Flywheel pulley size - educate me please.

terry.mortimore · #1 08-16-2009, 06:33 AM

Hi gang:

I'm gathering together parts to assemble my engine and I'm needing a flywheel.

The estate of a local homebuilder here has two, the only differance i can see between the two is the size of the V-belt pulley. The one with the larger pulley is in very good condition, but I'm wondering about the size of the pulley.

I assume the larger pulley would spin the alternator faster, would this be a problem? I'm wondering if the larger pulley is for a generator, rather than a modern alternator?

thanks, Terry.

caryr · #2 08-17-2009, 06:59 AM

the larger the diameter of the belt groove on the engine the slower the spin of the alternator.

part number 72565 seems to be the most popular part for the O-360 Lyco.

Mel · #3 08-17-2009, 07:21 AM

Quote:

Originally Posted by caryr

the larger the diameter of the belt groove on the engine the slower the spin of the alternator.

Nope! Terry is right. The larger the pulley on the engine, the faster the alternator.

caryr · #4 08-17-2009, 12:39 PM

my bad

I didn't think that thru long enough

I think the part number us right though.

I'm not sure I have seen wider or narrower pulley grooves on a Lyc flywheel.

terry.mortimore · #5 08-17-2009, 01:53 PM

Hi Guys, thanks for the replies.

I picked up the flywheel with the larger of the two pulleys because it was in better shape than the other one.

The part number on the flywheel is "76628 assembly" the pulley measures 9 3/4" inch in diameter and I count 149 teeth on the ring gear.

The engine I'm working on is an older narrow deck O-320.

I'm working with an older parts manual dated April 1970 and it lists this flywheel and states 3.25:1 alt. drive. So I hope I have not bought the wrong one.

Can anybody out there take an eye ball measurement of their pulley diameter to see if mine is going to work with a modern alternator?

Thanks, Terry.

647jc · #6 08-17-2009, 01:58 PM

It appears the 9 3/4 inch pulley is what is on most newer engines, see Van's Alternator Kit that describes the two pulley sizes.

Mel · #7 08-17-2009, 03:43 PM

You can slow down your alternator by changing it's pulley to 4". It will work fine with the standard pulley, and that's what most people use. But the bearings will last longer with a 4" pulley.
Of course, on the other hand, most aircraft alternators don't last long enough to wear out the bearings anyway.

terry.mortimore · #8 08-17-2009, 03:51 PM

Thanks guy's, you made my day.

Tailwinds to you, Terry.