[SEL] Cylinder/piston questions

[Judge Tommy Turner]

Michael,

    My "rule" that I use for my old iron is if the difference between 
the bore and piston is in the 1 to 1.5 thousandths per inch of bore 
range, its a great piston/bore fit for the old iron.  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.  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.

Tommy Turner
Magnolia, KY



Michael Tucker wrote:

> 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