[SEL] Cylinder/piston questions

[Michael Tucker]

Howdy all,

>I agree with a prior comment that the ring gap and fit is more 
>critical than the fact that you may have an undersize in the piston 
>between the grooves.

The rings fit very nicely in the ring groove and although I haven't 
measured it, the gap looks pretty good as well, especially since the 
rings have overlapping ends.  I'm sure that new rings and oil will 
help but the thing that bothers me about the compression loss is that 
it's not a constant loss as the piston comes up on TDC.  Instead, is 
looses some compression as it approaches TDC but just as it goes over 
TDC and the rod goes from pushing to pulling, what compression there 
is lost all at one time in sort of a loud pop.  This makes me think 
that the piston is moving around a little too much.  In fact with the 
head off, you could see the piston wiggle a little bit as it rolled 
over TDC.  That's what worried me that the cylinder was out of round. 
Although it is out of round just a bit, from the measurements I think 
that most of the wiggle is due to the piston wear and not the 
cylinder.

>If you want a more perfect fit on the piston, have it flame sprayed 
>and turned down to 5 to 6 thousandths less than your bore.  Do this 
>and put in new rings  and your hunk of iron should need a 
>compression release to turn it over.

 From y'alls comments on how much clearance there should be, flame 
spraying is where I think I'm heading with this critter.  Since I 
intend to work this engine on a buzz saw rig rather that just running 
it, I think that I need better compression than it has with its built 
in compression release at TDC!.  I'll definitely hone the cylinder as 
well as replace the rings and like you say, it should have 
compression to spare!  Tommy, do you know of any places here in the 
Bluegrass that do flame spraying?  What type of metal compound should 
be applied for ability to machine and good wearing properties?

Thanks for the help folks,
Mike
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Michael Tucker
Midway, Kentucky, USA
mtucker at uky.edu
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