Sudden belt letting go

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alexanderfoti
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Sudden belt letting go

Post by alexanderfoti »

I have my primary drive with 2 spa belts like so:

Image

But with SPA 875 belts.

Today I went to accelerate from some lights and lost drive, looked down and saw the front pulley spinning inside the static belt.

I pulled it back in and went over the whole frame to check for broken welds that would allow the engine to move, therefore changing the tension. I cant see anything that would cause it, everything is there, bolts all tight nothing broken (and I spent a long time with a pry bar).

My questions is, when belts wear, do they suddenly stop gripping without snapping or do I need to keep looking for another cause? The belts where well worn but the cords along the top of the belt are still intact no sudden breakage that I can see, I cut them in half and they both measured 882 on the inside edge so they have stretched somewhat, but both by the same amount.

Thoughts?
Eddy Wane
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Re: Sudden belt letting go

Post by Eddy Wane »

Alex.
Your drive belt looks similar to the "Brammer T link" type of machine tool v belt. This type of belting was designed for easy repair / adjustment by the T shaped metal pieces which twist and lock. This type of belt will inherently stretch over time and I would replace it with a more suitable automotive v belt. Although I do like the "Fred Bibnah" look.
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alexanderfoti
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Re: Sudden belt letting go

Post by alexanderfoti »

Eddy Wane wrote:Alex.
Your drive belt looks similar to the "Brammer T link" type of machine tool v belt. This type of belting was designed for easy repair / adjustment by the T shaped metal pieces which twist and lock. This type of belt will inherently stretch over time and I would replace it with a more suitable automotive v belt. Although I do like the "Fred Bibnah" look.
Hi Eddy

Sorry I didnt make it clear, that picutre was only to illustrate my drive arragnment, I have replaced that with standard SPA875 Belting.
gilburton
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Re: Sudden belt letting go

Post by gilburton »

You really need a belt tensioner on the bottom run.
At a pinch you could knock up something using a row of sealed bearing on an adjustable bracket or use something agricultural or from a car.
As long as it's wide enough to cover both belts.
Sam Brumby might be able to advise??
alexanderfoti
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Re: Sudden belt letting go

Post by alexanderfoti »

gilburton wrote:You really need a belt tensioner on the bottom run.
At a pinch you could knock up something using a row of sealed bearing on an adjustable bracket or use something agricultural or from a car.
As long as it's wide enough to cover both belts.
Sam Brumby might be able to advise??
I have a sealed bearing tensioner from a transit that I was going to use until I found a belt that was the right size. I have a A section belt that had a pitch length of 868 rather than 875 which seems to be working nicely, I will probably stick with spa875 belts and build a tensioner as you suggest. Just go to find where I put it :)
alexanderfoti
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Re: Sudden belt letting go

Post by alexanderfoti »

gilburton wrote:You really need a belt tensioner on the bottom run.
At a pinch you could knock up something using a row of sealed bearing on an adjustable bracket or use something agricultural or from a car.
As long as it's wide enough to cover both belts.
Sam Brumby might be able to advise??

The thing that is odd to me is that it went from being fine to slipping all of a sudden, no slippage under acceleration more and more if you see what i mean.
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coachgeo
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Re: Sudden belt letting go

Post by coachgeo »

With the belt off can you move either of the shafts the pulleys are attached too in any direction?
alexanderfoti
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Re: Sudden belt letting go

Post by alexanderfoti »

coachgeo wrote:With the belt off can you move either of the shafts the pulleys are attached too in any direction?
No play there, and the bearings are all good as well :s
albertaphil
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Re: Sudden belt letting go

Post by albertaphil »

Maybe your engine is finally broken in and you have a whole bunch more power...;-)

I would guess that just prior to your last stop there had been enough slippage to glaze the belt, which really reduces the friction. Then you start out again with maximum torque through the belt and squeak, there you are. A possibility anyway.
alexanderfoti
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Re: Sudden belt letting go

Post by alexanderfoti »

albertaphil wrote:Maybe your engine is finally broken in and you have a whole bunch more power...;-)

I would guess that just prior to your last stop there had been enough slippage to glaze the belt, which really reduces the friction. Then you start out again with maximum torque through the belt and squeak, there you are. A possibility anyway.

Heh that would be nice! It is a possiblity, I think maybe one of the nylon strands broke as well, giving enough of a release for the belt to slip?
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