Low compression numbers

[Boot]

Have a high mileage 80 model xs11 special still runs pretty good but it is starting to smoke a little when first started. also we did a compression test on it and the numbers came back a little low. they are 118,110,119,118 from left to right.i love the bike and would like to rebuild the motor. should i have the motor bored and go with an oversized ring set or just clean the bores up an replace pistons rings and all.

[DGXSER]

what you describe could all be valve related. The oil when starting is indicative of valve seals. And the compression could also be low due to worn valve seats, meaning the clearances are not what they need to be.

You can add a table spoon of oil to each cylinder when you retest it for compression. If the numbers go up, the rings are suspect. If not, then most likely valve related.

[Guy_b_g]

Not to insult your intelligence but you did the test with the throttle wide open, right?

[crazy steve]

Those numbers aren't horribly low, and they are even enough. Does the bike consume a lot of oil, or is the smoking only on start-up (after the bike has sat a bit)? If it's the latter, you may only need new valve stem seals and maybe a valve job.

One issue with these bikes is a near-total lack of 'replacement' rings/pistons. You can find first oversize rings (and some owners have filed these down to fit their standard pistons) but pistons are nearly impossible to find. Wiseco (as far as I know) is the only supplier for new pistons/rings, but theirs is a kit and requires an overbore. Not cheap either; $500+ , not including any machining. Arias Pistons will make anything you want, but expect to pay for it...

[petejw]

as the others have stated,
the numbers are fairly even across the board,
was then engine at operating temp and as guy stated
did you have the throttle open all the way,
at worse you might just need to give the head a service,
many of us have well over 150,000km on these engines.