Serious problem during break in (pics)

[Tar2001]

Engine started producing a ticking sound after 15 miles of break in... At 100 miles i knew that something serious is going on inside the engine. After checking everything else, injector kill test showed that there is a problem in cylinder number six... we removed the head as well as piston number 6 along with its connecting rod. Also remove piston number 5 which looks in very good shape.

The pictures tell the rest of the story, but I still don't know the cause.

Your help guys is highly appreciated in diagnosing the problem.

It's a KB 944 piston 060 overbore. Surprisingly the rings are not damaged at all...

I will post a few more pictures, but the left side of the piston is not even scratched.

Any suggestions??

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[SIXPAK]

What was suggested piston to wall clearance and is that what was done at the shop?

[Tar2001]

0.0035 done by a professional supposedly.

[Tar2001]

I have to wait till monday to know if the shop did the job correctly...
could it be a problem in the connecting rod??

[Tar2001]

rod bearing pics

[I6FAN]

Only 15 miles, wow! Being that the piston and rod bearing for that cylinder don't look good, I'd say an oiling issue. Check all bearing clearences. When I first saw this, I was wondering if you used the rod bearings with or without the oil squirter holes?

[Muad'Dib]

I used bearings without the holes and i have 2000+ miles on my stroker with no issues.


Did you check all the main caps for proper installation? Looks to me like #5 or #6 (not sure which) main bearing cap could be installed backwards (needs to be flipped 180). I would definetly check that.

[Tar2001]

Main bearing cap or rod bearing cap ?

[IH 392]

I don't believe it's a bearing cap issue?, that would have eaten the bearing at the split, if the crank even turned at all?, I also believe that its a clearance issue?, although I would double check the oil feed holes on the main that feeds that rod, I had a 258 that the #1 main feed hole was off, the main was ok but the rod bearing failed, and as said the splash from the rod could have been minimal and with minimum clearance on that forged piston, they need extra clearance, the machine shop gave my engine "a little extra clearance" on the rear cylinders.

[Cheromaniac]

Only 15 miles, wow! Being that the piston and rod bearing for that cylinder don't look good, I'd say an oiling issue. Check all bearing clearences.

I think it's more likely that the bearing and piston-to-bore clearances were too tight.

[Tar2001]

Main caps are correctly installed. The rod bearing is not really damaged, i guess it was caused by the piston scuffing problem.
I still have to check the piston to wall clearances. However if they turned out to be correct, how can i determine the cause of the problem.

I also read somewhere that when the scuffing is only present on the thrust side (like in my case) it is usually an oiling issue... Is that always a rule?

[doc65]

My first choice would actually be the oil passage in the crank that feeds that rod journal, or a bearing clearance issue on that rod not letting enough oil through, the cylinder walls aren't directly oiled, they just get spin off from the crank & around the rod bearing. Main bearing reversed top to bottom would be a distant second, but unlikely as that would cause a main failure on that journal as well as resultant rod & cylinder wear with the bearing plugging the oil feed.

Just my 2 cents worth

[SilverXJ]

Did you ever find out what caused this?

[Tar2001]

I did not find out what was the real cause... But i can confirm the following:
-the machinist is excellent, his work was rechecked with no prob. The piston to wall clearances were rather loose, as recommended by kb manufacturer.
- the guy who assembled the engine, on the other hand, is not excellent. I am not sure he took extra care to clean parts as he should.
- the rod bearings used did not have the oil spraying notch
- i did not check the injector of the scuffed cylinder. I used another set of injectors later on.

Luckily, the block was not damaged. I reordered a set of piston rings, cam bearings, main and rod bearings (notched ones) to be on the safe side. I had the engine assembled by a top professional, and it is now running great more than 10k mile.

Thanks for asking

[Retlaw01XJ]

Good the hear the block was okay, and you got it back together.
I'm thinking a possible cause could've been interference between the small end of the rod and the underside of the piston. That could cause the piston to not 'rock' properly and bind up.