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My 355 had its belts replaced 10 months ago (at 11,980 km). Two weeks ago I noticed a slight change in engine sound and a drop in power. The dealer checked the car and found the left bank cam belt had jumped a tooth on the inlet cam. This means pulling the engine out, replacement parts and engine back in -- not cheap!

An independent Ferrari mechanic with 30 years experience says this kind of thing is almost impossible with the 355. Someone else suggests faulty workmanship 10 months ago when the belts were replaced.

Can anyone offer any advice here? Is this a normal failure of the cam belt tensioner (the car's now done 16,000 km) or should I be asking some hard questions of the dealer?
 

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I've never heard of one jumping a tooth so I'd kind of think the tensioner wasn't properly installed. I'd be going back to the dealer. You spend the money to have the engine removed, you should expect the work to hold up for more than 10 months. Talk to the dealer first, see what he wants to do. If he blows you off, take it to your independant, document everything. Have him check the tensioner adjustment and double check torques before he takes it all apart. Take pictures. If everything is as it should be then you had a "shit happens" experience. If anything was not installed properly, you should try and re-coup the cost of the second installation through the court system.
 

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I know of 3 ways in which you can have a belt jump a tooth:
-over revving the engine
-part failure
-poor workmanship
I would be asking hard questions of the dealer and follow Pete's suggestion about documenting everything.
This is certainly not something that should or regularily happens.
You will also need to check the values to make sure there is no damage (run a compression check on the engine).
 

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Discussion Starter #4
Thanks for the informative and helpful commments. The conclusion from my research seems to be that I can't 'prove' conclusively faulty workmanship and may never be able to. It could be a stone, it could be belt whiplash from suddenly backing off at max revs, it could be component failure or it could be poor set up 10 months ago when the belts were replaced.

I've had a long chat with the dealer head and they have started to pull the car apart. They say they used the latest electronic gizmo from the factory to set the correct tension, but admit it is possible something in the set-up could have been done wrongly.

The engine should be out early on Monday and they offered for me to be there when the cam belt covers come off, so that I could see the tension on the belts for myself. We can then work out what the cause was and make decisions as to what needs replacing. I think the best I can hope for is that they go soft on the hours billed to the job. I'll keep you posted.
 

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Discussion Starter #6
Well, I went into the workshop this morning and watched the engine come out and the cam belt covers come off. The engine never left my sight.

A few interesting observations:

Firstly, when the pistons were aligned to TDC it was actually the right bank, not the left that had jumped a tooth on the inlet cam.

Secondly, there was a very obvious nick in the belt, suggesting that the damage had been done by a stone.

Thirdly, the belt tension on this bank was within spec (202 Hz). Ironically, the belt on the other bank was out of spec (150 Hz), although it had not jumped a tooth.

So I have to recognise that there was no faulty workmanship 10 months ago. We have decided to obviously replace both belts and to replace both tensioners and bearing assemblies. We're also replacing the alternator belt whilst the engine's out.

I should have the car back on Thursday afternoon, albeit some $4,000 poorer......
 

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Since I've stopped lurking let me throw out some flamebait. I don't own a Ferrari but I am generally technically inclined ...

First of all they couldn't even tell which belt had jumped the tooth until the engine was out -- so much for those diagnostic skills. I was wondering if they couldn't just move the belt back to proper position as a much simpler engine-in repair (not knowing the details of whether this is possible), but that would not have worked anyway if they did it to the wrong belt! "But doctor, you were supposed to amputate the other leg!"

Now then the one that was within spec on tension did not jump the tooth, the problem was caused entirely by a stone. So much for specs. The things you fixed for $4000 probably won't help if another stone finds your cam belt.

I read somewhere that on some Ferrari, the factory had recommended 55,000 mile belt changes, but that some shops say 30,000 "just to be safe". It may not buy that much safety.
 
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