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Discussion Starter · #1 ·
Hey guys Im doing a rebuild for a friend,it's an old Kohler 12hp off of a wheel horse. It needs new rings but Im not sure what size to get? I cant seem to find any specifications do I need .10 over .20 over I just dont know if you can help me out with this it would be so greatly appreciated :thanku:
Model-k301as
Serial-47742d
 

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Hey guys Im doing a rebuild for a friend,it's an old Kohler 12hp off of a wheel horse. It needs new rings but Im not sure what size to get? I cant seem to find any specifications do I need .10 over .20 over I just dont know if you can help me out with this it would be so greatly appreciated :thanku:
Model-k301as
Serial-47742d
What does the bore measure?
 

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Are you talking about the discoloration? My piston has the same thing, I was told its fine, just from heat? I could be wrong though.
 

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Are you talking about the discoloration? My piston has the same thing, I was told its fine, just from heat? I could be wrong though.
no look at the top ring land; that piston is toast; I would certainly take it by a machinist and have it measured (bore) to see if it is oversize, tapered, out of round. otherwise you will have a short lived rebuild and be doing it all over again.
 

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:banghead3 my mistake, Sorry about that.
 

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That piston looks rough but not as bad as others I have seen, is there any light scoring in the cylinder? With the way the top of your piston looks I would think there would be some light scoring marks.
 

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Go on ebay and get a rebuild kit with the gaskets, piston, rings, rod, and get some crank bearing too. i got all the parts for my K241 for around $250. they all worked out great. I took the block and piston to the machine shop and had them bore it .030 over and had it decked. if you get it all genuine kohler then expect to pay around $800 for all of that.

It looks like the engine got hot which is why your top land is all scraped up/melted. I would definitly get an oversized piston and have it bored for a quality job. It looks like it is standard bore but get it measured before you order parts.
 

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What does the bore look like? The damage to the piston may be just that, and limited to the piston. If that is the case, an overbore and new oversize piston/rings would not be necessary. The top land damage, as long as it has not impacted the bore, should actually cause little problems. The piston is squared on the bore more by the skirt than the top land of the piston. If it were melted, and 'gone', rather than scored a little, I would be more concerned.
My thoughts are to inspect the bore, and if not damaged, get a set of rings of the appropriate size, de-glaze the bore, and re-assemble. You might find that it runs very well without spending a largish pile of money. If the engine is kept to normal operating temperature, and fed a good, non-lean mix, it should run fine for a long time. IMO...
The worst you can come out is that it doesn't and you need to get a new piston, but I expect it to run well.
tom
 

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Go on ebay and get a rebuild kit with the gaskets, piston, rings, rod, and get some crank bearing too. i got all the parts for my K241 for around $250. they all worked out great. I took the block and piston to the machine shop and had them bore it .030 over and had it decked. if you get it all genuine kohler then expect to pay around $800 for all of that.

It looks like the engine got hot which is why your top land is all scraped up/melted. I would definitly get an oversized piston and have it bored for a quality job. It looks like it is standard bore but get it measured before you order parts.
uhh...I paid 325 for Genuine Kohler Rod, piston, Moly Rings, gasket set and seals, governor cross shaft, and carb kit...purchased at full retail through NAPA, for a Kohler M10S which is a K241 engine.

I wouldnt put that Chinese ebay crap anywhere near an engine unless I was just looking to do a fix and flip. I also paid 75 to havr my block punched out 0.030 over and have the head and deck milled true, have the crank polished as well. This was all in Late 2008.
 

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And that slash in the piston crown is the result of pre-ignition/detonation. Most likely running too lean and or with misadjusted points....
 

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Discussion Starter · #14 · (Edited)
Okay well Im going to buy a new ring and piston set for around 50 bucks but still dont know what size to get the original piston has no marking or indication on it saying what size it is so how do I know if I need an oversized or standard? If it means anything the bore size if I mesured correct is 85.50mm and the original mesurements are 85.7 so obviously the walls have worn so do I need oversized? If so what size? :dunno: Also I need to de-glaze the cylinder is the flex hone tool any good?
 

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Okay well Im going to buy a new ring and piston set for around 50 bucks but still dont know what size to get the original piston has no marking or indication on it saying what size it is so how do I know if I need an oversized or standard? If it means anything the bore size if I mesured correct is 85.50mm and the original mesurements are 85.7 so obviously the walls have worn so do I need oversized? If so what size? :dunno:
What kind of tool are you using to measure the bore? You got 85.5mm or 3.366"??

Sorry, but that's not likely..:sorry1:

The Cylinder Bore limits for a K301 from the manual are:

Bore Dia: 3.3755"/ 3.3745" or 85.7737mm / 85.7123mm

Max Diameter: 3.378" or 85.8012mm

Max out of round: 0.003" or 0.0762mm

Use a Bore guage and micrometer at least two ways in three different areas (heights) to measure the bore after cleaning it up thoroughly. The bore / piston wear is usually perpendicular to the crankshaft so look / measure closely there. The center of the bore is usually the first to wear due to the side-to-side forces of the piston as the engine runs. Bring the block over and I'll help ya measure if you'd like! :trink40:
 

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If the piston has no size stamping on the crown, it's safe to assume it's standard size. If it has no direction marks on the crown, you can turn it around on the rod and wear the other side. If it does have a direction mark (I didn't notice any in your photos), it is either cam ground and has an offset wrist pin and must be run in one position only.
 

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Do you consider Sten to be crap also?
I consider anything not in a Genuine Kohler package to be suspect...In small engines, you get what you pay for.

Considering that a failed piston, failed rod, faulty ring...can easily ruin a block, its just good insurance to pay a little more for the Stuff made by the OEM. Its really painful when you take an original engine, pay 25 dollars for a piston, when OEM is 48...and the piston is too light, or too heavy and makes a bad vibration, or the chinese piston cracks or fails and heavily scores the cylinder/block, possibly causing skirt failure which leads to rod failure, and so on.

I know my engine has the right parts in it, I know it was assembled correctly and I dont hesitate to push it as Kohler intended. The first rod, piston, and rings lasted over 2000 hours...I like those odds.

Ive seen some of these aftermarket kits in engines...the 2 ive had experience with first hand were in a K181 and a K321. One knocked, the rod was too big from the factory. The other one smoked, piston not shaped right, too small @ the skirt and allowed the piston to rock/slap. The bore still measured perfect from the bore out. Genuine Kohler parts got these 2 back in service.

And some people use them without any problems at all...

Your mileage indeed, may vary.
 
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