advice on tolerances.

Hello there, I am hoping that someone could offer some advice regarding the following measurements that have been made on my camshaft and bushes by a ( reputable ) engineering friend. I would like to know if the components are within servicable tolerances.The measurements as per the manual are in brackets - the bike is a '72 850.

Camshaft journals - both ends measured at - 0.8724 in. (0.8735)

Cam lift -exhaust- measured at 0.3215 and 0.3210 in (0.3220)
Cam lift - inlet - measured at 0.3195 and 0.3210 in (0.3320)

Camshaft bushes both measured at id 0.8780in (0.8750)

Thanks in anticipation for helping me to interpret the measurements.

.0015 diametral clearance sounds decent...

i don't have the book handy.

0.8735" cam journal
0.8750" bush id

According to the manual. I don't know how important it really is because it's an unpressurized, scrolled bearing. Did you measure all four of the lobes? Sometimes one of them will wear more of the others. Usually the left side exhaust.
P.S. Oops. I saw your measurements after my post includes all four. Reading , writing, and eating lunch is one task too many.

FYI - there is no 1972 850, the 850 came out in 73.

I'd make a wild guess that the cam tolerance specs were all the same on Commandos up to Mark III, maybe not the Combat...

Cam bushing is .878 and the journal that runs in it is .8724 that would leave .0028 gap all around for an oil film. It's a .0056 difference would it be on the timing side ? were the chain is pulling on it. You would like to see .003 for a .0015 gap all around clearance but I would bet it would run that way. Your call.

grandpaul said:

.0015 diametral clearance sounds decent...

i don't have the book handy.

Click to expand...

:?: :?:
Or a calculator ,the clearance could be less, but it probably didn't leave the factory much better and shouldn't make any difference for another 50k, it doesn't want to be to tight because it isn't pressure feed.

Thanks for your advice everyone - Splatt am I reading your comment right - you are saying that from the measurements I supplied you feel that there could be 50 k miles wear left in the components ? Hope that is the case as cost is an issue and it will mean that I can push on with my rebuild. Thanks again.

yes