Kohler Knocking

[Anonymous Poster]

So here's the story; remember this was a honed cylinder, same crank, new standard sized rod and piston. I'll start with the cylinder bore. Diameter is 3.253" (spec 3.254" wear limit). The cylinder has vertical wear marks on the sides of the cylinder that are in-line with the crank centerline. No deep scratches, no ridge at the top of the cylinder.

The piston has vertical wear marks that are on the same sides as the conn rod bolts. There also is some scuffing (shiny spots) at the very bottom of the piston skirt at these marks, and right underneath the first oil ring. Piston ring end gap on the old rings when installed in the cylinder was .024" (spec .010-.030"). End gap on the new rings was over .035" (spec .030" max)!! How can this be?? The rings were ordered with the piston as an assembly!

The connecting rod-to-crank running clearance was plastigauged, and is .003" (spec is .0025" max). End play on the crank is .004" (spec .003-.020").

Camshaft end play is .007" (.005-.010").

Now my questions are ... do the shiny areas on the piston mean there is piston slap? Will the oversize running clearance on the crank create the knock I am hearing? I'm curious that the wear lines on the piston are 90 degrees from the wear lines in the cylinder. I'm also concerned with the ring end gap. I'm almost tempted to bore the block, buy a .010 over piston and rings, and turn the crank .010 under and buy a new undersize rod.

Sorry this is kinda long, and thanks for all the help!!!

 

[rdbrumfield]

When you put the piston in the cyl, how much play is there. Rock the piston on the wristpin while in the cyl, at top and at bottom, notice any difference?
When the piston hits bdc the skirts are below the cyl wall, (some are), might be getting too much slack.

 

[bgott]

Your rings are oversized and I think you need to get some long feeler gauges to measure your piston clearance. Your bore is a little on the large side. Did you measure it with a bore gauge? An inside mike is no good to measure a cylinder bore. When I was in diesel school they recommended measuring the bore in seven different places up and down the bore. This isn't a six inch stroke engine so you could probably get away with three places. Cylinders wear tapered, not straight. If your bore is on the high side of specs and the new piston is on the low side the tolerance stack will give you one he11 of a loose piston. I'd go ahead and have it bored and the crank ground. In automotive engines you can buy .001 under bearings that would close up the gap, maybe you can find them for this engine. Measure your crank about three different ways around the diameter of the crank throw at three different places along the centerline, plastigauge won't tell you if the journal is egg shaped or tapered. From the wear on your piston it sounds like you have too much clearance in the bore, causing a slap when it rocks and the loose rod bearing is letting it get a little front to back rocking wear at the same time.

 

[RobS]

Some good advice coming at you and it looks like your checking the right things. Did you stagger the ring gaps around the piston OD? Just one more thing to check into /forums/images/graemlins/smile.gif

 

[SteveV]

Maybe some more basic things need to be examined here. You didn't really mention setting the valve clearances after the seats were ground. Shortening the valves is necessary in engines without adjusters. Did you mike the replacement head gasket to see if it was the same thickness as the original? The replacement rod needs to be checked for proper length, style and width. My first reaction, despite the "no ridge" would be to bore and hone for a new rod. Ring end gap; was the compression within spec? What did the original oil look like? Main bearings might be bad or the block cracked. Are the valves bent from the bad cam timing? The flywheel and that seemingly insignificant key are critical to timing. The key must be unmarked (which is finer detail from ungouged) for the correct timing. Did pulling the flywheel go ok? Is it running true and can you feel the mainbearings when it's mounted (end play is not making the knocking). The 1 hour run time suggests out of round bearing wearing in. Check the top ring to land clearance for damage against the old end of stroke. If you get through all that without finding anything, let me know, there's more. SteveV

 

[Anonymous Poster]

Aye, carumba!! Where are all those people who told me this wasn't rocket science now?!?! Ha ha.

The rings were staggered, assembled to the directions they came with. As stated, the ring end gap was above spec on the new rings. Ring-to-land clearance is in spec. Didn't verify head gasket thickness, took it to be good. What is the spec for this? The valve lash was set, then checked and adjusted at the 1-hr mark. Total run time was about 10 hours. 1 hour oil change just looked dirty, I imagine from the rings setting. Did not check the compression. Valves do not appear to be bent, I've not removed them yet. Since it never fired with the 180-out timing, I would not think this would be an issue. Steve, do mean mean "bore and hone" for a new piston, instead of rod? Flywheel came off fine with a pulley puller. I'm not sure what you mean by "can you feel the main bearings". The ends of the crank mic right at the middle of the spec range.


Thanks for the help. This has definitely been an adventure!

Jeff

 

[normde2001]

http://bbs.cartserver.com/bbs/a/5624/index.cgi You might want to kick this around with these guys, a bunch of small engine pro's in here. I don't believe you have rod bearings on that thing do you? What I used to do on motorcycle engines with no rod bearings was, if no visible scoring, to hand fit the rod/cap to the crank journal by honing the rod cap with an Indian oilstone til I got the proper plastigage reading. Also you said your new rings have a larger end gap than the old ones??? Large gap says worn or undersize rings. I would go with .010 oversize rings, and file the ends down if necessary.

 

[Anonymous Poster]

Update - getting the cylinder bored .010" over, and getting the crank ground .010" under. I decided that things were just too close to their limit, so let's start fresh there.

Concerning the specs, now that I'm doing this, do I just add .0100" to all of the specs? (Bore dia, crank clearance, etc). And I assume that there is nothing special I need to make sure of when I order the parts, just get the right sizes.

Thanks for all the help, and I'll let you know the results!

 

[normde2001]

That's pretty much it. Just make sure you can get the right size rod before grinding the crank, and don't forget there is always a short block.

 

[bgott]

You're right on the rings. I was thinking bearings when I said oversized. Being that this engine is supposed to have a standard bore, I wonder why they would have undersized rings? Maybe for a smaller, lower HP engine?