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Determining Prop Gov Drive Ratio on 540

lr172

Well Known Member
I have a narrow deck 540-C4B5 that I am rebuilding. I have decided to have the accy cover modified and will be installing the later revision camshaft with the integral gear (too much pitting to grind). This leaves the question of whether I will have the lower, narrow deck gear ratio or the higher wide deck ratio for the prop gov.

The Cam gear drives an idler gear and the prop gov drive ratio should be based upon these two gears, but I can't figure out if the cam gear changed or the idler gear changed or possibly both between the narrow deck and wide deck versons. Does anyone know if one or both of these gears have a different configuration between the narrow deck and wide deck engines?

Thanks,

Larry
 
Ok, Lycoming tells me that the cam gears are the same. Same # of teeth and same pitch. Therefore, something else in the arrangement accounts for the different ratios between wide and narrow deck. I should be able to assume that I will have the same drive ratio after the cam change.

This makes sense as lots of folks have had to go to the new cam and the service instructions do not reference a change in drive ratio.

I am trying to find SI 1439 that lists the details of the cam swap. However, I can't find it on the net. Does anyone have a copy of it?

Larry
 
Last edited:
Lycoming SI 1439

I have a hard copy, but dated at December 13, 1991. Don't know if there are later revisions.

David Howe
 
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