alternator belt queries/concerns

Hi again-

My boat was repowered from an Atomic 4 to a Beta Marine D722 (20hp). When we took delivery of her last month, it was apparent that engine maintenance had fallen by the wayside-the oil was just about black (since changed), coolant needed topping (and likely flushing but haven't gotten around to that yet), and the alternator belt was worn and needed replacing (lots of black dust).

I've since changed the belt. Before I installed the new one, I took a steel brush to the pulleys to address what appeared to be minor rust. I've only run the engine a bit since I changed it (mainly due to waiting to get our tank polished-we had some dirty fuel that resulted in some stalling issues while sailing her back to our marina), but have already needed to re-tension the belt after probably not even an hour of run time. I'm also noticing some chafing on the outside edges of the belt and some more black dust.

Is this normal for a new belt (is there an "adjustment" period before it doesn't need re-tensioning)?

cooper999 said:

Hi again-

My boat was repowered from an Atomic 4 to a Beta Marine D722 (20hp). When we took delivery of her last month, it was apparent that engine maintenance had fallen by the wayside-the oil was just about black (since changed), coolant needed topping (and likely flushing but haven't gotten around to that yet), and the alternator belt was worn and needed replacing (lots of black dust).

Click to expand...

If the oil was only "just about black" then it may have actually been pretty clean! The oil on a diesel engine turns black very quickly after an oil change.

As for the alternator belt: It may be that the pulleys around which the belt goes are not aligned/in the same plane for some reason. This could cause premature wear in the form of the black dust.

Thanks, Alan. Interesting you bring up pulley alignment. It seems my alternator is a 45A, not a 40A, which was originally on the engine. I'm not sure why the replacement is 45A (the PO didn't put it on there). Pulley alignment has been kind of difficult to assess with a straight edge as each pulley is shaped differently/rounded except the alternator pulley, which the belt seats rather deeply in relative to how it does on the crank and water pump pulleys.

The PO didn't change the oil at the end of last season, so I did (fearing the black color meant bad old oil), using 15-40 multigrade as recommended by Beta. It has yet to change color, though I've only run the engine for maybe an hour since the change.

Alan Gomes said:

If the oil was only "just about black" then it may have actually been pretty clean! The oil on a diesel engine turns black very quickly after an oil change.

As for the alternator belt: It may be that the pulleys around which the belt goes are not aligned/in the same plane for some reason. This could cause premature wear in the form of the black dust.

Click to expand...

Maine Sail is good on this stuff.

http://www.pbase.com/mainecruising/image/154214202

If the pulleys are misaligned, it may just take a washer/spacer to improve it.

Yeah, sometimes it takes a few tries to get the tension right. And a little black dust--a little--is common.

Agreeing with all the above. If the pulleys are all aligned properly and the belt is the correct size, and your tension adjustment is not slipping, then keep an eye on the belt and let it wear a little bit. My experience has been that new belts give off a considerable amount of dust in the first 10 hours or so. Dust production tapers off and then almost nothing after that, if all is well otherwise.

Keep cleaning up the dust when you find it so you can judge what is going on. Check the belt at various engine speeds, too. If it flaps or vibrates on the longer runs, it could indicate alignment or tension issues.

Thanks, gents. We're hoping to go out a few times this weekend (it finally stopped raining on the east coast), so I'll keep an eye on it. I always carry a spare, too.

New belt

New belts will stretch, and do require readjustment. No more than a 1/2 inch deflection mid point of belt , between pulleys.
Harold