Look at these pistons


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Bill B

Look at these pistons

Post by Bill B »

Engine on my 36K mile 82 is partially disassembled to insert another pulled stud. That's
done, but look at these pistons. The crowns are heavily encrusted. I cleaned them off 4k
miles ago when I did a couple of pulled studs, and they look worse than the first time.
http://www.billsworkshop.com/cbx/deposits.jpg
Causes? Is this a concern?

Any tips on removing the pistons without breaking things or losing the clips in the case?

The piston sides look generally OK, but I do see some small scores, as shown here.
http://www.billsworkshop.com/cbx/scores.jpg

Opinions? The bike seems to run very well except for the oil leak from the pulled studs.

Thanks,

xneric
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Post by xneric »

Bill, that sure looks like oil. Your pic of the scoring shows a pretty grungy oil ring. Since you have it apart, you should spend the time (and money) to do a complete top end overhaul. Certainly some new rings....hmm...perfect time for a big bore kit. Also check the valves and valve seals. Don't be cheap...you'll pay in the long run. The other problem is those pulled studs. That isn't a normal problem. Are you checking their torque? Have you checked your wrench? Good luck, Eric

Bill B

Thanks

Post by Bill B »

OK. I should do the valve seals and rings.

The studs problem is very odd, although I know of others who have had the same problem. I bought the bike from the original owner at 22K miles. He took very good care of it and never had any engine work done. At 32K miles I developed an odd oil leak and I found two loose stud cap nuts when I checked the top end. I mean finger loose. They would not torque beyond 15 ft lbs. So, this was completely spontaneous. I fixed those two only to have a 3rd give way in the next 4k miles.

Bill

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sr71cbx
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Carbon dating......?

Post by sr71cbx »

Bill B,
I concur with xneric on this one,looks like there is an oil control problem with the amount of snotty-looking carbon on the piston crowns.Seal those guides,cut the seats,and get some fresh rings in it and it should work just fine,also,while it's apart,pull out ALL the studs and either time-sert or heli-coil ALL the threaded holes,reinstall studs with silicone seal,and set the block & head on by themselves to allow torquing of head studs/nuts to load the threads properly 8) .I know all about studs pulling,I've been there & done that last year with my '79 turbo right before Death Valley '02!! :shock: Also,how are the cam chain tensioners(while it's down)?
Lotsa luck with it,keep us posted. :)

Bill B

Re: Carbon dating......? More results from the dig...

Post by Bill B »

Here are the pistons removed. There is crusty carbon on the pistons sides above the rings to the front side only (oil in chamber pooling there?). Funny the bike has never smoked, unlike my 79 which blows soot when hammered.

http://www.billsworkshop.com/cbx/pistons3-2-1.jpg
http://www.billsworkshop.com/cbx/pistons6-5-4.jpg

Anyway, the carbon deposits are scored up (I think this is visible) and on some of the pistons (#3) there is no crust on the side but there appears to be metal scoring in that area. The back sides of the pistons are fine.

These pistons are toast, right?

The bores look good - even see original hone marks, although there are a couple of slight longitudinal scores in a couple of bores.

What are my options? I assume a big bore kit would be the way to go. Which one? Who sells them? I assume you have the stock cylinder bored out, use the stock base gasket but the kits come with head gasket, etc.

WHO DOES BORING OUT HERE ON THE LEFT COAST near SF/Oakland area?

Also, when you said...

" set the block & head on by themselves to allow torquing of head studs/nuts to load the threads properly"

You mean with no gaskets initially?

Bill
79 & 82 X
ICOA 2924

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sr71cbx
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studs

Post by sr71cbx »

------Wouldn't hurt if you used an old gasket between the head & block.

Bill B

Re: studs

Post by Bill B »

sr71cbx wrote:------Wouldn't hurt if you used an old gasket between the head & block.
OK, will do. Thanks.

Received 2 educated opinions that the pistons, although encrusted with carbon, are not bad, and that if the bores are round, I should do the valve seals, rings and a light hone. Sounds like a plan.

Bill
79 & 82 X
ICOA 2924

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