12v / 300A alternator on 8v71

[ronells93]

My 1976 MCI MC8 bus conversion is running a 12V / 300A alternator.  After having a set of belts (4) break, I pulled the alternator and found that a bolt on the shaft oil seal had backed out, rubbed on the back of the pulley wheel and was likely causing drag that led to the belts slipping, overheating heating and breaking.  I removed the alternator and had a local mechanic look at it.  While he noted the minor scarring on the back of the pulley wheel, he said the shaft was still tight and the alternator should be good to go.  I put on a new oil seal and reinstalled the alternator.  I accidentally forgot to reconnect the lead to the voltage regulator.  When I started it up, all was working fine, but obviously the alternator was not sending signal to the tach or voltage gauge on the dash.  After realizing my mistake, I reattached the wire to the voltage regulator.  When I started the bus, the belts were screaming and the pulley was not turning.  I shut it off and adjusted the belt tensioner - still screaming, but pulley was turning - tightened some more, still screaming.  How tight should the belts be on these belt-driven alternators?  Could a faulty/failing voltage regulator be causing the issue with the belts?  Thanks in advance.

[buswarrior]

The alternator has to be right square to the pully, or the belts will throw off, as well as talk to you.

Did you put a straight edge in there to line up the pullies? Pretty much impossible to sight in by eye, there's too many lines and angles to fool your eye.

Get it close with the straight edge across the front and back of the pullies, not just the close edges... Then leave the fasteners just loose, fire it up and let the belts put it right where they want to run, and snug it up.

Happy coaching!
Buswarrior

[luvrbus]

 Is the system really 12 V ? when you align everything check the voltage ? is the air control relay working,when the 50D kicks in on full like 16v for the 12v  or 32 volts for the 24 v system they will melt the belts. Where are you buying belts from? the belts from ACE or the internet are not good belts a good set of 4 belts will cost you about 80 bucks maybe more now.I use the 1 piece belt on the MCI 5 and 8's with the 4 v's ( Mirco V) it will cost about a 100 + bucks since there is no such item as a matched set of belts made anylonger.Check your voltage the high charging rate is usually the ground between the regulator and the alternator.You shouldn't have any charge till the air pressure is up fwiw    good luck

[tr206]

Dumb queston does your alterator spin freely by hand? If so it must be under full load right off the bat. You could also charge your batteries before you start it up to reduce the load on the alternator when it kicks in. Like Clifford said one of your belts could be shorter then the rest so one belt could be trying to do the job of four.

[luvrbus]

Dumb queston does your alterator spin freely by hand? If so it must be under full load right off the bat. You could also charge your batteries before you start it up to reduce the load on the alternator when it kicks in.

That is the same 12v alternator Eagle uses only difference is the pulley for the 4 belts on the MCI setup,he maybe off on the RPM ,Eagle spinds that alternator with 3 belts lol most of the time with 2. mine always had one belt that broke,I changed Mike and Kays gear driven over to a 2 belt 160 amp alternator

[tr206]

That is the same 12v alternator Eagle uses only difference is the pulley for the 4 belts on the MCI setup,he maybe off on the RPM ,Eagle spinds that alternator with 3 belts lol most of the time with 2. mine always had one belt that broke

I hear yeah your right matched belts are a thing of the pass.