81 XR80 Bore

I am working on an 81 XR80 and it smokes pretty bad. I am guessing it is time for some new rings and probably valve seals. Does anyone know what the stoke bore should measure at? I have ordered a book but it's not here yet. The cylinder actually looks pretty good, no lip to speak of at the top. Using a telescoping gauge I get 48mm, and very little variation from top to bottom (.03mm). But without the specs I don't know if I am good with just a hone and rings or not....?

 

 

Thanks,

Rob

99% of the time a valve seal fixes the smoking

99% of the time a valve seal fixes the smoking

 

:thinking: Ok................then how do you explain Honda's that had only one valve with a seal, or "no valve seals at all" and didn't smoke badly? ;)

 

I've yet to see smoking badly all the time cured with only new valve seals....................... oil getting past the rings into the combustion chamber, which can be due to several problems causes this condition.

 

Old School Al

Edited by Old School Al

I by EVERY XR80, XR100, XR50 & XR70 I can get cheap, most smoke like crazy.

99% of the time that 1 valve seal fixes the smoking.

I'm sure it's the valve guides that are worn but a seal is a good cheap fix.

I've only seen a few bikes that really needed rings. If they need rings they need a piston also.

Either way without the specs I can't really determine what it needs for certain. I would rather spend $30.00 extra on rings while I have it apart. I bought and downloaded a manual since the Clymer I ordered is taking forever. The spec on it says that the XR80 bore is 47 mm (mine is 48 mm), but the weird part is that the book shows the xr75 bore to be 48mm. I double checked the casting on the jug and it should be an 80. Anyway, I'm back to square one waiting on the Clymer to double check those specs.

I can check my Clymer tomorrow but for some reason I was thinking STD bore on 80s was 47.5mm.
 

Also - smoke at idle / downhill = valve seals

smoke under load / uphill = rings

 

Wouldn't be surprised if last owner didn't break new rings in properly. Very easy to take temper out of small rings like that.

It smokes all the time. As much as it has been sitting and then beat on by kids and then sitting again over the years it is likely that the rings and seals are done. The intake valve isn't sealing tight either so it definitely needs some TLC.

Looks like some missing info on early 80s

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