[SEL] Cylinder/piston questions

[R and E Freeman]

Mike , looks like you have a worn piston but I'm not sure if it would make 
all that much difference to the blowby. Lots of people here would know more 
about that than me but I would think if the rings are OK and a good fit in 
the ring grooves it should seal up with some oil around there. Your smallest 
bore measurement and largest piston measurement would be close to unworn 
sizes so it was originally around 8 thou clearance. Modern engines would be 
tighter but in that I would think 6 to 8 thou would be OK

Ray Freeman

Portable Line Boring
http://www.plb.iinet.net.au
plb at plb.iinet.net.au
----- Original Message ----- 
From: "Michael Tucker" <mtucker at uky.edu>
To: "The SEL email discussion list" <sel at lists.stationary-engine.com>
Sent: Monday, May 23, 2005 8:49 AM
Subject: [SEL] Cylinder/piston questions


> 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
> -- 
> ____________________
> Michael Tucker
> Midway, Kentucky, USA
> mtucker at uky.edu
> ____________________
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