Kohler Knocking

[Anonymous Poster]

Hello, everyone. Hopefully I can get some advice here. I rebuilt a Kohler K241 10hp a couple of months ago; new piston, rings, rod, and valves. The cylinder was dingle-balled, it was not out-of-round or scratched up, and the crank checked out OK also. The piston and rod that I bought are the original size. The valve seats were ground. Everything was lubed very well when it was put together. I had some help from a friend who has rebuilt a few of them, and he also did the work on the valve seats and bore (him and his father have a complete machine shop.)

I did make one mistake when putting it together, the breaker cam was put in 180 degrees out, so it did have to be torn back down to correct this (crank and piston came back out). The connecting rod I bought had the posi-lock nuts on it, and these were tightened to 200 in-lbs the second time it was installed.

It had run fine until yesterday. I ran it for about an hour after the rebuild, driving it around the street and yard to get some time on it, varying the rpm's, and then changed the oil. Since then, I've got about 10 hours on it, doing some light snow plowing, all in low gear. Last night, it started knocking real good, and sounds like I might be where I was before the rebuild.

My questions are: What could be a cause of this? Do you think the rod was put together incorrectly? I've heard some say you shouldn't re-use the posi-lock nuts. Should I get the crank turned, and buy an undersize rod? As I said, the machine work would not cost anything, it's all available.

Thanks for any help!

Jeff

 

[normde2001]

It sounds like you might have "piston slap", (bottom of piston hitting cyl. wall). Not sure what "cylinder was dingle-balled" means, but was there any ring groove at the top, cyl. diameter still within specs., ring clearance within specs? Did you have to, or should you have honed the cylinder and gone oversize on piston and/or rings?

 

[thcri]

My last suburban had piston slap. It was a 98 and General Motors would not do anything with it. Under warranty they told me piston slap would not hurt a motor and all motors have it some. I was not impressed but did learn to live with it. I sold the suburban when it had 85,000 miles. When you rebuilt the motor, what did you use to lubricate the crankshaft and rods while you put the motor back together. My dad was a mechanic for over 25 years on Ford tractors. He saw a guy using I think STP. Dad pretty much yelled at the guy because STP was so thick it stopped all oil flow until the crank heated it up enough to get it flowing. Not so sure if that is true, but dad sure stuck to his theory. I guess it makes sense.

Murph

 

[rdbrumfield]

Take a stethescope and listen to the block as you turn the crank pulley be hand, if you hear a clunk clunk when you rock the crank back and forth it is most likely the rod.
This might be far out, but I have known it to happen. Check the intake for missing screws on the butterfly in the carb. If one of those gets in the cylinder it beats on the piston like a drum, sounds like a rod is going to go.
I once had a rod bolt break at the shank. It let the piston slap the head, but didn't break, sounded like a loud lifter. Had to tear it down completely to find the culprit.
That was a 336 Yanmar with 300hrs on it.

 

[chocolatehauler]

unfortunely you only have one option. take it out and take it apart. It won't get better, anyone of these posts could be right but taking it apart is the only way to find out, I vote for a loose con rod. /forums/images/graemlins/frown.gif

 

[Anonymous Poster]

Thanks for the ideas. I was wondering if it might be piston slap, or the loose rod. It's a sharp knock, not a dull thud, and you can hear it even when the engine is turning over from the starter. I didn't think about loose screws getting sucked in, I'll check for that. By "dingle-balled", I meant we honed the cylinder with the style of hone that has the little balls at the end of the wires, getting a good sideways marking in the cylinder so the rings would set. The cylinder was still within spec, no grooves in it at the top or anything, and it's not been bored over yet. We squirted 5W-30 over everything inside (cam, rod, crank, bearing), lubed up the piston and dumped about a teaspoon of oil on top of it when we put it together.

I had kinda resigned myself to taking it apart to find out what it looks like. It's just a pain doing all that work! Lol. If I do need to replace the rod, do you think the bearing for the crankshaft should also get replaced? Also, does anyone know the specs for the diameter of the crank at the rod?

Thanks!

Jeff

 

[Molerj]

I vote for a loose connecting rod bolt. Don't you just hate it when you have to tear something all apart again? Only good thing is you can do it alot faster the second or third time! Go to the site below, select parts lookup>kohler>k series>specs. Hope this helps. try here

 

[jrlichina]

Well you should have used a new rod bearing from the start. You should have measured the crank journal for size to see if had any significant wear. The next step is then to measure the rod big end size with the bearing in place and the rod bolts toqued to spec to get the clearance. Or you could have used plastigauge to determine the rod to crank clearance. This would have told you if the crank needed to be ground or polished and if you needed an oversize rod bearing. You should also check the side clearance of the rod and crank. And of course after you tear it down again look for loose rod bolts. Good luck!

 

[normde2001]

Jeff, considering the inspection and work you did on the cylinder walls, the fact that it ran well for 10 hours, and you can hear it at slow cranking, I'm moving away from my "piston slap" diagnosis, to "something came loose", something fell in it, or something didn't get oil. In any case, it should show up quickly with a teardown.

 

[Justaplain]

http://www.perr.com/forum.html

 

[Anonymous Poster]

Jrlichina, a new rod was used, and the crank was mic'd during the rebuild and found to be within the specs. Problem is, I've since tossed my sheet of specs, and couldn't remember the website where I found them. Thanks for the website, Justaplain! (Note to self - keep better records!). I didn't want to plastiguage the rod, as the instructions that came with it said not to reuse the posi-lok nuts.

After some initial looks, I'm agreeing with Norm, something is loose inside, and also sounds like it. Going to tear into it tonight, if I get a chance. And wouldn't you know it - it comes at a time when we are supposed to get 4-7" of snow!! Murphy is alive and well!

Thanks, all, and I'll be sure to post the results!

Jeff

 

[CamshaftLF]

Also make sure that the con-rod oil holes are facing the right dir, if I remember right the holes face the intake side of the block. If it has a splasher on the bottom of the rod cap. If you have a internel oil pump disregard the first part.

Cam in Pa.

 

[Anonymous Poster]

Well, got it taken apart ... flywheel wasn't loose, neither was the pulley. Drained the oil, it didn't look bad, no chunks of metal or foreign objects. There was some "streaking" in the oil when I dragged my finger through it, I attribute this to the rings wearing in. Pulled the head off, no scratches inside the cylinder. Everything looked OK inside, oil hole in the rod cap facing the correct way, looks like oil's been getting splashed up real well. The nuts on the rod cap were not loose (glad we weren't betting men!!), so I pulled it off. Inside of the cap looks good, no major scratches except for one faint wear line in it. Is this normal? The cam end play is within spec, I didn't check the crank end yet.

I'm going to mic the crank journal tomorrow. I guess my question now is, if the journal is in spec, what should I look for next? I'm kinda stumped here. I figured the rod is good since it was new. Maybe it could very well be piston slap? I've had 5W-30 oil in it, I figured I should be OK there.

Thanks for the help!

Jeff

 

[BillyP]

Just a thought but could it be crankshaft end-play?

 

[bgott]

Mitsubishi 3.0s in Chryslers used to have a bad habit of dropping valve guides. They would knock like a booger. Maybe?

 

[Anonymous Poster]

I've been out of town for a few days, haven't had a chance to check things out, but hopefully I will tonight. Thankfully, the 7" of snow that was forecasted for Friday night never materialized!!

I was also going to plastiguage the rod/crank if the crank checks out OK. If I do this, should I torque the posi-lok rod bolts to 260 in-lb or to 200 in-lb? The directions that came with it stated 260 in-lb and not to reuse them, I've found specs that state you can reuse them with a torque of 200, and I've had some DIY'ers say torque it down to 265-270 in-lbs.

I'm also going to check the crank end play. It sure doesn't seem to move more than .010", and is pretty hard to do at that. Spec on it is .003-.020", seems pretty liberal. The rod has about .010-.012" end play on the crank.

Thanks for the help, and I'll be sure to post the results.

Jeff

 

[normde2001]

Jeff, I think I would purchase a new set of standard rod cap nuts to use just for the plasti-guage test. You didn't say if you got a new wrist pin, but is the piston "snug but free" on the rod, (no side to side rocking play), also any rocking play at rod and crank connection, (plastiguage test)? Any vertical marks or scratches on the piston skirt denoting piston slap? Strange, you would have thought something would have jumped out at you on teardown.

 

[Anonymous Poster]

I was wondering if anything would show on the piston if this was piston slap - didn't really know what to look for there. But it looked good, no marks. Haven't checked the wrist pin connection yet, I'll do that. One question I forgot to ask - now that I've removed the piston, do I need to put new rings on it, and let it re-seat itself? Or will the same ones (installed at the rebuild) still be good to go?

Thanks!

 

[bgott]

You can use the same rings. Rings can be cracked and break in the bore but you have to drive them out past the cylinder ridge with out cutting it down first if it has one and generally abuse them.

 

[normde2001]

Those rings should be ok as long as no damage in disassembly, etc. By the way, did you check the end gap on the rings before assembly, according to specs? (Put rings into cylinder minus piston and measure gap with feeler guage). Too much gap means rings don't compress enough, and can cause piston slap.