ORIGINAL: LeeHop
Graham -
Wow. Thanks for sharing.
Could you say a little more about how this works?
"I drilled out the end of the cap screw to help prevent the compression setting from drifting as the engine runs."
Cheers - LeeHop
I had noticed the ends on the compression screws of my PAWS where drilled out and made hollow. I didn't really know why and no one I asked could provide a suitable answer. I discovered the answer on Ron Chernich's Model Engineering web site in a story about Peter Burfords .03 diesel engine
Notice the hollow point. Years of experience with Taipan led to this little touch (and one I first heard from David Owen and have mentioned in these pages before). The center of the contra-piston will probably be slightly raised. So would the tip of a "flat" comp-screw end. The result of these two not-quite flat surfaces registering against each other is a comp-screw that will unscrew under vibration every time. The hollow point allows any slight pip on the contra-piston center to be compenstated for, reducing the likelyhood of it unscrewing while the engine is running.
http://modelenginenews.org/pb/index.html for the entire entry on Peter Burford's marvelous little engine, the bit on the compression screw is about 1/3 down the page with a picture of the compression screw from Peter's engine.
Ron's site is a cornucopia of interesting stuff on small engines and well worth spending much time reading.
Hope that helps clarify.
cheers, Graham