Hi, I just purchased a new MDS 78. The engine is ringed and has never been ran. The compression seems very low compared to my ABC engines. Is this normal for a new ringed engine? Also what is the proper break-in proceedure for this engine?
Thanks
Bob

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It will amaze you after about 20 minutes, the compression will seem unreal. Use 5% nitro, 20% oil and slow and rich break in.

I agree with hobbsy! The ring has be seated. Run it on a test stand rich for about 20 minutes or more as stated and you should really see a difference. Plus you will be able to see how the engine will handle. [&:]

This true for all ringed engines 2 or 4 stroke one of my mag 52s appeared to
have 0 compression but after running it came right up It was so low I thought there
was a valve problem but up it came

Don't worry about it. Its probably a dykes ring which mainly seals against the cylinder during the combustion stroke-the combustion pressure pushes the ring against the cylinder creating seal. On the upstroke, there is less resistance (no combustion pressure) and less compression. Its a power saving feature that reduces engine friction. I've had supertiger engines that had virtually no compression and needed a little castor oil injected through the glow plug hold to seal the ring enough to draw fuel to start. The engine ran as powerful as other comparable sized engines in its class..go figure..

Robert,

I add to what David and Doug said; the ring is made of cast iron (probably meehanite) and like a cast iron piston, needs to be annealed to reach its final size and hardness.

Start the break-in with several (10-20), very rich four-cycling short runs, (20->60 seconds each, with periods of complete cool down between them. After that, you can extend the runs to several minutes.

Do it on a test stand. This method is more time consuming, but in the long run, it will prove to have been extremely beneficial to the lifespan of the engine. The ring will last much longer than with any other method.