Atco Commodore B20 - toothed belt problem

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Last seen: 2 months 1 week ago
Joined: 12/03/2020 - 15:26
Atco Commodore B20 - toothed belt problem


I have recently inherited an Atco Commodore B20 which has been 95% restored and is a lovely condition. However I have an issue with the toothed belt that drives the cutter (it's one of the later Commodore models), similar to that shown below:

When the belt tensioner is NOT in place, and I rotate the cutting cylinder by hand, the belt remains in a straight line and stays in place. However, when I install the tensioner, the belt drifts outwards and ends up rubbing the inside of the intermediate drive chain - obviously, the belt would not last long before it shreds!

I have tried bending the tensioner slightly to try and keep the belt in line, but to no avail; it just keeps on drifting outwards.

Is this a known issue, and is there any suggested remedy?

Many thanks...

Chris G
Chris G's picture
Last seen: 3 days 20 hours ago
Joined: 22/08/2017 - 14:00
Hi, assuming the toothed

Hi, assuming the toothed pulleys are running square and the belt is in ok condition?, I would also think it is to do with the tensioner. 

On the chain versions tension should be set to around 1/2" deflection of the chain on the opposite to the tensioned side, I'm not sure about the belt version but would have thought about the same..

Have you tried slackening off the tension to the point the belt is not riding off and checking the amount of slack at that point, could be just too tight?

wristpin's picture
Last seen: 5 min 43 sec ago
Joined: 23/05/2012 - 22:09
The belt does run tighter

The belt does run tighter than a chain but its a matter of finding the sweet spot of adjustment (bending) to arrive at the point where it runs centrally. As with any belt on flat idlers (and my band saw blade) the difference is a very small tweak.

A slight twist of the bracket is probably what's needed rather than bendining it in and out.

Last seen: 2 months 1 week ago
Joined: 12/03/2020 - 15:26
The belt tension is basically

The belt tension is basically set by the slider behind the idler wheel, so there is no real adjustment possible. It's actually a fair bit tighter than a typical chain arrangement.

Twisting the bracket is what I have actually been doing, rather than bending, but I obviously have yet to find the 'sweet spot'. I envisage a lot of undoing and tightening of the bracket bolt! If all else fails, I suppose that I could put some kind of very large 'washer' behind the cutter blade nut to prevent the belt from moving sideways. Am I right in thinking that the nut is a left-hand thread?