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post #1 of 14 (permalink) Old 11-11-2007, 11:30 PM Thread Starter
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I picked up a Powder Special with engine damage. Both pistons and cylinders were damaged. It doesn't seem to be an oil issue, it seems as though something came apart from below. I do not see any damage on or around the crank, I do not see any damage where the rods connect to the crank. What would cause both pistons and cylinders to looks like this?

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File Type: jpg cat_engine_004.jpg (96.5 KB, 58 views)
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post #2 of 14 (permalink) Old 11-13-2007, 05:25 AM
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Where all the wristpin c-clips still in tact when you tore it down? My old YZ80 lost a wristpin c-clip(these CANNOT EVER be reused!) and it looked very similiar. A piece of the c-clip had actually jammed straight thru the top of the piston and stopped half way thru the ring! I saved that piston as a good ole paper weight
Surely looks as if a piece of metal had broken free of something and got ingested into the jugs.
Look around for the obvious; wristpin c-clip, broken piece of a bearing cage, etc. Being there is contamination in both jugs, it's guaranteed to be in the lower end of the motor as well so if you havent tore that down yet, might as well start...
Good luck with it and keep us posted.
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post #3 of 14 (permalink) Old 11-13-2007, 07:25 AM
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Not to hijack the thread but.... If someone had a head that looked exactly like the one above but everything else was obviously rebuilt (new pistons, etc) what would the effect of that damaged head have on an otherwise good shape engine?

If Seth is rebuilding that engine could (should) he use the same head? I ask because mine must have had a similar catastrophic failure and thye rebuilt everything but used the old damaged head.

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post #4 of 14 (permalink) Old 11-13-2007, 08:46 AM Thread Starter
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I have the engine out of the sled. I don't have a clutch or flywheel pulled so I am going to take it to a shop and have them pull both. I will split the crankcase and see what I find.

I am not going to use the heads pictured. I have another set of heads that came with the sled that I will be using.

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post #5 of 14 (permalink) Old 11-14-2007, 06:56 PM Thread Starter
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Ok, I split the case and when I was turning it over, a small needle bearing fell out (see pic 1). It is .5" long and about the width of a pencil lead. The marks in the top of the head match up perfectly with piece that came out. Now the question, did this piece come from this engine? I check all bearing and they look good. I can't find a bearing small enough that this piece would come out of. Did it come from somewhere else when the previous guy messed with the engine?

What do I need to check and replace before reassembling? I have two new oe pistons, two replated to oe cylinders and a set of used heads. I also have all new upper gaskets (head to cylinder, cylinder to block, etc). Do I need new crankshaft seals? What about the water pump seal? I have a service manual CD on order to help me along the way, but I would like your input as well. I know that I need the clutch pressed back on and lined up, what other specail tools do I need? Also, what about timing. What things do I need to watch for?

One more thing, there are no washers on either side of both lower rods where they connect to the crank. Is this normal, the microfiche shows them as crank pin washers, but they are not present here. Is this normal?

Thank you for all of the help.
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File Type: jpg cat_engine_031.jpg (98.3 KB, 52 views)
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post #6 of 14 (permalink) Old 11-14-2007, 07:56 PM
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Are both sides damaged?

The most common cause of engine failure I've seen with Cats are rings turning and hooking a port. Check the pistons and see if the locator pins are still in place.

Yes, you can use heads that look like that, with no worries whatsoever. You might notice a difference in power measured on a dyno, but seat of the pants you'd never tell the difference between those heads and brand new ones.

I don't know about the parts fiche, but I don't seem to remember ever seeing washers on the big end of the con-rod.

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post #7 of 14 (permalink) Old 11-15-2007, 10:58 AM
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Check your old piston pin bearings to see if a pin is missing. I had one come out a few years back and the damage to one cylinder looked a lot like yours. I have no idea how or why it happened.
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post #8 of 14 (permalink) Old 11-15-2007, 12:40 PM
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The head and piston damage is from a broken ring. They can break for a number of reasons but often from losing their free play in the groove. (Too much oil can gum them up so much - with carbon oftentimes- that they don't move freely.) The loacting pins are often mentioned as a problem which causes rings to break. Perhaps, but I suspect sometimes they come loose after the fact when the rings starts to pound things around. (Just because it's missing, IOW, does not mean it was the cause.) A pin which comes loose will raise havoc on its own, not necessarily even involving the ring. That trouble will not show as much, if any, peening however, and might only show as cylinder scoring.

That bearing needle is probably from the wrist bearing and came out after the previous owner tried to fix it or have it fixed. They can't get out any other way (and carburetors don't really have bearings! D: so it didn't get sucked in.) I usually clean up the peening so that no really sharp edges exist that might cause hot spots.

The engine needs to be completely taken apart and cleaned up to remove stray bits of metal that might have gotten into the bearings. If there is much sign of metal in the lower case, it is never a bad idea to check to see that the case has not cracked or been breeched because of metal pieces getting wedged under the counterweights.
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post #9 of 14 (permalink) Old 11-15-2007, 08:35 PM Thread Starter
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I have taken the engine all the way apart and checked for other damaged areas. Everything seems to be ok. I have new crank seals and a new water pump seal on order. I have all new top end gaskets as well. I have two replated cylinders and two new oe cylinders. I also have a set of heads to replace the damaged one. I will get everything cleaned back up and start putting it back together. Any tricks or suggestions along the way?

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post #10 of 14 (permalink) Old 11-15-2007, 09:01 PM
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Don't know what you don't know so it's kind of hard to start, however....

Make sure you clean the case halves and then gasket with proper liquid gasket - just don't let it into the interior of the case.

Make sure all loose needles get back when assembling bearings.

Install the rings right side up. BTDT the wrong way... lesson #1 quite a few years ago. And, of course the pistons the right direction.

C-clips (wrist pin clips), the opening faces down - definitely not sideways as the reciprocal motion may compress them and allow them to pop out.

Install the manifold snuggly but not tightened to align the cylinders. That will prevent leakage around the manifold.

Make sure you torque incrementaly and in sequence. That applies to case, base studs, and heads.
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