New V-Belt - How hard should it be?

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KeelsonGraham

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Hi all, looking for some expert opinions. I’m trying to fit a new V-Belt to my Universal M-35B. The new belt is nominally the same length as the old one (990mm) but would be impossible to fit without exerting quite a lot of brute force to prise it over the rim of the sheeve.

The old belt fits on easily but I think this is because it has stretched by 15mm. It actually now measures 101 mm.

So, my question is, should a new belt be so tight as to require levering on, or should it slip on quite easily ( with the alternator at its slackest setting, of course)?
 
I’d be surprised if it has stretched - the belt reinforcement is there to prevent it. They normally wear on the v faces so they drop further into the groove. Is it possible that someone has fitted a different alternator or crank pulley?
 
bignick said:
I’d be surprised if it has stretched - the belt reinforcement is there to prevent it. They normally wear on the v faces so they drop further into the groove. Is it possible that someone has fitted a different alternator or crank pulley?
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The current belt is supposed to be a 990 i.e 99cm but its definitely measuring about 101 external circumference.

It certainly has worn to the point where its sitting low in the sheaves - but that shouldn’t affect the ease with which it comes off.
 
Belts are measured to the mean core dimension.
Pull it as near as possible onto the alternator pulley on the slack side with a bit of rag looped around it and wind the engine either with a spanner or jabbing the starter.
 
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A longer belt often means you run out of adjustment when you tensioning it during its life.

Also if you have a tensioner arrangement it can lead to vibration and harmonics that you wouldn't have thought were a thing.
 
How sure are you that the alternator was not changed on the past.?

I struggled to fit my replacement belt because the replacement alternator did not close sufficiently hard against the engine block.

On closer examination the new alternator was just a little different and caught on the engine mount/bracket.
 
Another possibility is that the new belt is a little too wide, or has the wrong v-profile. That would prevent it sitting correctly in the groove far enough, which would give the appearance of it being too short…
 
Was visiting mates boat a couple weeks back .... I could not believe what I saw ...

He 'prised' of the old belt and then tried to 'prise' on the new ... it snapped. His 'comment' was "s*** belt !"

I asked him why he didn't slack the mount so belt could go on easily - then tension ............ he reckoned he'd never slacked one before.
 
Almost certainly wider belt profile. Hold the 2 side by side & compare the width.
If it is the correct profile, as specified in the manual, or even just a bit wider than the old worn belt, then force the new one on. But do not be silly about it. It should soon sink into the groove. Be prepared to re tension after a few hours use, as the sides start to wear away & the belt sinks into the "V" of the pullies
 
Daydream believer said:
Almost certainly wider belt profile. Hold the 2 side by side & compare the width.
If it is the correct profile, as specified in the manual, or even just a bit wider than the old worn belt, then force the new one on. But do not be silly about it. It should soon sink into the groove. Be prepared to re tension after a few hours use, as the sides start to wear away & the belt sinks into the "V" of the pullies
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Get a narrower version. It will be easier to fit.
 
penberth3 said:
Then it's wrong for the pullies. You don't know much about belts, do you?
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The belt should drive more from its grip on the side of the "V". The driving force drags it into the V on one side of the circumfrence as the pulley rotates , thus increasing side grip. As it wears it will sink into the V a little but should not touch the bottom of the pulley. Once it does that the sides will wear as it begins to slip as it will no longer be possible to apply proper tension, without excessive strain on the adjuster & bearings .
Of course it has to be accepted that some belts are designed with double Vs etc & are set up differently. But these are not the subject of this thread.
That is my take on it, but others may know differently
 
KeelsonGraham said:
Hi all, looking for some expert opinions. I’m trying to fit a new V-Belt to my Universal M-35B. The new belt is nominally the same length as the old one (990mm) but would be impossible to fit without exerting quite a lot of brute force to prise it over the rim of the sheeve.

The old belt fits on easily but I think this is because it has stretched by 15mm. It actually now measures 101 mm.

So, my question is, should a new belt be so tight as to require levering on, or should it slip on quite easily ( with the alternator at its slackest setting, of course)?
Click to expand...

Not uncommon, post #3 has your answer.
 
Refueler said:
Was visiting mates boat a couple weeks back .... I could not believe what I saw ...

He 'prised' of the old belt and then tried to 'prise' on the new ... it snapped. His 'comment' was "s*** belt !"

I asked him why he didn't slack the mount so belt could go on easily - then tension ............ he reckoned he'd never slacked one before.
Click to expand...

If his engines normally had auto tensioners on I guess he might be right!
 
Refueler said:
1GM10 ... bog standard with manual adjusted alternator
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Your mates probably don't have spanners, just lump hammers.

The OP just needs to undo the alt mountings until he can get the belt on, if he cannot reassemble the bits with the new belt on, then the belt is wrong.
As said, belts are measured on the medium of the 'height' not the outside or inside.
 
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