Can anyone share thoughts and experiences upgrading the pulley system on their marine diesel propulsion motor? My Universal M25 is at home for this winter, for some repairs and refurbishment and repaint, and I'd like to do something about the alternator pulley. It just doesn't seem like enough belt for a maximum of 125 Amps (I have a heavy-duty alternator). I've heard of kits for adding a pulley for double belts. I've also seen high performance wide pulley for cars that take serpentine belts which are much wider. Any ideas? Note that the pulley on the crank on mine has an integral counterweight - how shall I deal with this if I replace that pulley? Thanks all, jv
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Here's what worked for me, John...
John, you should find this puzzle pretty inexpensive and straightforward to solve if you can find the right local electrical shop. When we 'finished' (boy, can I laugh at that...!) our fit-out and left on our shakedown to the Chesapeake, we began using a new 108 amp (hot) Amptech alternator plus other elements of an upgraded electrical system. I noticed lots of belt dust and found, after 6 months and in prep for our departure to the Caribbean, a fairly worn belt. The solution was to swap out the existing pulley for one with the same bevel and size, using the same belt(s), but a double pulley vs. a single. In our case, we already had a double pulley on the FW pump and the crank, but those can be added to your Universal if they aren't already there. The results were pretty amazing. No dust, period. No evident wear. And while I adjusted the belt tension twice on the shakedown, I subsequently didn't need to adjust them once while in the Caribbean for 18 months (almost always while on the hook and needing to make most of the Mother Ship's battery power). Some people end up spending amazing amounts of money to hang large frame alternators from specal brackets, or otherwise move away from the small frame, small belt arrangement we normally find on smaller diesels. I found that just increasing the # of belts was a great choice for us. Jack
John, you should find this puzzle pretty inexpensive and straightforward to solve if you can find the right local electrical shop. When we 'finished' (boy, can I laugh at that...!) our fit-out and left on our shakedown to the Chesapeake, we began using a new 108 amp (hot) Amptech alternator plus other elements of an upgraded electrical system. I noticed lots of belt dust and found, after 6 months and in prep for our departure to the Caribbean, a fairly worn belt. The solution was to swap out the existing pulley for one with the same bevel and size, using the same belt(s), but a double pulley vs. a single. In our case, we already had a double pulley on the FW pump and the crank, but those can be added to your Universal if they aren't already there. The results were pretty amazing. No dust, period. No evident wear. And while I adjusted the belt tension twice on the shakedown, I subsequently didn't need to adjust them once while in the Caribbean for 18 months (almost always while on the hook and needing to make most of the Mother Ship's battery power). Some people end up spending amazing amounts of money to hang large frame alternators from specal brackets, or otherwise move away from the small frame, small belt arrangement we normally find on smaller diesels. I found that just increasing the # of belts was a great choice for us. Jack
For 125 A you need either a single 1/2 belt.......
or two 3/8 belts. The issue is perhaps not the alternator, which is as simple as replacing the pulley but the crank shaft pulley. I'm not familiar with the motor you have but did modify my MD11C volvo from a single 3/8 groove to a double 1/2 pulley. Had a pulley sheave machined and pressed onto the existing and then dynamically balanced. You may be able to get a bolt on pulley but the concern about a crank pulley is balnace and centering. Be happy to give you my $.02 but need to know a few things like what size is the existing crank pulley groove width and are there any other driven belts. Multi v or serpentine belts can take a larger load (generally) than v belts and you can get pulleys for them also. Try a google search for both Gates and Grainger's and Mcmaster-Carr
or two 3/8 belts. The issue is perhaps not the alternator, which is as simple as replacing the pulley but the crank shaft pulley. I'm not familiar with the motor you have but did modify my MD11C volvo from a single 3/8 groove to a double 1/2 pulley. Had a pulley sheave machined and pressed onto the existing and then dynamically balanced. You may be able to get a bolt on pulley but the concern about a crank pulley is balnace and centering. Be happy to give you my $.02 but need to know a few things like what size is the existing crank pulley groove width and are there any other driven belts. Multi v or serpentine belts can take a larger load (generally) than v belts and you can get pulleys for them also. Try a google search for both Gates and Grainger's and Mcmaster-Carr
Pulley and alternator sizes on M25
John Could be your alternator's too big. The M25s can't really drive much more than a 90 amp alternator without putting undue side stress on the inner bearings in the engine behind the main pulley. Going to a 7/16 inch belt helps. Don't know if you have room for a double pulley on the main, I certainly don't because the back of the companionway steps are in the way. You could also check your regulator and if you have energy management, cut back on the output of the alternator to reduce the load. Since we have the same engines, check out the searchable information on the link at our website and the message board.
John Could be your alternator's too big. The M25s can't really drive much more than a 90 amp alternator without putting undue side stress on the inner bearings in the engine behind the main pulley. Going to a 7/16 inch belt helps. Don't know if you have room for a double pulley on the main, I certainly don't because the back of the companionway steps are in the way. You could also check your regulator and if you have energy management, cut back on the output of the alternator to reduce the load. Since we have the same engines, check out the searchable information on the link at our website and the message board.
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