Bob Engelhardt wrote:
Nice. What were the closest tolerances that you had to hold? Bob

'bout that much.

Seriously -- since I wasn't trying to hold to a particular compression
ratio, the only really critical parts were the threads and seats. The
glow plug was taken care of with a 1/4-32 tap, and the seats just needed
to be flat and smooth. I almost cut the mounting threads too deep --
they turned out to be just about the right size after my last rough cut,
and I had anticipated a few finish cuts to get that part right (I'm
still far from a thread-cutting expert).

If anything I missed on the step up to the squish band, and the
combustion chamber -- given that the thing needs 3 x 0.005" gaskets, I
should have made the whole thing 10 mils deeper. With just one head
gasket you could hear the preignition (or the piston whacking the head,
but I think it was preignition).

Making the _next_ one is going to challenge my ability to hold tolerances!

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com