MD7A and Balmar w/4" Pulley - What Belt Now?

[John Ring]

Greetings:

I know some of you have put Balmar alternators with the 4" pulley on your MD7A. I did, and the original alternator belt no longer fits, as the new pulley is a bit smaller than the old one.

Can anyone offer leads on what belt to put on there and where to get it?

Thanks in Advance,
John Ring
CD28 Tantalus
www.yachttantalus.com

[bottomscraper]

I don't know anything specific to the MD7A with the Balmar but here is some belt info:

You can measure with a tape measure around the pulleys. The tape should be about where the outside of the belt is. So a 3/4" wide tape measure usually works out ok. Here is a link to an online catalog for Gates belts. The part numbers give you some idea what size the belt is. For example part number 9451HD is a little over 45" long (note the "45" in the part number). A decent auto parts store should be able to help you out. Usually they will let you exchange it if you find it is a bit long or short.

http://www.gatespowerpro.com/Comergent/ ... nID=607514

[L.DeMers]

John,

I have the Balmar 80A alternator on my MD7B, which uses the engines flywheel as the engine's pulley. I went thru several belts from the local stores, all of which failed due to the heat and stretching, resulting in squeeling and slippage when the alt puts out 100 Amps or so. I found that NAPA carries a *Green* colored power belt (I think it was a 56 inch belt) that does not stretch and does work with the loads imposed on it. It is the only one I could find that does, and it is usually stocked too.

By the way, 80A is the limit for a single belt system. Any more and you must use a dual belt drive and pulley, which would be a tough thing given that the engines pulley weighs a couple hundred pounds (the flywheel).

Cheers,

[John Ring]

Thanks Rich, and Larry.

With the new Balmar 621 series alternator on the old MD7A, its is a very tough XX" long 3/8" belt that's now required. I found the mother of all belt web sites at www.evbelts.com. They sell directly to end users, and offer some pretty tough industrial belts and lots of other power transmission components. I'm going to give their Gates 3VX560 a shot (EDIT: THIS WAS TOO LONG).

The new Balmar 621 series (621-70-SR-IG) alternators bolt right on the old Volvo easily with the 1" spacer (included). The chart shows it making a solid 80 amps at 1500 rpm at the alternator.

I'd also recommend the optional Balmar 4" pulley (#12-4031) to keep the alternator speed reasonable when driven off the Volvo's huge 12" flyweel.

EDIT NOTE: A 3/8 BELT WILL SIT LOW INSIDE A BALMAR PULLEY, AS THEY ARE CUT TO ACCEPT 3/8" OR 1/2" BELTS. MEASUREMENT AROUND THE OUTSIDE OF THE PULLEYS WILL GIVE A READING TOO LONG FOR A 3/8" WIDTH BELT WHICH WILL SIT DOWN INSIDE THE GROOVE.

EDIT: THE 56" BELT WAS TOO LONG; 54" TO 55" SHOULD FIT. Looks like the Gates 6754 is the one (and yes, it's green!)

Best,
John Ring
CD28 #241 Tantalus
www.yachttantalus.com