Author Topic: Thompson Engine  (Read 415 times)

Offline rick41

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Thompson Engine
« on: September 16, 2020, 04:15:58 PM »
I have finished machining my Thompson single cylinder engine (sort of).  There are a couple of tube videos of this engine running.  They both show the engine running in a counterclockwise direction (viewed from the flywheel side).  I set my engine up the same way and got it to run a few seconds before the bolt holding the connecting rod to the crank unscrewed itself.  I put the bolt back in and tightened it.  Ran the engine and a few seconds later, the crank bolt unscrewed itself again.  I looked at the cam gear and it looks symmetrical to me, so I am thinking reversing the rotation would be fairly simple (correct?).  I am thinking that reversing the direction would result in the crank bolt being tightened rather than loosened.  My other option would be to loctite the bolt in place.  Thoughts?

On another matter, I would like to share my valve lapping dodge.  Don't laugh, it worked for me.  Valve lapping is mostly reciprocal rotary motion, correct.  I had an old electric toothbrush and I thought why not?  I put the valves in the head, applied a bit of TimeSaver lapping compound, coupled the valve to the toothbrush using bit of plastic tubing for a flexible connection and after a few seconds, My valves were lapped!  Sealed perfectly. Rick

Offline crueby

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Re: Thompson Engine
« Reply #1 on: September 16, 2020, 04:32:34 PM »
Regardless of direction, I'd think some loctite blue (which is removeable with a wrench) would be a good idea. No heat needed to remove, but it holds very well. Setting up the rotation to have any forces tightening sounds good too - though some engines were designed so that the rotation direction would put downward force on the crosshead guides.

Offline Jasonb

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Re: Thompson Engine
« Reply #2 on: September 16, 2020, 05:01:10 PM »
I'd go with a new pin that has a longer thread so that you can fit a lock nut on the end, drop of threadlock on the nut won't hurt and no chance of getting and loctite into the bearing. Another alternative is to tap the pin and fir a screw from the other side rather than screwing the pin into the crank web, again easier to use loctite without risk of getting it onto the bearing surface.