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Commando Belt Drive

Submitted by andrew_windsor on Monday, 28 August, 2017 - 01:00
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Commando

Hi ,

I have being going out on the Commando and clocked up about 1000 miles pottering around this season.

The bike in question is a 72 750 roadster and now and then in the past it was hesitant on acceleration and i didnt give it another thought untill it all went wrong.

I was heading out on a poachers run when i got a mile up the road and i got some serious slipping, i persumed it was the clutch getting oil on it .So i pushed on thinking it would burn off somehow and it didnt. I kept pushing on at at the five mile mark the penny dropped and i needed to get this bike back home and quick .

I did make it back i kept her in top just gently twisting the throttle. On strip down the teeth on the timing belt have been totally torn off and the belt still in tact. The pullies are fine and the belt wasnt too tight before it went on melt down because your get a whining noise.

Now is this belt the right one Continental HTD 920 8m . before i order another.

Thanks

Andrew

Submitted by john_holmes on Monday, 28 August, 2017 - 01:01

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The belt used varies from seller to seller, so if you identify the seller you may get confirmation.

Submitted by andrew_windsor on Monday, 28 August, 2017 - 01:02

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Thanks John, T

The belt was already fitted when i bought the bike 18 months ago. I fitted a belt drive on my Mk111 and it came from RGM . I scanned there parts list for belts and they were wider 31 as opposed to my 20. The pitch on my is 8m and all there"s are 10m. Why that belt disintegrated i will never know.

Submitted by ian_goodhall on Tuesday, 29 August, 2017 - 01:00

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20mm sounds very narrow for the job it is being asked to do. Most use 30 for road use and 40 for racing. They are just industrial belts and can be bought from bearing type suppliers and are much cheaper from them.

Ian

Submitted by keith_glassborow on Tuesday, 29 August, 2017 - 01:03

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I have a Norvil on mine and it has eaten two belts. The first a Gates Powergrip 920 x 8mm and the second a Contitech later used by Norvil but I dont recall the exact model. The first failed at 20k after being overtightened and oiled at various times in its life. The replacement lasted 6k and was just crap. It did get me home 13 miles unlike the Gates which would not drive at all. I'm now using this one which is supposedly an improvement on the original

https://industrialbeltdrives.com/quote/timing-belts/powergrip-gt3/

BTW 920 is the belt length in mm. I've not seen a 20mm width used on Nortons.

One thing which I don't think helped my second belt was the heavy wear on the front pulley. It became very rough on the tooth peaks and a replacement pulley with new Gates has minimised rubber dust buildup that was very evident with both earlier belts. It could be the belt but unlikely.

Keep it loosish, mine will take a 30mm diameter socket between top run and inner case boss. I seems too loose but is just right when hot after the clutch drum expands. See pic....

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beltdrive-jpg

Submitted by andrew_windsor on Tuesday, 29 August, 2017 - 01:04

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Hi ,

Thanks everyone for your help i have just tried the 30mm socket test and it wont fit even without teeth on the belt. I will go back on my word on the previous post with the belt not being to tight. The belt in question is a 20mm width i checked it with a steel ruler.

Will keep you posted on further updates

Andrew

Submitted by david_evans on Tuesday, 29 August, 2017 - 01:05

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The new Colorado Norton Works electric start features a 21mm Gates poly carbon belt. This means there is space for the lucas alternator. CNW must be satisfied with the performance of a 21mm belt

Submitted by keith_glassborow on Wednesday, 30 August, 2017 - 01:00

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Apologies, I wasnt suggesting you measured the belt incorrectly! I wonder whose that is? Re David's note, the 30mm fits fine except with a later Sparx stator (not the one in the pic). The front pulley outer sideplate rubbed on the encapsulation and I had to space the stator out by 080". It looks like Gates have a GT3 in 20mm x 8mm pitch.

Yes yours could have been a little too tight, they are a bit noisy and slappy when cold at "30mm" tension.

This was my Powergrip at 20k miles..

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27052012309-jpg

Submitted by john_holmes on Wednesday, 30 August, 2017 - 01:06

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The new Colorado Norton Works electric start features a 21mm Gates poly carbon belt.

The pitch also affects strength, 10mm pitch will be stronger than 8mm pitch so be interesting to see the pitch CNW use. Pity they thought to include only the belt as an option, a duplex chain would have worked as well and allowed for lubing the starter mechanism.

Submitted by andrew_windsor on Thursday, 31 August, 2017 - 01:00

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Hi,

Been offline for a couple of days i thought my computor had gone down it turned out i had run out of data on my dongle.

This is what i have been up to a huge clean up and strip down, i hoovered as much as i could out then WD40 sprayed in there with plenty of kitchen roll to mop up looks like new now.

The belt had been rubbing on the outer front pulley plate reducing it down to 20mm then the teeth started to fly off. Thanks K G for your reply and help and the others it is really appreciated.

I do seem to have a bit of wobble on the clutch basket, and i dont know how the old girl kept running and got me home the rotor and stator plate where truly gummed up .

Its all good fun and will keep you posted

Andrew

Submitted by keith_glassborow on Friday, 1 September, 2017 - 01:00

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Andrew

Are you saying 10mm got taken off the belt width? That's insane and the box has to be way out of alignment. That must have been a mess. Mine's not perfect but wont run off the pulley with the sideplate removed when turned on the K/S. I do use a second adjuster though. Good luck with the repair and alignment!

Submitted by miles_hodgson on Friday, 16 March, 2018 - 00:00

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I have a RGM belt kit on my 750, fitted 2004. Have now done approx 30000 miles with no issues.

 



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