> The 75 Bus makes a big puff of black smoke (almost?) every time I start
> it. The smoke dissipates after a few seconds and then things seem fine.
> Could it be worn rings? Can I afford to ignore the problem?
> 
As long as it stops quickly, you're fine, I believe. since (as opposed
to most cars) the cylinders are horizontal, the rings (really c-shaped)
all line up sometimes with the gaps at the bottom, so a tiny bit of oil
seeps through. This happens to me every now and then, and Ihave been
assured it is fine, as long as your engine is not sreally high-milaged.
As the miles rack up, and it continues, and gets worse, then it could
get to be a problem.
Just my thoughts,
Richard