I have the same engine; likely I have the same setup as you.
I went to some effort to twist/pry/whatever to get the mild steel
mounting ears such that the alternator pulley was in alignment with the crank and FW pulleys. Yours may need some attention to that end.
An alternator shop sold
me an alternator with a 1/2 inch pulley. Not thinking, I bought half inch, flat (no notches) belts. I was lucky to get 10 hours from them, despite my buying
the highest grade, strongest belts I could find.
Then I looked closer and saw that the water pump
pulley was appropriate to 3/8" belts. Further research
revealed that if you don't have a notched belt (I think what you're using is one such), heat won't dissipate over the hard turn needed on the alternator pulley. Moving to a notched belt led to my now exceeding 200 hours per change, and those always being a matter of running out of expansion room on the adjusting bar. The solution to that would be to get a new one fabricated, with more length.
However, I also found that my hot water heater
hose contacted that arm's end; I took a small chunk of relatively hard, plastic-wire-reinforced hose, slit it, and slid it over that point; no further wear occurred (in case you have the same issue) on that soft rubber hose.
Back to the belt itself, my solution to the length-of-belt issue was to use the next shorter one, the 7480. However, that is short enough that even with the alternator hard against the engine (which has perhaps an inch of space left in the adjustment arm) the belt must be manipulated to get on. My solution, which may not be available to you because of access issues, is to use a long #3 flat screwdriver, against the shaft pulley bolt head
and crankshaft/PTO extension to turn it, while using a very small screwdriver to pry it over the alternator pulley.
My case of wear is exacerbated by age; the water pump
pulley is pitted from past rust during extensive layups, and the PTO/crank pulley is similar, though not in danger
of failure. My not-very-good solution, again perhaps unavailable to you due to access issues, was to remove both water pump
belts and, with the engine cold and idling, use a file held against the angled faces of the crank/PTO pulley. During cooling
periods between such exercises, I manually rotated the water pump
(pulley attached) to do the same thing. Finally, I swapped alternators for one I had with a brass pulley. All of those efforts cut my belt dust generation enormously, while not fully. I need to find a replacement water pump pulley as I don't trust the age of the one I have to take it to someplace to have it turned down to smooth. Ideally it would be like the aluminum
RW pump top-hat-style pulley I bought from Trans-Atlantic Diesel
in that it would no longer be subject to rust, or like my alternator pulley, in brass.
As to the string trick, given the flat nature of the pulley bottoms, you'll have to push it to the front or back, all around the respective pulleys, to be certain of the alignment; due to the relatively flexible nature of the mounting brackets (which I manipulated during my alignment excersizes by using an extremely long crescent/adjustable wrench), unless you have a special cast or otherwise stable mounting bracket, it's not going to stay perfect, I'm afraid...
And, for what it's worth, despite all my efforts, and an apparently still belt when running once tightened, I still have some dust. and, based on the belting (like tire belts) which becomes more evident, and the top width, which becomes narrower as the belt slowly deteriorates, I do have wear despite all my efforts. However, I am getting more than double your life experience with what I expect is the same alternator....
Hope that's of use; on a fresh rebuild
, about the only problem points I'd expect would be either the pulleys or alignment; unless they were turned to absolutely flat and true, the pulleys likely are the cause of wear...
Edit: BTW, pix of my pulley and the replacement of my water pump can be seen here: