CMB 21RS motor head clearence

[sport hydro]

What would be good piston to head button clearence on a 2010 CMB 21RS motor. I am running it in a Phil Thomas sport 20 on 60% RedMax and a Y635 two blade prop.

 

[moparbarn]

.006" - .008", depending on what your setup, head button volume, glow plug heat range & cooling will stand without detonation.

 

[sport hydro]

Thanks, I try to not run on the raggad edge with the motor. I have been using the O'Donnell gold plugs but now will have to find another with simular heat range as the gold. The motor is completely stock, so the head volume is what came from the factory.

 

[Jerry T]

Ed I am at .013 on my sport 20 with the MAC 21. with an CMB RS head button, no need to burn up plugs, they are too expensive, I'd rather buy beer. LOL

Jerry

 

[shoboat]

Ed,

.008" clearance with a little more propeller.

M-440 would be a better choice.

What pipe are you running and how long?

Have Fun Testing,

Mark Sholund