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Swapping engine parts?

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

terrylee

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Finally dealing with my lack of compression in #2 cylinder (see "noise in engine" earlier thread on 6/20). Bought a parts bike and was planning to just switch engines for now and rebuild mine later. Turns out someone had tried to do some work on this engine and had snapped off several of the cam caps bolts. Then they tried to fix that and messed it up worse. So using the top of this engine is out. But I did tear it apart to see what the valves and pistons look like, since bike only has 28,000 on it. (Mine has 60,000) The valves look very good with hardly any carbon buildup. The pistons same way, but one has small scratches on one side that you can feel with finger nail. The others look fine, and piston bores don't seem to have any scratches, even the one with the bad piston. (Sorry if I'm using the wrong terms for parts) Is there any benefit to me using the valves, cylinder block, pistons (minus the bad one) and maybe the cams on my 850 engine? All the shims installed were 2.65s and 2.70, so valves certainly not tight yet. Planning to replace valve seals, hone piston bores a little, lap valves, install new piston rings and of course all new gaskets and o-rings? This will be my first time of doing a top end rebuild so want to do it right. terrylee
 
Can the head be repaired? Helicoil or sold inserts to repair the damaged threads? Failing that, using the best parts from what you have is a solid plan.
 
Thanks for the response. That what the po tried to do and made some of the holes a mess, and at least four broken bolts still down inside head. Just good to know I'll be doing things right. I just figured it would be better to use parts with less than half the mileage of my 850. Anything else I should do while have apart? terrylee
 
What was wrong with your piston?
If PO ovaled out the threads and you can't helicoil then fill them with JB Weld and redrill and tap the correct size. You do not have to put much tourque on these.
If the bolts are broken off in the head center punch and drill them out and tap them.
 
Chef, I could do that, but I thought it would be easier to use my 850 top head and just switch valves from parts bike to it. But if I shouldn't do that and stick with the head on the parts bike I will try to do that.
I don't have my 850 apart yet, so not sure if anything wrong with my pistons, but just thought parts with a lot less miles on them than mine would be a good thing, but if there is no benefit to that I'll stay with my 850 parts. terrylee
 
Went out to the garage and took another look, four of the holes have helicoils in them that no longer thread, 2 which were put in crooked, and three bolts broke off inside. I'm not sure but they look like some sort of metal inserts instead of helicoils. I might be able to salvage this, but will be some work. terrylee
 
Last edited:
terrylee said:
Went out to the garage and took another look, four of the holes have helicoils in them that no longer thread, 2 which were put in crooked, and three bolts broke off inside. I'm not sure but they look like some sort of metal inserts instead of helicoils. I might be able to salvage this, but will be some work. terrylee
Click to expand...


provided your old head is in reasonable nick meaning valve seats guides and cam bearings are ok why not just take the good valves out of the head and redo your old head it seems alot less work for same result no point making hard work doing up the trashed head
 
That's what I hope to do, won't know for sure till I get mine off. Just wanted to make sure this was ok to do. Want to do this only once, so want to do it right. terrylee
 
if they used a metal insert its a time sert, they work great for repairing stripped out threads, I put them in all my exhaust bolts . you can get them off ebay.
 
Several of them came out of hole when I pulled on them (they were already loose). And as suggested I would have to JB weld a few holes and retap as the holes are rounded out and a lot bigger than they should be. terrylee
 
How about posting some photos of the damaged threads. Timeserts are solid metal inserts and you have to drill out the old thread oversize to install them - larger than a helicoil. JBweld is a non-starter. If you have to resort to that, use the old head or have it welded.
 
Thanks Rusty, will keep in mind. I hoping to use the one off my 850. I'm getting ready to spend some time with the wife today, so will try to post pics. tonight. It would appear they used helicoils in some (one bolt came out with it attached) and metal inserts in some, two came out with the bolts and the hole is larger by quite abit where there were, and one hole is very rounded out at the top. I really appreciate everyones input on this, as I said I want to do it right. I measured the piston chambers last night and they are all at 69 mm, if have them honed am I going to have to get oversized rings liked .5m? terrylee
 
Terry, your photos suck. Please try again using the macro feature, and make sure you focus on the parts, not the background.

BTW, those rings won't work. Too big.
 
Sorry about the pics. my camera doesn't like to take close up pics., but I'll try again. Good to know about those rings, so that means I should stick with the standard size? terrylee
 
Sorry again, I tried to take closer and better pics. and my camera won't do it. As long as there is no reason I shouldn't (which I won't know till I get mine off) I will use my top head and save the parts one for possible repair at a later date. terrylee
 
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