vacuum pump drive gear dimensions?

airguy

Cleared for Takeoff
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airguy
I'm building up my IO360M1B for my experimental RV9A, and I suspect I have the incorrect vacuum pump drive gear installed on the engine. I've been told that the 4 cylinder and 6 cylinder lycomings have different vacuum pump drive gears and they are largely interchangeable but do have some different dimensions, but I cannot find any drawings or list of dimensions for the parts.

The one I have installed is total overall length of 3 1/16", and is about 1/4" too long to use for the optional SD8 standby alternator in place of the vacuum pump. I know many other builders that have replaced the vac pump with this alternator with no issue, and I believe the problem I'm having is due to having the 6-cylinder longer drive gear on my 4-cylinder engine. Can anyone here dig up some dimensions on that part for me please?
 
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