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Flying Blind - Overhauling Kohler Engine

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ncrunch32
Join Date: Dec 2003
Posts: 762 Kingston, NY
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2006-02-18          124762

I have taken my 1983 Kohler K301 12HP cast iron engine off my Gravely and have taken it apart in the basement. I will have a neighbor come over to give me an assessment of the piston, rings and valves. I am anticipating having to purchase a master rebuild kit for about $100 which has all gaskets, pistons, connecting rod and rings.

What I am perplexed about is that the sellers ask you what size piston you want - standard or .01, .02, .03 oversize. I understand that these are options for worn cylinder walls, but how do I assess which would be best for me? How do I measure the cylinder size? Is there a special tool I need to purchase to do this? Once I know the diameter of the cylinder, how do I know how much clearance I need? Do I subtract the clearance required from the cylinder diameter and get the largest piston under that size that will fit?


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kwschumm
Join Date: Feb 2003
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2006-02-18          124766

You use an inside micrometer to measure cylinder bore. The manual will have specs. On automotive engines if the cylinder is beyond a certain spec you usually have it bored out to the next standard oversize and install larger pistons. I imagine the Kohler is similar. If the bore is within specs you hone it out and install the same size pistons. ....

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ncrunch32
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2006-02-18          124767

Thanks Ken, I bought a service manual for this engine. Maybe I can find a range for the specs in there. ....

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kwschumm
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2006-02-18          124775

There are probably special tools for measuring but the inside mic always worked for me. It's a good idea to measure it at several different positions to check for out of round and also at the top, middle, and bottom of the piston stroke to take the widest measurement. They will usually wear more at the top than bottom. It's been 30 years since I've done that kind of work and I sort of miss it. ....

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harvey
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2006-02-19          124776

The best way at this point is take the block to a rebuilder/machine shop. Most auto supplys can steer you or check the yellow pages.

You will not have the machines (well maybe you do but then you'd know this anyway) to bore the cylinder or be able to check for minute cracking.

They'll tell you how much boring is needed/was done then you can order your piston set. ....

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shortmagnum
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2006-02-19          124782

You can get a pretty accurate inside reading with an extendable rod that will touch both sides of the cylinder wall. There are expensive manufactured units but you can make one easily out of a couple of pieces of metal. It would be like sliding a pencil into a drinking straw and then threading a screw in the pipe portion to clamp the inner part at the desired length. The pipe portion shouldn't be much larger diameter than a drinking straw. Of course you still need a micrometer to measure the apparatus length when you remove it but you can get a pretty inexpensive vernier or dial caliper for $15-$20 if you don't have one. They're good to have around. You can get an idea of the wear by measuring the upper & lower part of the bore vs. the middle. Your overbore would need to be more than this difference for equal diameters throughout.

The company might also have a maximum piston to cylinder wall gap. Just put the piston without rings into the bore and measure the excess gap with a feeler gauge. Again, you can get an idea of total wear by sliding the piston up and down and measuring to find the difference in bore diameter. There will be little or no wear above the point of ring travel. If it's out of spec, you'll still most likely have to have the boring done at a machine shop. If it's in spec, you can just hone the cylinder walls and install new rings.

These specs could be available on the net depending on how popular this motor is. Have fun, there's nothing more satisfying than hearing a freshly rebuilt engine fire for the first time.
Dave

....

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Billy
Join Date: Oct 1999
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2006-02-19          124787

All you need to measure the bore is a telescoping bore gage and a micrometer or caliper to measure it with. ....


Link:   TELESCOPING GAGE SET

 
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oneace
Join Date: Mar 2004
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2006-02-19          124788

Most machine shop around me will bore a cyl for about $40. If possible I would only go .010" or 10 over. That saves room for future rebuilds. Get the spec out of the manual of ask the parts guys and they would be able to get for you. ....

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Murf
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2006-02-20          124814

Before you do any boring, or order any parts, it is CRITICAL that you measure the cylinder.

You have to take three measurements in two directions each. Top, middle and bottom of the cylinder. Take each of those measurements twice, 90° from each other. This will tell you how much the cylinder is worn and where. The cylinder does not wear uniformly top to bottom.

You want to bore the cylinder JUST enough to get it back to straight, parallel walls.

That will determine how much you need to oversize.

Any good automotive machine shop will do the whole job for you for not much money if you leave it with them as a "fill in" job for a few days. Just explain what you want to do, and the range of over-sized parts available and they will determine the amount of bell-mouth to the cylinders and machine the block accordingly.

Best of luck. ....

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ncrunch32
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2006-03-12          125991

Engine assembly is complete. It turned out that the top piston edge facing the exhaust valve was worn somewhat. It looked almost as it had been scuffed over a one inch range. The piston is aluminum but the block is cast iron and the cylinder was fine. I installed a new piston, rings, new valves, new fuel pump, new fuel lines, cleaned carburator, new gaskets etc.

I got myself a telescoping guage, dial caliper and measured about 30 times at various positions in the cylinder. I was not happy with the quality of the telescoping guage but according to my measurements it appeared the cylinder was in decent shape andd within specs. So I got a standard size piston and it seemed to fit well.

Tools cost me as much as parts - telescoping guage, dial caliper, ring expander, ring compressor, valve lapping tool and compound, 2 types of valve spring compressors - one to get them out - one to get them in, fuel line, emery cloth. Parts cost me about $200 total - tools $200 total. About $200 more than I was hoping to spend.

It was too late to try putting the engine on the tractor today - that requires some additional work, new fuel line from tank - and this engine is heavy. So next weekend will probably be the day. Wish me luck! ....

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kwschumm
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2006-03-12          125992

I'll wish you luck. Hope you have a nice warm place to do this sort of work. It's a pretty good feeling once you rebuild one and fire it up for the first time. Well, it is as long as it runs :) ....

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kwschumm
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2006-03-12          125993

Just noticed your tool purchases didn't include a cylinder hone. You did hone the cylinders, right? And ream the ridge? ....

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ncrunch32
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2006-03-12          125995

Ken, I must admit I did not hone the cylinder. I read what I could on this subject. My neighbor said he could still see the cross hatching and to just put the pistons and rings in.

I did clean the ridge but with fine emery cloth. I also read one post that said you can use fine emery cloth in a diagonal pattern rather than honing the cylinder. My understanding is that you need a drill press to hone the cylinder, correct? ....

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AV8R
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2006-03-12          125996

No. A hand drill will work fine for this. You are not trying to remove any material from the cyllinder, just make the surface rough enough to hold the oil. ....

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ncrunch32
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2006-03-12          125997

AV8R, then I could do the same with emery cloth correct? I considered doing this but was afraid of the dust that I would get through the gearing below the piston. Obviously it is too late to do this now and I will take my chances. Now that I know how to do this and have the tools - it will be easy to take corrective action.
....

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Art White
Join Date: Jan 2000
Posts: 6898 Waterville New York
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2006-03-12          126003

Did the exhaust have a leak at tear down? ....

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ncrunch32
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2006-03-12          126005

Art, I'm not sure what you mean. The engine would run fine for about an hour - then black smoke would come out of the exhaust and the engine lost power. The exhaust valve looked fine when I pulled it but it is interesting that the top edge of the piston that failed faced the exhaust valve. I saw no other problems other than the top edge of the piston. As the subject says - I am flying blind :). ....

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kwschumm
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2006-03-12          126006

Like AV8R said, honing roughens up the surface to both hold the oil and provides a good mating surface for the rings to seat properly. If the cylinder is glazed the rings won't seat and the engine will use oil. A hand drill is fine for honing - if it needed boring more equipment would be needed but that's what machine shops are for. Hopefully the cylinder walls are still rough enough to seat the rings. Good luck! ....

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Art White
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2006-03-14          126085

That more then likely would have been an electrical problem. The highest heat in an engine will be at the exhaust valve. ....

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ncrunch32
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2006-03-14          126125

Got the engine on the Gravely last night. Got her started - that was great but carburator was spitting some drops of gasoline and I couldn't get the engine running right. Tonight I made a float adjustment and she's purring like a kitten. Hooray! ....

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Art White
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2006-03-14          126129

Congratulations! ....

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kwschumm
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2006-03-14          126135

Nice job! A great feeling, eh? My first engine rebuild didn't turn out so good. In high school I rebuilt a Chevy straight 6 235 cid with splash oiling. It never ran quite right - it was a little rough and reluctant to rev. My dad (a former GM employee) said I probably put the pistons in backwards. Apparently they aren't exactly symmetrical and I didn't know that. ....

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