Last year I Bought a new Webra 52AAR for My helicopter. After one gallon of running (PowerMaster 15%) , the piston came black and the retaining pin of the ring make a spot on the top of the piston.

I think it was to lean or the Nitro was to high. I heard that Webra need to run with 5% or 10% of Nitro or else I need to put a Shim on the head.

So I rebuild everything and I put a shim on the head. But how many shim I need to run this engine properly with 15% Nitro?

Do you have any advice?

Thanks?
Serge

Hi!
try onr 0.1mm aluminium shim.....at a time! You will notice when compression is right...mount the engine in a test stand and put on a 11x6 APC prop and notice how it works with different nitro contents and shims.
It takes a bit of time ofcourse....


Regards!
Jan K
Sweden

How can I know when the compressionis right?

Hi!
You know when you have the right compression as then your engine will rew the most and will be easy to set and throttle perfect...check rpm with a tachometer!

Regards!
Jan K
Sweden

Thanks for your advice

Serge...

Where is a source for shims? The're not listed in the online K&B and O.S. cats. Thanks