I just upgraded my Volvo MD2B diesel alternator from 35amp OEM to a Delco
120 amp.

The OEM set up had only a single vee groove pulley and belt.

I made a new engine double vee pulley to match the new alternator pulley and
modified the adjusting bracket.

Next I went to the local auto parts store (large local chain) to begin my
search for the correct belt size. My range of adjustment was limit due to
the much larger case size of the new alternator. Through trial and error
(many trips back to the boat), we established the correct belt length. (They
kept trying to offer me narrower belts while I knew my vee pulleys were
intended for 1/2" 38 degree.)

I then ask them to take back the one 'correct' belt they had in stock and
order me a "matched pair" of that size/part number. The next morning I
picked them up and it was obvious they weren't matched. I didn't even have
to look at the mfg production numbers, even though they were both Gates. The
computer system had brought one in from each near by store (each store only
stocked one of this size).

Next we tried ordering them from the main warehouse and this time I ask for
4 belts since I was confident that these would most likely be from the same
mfg batch. Never happened, even though they did come from the warehouse, of
the 4 belts, only 2 were the exact same length. The remaining 2, again,
don't even come close.

Note: I don't have an accurate way to actually measure belt lengths but I
install a pair, and measure the belt deflection while tensioned.

Something that these auto parts people don't seem to understand, is the belt
wear that results for unmatched belts. These guy incorrectly assumed that
the tighter belt would wear faster and eventually both belt would carry the
load. While, in fact, (as I understand it) the looser of the 2 belts wear
due to it's slippage and just get larger due to this wear and never carries
it's share of the load.

During my 23 year in navy ships, our matched belt needs were supplied as a
bundled set with batch number markings. When ordering, we had to use special
stock number designation to require that they be from the same batch.

I suspect I will have to go to a supplier of "Industrial" equipment belts to
ever avoid this problem in the future.

Has an one else ever been through this??

Thanks,

Steve
s/v Good Intentions