308 aluminum cam gears.....ouch

At least the plastic once on the two valve are better because it has the steel inserts.

 

Can you please post a pic of the gear once you remove it from the cam end? The "holes galore" feature can't be clearly seen.

Thanks - DM

 

What is the advertised "advantage" of the round tooth plastic/aluminum set up?

 

Scary. One of the first issues identified on my 76 308. Was very difficult to find an OEM set of metal gears. Image Unavailable, Please Login Image Unavailable, Please Login

 

Who would do that and why would they drill so many friggin holes in it?

Missing the sarcasm font I'm guessing? Or you didn't see his first pic.

 

Ferrari did the same thing starting with the TR/348 (but in steel?):
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Makes setting the cam timing less of a skill operation (i.e., there's always a hole pair that lines up between the cam and cam sprocket without needing to change the belt to cam sprocket relationship.

Could also be that Ferrari increased the thickness of cam sprocket where the holes are when they added more holes and/or changed the diameter of the holes and pin slightly to add more strength between the holes (but don't know that for sure).

 

I've made more posts then I care to remember about this. Long story short, automotive engineering moved away from the trapezoidal tooth in the '70s to a curvelinear tooth aka "round". Efficiency, power handling, tooth ratcheting goes away...
Lots of really good reasons to update that design.
As to the issue the OP is seeing, that is not due to the tooth profile.

 

I'm probably going to regret this... But it's an itch that needs scratching. It takes a tremendous amount of force to shear like that.
Run a force vector diagram from the crank to cam to see where the problem arises from. You'll notice that there's simply not enough resistance to induce material failure like that from the valve train. Not arguing that swiss cheese holes didn't make things worse. I'd hazard a guess that something in the valve train went wrong and stopped the cam, that force sheared the pulley. Or maybe the air pump siezed up.
Only other possibility outside that I can see, bad install, pulley wasn't sitting correctly and the tq of the bolt cracked the pulley and it all went south from there.
Maybe the timing was out from the get go, just enough to have pistons and valves play the kissing game, eventually a valve gives up... Bam! That'll shear an aluminum pulley. That's just my thoughts...

Wait.... Was the slotted locking washer in the correct indexed location? Looks like it isn't. That leaves a gap and the bolt tq force sitting on the pin only. Let's the pulley 'slop' around... That'll kill it. Bad installation.

 

Where can you buy steel 2V gears and how much are they?

 

So apparently the gear failed but the belt didn't break?

 

So the curved teeth on the gear is fine.

Is using plastic just a cheap way out? I see no other reason than that

 

Reducing the manufacturing cost was probably a strong factor, but using a plastic form for the teeth molded over a steel core is also some good engineering to reduce the rotational inertia of the cam sprockets. Most of the "problem" with the plastic cam sprockets is the Mechanic/DIYer trying to force the new timing belt on over the fence with the Tensioner assembly mounting nuts tightened = breaks the fence (even if the Tensioner is fully compressed). The Tensioner needs to be fully compressed AND the nuts holding the Tensioner base to the engine left very loose to give enough slack to get the belt on without putting any force on the fence.

Note that on most later models, the cam sprockets have no fences (both fences are on the driving pulley), but even those fences went thru some attachment design evolution where they tried to keep the cost down by doing a deformation attachment process, but eventually had to add some welds for extra security.

 

So do you have plastic or steel ones on yours?

Because I'm doing whatever you and Newman do

 

Wise decision indeed...

Rgds

 

Just adding some supporting pictures to the above post for posterity.

Pictures are of the kit which I installed on my own car back in 2010 or so (and which I remain well pleased with):

OEM (obviously, lower sprocket shown):

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Aftermarket:

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The Gates Racing round tooth belts which are used with this kit are approximately 20% wider than the OEM belt, and they also contain an approximately 20% greater count in the number of teeth (count them yourselves, if you wish). As a result, the force placed upon each tooth during operation is considerably lower for the round tooth belt design vs. the square tooth belt.

This past winter I replaced the round tooth belts seen in the second picture after about 11 years of use. A -very- close visual inspection of each tooth on each belt showed -no- signs of cracking or potential trouble spots. They were both like brand new, but I replaced them anyways (just because I was in there).

By contrast, the OEM square tooth belts which were on my car when I bought it way back when - who knows how long they were on the car - were showing signs of beginning cracks forming on multiple teeth at the 'sharp' inside angle at the base of each tooth.

For further future reference, here's a picture of the aftermarket top cam sprocket, one of four:

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Notice the 10 timing adjustment holes around the center hole, which I would like to compare to the picture of the failed sprocket as posted by the OP once it is removed from the cam - as was already requested in my (non-sarcastic!) reply in Post no. 3 of this thread. The presence of the cam attachment bolt in the picture blocks easy visual access to the timing adjustment hole location which is under discussion here.

Hope that these visuals help the cause - DM

 

Have you ever played with the timing adjustment on your car with that thing?

 

Can't give an easy yes/no answer on this. My ex-308 had the stock plastic gears, and I never had any noticeable trouble/wear (even after 130K miles). I would like to see/understand how they molded the plastic part onto the steel core to see if the cracks that 4right's picture show are a real problem or just cosmetic (in a good overmolded design there should be a lot of features that naturally mechanically captivate the overmolded piece onto the core. I can't recall any reports of the plastic overmolded piece flying apart in big chunks. Additionally, 4right's 3-hole cam sprocket is an early cam sprocket so don't know if the design went thru some evolution by the time my ex-'78 was made with the 5-hole cam sprockets). If I was going to buy new ones, I'd certainly evaluate the steel option; however, I'd like to see it look more like the TR cam sprocket shown in post #7 (with a fence) rather than just being a big bulky exact copy of the stock 308 plastic cam sprocket done in steel -- that would be way too much extra steel material/inertia. If a properly-designed steel one with a good fence design/attachment was available at reasonable cost, I'd probably go with that if I needed new ones, but wouldn't do anything special to replace the stock plastic ones if in good condition -- at a major service, upgrading to good steel ones wouldn't be crazy IMO.

Would echo smg2 point that it would be great if Paul could post some autopsy photos/analysis -- was it a mis-assembly issue, or just a metal fatigue/cracking failure, or ?

 

What did my 84 QV come with?

 

The online US 308QV SPC pictures show that if you bought a new one today it will be a steel one:

https://www.ferrariparts.co.uk/part/ferrari/113098

but the supersession chain indicates that some 308QV came with the plastic ones. Compare what you have to the SPC photos (steel) and 4rights' photo (plastic).

 

The FRP nylon pulleys are not a bad thing, unfortunately I've seen lots of them fail, most common is the fence comes off. Second is the molding starts to crack and comes free of the inner steel core. As to why that happens, I've not seen enough of them that fail in the same way to go oh it's "X". The fence coming loose/off is a mold attachment issue. The pulley teeth mold coming apart, sometimes oil intrusion, sometimes moisture and rust, so I'd put them in the deferred/poor maintenance bucket over crappy mfg/design.

Lots of the nylon pulleys are perfectly fine.

 

Steel was common to the early yrs,carb.. the nylon showed up right around the 80/81yrs.. but I've seen metal on the qv's as well.

Keep in mind guys, the 2V is not interchangeable with the later qv or 328. So early steel pulleys will not fit to the qv/328 engines.

 

In what way? Maranello Concessionaires says the same (updated) cam sprockets are used on 2V and QV:

https://www.ferrariparts.co.uk/part/ferrari/113098

Or are you saying only the early steel 2V cam sprockets don't fit QV?

(My ex-1978 had the plastic cam sprockets)

 

On the end of the camshaft is a centering ring, like on wheel hubs. They are different O.D's between the 2v and later qv/328. The qv and later is 1mm smaller.

So no they will not fit correctly. You can place a 2v pulley on the later cam but it will not be hub centric. That's bad mojo Jojo ...

 

It would be interesting to see more data on the exact failure here.
Many may recall the threads here ages ago when I started on the road to engineer new pulleys. Getting the correct material and anodizing was critical. Worked with Gates engineering on many details for belt wear etc...

The cheaper metal option is 6000 series aluminum, also not a good choice. 7000 series is preferred. Then the anodizing must be mil-A 8625 type III.. with a min of... Well I'm going to leave the secret sauce spec out...

Let's assume the OP pulley in question is 6000 series type 0 and using a basic base anodized finish ment for painting. That's worst case design spec and exceedingly common in aftermarket parts, why? It's cheap. That's the unseen cost Delta in crap parts vs quality... But I digress. Back to the assumption scenario.
If the part was mfg like this, it would deform upon installation. That's not good, it loses right away the TQ spec used to hold it in place. Let's keep going, operating temperature. At temp the camshaft will easily hit 215-240 degrees Fahrenheit. The aluminum pulley will as metals go, expand, since it's a soft series it'll deform under expansion. This cycle due to thermal expansion/contraction will cause the pulley to come loose enough that it can 'walk' or come loose. Eventually leading to failure. Did that happen here? No idea. But it's a possibility in a worst case design/mfg.