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Piston and rings

  • Thread starter Thread starter terrylee
  • Start date Start date
T

terrylee

Guest
I'm starting my top end rebuild on my 80 850. Got cams out and all cylinder nuts loose with out snapping a single one! I am planning on using pistons and valves from parts bike (see earlier thread) that had only 28,000miles instead of 60,000 like mine. But per earlier thread, the top cylinder cam bolt holes were shot. So I plan to use my cylinder head instead. I'm a little strapped for cash, and have most of what I need except new rings, so wondering if I could use the pistons and rings and bottom cylinder from parts bike on my engine, without creating any problems? I'm planning to deglaze the cylinders, since they look in very good shape. terrylee
 
Sure, if the rings are not damaged, and not worn, they should last a long time. Break it in hard just like new rings.
 
As long as they measure within spec , Personally I would use them. I re-did the top end on my 850 which had 33k on it and reused the old rings that came in it. Why should it matter if they are from a different bike? If they're good, they are good.

But, as always, your mileage may vary.
 
Thanks for the advice. They look good and even very clean, I will do all the specs on them and see. terrylee
 
Everything appears to be within specs. I don't think I can use piston #3 as it has couple of small scratches on one side, one you can feel with your nail. I don't see any scratches inside the cylinder bore though. Hope to order o-rings I need next week and try to get the bike running so I can ride this season, as I haven't been able so far. terrylee
 
I think I could buff them out, but not sure how to do it and not mess it up worse. Maybe a dremel with soft wire brush? Or some low grit sandpaper? I'll try to post a pic. later, heading out of town in a while. terrylee
 
Fine grit sandpaper attached to a flat object can be used to remove defects from pistons.

And as said before, pictures are necessary in order to give you an honest opinion of what we would do in your shoes.
 
Some skirt scuffing won't hurt anything. I'd be leary of removing material from the pistons if you start sanding on them. At most, knock off any burrs on the edges of the scratches and leave the rest alone.
 
My camera does not let me take close up pics. that you can see. I lightly buffed the scratches with 400 wet and dry, very lightly. The scratches are much less and can barely feel when running finger nail across.
 
Personally, I would now use 1000 and then use 2000 to get them to a mirror finish.
 
top end taken apart

top end taken apart

Finally got my bike torn apart. Didn't take long to figure out why I have low compression in #2 cylinder, ex. valve head is cracked. Doesn't appear to be any damage to anything else, but haven't got valves out of the head yet (need to make c-clamp tool). Glad I have valves from parts bike! As well as pistons, since ones in my bike have lots of carbon built up and even some carbon lying loose on top of piston#4. Part bike ones were not bad at all and I've already cleaned them up even more. Also going to replace front cam chain guide as mine has several hairline cracks in it. The back one does too, although not as bad, but I can't afford over $360. to replace it (one on parts bike is worse). Anybody got a good used one, or should I even be concerned about it? Hope to order rest of parts I need next week and try to get some riding in sometime soon! terrylee
 
You can remove the valves using a Squaredancer Lynn trick: Stuff a rag in the combustion chamber area and flip head face down on a sturdy workbench. Get a socket and place it over the valve spring keeper (remove the bucket first), then wack down firmly on the socket with a medium heavy hammer. The spring retainer will be forced down and the keepers will jump up out of place. Works a treat. Much faster than using a c-clamp.

Good luck
 
I actually did that to get the valves I'm going to use out of the part bike destroyed head. But I broke one of the valve guides doing that, so a little leary about doing that on head I'm going to use. Or at least it was broke when I removed valve, so I assumed I did it. terrylee
 
Did go ahead and remove the valves from my head using the rope, hammer, socket trick. Didn't break anything. Boy are those seals hard to get out! So now order parts Thurs. and make a valve spring compressor tool and will be set to start putting things back together. Going to lap valves and deglaze piston bores. Can't wait to see how this thing runs after this rebuild! terrylee
 
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