Engines > Restoration of Model Engines
Restoring 2" Case Reverse Slide Issue
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Bobsmodels:
Hi
Anyone out there who has built a 2” Coles Case, I am rebuilding the valve gear. Things are moving along well. I have most of the new tight pins made and the holes that were egg shaped cleaned up and bushed. I am keeping all the linkage tight ie minimal (no) play. The cylinder valve face has been ground down smooth and a new valve will be made.
My question for the day is the slide that runs in the bronze reverse block. The one on this engine was made of a real hard plastic. It appears to have little wear. It tore up the bronze reverse block, the sides were all gouged out. I am not sure how this was caused. It is likely the fit was loose so the slide just dug in on each stroke. One side was the worse, which made sense as the engine was run 95%+ of the time in the CCW direction looking from the Crank end. This engine was used a lot and run at 600RPM most of the time, running a silage cutter. See video to get idea of speed.
http://www.youtube.com/watch?v=tqrzFl-eKuU
My issue is the material for the slide. The drawings call out steel. This one was a really hard plastic material. Both make sense ie. hard running on soft. The Coles instruction sheets recommend wood for easy replacement.
What have you used in building yours?
Any other advice on the Woolf valve gear that will help in the rebuild would be appreciated.
Thanks
Bob
gbritnell:
Hi Bob,
The slide on the Woolf reverse setup gets a lot of pressure put on it by the angle that it has when running. My suggestion would be to make the block from drill rod, harden and polish it. This should provide a nice slick surface to rub against the slide. I would also use a heavy oil like way oil to keep it lubricated.
gbritnell
Bobsmodels:
George
I was thinking about that approach ie hard. I do have some A2 I could use. I also thought of Teflon (PTFE). I had a 1/4 scale Minneapolis and it used Teflon, replaced it after 20 years of running.
I like the idea of a hard polished one and may just give that a try. I was surprised at how the plastic chewed up the bronze.
Thanks
Bob
gbritnell:
Hi Bob,
Just from my readings generally the softer material (the plastic) holds the abrasive material (dirt, grit and material from the guide) and wears the harder material ( the bronze)
Just a thought.
George
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