Rings?

Been getting some blue smoke from my left cylinder - more lately. Ran a compression test yesterday (warm engine, throttle fully open). Left cylinder read 120 PSI. Put a tablespoon of oil in the plug hole and ran it again - 180 PSI!

Sounds like I need new rings, no? Any other advice/suggestions? Realize remote diagnosis is difficult at best.

Thanks all.

You could be spot on, but you didn't supply the data from the other cylinder. I generaly look for a difference that doesn't exceed 10%, if they are balanced, even of low you can get by nicely until, maybe next winter. 120 PSI on a 8.5:1 motor doen't sound that bad, low maybe, but I couldn't find a spec in the factory manual, so I can't say for sure.

Intake valve guide seals can cause the same smoking issue. To replace them is to get so close to the barrel you maight as well refreash the top end.

How many miles/years do you think are on the top end?

Regards,

RS

PS: I have the ring compressors and other tools you may need, if you don't. Just around the corner in Stow

Thanks Bill. Odo says 8K-ish, but who knows if it's right? I had trouble getting the compression gauge to thread into the right hand cylinder (those threads are not great, at some point I should do something about them but they've held up so far with an occasional run-through with a backtap).

No way I'm pulling this apart before winter anyway as it runs great (scary to think it could be better!) So this is in the winter project pile anyway. (Along with my automatic cam chain tensioner, lapping the oil pump gears, and swapping in the eBay tranny I'm rebuilding (or rebuilding the existing one, perhaps in situ).)

Have the tools for re-ringing but an experienced hand is always welcome so may press you into service next winter if you're willing. How are you on head work - wouldn't mind doing those valve guides also.

Keep looking for ya at MotoMarket but not yet. You planning on the Auburn and/or Oxford Brit bike meets? May 24 and June 7, IIRC.

I'd be happy to lend a hand, let me know.

I may go down to the British Iron meet as a spectator, my ride won't be ready by then. I haven't been to the Moto Market for some time, I'll see if I can fix that.

RS

Appreciate it Bill.

Will you ride the Duck or something else out to the meet? Wanna meet us and run out together? Not sure at all of leave time or route yet (my friend is the leader, he tells me where to show up and I do!) but we could probably arrange a meetup if you're game. We take the Pike out, usually meander back on lesser roads (more fun!). My son's HS grad party is that day, so I"ll probably be cutting out early and heading back by mid afternoon. - BrianK

Compression increasing with oil in the cylinder is almost surely rings or piston wear. It kinda depends on when you see the smoke... at idle or decel, it's usually valve guides or seals, under power and load it's usually rings or pistons.

And then there's the familiar phenomenon of MULTIPLE CONCURRENT FAULTS!

I get blue smoke both at idle and underway. Could be needs rings (maybe even overbore) AND headwork. Guess I'll find out when I get in there.

This Commando is my 401(k). Unfortunately, I could never sell it for what I have in it, and wouldn't if I could! Ain't love grand.