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Primary belt drive

Submitted by nick_ohare on Sun, 03/05/2015
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Commando

I have just bought a 72 750 which is fitted with a Mick Hemmings belt drive on the primary. My previous commandos had the chain drive which worked just fine. What are the good and bad parts of this new fangled technology?

Cheers Nick

Submitted by david_evans on Sun, 03/05/2015

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The advantage is generally a saving in weight as the front pulley and sometimes the clutch drum are alloy. It is also feasable to change the primary drive ratio. The idea being to spin the gearbox faster for less stress and gear down on the final drive ratio. The disadvantages are a requirement to get the pulleys perfectly lined up or the belt can get worn away against the side guide plate. You can run the clutch dry but the clutch centre bearing needs to be a sealed item. The advice to manage the alignment of the two pullys is to fit a second gearbox adjuster screw on the left hand end of the top gearbox mounting.

Submitted by nick_ohare on Mon, 04/05/2015

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Thanks for the info David. I will check alignement. The difficulty I have is that the previous owner has passed away, so I will have to check on the clutch centre bearing to see if it is sealed. The clutch is very smooth to lets hope it is all OK. The belt drive is a Mick Hemmings item I believe. I will check the paprework to see if it was fitted by him or the the PO.

I have to say that the advantages seem rather slim for deviating from standard. I am more interested in reliability than weight saving!

Thanks Nick

Submitted by phil_hannam on Mon, 04/05/2015

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Two other very important points with regard to belt drives ...... Generally they must have some form of cooling if used for lengthy rides and/or the pulleys are Alloy. The belts have become much stronger in recent years but over-tensioning can occur if the pulleys get hot and expand. Drilling a set of small holes in the outer case is one way of sorting this. But it does change the looks of the case.

Secondly.......getting the belt tension correct is essential. Like chains it is safer to run them a little slack rather than over-tight. The tension required will depend on the make of belt and the type of pulleys.

Submitted by nick_ohare on Mon, 04/05/2015

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Previously Phil Hannam wrote:

Two other very important points with regard to belt drives ...... Generally they must have some form of cooling if used for lengthy rides and/or the pulleys are Alloy. The belts have become much stronger in recent years but over-tensioning can occur if the pulleys get hot and expand. Drilling a set of small holes in the outer case is one way of sorting this. But it does change the looks of the case.

Secondly.......getting the belt tension correct is essential. Like chains it is safer to run them a little slack rather than over-tight. The tension required will depend on the make of belt and the type of pulleys.

Hi Phil, thanks for your input. It looks as though the early part of my ownership is going to be fraught with paranoia about belt tension and overheating. I do not recall this being much of an issue with the chain drive. I would check every 500 miles or so and never had to adjust but I only did a couple of 200 mile runs at the longest mostly shorter runs. The thought of drilling holes in the case is not what I want to do. It is an important part of the aesthetic after all.

I will have to do a few runs and see how she goes. Any idea where I can lay my hands on the instructions for correct tension?

Cheers Nick

Submitted by david_evans on Mon, 04/05/2015

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Don't quote me on this but as a rule of thumb you should be able to twist one run of the belt through 90 degrees.

Submitted by nick_ohare on Tue, 05/05/2015

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Hi David thanks. for the unquotable advice! Any other suggestions or a source for a print out of the instructions?

Cheers Nick

Submitted by karl_nixon on Tue, 05/05/2015

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Previously nick_ohare wrote:

Hi David thanks. for the unquotable advice! Any other suggestions or a source for a print out of the instructions?

Cheers Nick

Have you tried to contact Mick Hemmings he is a very nice fella to deal with an should be able to answer your questions and possibly even send you a copy of the installation instructions.

Submitted by nick_ohare on Wed, 06/05/2015

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Hi Karl,

Good suggestion, I did have a look on his site but couldnt find anything. It is worrying that I didnt think of giving him a call myself! Getting old is my only excuse! Thanks Nick

Submitted by tony_harris on Fri, 08/05/2015

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Dave is right. If you can twist the belt 90 deg in the centre of the pulleys it will be fine. I have run many miles without any cooling holes with belt drives just adjust it with the 90deg twist and it should be fine.

 


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