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Discussion Starter #1
Hello guys.
I recently bought a used 03 954rr engine (approx. 30k miles). I had an old head lying around which was serviced at a machine shop so I decided to slap it on before putting the engine in the frame.
When I removed the old head i discovered that I was able to rock the pistons back and forth, so I looked at the haynes manual which said that the piston to bore clearence should be between 0,02mm - 0,055mm (mine were around 0,08).
Is this normal for a used engine or should I expect to hear the dreaded knock knock?
Any advice would be much appreciated. :)
 

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I can't accurately speak about the 954 and what is acceptable clearance. It would seem by watching your video and looking at the specs you provided that there is substantial play with the piston inside the cylinder. According to my old 93-95 900RR manual, the spec is .015 to .050. Granted, that is with a standard steel sleeve and un-coated piston. Your piston skirts are coated with a Teflon style coating and the cylinders are an aluminum impregnated coated Alusil. When the Alusil wears (and it does), the thrust force of the piston on the walls becomes an issue and wears the aluminum bore.

From my VERY LIMITED knowledge on the subject, I would say that your bores are now oblong a bit, thus the excessive gap. It might result in piston slap, and may go away as the engine warms up and the pistons expand a bit or may not.

I would guess that if you took the pistons out you would see some scoring on the skirts and cylinder walls. All that being said, I can't be certain that you have an issue other than your clearance being beyond the top end of the recommended specification.

I hope that helps out.
 

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Would this help? It's from the 929 WS Manual but NOT 954. I'm assuming tolerances would be the same.
 

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Did you measure at the skirt of the piston? That would be where the most wear would be I suspect. It may show a larger reading, especially if you can rock the piston.

Does the bore have score marks? The scoring would make it harder for the rings to seal.
 

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Discussion Starter #7
Thanks for the response guys!
The cylinder walls were indeed scorned, but nothing excessive considering that all 3 of the 954rr engines I have worked on had them. My old engine had them too without there ever being a compression issue even though it did eventually fail, but that was due to spun crankshaft bearings. I've talked to a few other guys with 954s and they said their engines had them too. I've heard it had something to do with the shorter skirts on these pistons.
My old engine used to be very loud when dead cold. Sounded like a chain rattle or piston slap or both almost as if it was going to fall apart, but as it got closer to operating temperature it quieted down and as it got fully warm it started purring like a kitten. I've heard from the people I've talked to that it's pretty much the same with their engines.
Perhaps this is due to this clearance issue. The specs in my manual were the same as the ones Nigel posted and I did my measurements above the piston rings as I did not want to split the block.
Anyway I've reassembled the engine so I guess I'll just put it in the frame and hope for the best.
 

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Discussion Starter #9
if it's any consolation, Ive just rebored my 929 making it into a 954, with new JE pistons. They rattle from the first moment you run it, and then quieten down completely.
Let's hope mine queits down aswell. :grin
 

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Erm....I mean they all rattle when cold, and quieten down when the engine reaches working temperature. Something to do with the short skirts. I now rattle a bit around short skirts but that's just my brain trying to recall what the appropriate response should be.....
 

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Discussion Starter #11
Yes, I have been told the same. As far as my understanding goes, that is also the reason why they have those scratch marks on the cylinder walls. I'm just hoping that the clearance issue is just normal wear and tear as I did not measure the clearance on the old engine before disassembly. The scratches on the old one looked pretty much the same and as I mentioned earlier it never had compression issues. Overall the engine seemes to be in OK shape.
I opened the oil pan to look for shavings (non found) also I cut open the oil filter, and that was clean too. The head looked considerably better then what my old engines did. Valves on cylinder 1 and 2 were black, because it was burning significant amounts of oil (valve seals), but this head looked clean.
I'll put the engine in the frame when the weather clears up and we'll see if it works.
 
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