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48 surpass compression loss

Old 08-08-2003, 02:50 PM
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Default 48 surpass compression loss

I would appreciate your thoughts on how to deal with a significant compression loss on my 13 season old 48 surpass.

After the first 12 seasons of regular use, the engine would not hold a needle setting. There was little compression left, and I was told it was time for a new ring.

I followed Harry Higley's excellent book and took apart a 4 stroke for the first time. The sleeve, indeed all the internals looked great. I lapped the valves ala Higley. No significant change in compression. I replaced the pushrods, because one had a slight bow. No improvement. I replaced the ring, slightly abrading the sleeve again ala Higley, and the engine ran like new after a short period of breakin.

I thought this puppy was good for another 12 years, but with less than 30 flights since my new ring, the compression is again near zero and I am again starting to fiddle with the needle.

By the way, since overhaul, I ran only Wildcat 18% all synthetic Heli fuel, 15% nitro. It was running like a charm.

Should I have replaced the sleeve with the ring? Is it worth the expense, or do all good things finally come to an end?

Thanks in advance, GoNavy.
Old 08-08-2003, 04:55 PM
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Default 48 surpass compression loss

Compression loss in your O.S. Max FS-48 Surpass can be caused by a bad piston/ring/liner fit, or bad valve sealing. On a well-used, but not abused, engine, the main area for compression loss is the ring-to-liner fit, but the fit of the ring in the piston can also be a contributing factor.

Usually, if we replace a ring, we also replace the liner, since the fit between these two is the most critical, but we sometimes have to replace the piston. It depends upon how well the ring fits in the groove. It should move a bit, but a lot of visible movement indicates a worn ring groove.

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