Real life vs Kohler specs on a K301

[tobo127]

Gentlemen, for those that do this for a living and have the experience of having done multiple rebuilds, what do you generally find for piston to bore clearances when checking machine work before assembling your engines? I see the spec in the manual at locations of just below the oil ring and also bottom of skirt. I was wondering how close you find your dimensions are to those specs when you get your blocks back from the machine shop. I know ideally they would be as spec'd but what do you find for actual dimensions? I keep reading everyone should check and verify the shops work and new parts dimensions. Just curious if they're tight, do you hone to bring the bore to spec,........and if loose, how much before you question proceeding?
The reason I'm asking, the machine shop I'm talking to is questioning the .0065 to .0095 clearance below the oil ring. To him it sounds a little loose so he wants to verify it's not a misprint. I figured what people actually see on multiple engine rebuilds would be proof as to what works or not.

[J-Mech]

My book shows .007-.010, so not sure where you got those numbers. They're close, so NBD, but it always amazes me when you find differences.

If the piston manufacturer lists a spec with the piston (instructions in the box) then go with it. Otherwise, the book spec is correct. It's an air cooled engine, so they run a wider clearance spec than a water cooled engine because of expansion. I'm not sure how many air cooled engines your machinist has bored, but if he knows anything he should know that that is normal. As far as what works and how do you know if it's ok even if it's out of spec..... well, if the machine shop goofs, then it's their job to correct it. If it's too tight, then they didn't finish their job. If it's too loose, they goofed the finish. I like to see numbers in the middle of the range with exceptions made on special builds. If you find that a bore is too loose.... well that's your call. They'll run, just not as long of life as it starts out basically "wore".

[ol'George]

I've seen those Kohler specks too and questioned them.
I know that is what they publish, but dam that is loose.
Normally that spec would be beyond repair limit and recommend to rebore oversize.
I would think that much clearance measured @ the skirt would rattle.
I know it is not a small block chevy but that much clearance scares me on a new bore.
old rule of the thumb is usually .001 per inch of bore.
A forged piston runs a little more clearance, and they rattle a bit till they warm up.
Other air cooled engines don't run that loose.
I think your machine shop is smart to question, ya can't make the hole smaller after it is too big.
I would like to hear what others experience is on using a tighter clearance.
Did it seize? or was it ok?
Inquiring minds wanna know!

[tobo127]

Originally Posted by ol'George

Did it seize? or was it ok?
Inquiring minds wanna know!

Nothing wrong with the engine as far as I know. I just bought this tractor and had no history of past performance (non-running but at a good price, knowing that if it needed engine work I'd still be ok with it) so I tore it down to check the sump for extra parts floating around and the condition of the balance gears. While in there I noticed the rod clearance was excessive. Taking the crank out for a regrind I decided (why wouldn't you) to check and bore the cylinder. That's how I got to this point. The block is still a standard bore so I was planning on a .010" oversize when the machine shop questioned the clearance. His shop floor is full of blocks so I'm guessing he's been there before. Maybe he was just working on a small block and had other clearances in mind, not thinking of the air cooled issue as mentioned by J-Mech. I just as soon he question as to what he thinks is correct, at least it shows he's thinking. Initially, I brought the block in to get measured so I know what piston to order so he can have it in hand to hone the cylinder to.

[ol'George]

ok,
think you misunderstood what I was asking.
I was wondering if anyone ever put a Kohler together with say
.004 tho. clearance and what was the outcome?
I would for sure go on the low limit of .0065
Are you going with Kohler piston or aftermarket?
if aftermarket What is their recommendation?

[tobo127]

Originally Posted by ol'George

ok,
think you misunderstood what I was asking.
I was wondering if anyone ever put a Kohler together with say
.004 tho. clearance and what was the outcome?
I would for sure go on the low limit of .0065
Are you going with Kohler piston or aftermarket?
if aftermarket What is their recommendation?

I'm going with aftermarket items because I only need the parts, I'm not looking for the patent rights from Kohler. You'd wonder if they make engines for a living then why are their parts so bleeping expensive (seeing as most OEM parts are probably made by others anyways to their specs). Seems like others use and have good results with aftermarket parts. Maybe it'll be a lifes lesson, who knows.

[J-Mech]

I've said my peace. I think that the spec is fine, and I advise you adhere to it. I will reiterate and say that I think the middle of the spec is what you should shoot for. I can state my reasons in a long winded explanation, but I don't want to type that much.

Here's my question to the OP:
IF you do decide to throw the recommended limit out the door, and go by someone's opinion, are you willing to gamble your dollars that it is correct? If it scores the piston, are you going to quietly tear it back down, bore it again and rebuild it and pay the cost? Or are you going to say "Well some guy on the internet said I could!" or go back to the machine shop and say "It's all your fault!" and demand that they pay for it? Are you willing to take the risk....??????


I think if you do, that's just silly.


You guys need to read this thread:
http://www.onlycubcadets.net/forum/s...ad.php?t=34585

Pay attention to dvogtvpe's posts.

[tobo127]

Jon, the numbers I got were out of the Cub Service Manual in the Tech section for the 1x6/7 series (Manual GSS-1404, page 1-4 under the piston to cyl bore clearnace spec). Thought I'd check another source and it looks like the numbers in the Kohler service manual are basically the same but are rounded up to the nearest thousandth. Cub says .0065 - .0095, Kohler says .007 - .010
If being picky, I suppose Cub, by their numbers, allows a little bit tighter fit (but who's counting?). I think Kohlers numbers probably trump other values and should work. Sometimes too much information just confuses the issue!

You say you "like to see numbers in the middle of the range". Do you tell your shop to cut it that way (in the middle)? How do you usually get them if you don't say? Just trying to get an idea of what the norm is that machine shops use for a target. Would you feel comfortable if it came back on the tight side but still in spec? Or feel better if on the loose side but still in spec? Or does it really matter as long as it's in spec? Maybe over analyzing this, that's why there's a spread!