Alternater belt md22l wear/slipping

[Jam]

Hi
Last year continually tightening belt as slipping, thought this was due to alternater not being tightened enough and that may have moved  and my brain was caught in this loop!!! Evenaully realised the  bearings were slowly seizing and thought that this was wearing the inner circumference causing slippage and more wear. During winter they stuck completely as was unable to rotate alternater pulley by hand.  Alternater was fixed, new bearings etc and belt was tighten as per instructions, however noticed again the belt was loose last wend.  I have done very little mileage since boat went in and have retightened again. All pulley wheels look in good alignment and the belt was supplied from Keypart as per this engine type: it's a toothed belt.  I am sure the alternater has not moved and I am unable to explain why I have had to tighten, only once so far this season so far.
Any ideas appreciated.....
John

[Lyra]

Is this a new belt or the one that you used before the alternator seized?
If the latter I would suggest replacing it because it may have been damaged.

[Jam]

New belt
J

[Yngmar]

The belts do wear. They don't wear on the top or (toothed) bottom, they wear on the sides. As they are V-shaped belts, wear on the sides means they ride lower in the also V-shaped pulleys - therefore they need tensioning now and then. About once a year I'd say is okay, and once a few hours after a new belt was installed, more is a sign of trouble. A sure sign of excess wear is black dust on the alternator or the timing belt cover, which is the bits that came off the alternator belt.

Carry a spare belt, it's only £10 - the one for the MD22 standard alternator is a Gates 6219MC (AVX10 x 975 La, meaning 10mm wide, 975 mm long), although on my upgraded Balmar alternator I found the slightly longer 1000mm belt (Gates 6220MC) was a better fit.

[MarkTheBike]

could it be the pinch bolts not holding the alternator in place firmly enough (i.e. not tightened enough initially or a damaged thread)? Just a thought - happened to me on a car once...

[Jam]

Pretty sure it's tight, there was some dust on the timing belt case though indicating some wear.  Hopefully will not have to retighten again too soon, will see how it goes and hopefully not a repeat of last year.  Pretty sure this was due, last year, to the bearing though making it difficult for belt to turn alternater causing slippage and wear.  Maybe this is the new belt settling in👍
Thanks
John