Building a Hot-Rod Kohler K301
Contents
1. _ _ _t _ _ hh i SS SS SS S S S SS S S SS SSS SSS S S have about 8 hours on the engine now Break in oil changed at 5 hours came out almost as clear as it went in a good sign I m using the stock muffler instead of the loud pipe due to obvious reasons don t want to be ex communicated from the neighborhood Also feel a Quiet Line should remain quiet But the exhaust note now has a deeper quality under load and the idle even though steady and misfire free has just a hint of being un stock When mowing notice that the engine barely drops any rom when getting into the high grass have the governor set at 3900 rom no load but still throttle back to 3600 for continuous duty must say that really like my hot rod and encourage anyone else that such an undertaking is worth it These modifications will work equally well on a K321 or K341 totaled up the receipts and have about 500 into this engine One of the best parts of the project was getting the nice compliments from you guys on this web site sincerely thank all of you for your encouraging commentary Lastly must give credit to my shop crew B the cat and Mac the dog without which this project would have progressed at a somewhat faster rate Thanks to B for uniformly depositing cat hairs all over my bench and clean parts and Mac for always lying right where need to be standing2. Building a Hot Rod Kohler K301 For an IH Cub Cadet Garden Tractor Posted by David Kirk on 5 29 01 through 5 31 01 A Loud pipes save lives Actually 4 this picture shows the first test run of a modified Kohler K301 I built up Sema for my 1250 Cub Cadet It was a winter project so took my time and put together a hot rod Kohler something l ve wanted to do for a long time The modifications are typical for L head flathead engines and in this article l Il try and describe what did and show pictures of the parts as the engine went together Now the obvious question is why not install a K321 14 hp or K341 16 hp engine if you wanted more power First of all like the K301 as it is the small block of the 3 25 stroke engine series The small bore means low reciprocating mass thus smoother running and better cooling as the same flywheel hence cooling fan is used on all three engines Secondly it is the right engine to be installed in the 1250 Third the challenge of making the K301 perform hopefully as well as the K341 is reason enough Fourthly am a frustrated hot rodder at heart that can t afford to build a full house V 8 but the next best thing is a Killer Kohler for my Cub ee purchased a rather worn K301 AQS engine from a local used parts supplier Teardown revealed that cylinder bore and crankpin were worn but this was to be expected The block was the first i and most important item
3. a S E E E S E E S E E The piston decided on using is also a Kohler part The service manual identifies this type of piston as style D Mahle the premier piston manufacturer known worldwide for their state of the art components makes it The air cooled Porsche 911 engine has utilized Mahle cylinders and pistons for many years This particular piston Kohler P N 47 874 18 010 oversize has a cam and taper ground skirt recessed pin bosses for a short and therefore light wrist pin and just looks robust and modern compared to the other styles of pistons available It is supplied with the wrist pin pin retainers and piston rings The top compression ring is chromed iron second comp ring and a 3 piece steel rail expander oil ring is used This part is good to go right out of the box no special prepping required The book specified a skirt to cylinder wall clearance of 0045 to 0062 chose 005 about right in the middle of the tolerance band and had the cylinder bored to obtain this clearance Remember this engine will be used for mowing and snow throwing so must have a good life span As for the camshaft learned from Cub Cadet dealer Scott Madson that he has a supplier that regrinds cams to quarter scale puller rule specifications Referred to as a cheater cam you supply your cam to Scott along with 55 wait two weeks and it is returned via UPS right to your shop doorstep This price is very reasonable compared wi
4. ainers Keepers and valves are stock Kohler parts used the more expensive Stellite exhaust valve P N 235838 for good durability Both valves were swirl polished They were then chucked in the drill press and using a file the lower edge corner that meets with the 45 degree seat surface was radiused slightly This has shown to raise airflow some 5 when tested on a flow bench Not as trick as a 3 angle valve job but nevertheless better than Oo be The exhaust valve used in the K321 and 341 is larger than the K301 part It was tempting to spend the extra money in machining costs to refit the block with this larger valve But some basic calculations on valve curtain area to available port cross section area showed minimal potential benefits Thus decided to stay with the stock component This picture shows the engine starting to go together I ve found that a standard automotive engine stand works just fine for the Kohler too Here the stator is bolted into place used grade 8 socket head screws with Loctite instead of the stock slotted head screws Note that the bearing plate is left unpainted as well as the other aluminum components wel Here the oil pan dipstick tube and head 4 are bolted on and carefully torqued to book specs know it s anal but paint both sides of the flywheel after masking off the magnets Don t like the thought of bare iron rusting Final assembly is almost complete Note th
5. e billet aluminum breather cover with a road draft tube got tired of dandelion seeds and grass clippings sticking to the oil film that invariably gets on this side of the engine from the stock breather slot designed the cover and a machinist friend with an N C mill made it for me The poor photo doesn t show the 90 degree brass elbow 1 8 pipe thread that screws into the cover and that the rubber hose plugs in to The stock spark plug Champion H 10 is replaced with the next colder heat range H 8 stock number 587 from NAPA Mac guards the treasure Here the engine Is bolted in and we re getting close to the first run During this time the tractor engine bay was thoroughly cleaned and new rubber mounts were installed on the engine mounting rails The PTO clutch was also inspected and cleaned Those with sharp eyes will notice I m using a Walbro carburetor discovered that these carbs can be recalibrated to work as well as the Kohler carb It involves removing the idle calibration pocket welch plug and drilling out the progression hole using a 030 diameter drill in a pin vise The welch plug diameter is 3 8 incidentally The original hole diameter was 022 and thus caused that awful lean spot right off idle I m amazed that the as supplied calibration was so far off Here is a rather blurry close up of the Walbro carburetor The governor rod was modified to be equipped with a ball joint at each end a much
6. inder the cooling airflow in a hi performance air cooled engine The block was then immersed in an ultrasonic cleaner with hot soapy water and allowed to soak for several hours It came out hospital clean and had a nice golden color on all the machined surfaces It was then masked and painted with flat black engine paint that must be baked at 400 deg F to set properly An industrial oven was used for this You don t dare use the wife s oven gives the pizza a funny aftertaste Total time spent on the block about 20 hours This is another blurry picture of the block from the intake port side showing the thermal isolator attached Standard carburetor mounting bolts were replaced with studs and hi temperature lock nuts The cylinder head was bead blasted all over and left unpainted as was the oil pan and bearing plate Bare aluminum parts will dissipate heat better than when painted The head was decked 040 raising compression ratio to 7 45 1 The spark plug hole was blended into the combustion chamber roof by careful radiusing using a hand grinder and an old spark plug as a gauge Next in the build up of the Killer Kohler was the crankshaft It was sent out to have the crankpin ground 010 under as it had worn out of service limits for a standard rod After getting it back it was polished all over using a hand grinder The finish reduces windage losses but more importantly a smooth surface is less prone to fail d
7. more precise and better looking setup than stock This shows the right side of the engine where the Mercury Le outboard voltage regulator replaces the stock item This P gt contains the tach driver circuitry K for the instrument panel Lo m mounted Datcon tachometer The chrome coil is an aftermarket unit made by Compu Fire Ignition timing is set at the factory recommended advance of 20 degrees btdc With the crankcase now filled with 1 5 quarts of Resolute brand non detergent 30 weight the battery attached and gas in the tank I m ready for the first start Crank thru two compression strokes with full choke fires and kicks the Bendix drive out Choke off cranks thru two more cycles and she lights off with a puff of blue smoke out the stack reminiscent of a Pratt amp Whitney That s the excess build up oil in the cylinder burning off nothing to worry about With the straight pipe can feel the scorn of the neighbors already she definitely barks let it idle at 1500 rom and warm up for about 15 minutes Can t resist a blip or two on the throttle sounds like a 1 cylinder Harley on steroids Shut her down let it cool back to room temp and then re torque the head bolts to proper specs Now all that s left is to reinstall the head baffling PTO clutch and the front end hood assemblies There is nothing quite like the first start of a new engine or even a rebuilt one It is always a magical experience for me
8. th cams from other suppliers running in the hundreds of dollars The cams are recarburized and the surface finish appeared very smooth When acam is reground the base circle gets smaller and this throws the geometry of the compression release off a bit Thus a little rework is necessary here and involves hand grinding and radiusing the sharp edges on the tab Final tweaking and bending of the tab is necessary after valve train and cam are assembled in the block The cam lobes were polished with a ScotchBrite pad before assembly thus removing some of the scale that remained from carburizing degreed this cam after assembly and it s noticeably more aggressive in duration and overlap but lift is same as stock at approximately 312 The valve opening and closing acceleration rates are higher than original as well Total time spent on the camshaft about 2 hours For lifters chose these large base parts available from Midwest Super Cub for 10 each While a large base lifter was not really necessary with this cam the original lifters showed some wear and needed replacing anyway These parts are actually lifters from a Wisconsin engine that just happen to fit a Kohler After assembly found that the lifters were too long and held the valves off the seats slightly had to surface grind down the adjusting screws approximately 060 to allow ample clearance Next in the Kohler build up is the valve train The springs ret
9. that started work on had the cylinder bored 010 over and the valve seats re cut this work being done by the local automotive machine shop then ported and polished both inlet and exhaust runners using a hand grinder Both inlet and exhaust valve pockets on the block deck were radiused and blended into the deck surface known as a partial relief in flathead terms These modifications remove some of the restrictions to gas flow allowing better breathing and ultimately better performance At the carburetor mounting surface Kohler provided a lead in chamfer that attempts to correct for possible carburetor misalignment to the inlet port On a production line built engine this is a good feature but for a hand built engine it can be improved upon The chamfer forms a discontinuity that is disruptive to gas flow Thus to correct this the carb thermal isolator was screwed down to the block and JB Weld used to fill up this chamfer After hardening and using the isolator as a template the excess was hand ground away The result was a perfect uniform blend from isolator to inlet port diameter Also not shown in the picture is the amount of casting flash that was eliminated between the cooling fins and the valve port areas in the cooling air circuit several hours were spent with a hacksaw blade and rat tail file getting this flash removed Remember higher power outputs create higher heat loads and you want nothing to h
10. ue to reduced stress concentrators After polishing a coat of Hoppe s gun bluing was applied to make it look nice and prevent rusting The crankpin was left un blued but polished with 600 grit emery cloth lightly Total time on this part about 4 hours a a a a a a a a a a eS a a a eS a l The next important component is the connecting rod Don Vogt a highly respected engine builder turned me on to this one Kohler made an 18 hp version of the K341 which they called the K361 It was a K341 with overhead valves But the con rod used in this engine is an Alcoa aluminum FORGING instead of the standard die cast part Best of all this lovely rod fits right into the other engines perfectly It has the same external dimensions center distances and mass as the die cast rod The Kohler part numbers are 45 067 16 for std crankpin diameter 45 067 18 for 010 under crankpin diameter This rod is a must for a high performance engine unless you want to spend more on a fully machined billet rod from Midwest Super Cub The Kohler part will set you back about 100 but it s good insurance against failure The outer shanks of the rod were polished to an almost mirror finish again to reduce stress risers The oil hole to the crankpin bearing was chamfered and all sharp external corners and edges were radiused The oil dipper leading edge was sharpened as well Total time to prepare this part about 3 hours ee E E E S a e E
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