Belt dilemma

Preventative maintenance is always a good thing.

Replace both belts and both bearings. You will sleep better at night.

 

I believe the change to the "inboard lip seal + outer sealed bearing" was done early in the 1978 US 308 model year on the F106AE engine family -- so your '77 probably has the (flakier) "inboard open bearing + outboard lip seal" arrangement (but it's not impossible to swap engines so you'd have to check).

Even though the 5-8 drive side lip seal may not be leaking, if it's never been replaced, it's probably hard as rock -- how many total miles and have these areas ever been refreshed before? Also, I'd check the 5-8 side for excessive bearing play before deciding if it would be better to do both sides now, or just the 1-4 side now and do the 5-8 side at the next belt change.

Based on your low annual mileage usage, even if replacing both belts, I'd reuse the tensioner bearings and keep the Jan 2008 date as the last major service marker (i.e., even if you replaced all the belt stuff, you are not putting in new cam seals, dist seals, etc. so not really a complete major service redo) -- JMOs.

 

Belts are cheap and bearings reasonable. Well worth the $ for preventive maintenance IMO. You are there anyway and they are easy to do, so why not.

JIM

 

Steve,

There's no dilemma for the cost of these parts. Check out my version this year and feel free to ask questions:

http://www.ferrarichat.com/forum/showthread.php?t=248319

Lee

77 GT4

 

No, not only is the outer cover changed, the internal gears+shafts are different as well.

And ~33 years! I'd say that you could do the outer bearings and lip seals on both sides without regret. I had the (better) later design, and the outer bearings were in pretty bad shape at ~90K miles -- so ~60K miles on the old design is not an unreasonable max life IMO (the radial load on the outer bearing in the early design is probably 30~40% higher than the later design). Please give us a data point when you do the work by guesstimating the radial play at the drive pulley before and after replacement.

 

Replacing the cam drive bearings is a straight forward job, however you do need an internal bearing puller of yo can attempt to fabricate one. The out bearings are double sealed-not shielded where as the inner bearing run in oil and are open. When pressing the new bearing back in plase be cautious and do not press or tap on the out race as you will damage to the bearing. The Ferrari retaining nuts are a must and/or a suitable bearing nut. These nut are face controlled and exert an even pressure on the components, a nylock nut of any grade is not face controlled and will shorten the life of the bearings.
How do I know this, I am an old time Bearing Engineer. Good luck kdl

 

Steve is spot on here. I just did mine earlier this month (with 50K on the motor) and the outer bearings were toast. Both were almost devoid of grease, both had significant discoloration of the balls and races due to heat and they had been so hot I had to scrape melted (nee COOKED) rubber from the bearing seals and the shaft seals off the inner snap ring when I removed it. The outer bearing seal was so hard and fragile, I got it off in many pieces. Pic below, keep in mind A) the cage has to be destroyed to used the blind puller - so I did that, the cage was fine when I got to it. B) this is the BETTER of the two bearings - this is the front. The other (rear) was practically bone dry and more heat discolored. To get back to your original title, change both belts... cheap insurance.

Rick
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It's easy to throw money at a ferrari. What's tougher is to throw it intelligently, and perhaps in so doing have a little more in the bank to pay for your kid's college educations (or your own retirement).

As suggested above, based upon your low usage and recent repair work, I'd replace the belts and re-use the tensioner bearings assuming everything looks OK with the bearings (no oil/debris contamination, no excessive grease leaks, smooth operation and feel, no discoloration/blueing, no excessive humidity in storage, etc.).

 

According to the eurospares website, the drive shafts are the same up through 1980, and from 81 up through the QV use a different part number. I didnt dig into it very deep, but assume the changeover occurred at the same engine serial number that other changes in the cam drive took place.

Also, the bearings should be the same width regardless whether they are sealed or not? And if so, wouldnt the new style sealed bearing fit the older cover?

And a technical question, what was wrong with the original bearing being open to engine lubrication that would have changed for the better having the bearing sealed? My experience has always been that oil bath ball bearings last far longer than sealed bearings, provided adequate maintainance is kept up. Could it be Ferrari saw how awfully Americans maintained things (like not changing oil often enough), and coupled with stricter EPA 5/50 emission warrantee and all, weighted the change?

I would second the thoughts to just fix whats wrong as best as common sense dictates and continue on toward your next scheduled service. However, if you replace both belts, both tensioner bearings and both drive bearings now, you could conceivably reset the clock for 30K miles/or 3 or 5 years, and leave the rest of the engine alone for now. This all assumes the last service was thorough, along with degreeing, etc..

 

Can't agree with this. The (euro) SPC labeled as "308GTB 1980" at eurospares shows that 4 different gear+shaft PNs were used up thru 1980: 104913, 109616, 112017, and 112856. The US 308 SPC 161/78 (1978) shows two different gear+shaft PNs specifically associated with this change: 104913 and 112017 (my guess would be that the additional PNs in the euro SPC are for the dry sump engine). Also, in the old design, the lip seal rides on an OD feature of the sprocket; whereas, on the new design, the lip seal rides on an OD feature of the gear+shaft -- so the shoulder on the shaft of the new design that contacts the inner race of the outer bearing has to be extended further away from the gear and the OD of this shoulder has to be a good quality surface for the lip seal to contact.

The outer dimensions of the bearings are the same (so the bore size is OK), but the axial positions of the bearings relative to the gear are different so the grooves in the bore for the snap rings that retain the outer race of the outer bearing are in different locations.

No argument that, if all things were equal, the splash lubrication would be superior. The problem is that the geometry for the older splash lubrication design is poor. The primary reason for the change wasn't to go to a sealed bearing -- it was to reduce the overhang distance from the pulley to the outer bearing. These sketches aren't exactly to scale, but they are in the right ballpark -- they illustrate the benefit (lower forces on the bearings for the same belt tension) of moving the outer bearing closer to the belt centerline (a secondary benefit is the radial play of the pulley is also reduced for the same amount of radial play in the bearings). Going to a sealed bearing was a (negative) compromise that they were willing to accept in order to improve the geometry and reduce the bearing loads, and, hopefully, improve the outer bearing (and lip seal) life:
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nice statics lesson Steve, i found myself summing the moments to check the reactions

 

Steve, Great job explaining and showing the differences!!

Rick

 

To: Steve Magnusson,

As one who has paid the price (literally), seems as though they could have made the sealed bearings a larger diameter and "deeper". Comment?

 

Yes, but that requires a much more serious change to the outer casting (which takes a lot longer to implement and is much more costly); whereas, the change they made only requires a machining change to the existing casting (that can be implemented very quickly and lets you use the existing inventory of castings). Also, bigger is not always better -- even though the load rating will be higher for a larger diameter ball bearing, the ball speed can become a limiting factor.

In fact, let me say a few words in defense of the original designer -- one problem is that manufacturer's bearing life calculations are typically based (and tested) on the bearing being fairly heavily loaded compared to its static load capacity (like a slow-speed wheel bearing). When you use these life calculations on a very lightly loaded ball bearing in a high-speed application, the resulting predicted life comes out to be a very, very long time. Consequently, even though the radial load on the outer bearing is 2X the belt tension with the old configuration, this life calculation still would still (wrongly) predict a very long lifetime for the outer bearing so I can understand why the original designer might have accepted this 2X higher load for the benefit of keeping the outer bearing splash lubricated (because the manufacturer's equations would still have shown a very long life at the higher load).

 

All valid points. Thank you.