Roguedog

I have repeatedly heard that there is a difference between the 25VF and 25FV-DF crankshafts. Does anyone know the actual crankshaft dimensions or specifications. I know the stroke is the same. Is it that the crank pin locations different, either advanced or retarded from one to the other? Or is it the intake port on the crank that is advanced or retarded? or a combination of both. I know that they stamped them differnet. eg VF and VF-DF.

I was under the impression that all timing was acheived thru liner porting.

Bryan

Kweasel

My Feedback: (29)

The difference is in rotor valve timing. The DF cranks are open a little longer than standard. The DF crank will not idle as well and spit more fuel out of the carb until the rpm is up.

Roguedog

Thanks kweasel for your reply.

I'm going to make a guess that rotor valve timing has to do with where they grind the intake port on the crankshaft. Am I correct? If not, could you expand on exactly what you mean by "rotor valve timing"?

Kweasel

My Feedback: (29)

The rotor valve timing is when the window in the crankshaft opens and closes. A standard sport engines window may be open 180-190 degrees, a ducted fan will have over 200.

Roguedog

Awsome info kweasel.

Could you refer me to a book or website where I could read up on this type of RC engine technical information, eg rotor valve timing, liner porting, etc.?

Thanks again.