[SEL] Cylinder/piston questions

[Michael Tucker]

Howdy all,

I was able to start evaluating the mechanical status of my new toy 
today.  It's a 1907 (serial number R1434E) 4 hp, screen cooled, 
hit-n-miss IHC Famous.  Although the rings were essentially dry, when 
pulling it through compression it seemed to be loosing a lot of 
compression past the piston at top dead center.  So, with the help of 
my machinist neighbors tools I took some measurements of the piston 
and cylinder.  The cylinder is in great condition with no hint of a 
ring ridge.  Up at the head end of the cylinder the horizontal 
diameter is 4.8025" and the vertical diameter is 4.8060".  At the 
flywheel end of the cylinder the horizontal diameter is 4.8010" and 
the vertical diameter is 4.8035".  So, there is a tiny taper and the 
cylinder at top dead center is only 3.5 thousandths out of round.  I 
think that I should be VERY happy with those measurements.  The 
piston is what I'm a little worried about.  Although it is absolutely 
round up by the rings and at the end of the skirt, between the first 
and second ring the diameter is 4.780" and at the end of the skirt, 
it's 4.794".  So at the top of the piston, that gives me a vertical 
difference in the diameter of the piston and cylinder of 26 
thousandths and a horizontal difference of 22.5 thousandths.  In a 
perfect world, what should the difference in piston diameter and 
cylinder diameter be?  Although the rings look to be in pretty good 
shape, do you think that they could be the reason for the blowby?

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