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mattd860

Rebuilt Kohler K301 Issues

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I brought the motor to the machine shop today and they measured the bore. It measured 3.385" which is exactly .010 over.

Now they didn't bore the cylinder with the piston in hand but the clearance between the cylinder wall and the piston shouldn't be that large!

I left the engine mostly assembled so I can prove to them that timing and everything else was correct. Tonight I will disassemble it further and bring the stripped block and piston back to the shop tomorrow so they can measure the piston too.

I'm thinking the ebay garbage .010 piston I got is....well.... garbage?

Since it appears the shop DID bore the cylinder out .010 over, anything done by them to resolve the problem will be on my dime.

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My local machine shop will not bore the block with out the piston.They are allowed so much plus or minus when manufacturing these pistons.Did you check your ring gap?

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My local machine shop will not bore the block with out the piston.They are allowed so much plus or minus when manufacturing these pistons.Did you check your ring gap?

I haven't check the ring gap yet but will tonight when I remove the piston from the block.

What I don't understand is this: People buy new pistons all the time without machining the cylinder :thumbs: . I understand machining the cylinder to match the piston will make a much better mate, but the tolerances should be at least acceptable otherwise.

I will know more later but I think the piston I bought is just plain out of tolerance.

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You can't check the end gap on the rings with the piston out of the cylinder. Or am I misunderstanding what you meant?

Maybe you have a set of standard rings on a .010 piston.

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You can't check the end gap on the rings with the piston out of the cylinder. Or am I misunderstanding what you meant?

Maybe you have a set of standard rings on a .010 piston.

I acutally think I might have .010 rings with a standard piston even thought the piston is stamped .010.

I was going to measure the ring gap by takeing the rings off and inserting them into the cylinder. Isn't that how it's done :thumbs:

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when you place the ring in the cylinder use the piston turned upside down to square up the ring in the bore about 2 inches down ( i think) and then use feeler gauges to check the gap of the ring were the two ends meet.

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Ring gap is .013"

I butted the old STD piston head against the new .010 piston head and they look exactly the same but the shop will mic it tomorrow.

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You can't check the end gap on the rings with the piston out of the cylinder. Or am I misunderstanding what you meant?

Maybe you have a set of standard rings on a .010 piston.

I acutally think I might have .010 rings with a standard piston even thought the piston is stamped .010.

I was going to measure the ring gap by takeing the rings off and inserting them into the cylinder. Isn't that how it's done :thumbs:

Yes, that's how you do it. I think I misread your previous post.

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Brought the block and piston back to the shop today and they re-checked the cylinder and measured the piston. Cylinder is 3.385" and the piston is exactly 3.375" which is within tolerance. It might not be perfect but when the aluminum head heats up, it should expand some to cover the gap. Furthermore, since the ring gaps are also well within tolerance, compression is probably not being lost through the piston/cylinder.

They then proceeded to check to see if my valves were sealing. They determined that the valves were adjusted appropriately however the intake valve was not sealing. They sprayed the valve head with WD-40 and then blew compressed air through the intake and you could see it bubbling on one area of the intake valve and no bubbles on the exhaust valve.

So most likely that's where compression is being lost and why I couldn't get the motor started! The loose piston was just a rabbit trail although it did force me to go to back to the machine shop where they inspected the leaky valve so for that I am grateful. I would have never suspected the valve if I never went to the shop.

After they grind the intake valve and seat I will report back here.

Thank you all for your help thus far.

(PS. YES I did lap the valves and seats during reassembly)

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Out of curiosity - how do I properly gap the bearing plate? When I originally took apart the motor there was one rubber gasket and 2 paper gaskets so that's what I always put back on the motor when installing the plate.

But what is the proper way to do it? What do I measure to make sure I have the correct amount of gaskets (spacers?).

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I am glad you are getting this thing worked out. Nothing sucks worse than going to all that work and you feel worse off than when you were at square 1. I myself NEVER do an overhaul without getting head work done as well. A person could have seats that are bad or valve guides or weak springs. This a very expensive lesson that I learned the hard way. On a Detroit diesel I had in my semi tractor, I went the cheap way. I lapped the valves myself and had a good seat on them, Put in the old springs and retainers and thought "cool, I just saved $400.00", feeling proud of myself, put it back together and ran it. Long story short, my $2300.00 inframe major, lost a retainer. Valve dropped, destroyed a $200.00 piston, and a $900.00 head plus a $110.00 injector. Plus another week of down time. All total it cost me $4000.00 to save $400.00 on top of the original $2300.00... Lesson learned. I also am a firm believer in put back what you took out. You only changed the piston and rings so nothing else changed. The rubber gasket and 2 paper ones are what I'd put back. hope this helps. Pat

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Out of curiosity - how do I properly gap the bearing plate? When I originally took apart the motor there was one rubber gasket and 2 paper gaskets so that's what I always put back on the motor when installing the plate.

But what is the proper way to do it? What do I measure to make sure I have the correct amount of gaskets (spacers?).

Section 12 of the Kohler service manual explains how to re-installed the bearing plate and check for end play. It tells how to add or remove shims to get the proper measurement.

Section 12.10

Bob

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The Kohler manual gives a great explaination.

You have to bolt on the bearing plate to check the end gap.

If you are using the same crank and bearing plate I would put it on with the gasket, then the two spacers as it was before. Then get your feeler gauge and check on the inside the distance between the bearing and the crank. If it is off you have to take the bearing plate off and add or remove spacers.

See pic 12-32 in the manual. It is actually easy to do. I only had to do it 4 times to get it right.

but a normal person should only have to do it twice. Measure the gap with the feeler gauge and it will let you know how many spacers to take in or out. They are .005 each. My rebuild kit came with 4 and I used 0.

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Got the engine back together and on the tractor today. Fired right up and ran well... so far. Hopefully I don't jinx anything by writing this :thumbs:

Bought a new Walbro Carb and installed that too so no more backfiring or stumbling. So it looks like we're back in business.

I just went out the garage to cold start the motor (30

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That is really good news. I'm glad that all is well so far, and I'm glad you stuck with it and didn't give up. :thumbs:

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