I know what you mean, it would be good to see what is going on at the moment of destruction. The reality is the belt will last a good length of time i.e. I have done countless blasts, drag runs and track days where it really gets a beating but ends up ok. I have checked it before and after and there is no visible sign of wear i.e. a slow wear and tear process. They literally appear to go bang when coming off the throttle at high rpm.

I love the coop, it ticks so many boxes despite having driven and owned other performance cars. Of course it has limitations being fwd as expected but whether it is on the street, track or strip it's a true "jack of all trades" car with real supercar grunt and looks to match. Where does one go from there except to the real mccoy

That's the spirit Mr Flea! Mr C

From my experience don't go for a wireless spy cam, they don't like the electrical noise you get in an engine bay, plus the resolution isn't the best. A wired bullet cam is a better bet. Good idea though

Thinking about why the belt should shear on lift off, it must be put under some extra stress at the point but whats happening.

I know the air-con disengages the clutch under hard acceleration to reduce the load on the engine but could the alternator be doing the same ? If it did then as soon as you lift off the throttle the alternator would immediatley act as a brake due to the load placed on it.

Could the powersteering pump be doing the same, its spinning very quickly and producing its maximum pressure (Im guessing this is regulated in the pump) but the flow will be at its highest I would imagine, would this high flow then cause the pump to act momentary as a motor, even if its for a milli second, the engine has suddenly reduced rpm but the pump is still going at the original high speed, could cause stress on the belt ?

Could this be the same for the water pump ?


Just thinking aloud really Leight and trying to figure why its only on lift off. Gutted its happened again though

Leighton, sorry to see that you have done another belt and potentinally more damage this time

As with what Jimbo is saying above, thinking out loud, when on full chat the engine will tilt back due to the torque and when coming off lurches forward, would there be anything that causes a brief slack point on the belt that allows it to slip fractionally?

Engine mounts are all ok? ( I know this should really affect the belts, but a seriously rocking engine can't help)

I think you could be right. Barbz was thinking that a floating tensioner that is used on the Stilo 2.4 might help prevent any slackness which as you say could happen when the engine suddenly goes from positive acceleration to an abrupt deceleration.

Think so, I haven't noticed any play in the engine mounts. I have the uprated top left mount but will check the others.

Jesus, gutted for you mate.

The alternator system is completely self-contained; if the output voltage is low, the regulator increases the field current to increase the voltage.

But... the electrical load should be pretty constant. The lights, aircon clutch, and fans/screen heaters are the biggest load; the ECU requirement is only a few watts, and the injectors are of course turned off on over-run anyway (though I think the sparks still happen).

Hmmm... I wonder how fast the aircon clutch comes in once you come off peak throttle? If it's instantaneous, you've got a few hundred watts load on the alternator as the a/c clutch engages, *plus* whatever the pump load is on the aircon itself, and all that's going onto the aux belts. I don't know what the load is on the aux belt in normal running, but that's got to have the potential to be a serious and sudden shock load...

Ideally, you'd want to wait until you were either at idle or steady speed again before you turned it all on again, I suppose, when the engine is back in closed loop and the loads are more nominal.

It's really bizarre that I have never had one go. I would change all the pulleys including the cam pulleys and the tensioners at the same time. I somehow had a buckled inlet pulley once not sure how it happened.

Bad news that man Gregs idea sounds good

Really sorry to hear about this Leight - I hope it's not too bad for you - there has got to be something out of alignment or worn I think, the question is what?

How many cars do we know of that run with aircon and a fair bit over 400 bhp?

I thought that there was no way that the aux belt could fowl up the cambelt with the protection pulley (which is why I got one...)

Same here.

Ross

I think some of the new cars are coming fitted with free-wheeling alternators which disengage on over-run. Don't know whether you could adapt one to fit and work,seems a lot of work though for something that runs fine on other high powered Coop's .

Has the crankshaft pulley been the same one for all the breakages or was it swapped when you had it adapted?

Baz

I believe I have had 3 different pulleys now, my original which saw off 3 belts, the prototype protection plate made of aluminium which saw a couple of belts before the plate bolts sheared and finally my current pulley where the protection plate is made from steel and that has had four belts go.

I am pretty sure that the belts are running true and I am certain Barbz has checked all these things a few times. Watching at idle looks fine and as I say there is no rubbing or signs of the belt degrading over time they just go in an instant. I'm starting to think that a moment of slackness when the engine brakes and lurches forward is perhaps enough to kink it slightly and force it off the pulley or tensioner as it's still running at high rpm. I'll check/replace all the engine mounts to make sure there is no excessive rocking.

I know its a bit of a pig but do you know or can you tell where they brake most often at the top or the bottom of the belt system or do they brake randomly. I know you mentioned they seem to brake on liftoff at v.high rpm, where there would be some sort of large braking motion in the belt like a kick back. You really need some sort of eye in the area you think it brakes, run up the power and watch carefully.

Most of the time the belts are totally shredded so no signs there but I have had a one which was still intact albeit with damage on one of the edges. Thinking about it now I'm pretty sure they come off the main crank pulley as I have pulled the remains of a couple of belts off the power steering pulley.

Would there be any mileage in altering the size of the pulleys to be larger so the overall speed/rotation of the belts is slower. If I understand correctly Leighton you run the highest rpm of any coupe and is that simply the root cause.Whilst it is going away from 'standard' your car is also far from standard.

Jamie

So what your saying is you think the belts snap nearer the bottom and around the area of the crank pully ? Also what gear do they brake in any sort of pattern ? sorry for all the q's im quite interested.

Yes I guess gearing the pulleys to run slower might help, would then need to get a custom belt to fit. There are a number of kevlar v-belts available for jap motors so could be worth trying to match one of these to a different sized pulley. As for the rpm, well I don't often venture up to 7800rpm and on this occasion it went at a little over 6000rpm.

Not sure whether they break at the bottom or top of the pulley but normally they shred along the belt not through it.

Probaly talking out of my ãrse on this. But if the indication is the belt is slipping off the pulley. Could a pulley be machine with a lip? So in effect the belt is held in a track on the pulley.

Forgive me for meing clueless but,some cars use chains rather than belts on the engine.

They're supposed to last alot longer but I don't really know that much on the subject.

It it possible to retrofit the fiat engine with a chain rather than a belt?

Good idea Ali... VW use chains... but only on the cam side, this means tensioners etc... but on the aux side the tension could be set up a little easier I guess.

For using chains you need to keep them enclosed and some sort of oiling system. Complicated.

I'd prefer machined ally pulley' with extra lips each side, strenghtened belts and some sort of protection plate to cover the cambel bottom pulley.

P.S Presumably if you alter the size of pulleys then it might have an effect on the components performance. An alternator with a smaller pulley might be spinning too quickly, or too big and it won't be spinning fast enough.

In my simplistic view of things dont you either have two choices

get an uprated (kevlar) aux belt

machine up some new pulleys and use a wider aux belt

I think the reason for the belts snapping needs to be found before coming up with solutions.
The big question is why is it only Fleas car doing this, of all the high power high reving cars I can only ever remember this happening to poor Leighton.

Engine mounts are a possibility although I cant see how they can cause any slack in the belt, all the ancillaries driven by the aux belt move as one with the engine unless the engine lurches forward with enough force on lift off to cause some slack but I cant see it happening ?

Thinking out loud again, you have fitted a solid engine mount on the upper torque link but the gearbox side is standard. If there is a little play in the gearbox side then the engine would twist or yaw slightly as well as rock forward when you lift off the gas. As the belts spinning quickly they would have a sort of gyroscopic effect (by that I mean like if you hold a spinning bicycle wheel in your hand and then try and turn it, it resists the movement)this would try to resist any twisting/yawing motion so that could be enough to pull it off the side of the pulley ?