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Primary belt drive failure

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Hello everyone,

I have had the belt fail the teeth stripped off. The belt had approximately 7000 miles. Does anyone know if this is the normal life of the belt or have I been unlucky.

Regards Alan

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Considering the age, usage, the environment it has been subjected to, the miles you have had from it suggests that it has done very well. 

Belts fail, usually suddenly, two failed for owners attending the Austrian rally last August. Road use - use a chain, track use - feel free to use a belt. How often do you hear of a chain leaving someone stranded, they fail, but usually after very high mileage or incorrect installation, usually the chain is still functioning when the owners find bits of it in the chaincase.when doing other work.  

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I put a new primary chain on my Dommy this year ,the old one had been on there from the 1960's. Still looks the same as ever.  If the new one falls appart ,i'll put it back on!.

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7k miles is very poor. I have the Norvil belt kit using a Gates belt. I changed it once after several years use more because I thought it was time to rather than there being anything wrong with it. Belt alignment and tension are important. Run it loose rather than tight.

Ian

It is a Norvil belt kit fitted 2012. I have had some oil get into the case from the crank oil seal, maybe that has contributed to the failure.

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My RGM belt drive conversion got me to the brilliant Ardingly Show and back yesterday. No problems encountered with a total of 4000 miles now  covered in 12 months of hard riding.

The camshaft belts on cars are generally good for 80 to 100k miles. For Harley owners with rear belt drives the recommendation is to change the belt before 30k miles have been ridden. I believe that hidden inside the notes I got with my primary conversion kit it suggested a change at 30k as well.

There are 3 main causes of failure of these belts. 1) The belt was too small or made of inferior materials. 2) It was fitted with the wrong tension or the tension has not been checked often enough. 3) Wear in the gearbox bearings has allowed the belt to move sideways and rub against the keeper plate or crankcases. Either ending up with excessive heat due to friction that causes the belt to shed chunks.

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The belt was part of the Norvil kit. Installed as per the instructions. I have renewed all the gear box bearings and seals.

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Out of interest, Ducati cam belts have to be changed every 15,000 miles, or 2 years, whichever comes first. You can guess which usually comes first!

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Bear in mind where car cam belts are concerned that, although they may do 80-100,000 miles, there is a time limit on them too, typically 7 years, whether that mileage is reached or not.

Yes, yes, manufacturers, and models will vary, but that certainly applies to my diesel Ford of current-ish manufacture, before you start jumping at your keyboards all at once! 

I am making the point that belts have a use-by date..

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I change my Ducati timing belts religiously every two years although they reckon they will go for three with no worries.

If a cam belt goes it will wreck the engine, probably beyond economical repair, but at least if a belt drive snaps it will only wreck your day.

A chain is heavy and has a lot of inertia when on the move. When they snap, they tend to pile up in one place with a lot of force and try to burst out of the cases... Sometimes with success!

A belt is much lighter and has less inertia. I imagine the tendency is not to pile up like a chain as it is not articulated in the same way.

I would feel safer about a belt breaking inside the cases than a chain, but has anyone had any experience of, or heard of a belt breaking the cases?

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Never heard of a triplex chain failing so it wrecks the case either. As far as I'm aware the only two Commandos that failed to get home from the Austrian rally had failed belts. In 25 years, never heard of someone being stranded due to a triplex chain failure. Belts, yes.

I fully get the belt drive, but see it only ideal for the track. No doubt they are getting better, but the random failure rate, for me is not worth the gamble. 

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Most of these drive belts are from an industrial application and are probably made in different tensile strengths. If you have got a broken belt, take it to your local bearing traders and ask for the strongest available. When you've got one, get another one! If you are going touring, especially abroad, even if you aren't able to fit it yourself it is a no-brainer not to take a spare.

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If you are going to an industrial supplier, ask them about the oil resistant qualities of the belts that they have available.

Mike

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Yes I know that there will not be any oil in the chaincase if you fit a belt but some might migrate in there from the crankshaft seal, or even from the gearbox.

Mike

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I fitted a Rgm belt after my primary chain was damaged when the gearbox main shaft bearing failed on a trip to France in the 80's, changed the belt once as a precaution, been fine for over 100k miles. I had a primary chain snap on my mk3 commando after Bremen. 

To be honest I have a few Commandos and wouldn't change from chain to belt due to the expense.

Belts fail in my experience when they are over tightened , 7k miles suggest a problem. 

If you have a belt stick with it , just adjust it properly 

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I know someone who snapped a crank by having the belt too tight, Ooch!

Mine came with a belt that was too slack and rode over the keeper plate and wiped out the alternator Ooch! 

I`ve got a chain in there now, no problems and the chaincase is oil tight. 

Al.

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I have 2 Harleys with rear belt drives, 2011 and 2008. Both have done over 60,000 miles.  I believe you don't change them, they just keep going.  No oil,but plenty of weather, water, grit, and the occasional gravel stone.

At the INOA, Vermont, USA, some years ago, there were Commandos with rear belt drives that had been installed for many years.

RossH.

I agree with Gino, 7000 miles is not enough for a belt. A friend of mine had two Belts fail on a Fair Spares kit so bought another from an industrial belt supplier. I’ve had my RGM kit on for over 20 years and done over 25,000 miles so far on the original belt. Maybe I should replace the belt to be on the safe side. Ive had my Alton E kit on for the last two years with the belt drive. I get oil leaking through the crankshaft oil seal so the belt does get oil on it. Checking to make sure the belt is running straight might be a good idea when you fit a new one and don’t have it too tight. I’ve kept my chain and sprockets in case I need to revert to original set up one day. 

 

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