Engine belt question

[brak]

More questions for one day - as any day of working on a boat brings

I noticed a lot of black dust around the alternator on the engine and on the nearby bulkhead. Looks like my engine belt is being worn out. I know alternator tension was not adjusted in a long time so presumably it is not more than it used to be. Could it be that the belt is getting old? Anything else I am missing? I tried to adjust the alternator tension, but without appropriate tools I can't really say if what I did is any better than how it was previously set.

[PBzeer]

Could be lack of tension, or the pulleys are not quite in alignment, as well as the belt getting old. I had the same problem that went away with a new belt and proper tension.

[Faster]

A certain amount of belt dust is inevitable, I think, but an excessively loose belt will generate more, as will one that is getting old and starting to break down.

On the other hand a poorly aligned belt that is rubbing on the cheek of the sheave will also generate more than the normal amount.. something else to look at.

Replacing it pretty inexpensive bit of piece of mind..... if the problem persists then look for other causes.

Edit: Sorry, PB - typing while you were posting!

[brak]

Thanks guys, will replace it tomorrow. Good thing I have a spare belt. other than pushing belt with a finger and looking at it just so - is there anything more scientific to tensioning it? the engine manual says that it has to move 10mm under 10kg of pressure, but how would I create the pressure and measure the deflection???

[PBzeer]

It should basically just have a little give to it when you push on it with your finger, midway between the pulleys.

[Omatako]

Check also that the cheeks of the pulleys are not rusted. If they stand for any length of time they build up small amounts of rust. This packs on over time and the surface gets quite rough and eats away at the belts. A quick dressing with some water paper will take care of it.

Andre

[Valiente]

Obviously, this isn't going to hold for every belt in every situation, but I have heard the rule of thumb that a properly tensioned belt should deflect under light finger pressure the thickness of a dime. Whate PBzeer said, with a parameter!

10 mm or 1 cm. under 10 kg. of pressure (a hard push with the forefinger) seems a lot of deflection to me. But then I carry spare belts!

[trantor12020]

I've same problem. Retensioning the belt solved it. In fact, engine seems to run smoother after that.

[BarryL]

Hello,

Just be careful to not over-tension the belt. If you do, you will wear the alternator bearings and the water pump bearings. Make sure the belt doesn't slip, there should be some give when you press the belt.

Barry

[brak]

Replaced the belt today - the old belt wasn't even Yanmar, looked like a car belt to me. Tensioned it to "pretty tight but can push" - I'll let it run for a while and see how it feels. Thanks to all!