308 Timing Belt Problem

The most likely scenario IMO is that the broken flange was partially damaged during a prior timing belt change (could be the last one done or any of the changes done before that). If you try to put (i.e., force) the timing belt on by only fully compressing the tensioner assembly's spring mechanism you will likely partially break/crack the flange away from the sprocket -- but not completely -- more like over about 120~180 deg so it's not that obvious (and you can note that the 5-8 exhaust sprocket has the flange on the side that the timing belt has to go over during installation -- you might want to have a close look at your 1-4 intake flange to make sure that it's not partially broken too). This greatly weakens the flange-to-sprocket connection so eventually the fracture grows until the whole thing comes off as happened to you. The plastic sprockets are nice and light, but you can't put any force at all on the flanges during belt installation -- which requires fully compressing the spring mechanism AND loosening (or leaving loose) the three mounting nuts on the studs which lets you cock/tilt the whole tensioner assembly and get more slack into the belt (so not need to "force" the belt over the flange).

The inner bearing failure at the lower drive sprocket is unrelated IMO -- the outer bearing is much more vulnerable, and, if anything "external" was bad enough to hurt the inner bearing, the outer bearing would fail too/first.

 

Hi Dave,

Last april i completed my first major and had a partially failed lip on the back intake cam. One of the guys here came to my rescue either Sean or Scott, (sorry guys), and sold me a good used pulley.

Verell of Unobtanium Fame has posted an epoxy fix, that he feels comfortable with, but I chickened out and bought a used one.

You could also go to adjustable, ($1500 or so) pulleys or, i believe Nick, (and others) offer new billet pulleys.

I am way not a Ferrari Tec like many who post here, but i would agree with magnuson that it seems unlikely that a lower bearing problem caused this problem. The pulley lips are so fragile.

Sorry to hear about your bearing problem, i hear it is a big pita.

In sympathy,
chris
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WOW!

My hemmoroids are bothering me just looking at those pictures thinking of the extent of damage that could have been done if a complete failure!

 

When lower drive bearings fail the pulleys will no longer all have a parallel rotational axis causing the belt to ride to the edge of the pulley.

The flange on the plastic pulleys were not always all that well attached to begin with. Your car is almost 30 years old, I would say it had a pretty good run. Many, in fact most belt drive cars out there, Ferrari as well as other makes including TR, 355, 360, 456, 550, just to name a few do not even have a flange or fence on the pulley. They were found to be completely unnecessary and only provide a false sense of security. Replace the pulley, the lower drive bearings and drive it. I think any further analysis at this point is just using up driving time.

 

Totally agree

 

The bearings wear out. They have been redesigned a couple of times over the life of the 3.0 liter engine and you have the earliest design. You make no comment on how old they are. BB's have the same design and I replace them every 30 k miles or less on those cars. Yours were probably due.

 

So,
Does this issue with the drive bearing and pulley exist on the 328? Just wondering as I get ready to get by belts and tensioner done soon......

Thanks in advance,,,,,,

RG

 

328 has the latest and greatest design. When the belts are being done the bearings should be inspected too.

 

it would be nice if we could establish some preventative inspection critiera. how does it look? where does the wear show first? how can you see the condition of the parts without any disassembly?

 

I think Brian answered these questions. The bearings failed because the car is 30 years old. Had someone overtensioned the belt, the overload would have worked to take out the outer bearing, not the inner. The inner is a smaller bearing under a lot less load, its simply old and it wore out.

The failure of the inner bearing allowed the shaft to pull upwards at the outer end, which in turn drew the belt to the outer edge. Now the belt was running out of track.

As to your Toyota and the water pump, again, the outer bearing would have taken the abuse. Also, your car is over 30 years old. Mileage, even though its low, may not have as great a factor on the bearing as old crusty oil or rust that have formed during periods of non use. But again, its served the car for 30 years. A Rolex watch would have been torn down, cleaned and reassembled several times in this length of time, so perhaps you and many others expect a bit much from an engine; even a Ferrari wears out sooner or later.

But its intersting to note how many posts there have been the last two or three years regarding these drive bearing failures. Prior to that period I never heard of it, and lately it seems almost epidemic. Several possibilities exist. First, the cars are just old. Second, the internet allows a broader spectrum that allows discussions no one ever had access too before, or third, there is an oil issue that is starting to rear its ugly head. Too many synth guys running to far without oil changes, or something missing in the oil? Probably a mix of "all of the above".

 

You do not need to be aware of the various parts that wear out and need to be monitored, your mechanic does. And if he did not know that, you are using the wrong guy.

 

It has all been stated accurately but I will add a couple of observations.

These plastic toothed pulleys have to be looked at closely as there is a fair amount of tooth wear on them now. Inspect the area where the belt doesnt ride and you will see how much narrower the pulley tooth is now. Worn teeth will cause the belt to wear much faster hence the need for belts sooner as the parts wear. For this reason alone I will not mix and match pulley sets, all with the same wear or all new. This car must be a late 77 as the mid range and earlier had the steel pulleys.

I am involved in a 360 that took out the outer drive bearings. Belt tension IS a factor and on this car someone decided that there was no need for the tensioners to be functional. If you are lacking the proper tools or knowledge to do the job properly, bring it to someone that does. Every day brings something new, many are "caused failures" due to lack of tools/ knowledge hence improper settings. I have seen 2V cars with failed drive bearings where high C could still be played on the belt when it if flicked with a finger, that friends IS "caused". Whats a belt service cost? Depends on who did it last, if they were on their game that day and what it needs when it comes apart is the only answer I can give now. Too many varriables today.

Dave

 

The old "Act of human intervention" again.

 

Can't you renew these cam drive bearings/inner outer and seals, without cracking the engine open?

I thought there was a "tool?"

 

You can replace the outers with the motor together by using a sykes tool or something homemade, but the rear bearings are behind the gears, the front cover needs to come off. The cover can be removed in the car, but by the time you fight with it I think anyone who has done it would agree you should just pull the engine. From the pictures that have been posted here I wouldnt even try to do the job in the car, just pull the engine.

 

Thanks, oh mechanical ones..!!!!!

 

Paul, I'm afraid I can't agree. I've done it both ways several times. It's about 12 to 16 hours LESS work to do it with the engine in the car, at least for an injected car with A/C where there's a lot of things to disconnect & reconnect for an engine pull. I've also discussed this with a couple of the local professional techs & they agree with me (and both were very surprised an amateur had been able to do the job successfully)!

However, having a lift makes a BIG difference when doing it with the engine in. If you don't have a lift & are doing it with the car up on jack stands, then maybe there isn't as big a total time difference as you'll waste a lot of time twisting around to get into the right position to access things.


david,
I'm surprised to hear that it was an inner bearing that went. Those tend to last almost forever as they're running in filtered oil.

In the timing drive bearing failures I've delt with & seen posted in Fchat, it was always an outer bearing that went. The outer bearings on all but the earliest cars are sealed bearings. The lubricant tends to break down after a few years.

Brian's rule of thumb is change at the 30K service is a reasonable one. I'd like to add change the outer bearings every 10-12 years even if the mileage is low as the lubricant is going to be on it's way out.

One check I make every time I have a timing belt off for service is to see if there's any axial play in the timing drive shaft. You shouldn't be able to feel any. If you can, then the bearing is on it's way out fer shure.

 

All of our equipment at work is run via timing belts, toothed pulleys and servo drives. I probably have several hundred 8mm pitch pulleys in the parts storeroom which are quite similar in construction to those used in the 308 (metal version). They are available in no flanges, one flange or two flange variations. The flanges are just a press fit on the pulleys, the better brands may have 3 or 4 spot welds to back up the press fit. In the last 10 years I have only seen a handful of flanges come off, usually due to some sort of ham handed abuse by someone (that may have been me on occasion). A mis-position tensioning device (screwdriver/crowbar/hammer) usually makes quick work of a flange. The ever popular "gear puller on the flange" is guaranteed to pop the flange off. I have never seen a belt force one off, the belt gets shredded first.

Hopefully 308 pulleys don't get this kind of abuse but it has happened. Most of the time the flange can successfully be pressed back on and a few peens or spot welds will make for another couple of decades of use.

 

That inner bearing is under several times less load than than the outer, its purpose is only to hold the shaft in alignment. To create enough belt tension to harm that bearing would likely snap the belt, and even then I doubt that bearing would be harmed. Also, the belt gains slack as the engine and belt heats up, not less, so I think you can stop trying to blame the shop that worked on the car.

That bearing was old, tired, coked up from 30 years of long periods of storage, extended oil changes, whatever. It was 30 years old. You had a belt change and later the bearing went bad, well, it was probably going to go bad anyway. Just be glad you caught it before it threw off the belt and bent all your valves, holed your pistons, or even worse. For a car everyone says is so unreliable and of such poor quality, they sure seem to stay together a long time. A Rolls Royce wouldnt run any longer without parts like this failing.

I really think everyone needs to stop looking for someone to blame, or the next thing your going to see shops either refusing to work on these cars (I certainly wont), or they are going to demand engine out service with replacement of many more parts and the costs are going to escalate.

 

Paul,

I'm with you 100% on this point. Pull the engine and do the job correctly. The modest extra time to pull the engine will result in a better job and the rest of the major service can be done with the engine on the bench.

David