Timing Chains vs Timing Belts?
 

just a general question, I know the 928's timing belt job can be a pain in the ass and what not. but anybody hear of someone changing the belt over to a chain? just wondering.

Never heard of it but I suppose it would be like on the ford mustangs (or similar). The timing belt is not really that hard, I have however run into broken w/p bolts on removal. If doing it for the first time it can be a challenge, but just check everything twice when putting back together.

I never seen an external chain for timing. They are internal and are lubricated with the motor oil. I would think that without the oil the wear on the gears would be pretty bad. But I don't know about all cars just the ones I've worked on.

+1 I think you nailed this question.

he did. thanks. I was hoping it didn't sound stupid. lol

There were many engines with external timing gears and chains, Chev 427, 350, Dodge, AMC. The chains were under a cover and went around crank and cam but not in the oil pan. Some had nylon tipped Cam gear. They ran dry, not oiled. The 928 has a very long belt and the mass of any chain that long might be a problem. I am sure they looked into it in Stuttgart back then, you know, the same guys who gave us the V2, the Saturn 5 rocket, those guys.

350 chevy and 427 chain not lubricated? What year was that?

Gee, I could be wrong but when I took them apart I never saw any oil in them. I know the cover went around the crank/cam gears which was sealed. I never saw oil pour out of the cover when removed as I recall. Was there a passage for oil to get back in the pan from the gear cover?

Yes. On most a washer to sling, a slot to return.

Nylon coated aluminum gears ran quietly, but with age the nylon crazes and then disintegrates, then chain drags across the gear and you have a mess.

Cogged belt is a very good solution. It should be a minor worry with a 928.

It's been awhile since I had a timing cover off. Sorry about the mistake. I had only worked on older push rod motors back (60's) then. I guess they always looked pretty dry when I removed the covers, probably sludge blocked or something.

I remember now at least on my 67' 427 Vette, the bottom of the timing cover fit into the top of the oil pan so oil could drain or be lubed through that opening. It threw me until I thought about it more. Also some engines had timing gears instead of belts or chains, I think mostly on big inline 6's . Not sure if gears are still used today or not in that application.

Porsche was way ahead in many ways, big timing belt, 32 valve DOHC, Trans and gear box in rear, motor in front, and sophisticated rear suspension. Funny how Corvette implemented many of the same in later years. I did the T-belt on my 928 last year. Not too bad if you take lots of time.

I'm not an expert. Maybe there are other systems, too.
Kids bought a 64 Buick with the oddfire V6 (later the Jeep Dauntless engine).
Brokedown at FoodLion / timing issue.
Found hard chunks of nylon / polymer in the pan, along with aluminum.
Eventually I had to disassemble and completely rebuild it.
It had a slinger and return, which I think is pretty common.
That's why the timing covers have double lipped oil seals.

photo evidence. (looking at this Buick V6 chain, its hard to imagine a 7 foot chain driving a 928 engine, or even two shorter ones)

slinger washer is cone shaped, nearest the block, laying on the workbench.


Rebuilding the engine was interesting, rebuilding the 2 speed aluminum automatic transmission was fun.


http://forums.pelicanparts.com/uploa...1293994827.jpg

Hey Guyz this is one of those topics that the pros and cons of both systems are based on engine type and propose. Just talking about the 928 4.5L engine it's easier (for me) and better to stay with the belt. "why" if the belt brakes, my engine is still good. But when you get to the 4.7 and 5.0 the your valves and pistons take a dump on you when the belt brakes and your talking a lot $ to fix. I would love chains on those motors. What sucks is that they take longer to change and if you don't know what that engine noise is and your grinding you engine walls because of the chain having to much play that can be more expensive than valves and pistons.

These belts are actually pretty easy to replace.
Time consuming but easy.
Just go in on a rainy weekend every 30K miles or at intervals of every 3 years or so.

Metal timing chains do wear and stretch. The last one I replaced (that had jumped timing) had 105K miles on the engine. The chain was, at most, 26". If you figure that much wear on a 7' chain, you could expect to replace the chain about every 30K miles.

The 911 uses timing chains so I'm certain they gave it some thought in Stuttgart back in the day :)

But with all the accessories driven by the belt, and the expansion and shrinkage of an aluminum engine of V8-size, a belt is just an allround better solution.

The 32 valve engines have both, so best of both worlds maybe? :D

http://bilgalleri.dk/uploads_xl_wm/1...008%2009:42:23

I didn't know that. Great picture!

And the 911 chains with hydraulic tensioners and nylon guides and the like have been the sources of many problems, retrofits, upgrades, and outright failures over the years for 911 owners. I am not confident they are any "better" than our belts.....although the last of the air cooled 911's seems to have finally got it right regards the chain system

So, getting the chains to work properly on the 911 took 30 years - image if Porsche had gone with the solution on the 928!! :o