cambelt failure...

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cambelt failure...

Post by gtv-racer » Tue Nov 04, 2014 4:07 am

The cambelt had a failure on my alfa 75 3.0 supercharged engine. It striped the teeth.
But why is the question?

All the teeth had damage in the bottom of them. Also the tensioner (mechanical and not oil fed) had a broken spring at the back. The items where brand new and dit about 5000km?

Annyone?
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Re: cambelt failure...

Post by Theunis » Tue Nov 04, 2014 5:49 am

Hi,

Did you damage the valves in your engine, or did you have non stock pistons (with the engine being SC)?

From what I have heard, the mechanical tensioner as fitted to the "newer" 12v engines is not that reliable. The tensioner probaly failed and the the belt got damaged because it skipped teeth due of the lack of belt tension.

T
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Re: cambelt failure...

Post by gtv-racer » Tue Nov 04, 2014 7:38 am

valve damage : yes...
Stock pistons in the engine.

i find out about the new belttensioner in combonation with the new type belt a couple of days ago :(
that explains why my tensioner is gone bad.

But what i don't understand is that every teeth on the belt has damage. In my opinion that isn't slippage of 2 times one teeth. Because more that two teeht causes the valves to touch the pistons. And two teeth slippage doesn't damage the belt i tink all the way around :?
Last edited by gtv-racer on Tue Nov 04, 2014 7:40 am, edited 1 time in total.
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Re: cambelt failure...

Post by Theunis » Tue Nov 04, 2014 8:12 am

What I mean was that the belt looses tension, it start to skip a few teeth, the valves the touch the pistons. Then the cam shafts stop turning because there isn't enough traction with the belt, or it is jamming because of bent valves , but the crankshaft still drives the belt, pulling it over the stationary cam pulleys.

Where you driving when it happened?

Is there different teeth profiles on the belts and pulleys between the older and newer 12v engines?

T
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Re: cambelt failure...

Post by gtv-racer » Tue Nov 04, 2014 10:15 am

I was driving at aprox 80km/h.
Stil i find it a little wierd. Theeth where only compleetly gone at the crank pulley when i dissasembeld it :|
But i guess it could be like you sad in seconds before desaster :lol: :cry: :cry: :cry:
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Re: cambelt failure...

Post by 75evo » Tue Nov 04, 2014 11:54 am

I wonder if a stray object got in between the belt and pulley, then it skipped, had valve to piston contact. Then the belt had slack in some parts, and was over tightened in other parts due to valve to piston contact. The force of the crank turning and it being over tightend in some parts stripped most of the teeth.
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Re: cambelt failure...

Post by gtv-racer » Tue Nov 04, 2014 1:11 pm

Cambelt covers where mounted.
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Re: cambelt failure...

Post by kevin » Wed Nov 05, 2014 3:17 pm

Check cam caps to see if any seizure marks . It did happen to me many years ago on my TT 12v . As it was low comp motor I stripped teeth and did not touch valves .
But your case is different with broken spring . I have read of quite a few failures with the 155 tensioner conversion on forum but none recorded at Glenwood or at Alex Jupe and that's a huge amount of GTV's done there . Is it climate related ?
Also the two types of belts available at moment have a slightly different fitting in terms of teeth fitting deep into pulley groove . Sorry can't remember if it was the gates or dayco.
I have seen some engines with heads skimmed so much that you cannot use the 155 tension conversion as there is to much slack in belt at max rotation on tensioner so have use old tensioner and fix it in locked position .
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Re: cambelt failure...

Post by gtv-racer » Wed Nov 26, 2014 4:01 am

This is what Barry wrote on the old forum:

The problem with the "new " type tensioner on the old type motor is the fact that the old type motor runs a very shallow squared off timing belt setup..When fitting the "new" type tensioner,it has way too much movement and the ability to move through this range very easily..
The answer here is to limit the movement of the pretensioner part so the it cannot give enough for the belt to jump..I simply drilled 2 holes either side of the fulcrum "leg" ,fitted 2 x 4mm bolts about 25mm long to act as stoppers...these act as stoppers ..it works fine then..
Other than that,when used on the 155 type belt ,the belt has deep half round teeth that need a lot of freeplay for the bely to jump..the "new" type tensioner goes hard against th stop before this belt can jump..

So the cure here is to limit the travel or use the old type designed for that square belt..

I see seizeure marks on my camcover caps . But i think thats due to the broken spring.
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Re: cambelt failure...

Post by 75evo » Wed Nov 26, 2014 9:39 am

Why don't you do as Barry said with the 2 bolt stoppers, 155 V6 cam pullies and new style belts? That would be better all around. But the 155 V6 pullies may be off a bit in terms of alignment with the crank pulley because the 155 V6 has physically shorter cams.
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Re: cambelt failure...

Post by MR2 Zig » Wed Nov 26, 2014 7:23 pm

Do the new type pulleys fit to the cams and crank the same? Is it possible to retrofit the new belt and pulleys to the older 12v engine?

Thanks,

Scott
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Re: cambelt failure...

Post by fedezyl » Thu Nov 27, 2014 3:10 am

It is as I have done just that on my v6 Giulietta, i have a 164 v6 and changed all pulleys to the 155 type, it's all plug and play, no mods needed.
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Re: cambelt failure...

Post by kevin » Thu Nov 27, 2014 9:56 am

What about the tooth pattern on crank .
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Re: cambelt failure...

Post by Giuliettaevo2 » Thu Nov 27, 2014 12:55 pm

That pulley also need to be changed!
Drive it like you stole it...
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Re: cambelt failure...

Post by fedezyl » Thu Nov 27, 2014 3:52 pm

Yes, you have to change them all, crank pulley, cams and oil pump, i'm using the new type tensioner too, so far so good.
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