Yamaha xt 500 smoking issue

Hey guys i posted a add over the summer about the honda cl350 jetting
issue.
thanks to some of your guys input it is running great. Now i have a
Yamaha xt500
i picked up this summer for 50 bucks , what a steal right it was a
little bit
better than a basket case . The biggest issue was that it was missing
a SWING
ARM. Any way i took the motor down becuase?the top end?was slightly
frozen .?I
purchase a used cylinder from ebay and i got a used piston with rings
from a
buddy of mine who had a Yamaha sr500 and had the pison as a spare .?I
put the
thing back together and started it and it started blowing white smoke
immidiately. That was about a week ago and it is smoking a little less
if not
the same, it smokes just like a two stroke if not more. i asked my
buddy what
was the status on the motor that the piston came out of and he said it
ran
perfect so i am looking for any advice on what the problem?might be?
and how i
would go about fixing it. any input is welcome.? THANX.

 

Hey, Irondog before you bash me any more let me explain, the cylinder
i bought from ebay was already honed, the only thing that i neglected
to do that was stupid on my part was to check the ring end gap and to
check bore to see if it was oversize. Knowing that the bore was
already honed , chances are that the cylinder was oversized and then
honed or the seller i bought the cylinder from was considerate and
honed the cylinder before he sent it to me.

 

I still can't believe you didn't mic it or check the
diameters of the piston and cylinder some way or other.

You don't really know what kind of clearances you're
running and even if you bought it from a buddy, you
don't know whether the piston is good or not. The skirt
could easily be partly collapsed even if it looks OK.
I've had this experience with pistons that looked perfect.

Pull it apart, measure the bore, measure the piston in
several places to make sure it's really OK and measure
the end gaps on the rings. I'd probably go for new
rings myself and be done with it.

It really doesn't make sense to try to put an engine back
together without checking all your parts clearances.
Either buy a micrometer and guage for the bore or
take it to somebody who has this stuff and knows
how to evaluate the parts you're trying to use.

While you're at it, what kind of shape are the valves
valve guides and valve train in ? Might's well get it all
fixed right at the same time.

Best of luck on your project. I think you've got
some work and a learning curve ahead of you.