Smoky engine

Hi to all, first post.
Any hints in telling wether its rings or valve guides with engine running?
'73 850 interstate.
Also, any commando owners in East Lothian?
Cheers

As a general indication, ride the bike and observe if under accelleration blue smoke increases then its most likely to be piston rings. When decellearating quickly, i.e. throttle off, coast and then blue smoke emits its more likey to be inlet valve guides or their seals.

This road test is more informative than a static test which can depending on how bad the wear is can also indicate what's most likey to be the problem. However, the very least is the head has got to come off so with the exposed cylinder bores you might also get a visual clue as to the probability of the rings being worn as well.

You can also run a compression test "dry," in the usual manner, and then "wet," after adding a tablespoon or so of oil to the test cylinder. If compression is higher "wet," it's more likely rings than valve guides.

Another thing to keep in mind is that if smoking on trailing throttle or at idle, the guides and seals can be fine but they can have excessive clearance in the head, with oil going down the outside of them. There is a lot of vacuum with the throttle shut which will try to pull any oil sitting on the floor of the intake rocker box into the combustion chamber.

Now that our bikes may have a had a number of guide changes, this problem is getting more common.

Russ

Thanks for the replys, it will give me something to go on. Excellent site by the way.