4" alternator pulley

[Ted Farmin]

I am trying to find a source for a 4" alternator pulley for the 35 amp. alt.
that I got from Van's. The one that I got from Van's would be turning
9200 when the engine is at 2600. I have checked cowl clearance and can
just get a 4" inside at full adjustment of the belt.
Ted

[Harvey]

Ted,

I got a 4" alloy pulley from an engineering /hardware store. A fairly common, garden variety/universal V-belt pulley. I had to bore the centre out to suit the 35 amp Vans shaft, but otherwise has been working fine for 200 hours.
Martin in Oz

[gmcjetpilot]

Originally Posted by Ted Farmin

I am trying to find a source for a 4" alternator pulley for the 35 amp. alt.
that I got from Van's. The one that I got from Van's would be turning
9200 when the engine is at 2600. I have checked cowl clearance and can
just get a 4" inside at full adjustment of the belt.
Ted

I think you math is a little off.

Lycoming has two sized pulleys:

7.5" ( for generator planes, obvious older)
9.75 ( for alterantors)


If you had a 4" alternator pulley the worst case ratio is 9.75/4= 2.4375


So at 2600 RPM x 2.4375 = 6338 RPM.

A 3" pulley would be:

So at 2600 RPM x 3.25 = 8450 RPM

I think a 3" or 2.9" pulley is fine. You could go with a smaller alternator pulley if the flywheel pulley is smaller. The alternator speed would be lower for the 7.5" Flywheel pulley. Also at idle say 1000 RPM you will be below 5000 RPM and may only be making 2/3 rds of the rated power if you go with a 4" pulley. I would not worry to much about the alt rpm.


You do want your alternator to run at least 5000 RPM and efficiency improves up to about 8000 RPM. After 8000 RPM there is no advantage to run it faster. The Honda/Van ND 35 amp alternator is of an older design and may not be as happy to run at high RPM as the new NipponDenso alternators, but anything under 9000 RPM should be OK. George