Cam belts - cautionary tale
 

This is what happens to a cam belt if the engine isn't used reguarily - new belt on the right :o

This is why I smile when I hear folks say " It's only done 2000 miles in the last year... the beltswill be OK for ages yet "
The number I've seen at Nelly's off low mileage bikes that take this shape, and yet mine which had 10K on them in 2 years still roughly kept their original shape.
Change them...you know it makes sense!

So whilst the belt has formed this shape, would it slip from the cogs or snap if it ran or would it loose this shape?

just had mine done and mine were like new when removed, 3 rs old and not many miles but engine turned over regularly.

By the way, if you screw/nail your old cam belts to the fence or side of your shed, there great for storing bean poles!

so were your belts 3yrs old Bob?

More likely to jump the cogs due to the tension being too slack on certain sections (with kevlar belts it is unusual for them to break these days) has the same effect as the belt breaking though - catastropic :o

At 60 quid for a pair of belts, that's not a risk I would take on any of my bikes.

but its not just the belts, its the £200 to fit them!

Not if you have them done at service time anyway......

.....er, assuming you pay to get your servicing done (I do, because I am a mechanical incompetent).

please, dont get me onto servicing costs or my complete lack of mechanical competence...

Is it generally accepted that belts are OK for 2 years or 6000 miles, or is it thought that a bike with recently changed belts but stood for a given period of time will need its belts changed, and if so what would that time period be?

I know the aircooled belts are 12,000 miles - or 2 years, whatever comes first.

AK picked up one of the engines (now in his 'monster special bike') which had new belts on but the engine hadnt been run in over 18 months, so he changed them as a matter of course.

note: they looked fine, the tension was fine... when he removed them, they were just like Henners ones:o rather out of shape:o

C
:)

[Edited on 13-6-2005 by CK and AK]

Not quite sure what to make of this post. I worked for a company for 8 years designing belt drives for most modern cars. A modern timing belt in a vehicle is normally capable of 60 000 miles, and some of our drives were good for 150, even in highly stressed applications.

Even with the difference in loads, engine speed etc I am surprised these belts are only good for 6K. (I am not disagreeing by the way, just surprised)

Has anyone ever had a belt let go?

You may want to check out the 851/888 forum for the sad tale of Robin's (Red SPS) 888 SPS, a very rare and expensive model which Robin spent a long time researching and tracking down and buying, only for a belt to let go, resulting in (probably) a 10k engine rebuild (no I'm not joking).

Is it worth 60 quid a year for peace of mind, if nothing else ?

In my book, yes it is.

I wonder about loadsa things like this with bikes, not being technical doesnt help! But how come a car can do 60k on belts, 20k between services etc:puzzled:

Not many cars rev to 11000 rpm and make 120 bhp per litre. (SPS)

Or a lot more

Not had a belt go personally, however, the point is that on many Ducati engines, prior to the Testastretta, the pulley arrangements, in particular the extreme angle between the upper timing pulleys, put the belts through very high stress and if the engine was left unused for a length of time it could stretch the belt. The narrowness of the belt made matters worse.

but even these little jap cars, 600cc supercharged things, dont need servicing like a bike, surely they must have some extra stress? Is there a direct link between high revs = more servcing?

So if I'm unable to run the bike regularly I should change the belts how often?
I agree with the bit about "if your unsure when they were last changed change them" but am now unclear about the recommended change frequency for a bike that sits does not run regularly. Clearly its not 2yrs or 12000 miles

Honda's VTEC engines in the Type R's or S2000 rev up to about 9K if pushed and make over 100BHP/Litre the S2000 makes something like 120BHP/Litre I think? But I think that motor uses a chain rather than a belt

Jon, I did say "not many"............

I can understand that bikes need servicing at shorter intervals. In part it is the unacceptable weight penalty of extra oil, self adjusting valves, auto tensioners etc that mean a bike service interval has to be shorter. I would question how short though? 6K for a kevlar belt is short IMO.

With advances in technology the car industry is moving to the point where you will not need to service your car at all. The engine will in effect be a sealed unit that you throw away after 15 years or 150 000 miles.

Bike service intervals seem to get shorter and shorter. People are prepared to accept things on a bike that you would not accept with a car. I moan that the wifes car cost £125 to service after 10000 miles.

Personally I think the way to go is run the engine at least every week. That way the belts shoud stop in a different position each time preventing the stretching seen in the photo. Some folk change their belts every 12 months/6,000 miles (R engines require it) others take Ducati at their word and do it every 24 months/12,000 miles. You pays yer money etc.

On a V twin its likley that the engine will only stop in one of two positions.

Doesn't matter Paul - the belt doesn't match the engine cycle.

:o Blimey, how out of shape are those!

Bet you're pleased you've not used the R much since you bought her!

I know of a case in the past week where a set of 200mile old Kevlars disintegrated leaving hte bike with a hefty rebuild requirement so rest assured there are 'duffers' out there and no end of changing them will avoid that.

As long as you're abiding by the OEM's directions, you'll be covered.

If you dont' ride her much, instead of starting her up each weekend (now were talking rocker problems) just stick her in gear push her forward a few feet and hey presto belts in a new position and rockers saved !

Delooney

Ever seen a truck or car tyre develop a flat spot after the vehicle has sat for a long time? you drive the vehicle and you can feel the thumping for a while , then what happens the tyre blows up or after a little bit of heat build up it goes back to being round;-- what does the work shop manual say?Some belts unexpainedly fail;--belt tension is very important,how long does the belt stay square after starting the engine? I dont believe any of it! I do believe it is important to idle the engine untill you have enough oil in the heads before you apply high revs,failure to do this results in premature rocker failure BUT disconnecting the side stand switch and idling the bike hammers out the clutch;--carnt win! the whole thing is worthless conjecture
breakout

You forgot the 'take the spark plugs out' bit-have you ever TRIED to bump start a Ducati-I have and failed miserably.

John

2 years or 12000mls and i think that is just being safe i inspected mine when they came out after 2 years and they were like new no mishaping or chafing bike was used nearly every weekend.

when they get put away for the winter (mine wasn't ) or are stored thats when they get affected you are probably talking months for them to go like the ones in Henners pic .

I think people get paranoid after hearing scare stories about them from uninformed sources, as was said previously the belts may be cheap but fitting them ain't as not all of us are able to do it

Now what we all need are nice bevelled gears to run the cams from....


I'll get my coat

:lol:

Done it twice ! stuck it in second

got a push to get it rolling and hit the button

fired first time

[Edited on 13-6-2005 by Nigel C]

cam belts, don't even go there, I cannot overstress how important it is to keep them in good steed.
A few hundred is cheap compared with thousands.

When I finally get the sps back in working order, which touch wood, will be quite soon now. It will be an area of my bike that gets maxiumum attention what ever the cost, which will be a lot less than it's costing to fix at present.

WTF??? you must be joking, who quoted that then??? must be ohhhh £100.00++/hour labour charges, robin bastars:sing:

In my humble opinion belts don't just break IF there is no aditional loading on them other than in tolerance valve operation.

If/when they break its not old age but more likely seized idler/tensioner bearings, tight closer clearance, poor adjustment, loose pulleys etc etc.

Or P--S Poor quality control in Ducati case,but agree totally age is not a factor.

pulleys
 

I have noticed that some belt failures are the obvious result of the fitting of pretty aftermarket pulleys.The problem is how the belts fit to the pulleys,they should not contact the belt across the tops of their teeth when they do this, I have noticed after failure, the tops of the sprocket teeth are abraided (damaged) this is symptomatic of the damage done too their adjacent running surface,-which is the kevlar belting at the bottom of the belts grooves.This belting transmits the power to turn the cams and obviously mechanical damage to this structure is to be avoided.Also as the volume of the female sprocket groves is greater than the volume of the male drive teeth on the belt, the teeth on the belt are not under compression and are much more able to be pushed over;-this cyclic plastic deformation is larger than would otherwise occur and will lead to premature failure.I believe a new belt should not contact the pulley across the tips of the pulley teeth but rather should be located radially by the belt teeth sitting in the sprocket grooves and there should be clearance across the tops of the teeth.belts also fail as tyres do as a result of total heat cycles(note 999r and the race bikes have ventilated belt covers to lessen the serverity of the heat cycles,and the belt need not perform any additional 'worthless ' work like trying to turn a damaged valve train ,obviously belt tension is critical and tricks and rules of thumb shouldnt be employed unless you know what you are doing and are prepared to handle the outcomes,anything which changes the belt friction (silicon sprays etc should be avoided.Lastly SOME BELTS ARE BAD BELTS, and if you are rude to your bike it may be rude to you ;-always wash and service your bike,whilst talking nicely to it.breakout