[SEL] Compression question

[curt at rustyiron.com]

Russell,
Your idea of moving the ring set down the length of the bore sounds like a
good idea at the outset. However, if you have a look at the inside shape
of the piston you'll find that the ID of the piston is small in the area
under the rings. The area just aft of the bottom ring will step up for a
much larger ID. This is done to conserve weight of the reciprocating mass.
I'm doubtful you'll have enough metal to add an additional ring groove w/o
cutting thru the ID of the piston in this thinner cross section.
Obviously I've never worked on a Hornsby engine, but I've made quite a few
piston patterns & core boxes for American made engines and just about all
are made this way. Before you chuck your piston in the lathe, have a look
at this and make lots of measurements to make sure you don't make a tragic
mistake and cut your piston in half.
Curt H
Bessemer City, NC


> Quite some time back I bought two very average looking Hornsby oil
> engines; a 2 and 3hp types. They came with enough bits to make one
> complete engine etc ................... Well I have hunted extra bits now
> and have enough to basically complete both. One will is going to a good
> mate whom is doing all the work (he has spare time) and the 2hp I will
> keep. Although not at the point yet of putting the piston back in and
> seeing how much compression it actually has, (my 2hp) I noticed there was
> a very small amount of pitting at the top of the bore. Now it's not much
> and only time will tell if it's even going to be a problem. How ever if it
> is a problem; I was thinking instead of boring or sleeving. Could I just
> cut another ring groove further back along the piston; remove the top ring
> and put in the lower new groove?? This would avoid the pitted area mostly
> and the majority of rings would be running in a clean bore? Any issues
> with something like this?
>
> cheers all. Russell
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