal had and the location of the low side or "flat spot," the crankshaft will have a slightly longer or shorter stroke. Otherwise, if the severely worn journal were to be reground "centered," it would have to go to .020" undersize, and the stock stroke will be retained. The decrease or increase of the stroke on a crankshaft with a worn STD, .010" or .020" journal can vary from .001" to .005". and as much as .010" on a STD journal that's been reground to .020" undersize or even .015" on a STD journal that's been reground to .030" undersize! So when a pulling club's rules state that an engine must have the stock factory length stroke, and if a crankshaft was reground, it may actually have a slightly longer or shorter stroke.

When having a crank journal reground for an undersize bearing, it'll be a good idea to indicate to the crank grinder person that you want it ground for high-performance use by writing (with a bright-colored paint marker) the word RACE on one of the counterweights. The grinder person will then give the journal an additional .001" of oil clearance to prevent overheating both the bearing and journal. By the way - the extra .001" of clearance will not cause the rod to knock

More Information About the Crankshaft Journal

The heat-treating or hardening process that Kohler uses on the rod journal area obviously goes deep into the crank. Because it's been proven that when the journal is ground for an undersize bearing, a .010", .020" or even a .030" undersize bearing can be used with no problem. Myself and many other pullers use undersize bearings in our pulling tractors, and we have no problems with the crank journal wearing. Heck, I've been using a .020" undersize bearing with the same crankshaft in my 30 c.i. tractor for 5 years and in about 75 pulls, and the crank journal hasn't worn at all. Most crank journals wear because of dirty motor oil or the wrong viscosity of oil is used. Not because of "soft metal" in the journal. Actually, the bearing material is not supposed to make contact with the crank journal. They're supposed to be kept separate by clean motor oil. And as far as cast iron Kohler crankshafts breaking is concerned, an undersize journal shouldn't make a cast crank break. I've always seen them break next to the journal, not in the journal area. As with anything, crankshafts break because something makes them break. Either out-of-balance parts, dirty flywheel taper/crankshaft taper or a manufacturing defect makes a crankshaft break. By the way, a crank journal that's been turned .030" undersize will help to produce slightly more rpms and horsepower because there's less bearing surface to cause friction. Some NASCAR engineers do this to their racing engines. It works.

How to Fix a Broken Off Crankshaft Stud (this happens a lot, by the way)

The easiest and quickest way to fix a broken off crankshaft stud is with the crankshaft in the engine is to place the engine on a drill press table with the crank end facing upward. To install a 3/8-24 NF bolt, drill an 11/32" hole in the crank end at dead center, 1-1/2" deep. Or to install a 5/8-18 NF bolt, as a pilot hole, drill an 11/32" hole in the crank end at dead center, 1-1/2" deep. Then enlarge the hole with a 37/64" drill bit. Place either a 3/8-24 NF or 5/8-18 NF tap (whichever you choose to use) in the drill's chuck to start the threads straight into the crankshaft (to avoid starting the threads crooked). Finally, install either a 3/8" or 5/8" diameter grade 5 bolt with a lockwasher and wide flat washer to secure the flywheel to the crankshaft.

Another method to fix a broken off stud on a crankshaft with the crank out of the engine

Chuck the PTO end of the crank in a metal lathe chuck, with the flywheel end supported by a steady rest. To install a 3/8-24 NF bolt, drill an 11/32" hole in the crank end at dead center, 1-1/2" deep. Or to install a 5/8-18 NF bolt, as a pilot hole, drill an 11/32" hole in the crank end at dead center, 1-1/2" deep. Then enlarge the hole with a 37/64" drill bit. Place either a 3/8-24 NF or 5/8-18 NF tap (whichever you choose to use) in the drill's chuck to start the threads straight into the crankshaft (to avoid starting the threads crooked). Finally, install either a 3/8" or 5/8" diameter grade 5 bolt with a lockwasher and wide flat washer to secure the flywheel to the crankshaft

Removing and Replacing the Governor Gear Assembly in a Single Cylinder Kohler Engine

Remove the internal parts of the engine (mainly the crankshaft and camshaft). Remove the governor gear retaining screw (the Phillips head screw that's on the side of the engine block). The governor gear should now just slide off the stub shaft. Be sure to remove and save the small thrush washer that's on the governor gear's stub shaft! (A lot of people are not aware of this hardened/heat-treated steel thrush washer and it usually falls off and gets lost while washing inside the block.) Install the new governor gear/flyweights assembly in reverse order of removal.
By the way - The governor gears can be lightened so engine rpms will raise more than usual when it's under a load. Drill an 1/8" hole through each flyweight sideways and not from the top. This does not weaken the weight material. When the load hits, the engine rpms will climb.  The most popular governor gear assembly nowadays for stock garden tractor pulling are the ones that's made of cast iron. These were used in the 4hp, 7hp, early 10hp and early 12hp K-series Kohler engines 'til the late 1960s. These are are no longer available from Kohler or any source. There's nothing really special about them, except when the governor linkage is disconnected, they can withstand very high rpms and won't explode (break apart) like the plastic governor gear assemblies sometimes do. The reason the cast iron ones are so popular nowadays among stock pullers is because some pullers like to compete in two separate classes, one class that has an engine rpm limit of around 4,000± and another class with a higher rpm limit, or open rpms. The cast iron governor gear will fit all Kohler K-series and Magnum 10hp-16hp M10-M16 / K-241-K-341 flatheads and 18hp K-361 OHV single cylinder cast iron block engines. And the plastic governor gear assemblies will hold up just fine in an engine that will never run above 4,000 rpms.

How to Get More Power Out of a Stock Engine

It takes three things to make an internal combustion engine run: compression, carburetion and ignition. Actually, it takes four things, including the starting system. If an engine won't start or if it's hard to start, and it has adequate compression, the carburetor and ignition seems to be working fine, then the only thing left is the starting system. Perhaps the starter motor or battery is going bad. They probably appear to be operating normal, but maybe one or the other isn't cranking the engine over fast enough to produce adequate compression to start the engine. I've seen this happen a few times. But if the compression, carburetion or ignition is weak or defective, power will be decreased dramatically. When checking for loss of power, always check the following things:
ü Carburetion is when an adequate amount of fuel and air enters an engine smoothly.
ü Check the ignition timing. Chances are, if the timing isn't advanced enough, the engine will lose power and run sluggish. Check for a worn points lobe on the camshaft, too.
ü Compression is when the air/fuel mixture is adequately pressurized in the combustion chamber on the compression stroke. The secret to gaining more horsepower and torque is increase the compression ratio and improve the air flow in and out of the combustion chamber.
ü Another way to gain more power from the high rpm is to install a special camshaft along with larger diameter valves, stiffer valve springs and porting/polishing the intake and exhaust runners.
ü Apply epoxy (such a JB Weld) inside the intake port and smooth it so the air will flow without any restrictions into the combustion chamber. This works great. But before applying the epoxy, make sure the port is absolutely clean or the epoxy won't bond to the engine block

When it's time to put more muscle in your engine

In order for an engine to turn at extremely high rpms (6,000+), the compression ratio and air flow in and out of the combustion chamber must be increased to the maximum. The secret to increased engine performance is to get as much air (and fuel) into the combustion chamber, and get it out as quickly as possible. (Remember - engine performance is entertainment to the spectators.) For the compression ratio to be increased, the air entering the combustion chamber must be squeezed as tight as possible. To raise the compression and increase the air flow on a flathead engine.... Mill the stock cylinder head .050", or mill out a specially designed combustion chamber in a billet aluminum head so the air can be squeezed tighter. Click here for more info on this. Pop the piston out of the cylinder a few thousands of an inch. Doing this is the same as using dome pistons in an over head valve engine. Click here for more info on this.
NOTE: the cylinder head can be milled .050" and the connecting rod offset .020" for piston pop-out. Being the cylinder head gasket has a compressed thickness of .050", this will give the top of the piston a safety margin of .030" clearance. Install a special camshaft with increased duration and valve lift. Cams with increased duration holds the valves open longer to trap the air in the combustion chamber at higher rpms. This builds up more compression in the combustion chamber. Click here for more info on this. Install oversized intake and exhaust valves, along with offset valve guides, or at least for the intake valve. At very high rpms, a bigger intake valve will allow an engine to draw more air (and fuel) into the combustion chamber, and the bigger exhaust valve will allow quicker and easier exiting of the exhaust gases. In a high-compression and high-rpm engine, air must pass through the combustion chamber very quickly with no restrictions. Bigger valves will allow this. More air that's crammed into the combustion chamber means higher pressures, higher rpms and more power. The offset guides will move the valve head(s) closer to each other and closer to the piston, to retain (with a stock head) or create (with a billet head) a smaller combustion chamber so the air can be squeezed tighter in the combustion chamber. Click here for more info on this. Enlarge and smooth the ports in the intake and exhaust runners. In addition to the larger valves and bigger cam, porting and polishing will also allow an engine to pass more air (and fuel) through the combustion chamber. Otherwise, this area would have restricted airflow or be a "bottleneck" and very little will be gained. Click here for more info on this. Apply epoxy (such a JB Weld) inside the intake port and smooth it so the air will flow without any restrictions into the combustion chamber. This works great. But before applying the epoxy, make sure the port is absolutely clean or the epoxy won't bond to the engine block. In addition to the bigger cam, larger valves and ports, the venturi that's inside the carburetor throttle bore must be removed, or a larger carburetor can be used. Doing this will also allow an engine to draw more air (and fuel) into the combustion chamber. Use of an unrestricted air filter or a velocity stack will help, too. Click here for more info on this. Increasing the length of the piston stroke in the cylinder will also increase the compression ratio.
The only things that can cause an engine to overheat and loose power are as follows: Clogged cooling fins or broken fins on the flywheel Too high compression ratio for the grade of gas being used Ignition timing advanced too much Lean fuel mixture Vacuum leak at the carburetor, which will also cause a lean fuel mixture

How To Get Maximum Horsepower and Torque from a "Basically Stock" Kohler 10-16hp K-Series or Magnum Engine

Approximately 48% more horsepower and torque can be produced from a basically "stock" single cylinder flathead Kohler engine. This means that approximately 15hp can be produced from a 10hp, 17hp from a 12hp, 20hp from a 14hp and 23hp from a 16hp governed engine at 4,000 rpm (the factory setting of maximum rpm for virtually all small gas engines, including all of Kohler engines is 3,600) on Premium gasoline! And if the majority of the fins are removed from the flywheel, or if a steel flywheel is used, this will add about 3-4 more hp per engine! Also, about 10% to 13% more power can be produced with E-85 or methanol fuels! Click here for information regarding E-85 fuel. The above figures was computed using Mr. Gasket's DeskTop Dyno computer application. (Do a search on the Internet for this application.) And even more power can be produced above 4,000 rpm! But be sure to install a billet steel flywheel, connecting rod and scatter shields whenever running an engine above 4,000 rpm! The compression ratio must be increased in order to increase the power output. Click here for references to various compression ratios. After modifications have been made, the increase in power will definitely be noticeable! Rather if it's used for pulling competitively or just for yard work, a "built to the max" stock engine will perform much better with the modifications listed below...

Here's Some Basic External and [Fairly] Low Cost Performance Improvements That Can Be Done

Perform a quality tune up. Install new ignition points, condenser and spark plug. Set the ignition timing at 20º BTDC. Don't trust a feeler gauge in the point gap. Use an ohm meter or test light (with the engine not running) or an automotive inductive timing light (with the engine running). Index the spark plug. This is when the open gap faces the piston. It helps to produce a little more power, especially at higher rpms. Only on the 10-16hp flathead Kohler engines, mill the stock cylinder head approximately .050" to increase the compression ratio. Remove just the "ridge" that mates with the head gasket. 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 done on a vertical milling machine with a flycutter and not on a sanding disc. Use the sanding disc only if a 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! NOTE: Do not mill the head to increase the compression on the 7hp and 8hp cast iron block Kohler engines. Because on these heads, the clearance is already very close between the valves and head. If it's warped, have it resurfaced on a flat sanding disc or belt sander. Or install a high compression, "LP" cylinder head. For more information, click HERE. (NOTE: This may not be a low cost improvement if you're purchasing one of these heads off eBay.) Perform a quality valve job. Grind a 30º angle on the face of the intake valve and seat only, and undercut and swirl-polish the intake valve head so more air/fuel will enter the combustion chamber. Because any restriction of the intake system will cause an engine not to produce more power. And for the exhaust to exit the combustion chamber quickly, grind a 45º angle and undercut the exhaust valve head. Because any restriction of the exhaust system will cause an engine to lose power. Click here to learn how to do a professional valve job. Set the valve lash (clearance) at .010" for the intake and .014" for the exhaust. Make sure that the ends of the lifters and valve stems are ground square for proper adjustment. For ordinary yard use, heavy towing, garden tilling, snow removal, etc., for a 10hp and 12hp engine, install a #30 (1.2" throttle bore) carburetor. (The #30 or 1.2" bore) carburetor originally comes on the 14hp and 16hp engines.) Either a Carter, Kohler or Walbro carburetor will work equally as well. Or have a #26 Carter or Kohler carburetor bored. (A #26 carburetor will flow more air than a stock #30 carburetor.) Rework the carburetor (bore out the venturi, grind the main nozzle, etc.) as described in my carbfuel.htm web page. Enlarge the ports the same size as the carburetor throttle bore (only if the carburetor have been bored out) and polish (smooth) the intake and exhaust runners. Just smooth up the exhaust port and remove any rough casting slag. Being there's no long intake tube for the gas to atomize in before it reaches the combustion chamber, the Kohler OEM thick carburetor mounting gasket (which is actually a piece of plastic-like material sandwiched between two gaskets) isolates the carburetor from the engine heat so the gas will atomize better when it before it enters the combustion chamber. Atomized gas vapors mixes with the air better, and make the engine produce more power. For up to 4,000 rpm, you can either re-use the stock OEM valve springs, or to reduce "valve chatter" and to insure proper valve action, install new OEM springs. And it's safe to re-use the OEM retainers and keepers. To reduce valve float and loss of engine power above 4,000 rpm, use the "lightweight" valve springs (slightly stiffer than OEM) from either Lakota Racing (, Midwest Super Cub ( or Vogel Manufacturing Company ( If you use stiffer springs, the camshaft could break and/or the center of the valve heads may collapse overtime. For pulling competition only, remove or disable the operation of parasitic accessories from the engine (which robs horsepower and causes drag on the engine), such as the starter/generator, alternator charging system, and including reducing the height of the fins by about 3/4 or removing all of the fins from the flywheel. (Personally, I use a reciprocating saw to remove about 3/4 of the height of the fins on my Kohler flywheels. And I ALWAYS have the flywheel dynamically precision balanced afterwards!) The generator part of the starter/generator unit and the alternator system uses about 1-3hp of engine power when it charges the battery at a full 15, 20 or 30 amps with the engine running at 3,600 rpm. So to conserve this power for pulling, disconnect the generator or alternator from charging the battery (and powering other accessories as well) simply by splitting the wire that connects to the FIELD terminal (the smaller wire and terminal) on a starter/generator unit and splitting the wire that connects to the center terminal on the voltage regular of an alternator system. Then connect an ordinary OFF/ON toggle switch in that wire or circuit to turn off and on the charging current. And it'll be best not to spin the starter/generator when pulling. It can use up to 2hp just to spin it. Install a heavy spring on the generator/starter so it'll remain close to the engine. To start the engine, install the belt on the pulleys, then pull out on the generator/starter with a fabricated handle to tighten the belt. After the engine starts, flip the belt off. But use caution doing this for an obvious reason! The wasted energy that's needed to spin the starter/generator needs to be put to the ground. Besides, wouldn't it be better to spin the tires than the starter/generator?
Remove the flywheel fins ONLY if an engine is governed up to 4,000 rpm, and absolutely have a [cast iron] flywheel dynamically precision-balanced afterwards! If an engine is going to be operated well above 4,000 rpm (with no functioning governor), and rather if your pulling club's sanctioning rules require one or not, definitely install a steel flywheel (with no fins).