[SEL] Cylinder/piston questions

[Mark Empson]

Mike ,
The difference in piston diameter from head to skirt might very well be by
design in that the head of the piston is in contact with combustion and will
inherently be hotter ( more expansion ) this heat is transferred to the
cylinder via the rings which have a gap that allows them to expand and not
tighten up in the bore . The piston to wall clearance is measured on the
skirt which is meant to guide the piston in the cylinder . The seal between
the piston and rings happens on the ring lands thus the need for a fairly
tight fit there as someone else said .001 - .002 would be great but I
wouldn't be alarmed if it were .005 . In my opinion glaze hone the cylinder
and install new rings .
Mark Empson
----- Original Message ----- 
From: "Michael Tucker" <mtucker at uky.edu>
To: "The SEL email discussion list" <sel at lists.stationary-engine.com>
Sent: Sunday, May 22, 2005 8:49 PM
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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