Cambelt pioneers

[NeilRoshier]

A snippet of information passed onto me was that Glas of Switzerland pioneered the use of a toothed belt to drive OHC/DOHC....is this true?
It would seem that the technology was put into production during the mid 60's by Fiat. Were there any advantages apart from the NVH?

 

[GraviMan]

Yeah - a regular income to the parts department supplying replacement valves, pistons and cambelts! ;-)

Cambelts are just cheaper than chains. Sorry for being flippant, but I notice Ford have gone back to shaped PTFE block tensioned chains. Probably be my next car...

Mart

 

[SMOKEY44211]

I believe the fist use of the cog belt for cam drive was in 1966 on the Pontiac OHC 6. It was big news at the time. The valve train layout didn't lend to any catastrophic damge when the belt failed.---------Phil

 

[Chumley]

Timing belts require no lubrication and don't add wear particulate to the engine oil. Because of that, the front of the engine block and cylinder head(s) can be shortend up by about an inch as opposed to using a timing chain or gears which require sealed lubrication. Timing belts usually require only thin sheet metal or plastic covers.

Timing belts offer a nice weight saving over chains or gears in OHC applications. (both dead weight and rotational inertia)

After seeing years of successful timing belt use, I'm convincened that they are generally more reliable than timing chains as long as one follows the maintenance schedules and doesn't abuse them. Chains usually make lots of noise before they fail. Toothed belts object less before catastrophic failure. Many timing belt failures occur well beyond their suggested change interval, are oil or coolant saturated, or were trying to spin failed water pumps, or other failed idler/tensioner pulleys when they give up. Then the whining begins!

Chumley

 

[NeilRoshier]

Chumley thanks for the information. I had not considered the block issues.
Smokey the cog belt seems to have been released on a number of cars in 1966, I will try to find any earlier. No doubt there were a range of companies working on the technology at the same time.

 

[SMOKEY44211]

Chumley. The block and head isn't neccessasarily longer chain vs belt drive. Tension stregnth of a roller chain is about 75% of the width of a cog belt of the same rating making the overall length shorter on an engine that incorperates a roller chain ohc drive. If memory serves me correctly Goodyear Rubber co. developed the cog belt for use in machinery back in the fifties. The dragsters that used the roots style superchargers started to use it in the early sixties. Back then it was often reffered to as a gilmer belt. I'm positive that the Pontiac 6 was the first to use it in mass production. After the intial fears of durability were put to rest the other manufacturers followed suit.-------------Phil

 

[Chumley]

Smokey: Pontiac I6 engines, Chevrolet (Vega), Ford (Pinto) all used timing belts in the late/early 60's/70's with minimal belt problems.

Your're right, belt based blocks and heads aren't "necessarily" longer, but we're not discussing any specific applications. Compare a few similar displacement Mercedes and BMW engines that use timing chains with those built by Audi that use timing belts. Weigh the blocks, cylinder heads, and related components. Look at the castings, machine work, and related components. Belts and chains both have their advantages and disadvantages. Engines with timing belts are cheaper to build. Those with timing chains might be more durable but with an added weight/fuel/maintenance penalty.

Pick your poison.

If you are the kind of clueless idiot who owns an interference engine that ignores maintenance schedules and says to yourself, "Why should I pay to have the timing belt replaced if there are no symptoms?" You should buy an engine with a timing chain.

Please, lets not get into a "racing engine" vs. "production engine" discussion. It's as silly as saying "A, . . . well gee, at Raytheon when we build rocket engines we do it like this, but at General Electric when we build supersonic aircraft engines we do it differently!" Apple, meet orange!

Chumley

 

[bub579]

I vaguely remember reading Glas was first back in the 60's. Having seen my share of cam drives, the Lambo V12 triple row chain with manual tensioner(one notch tighter at every tuneup) was top of the line. Of course the shaft driven bevel geared Crosleys and Porsche 904 don't count. Funny how a lot of folks are going back to chains. Wonder why? bub

 

[GraviMan]

"Funny how a lot of folks are going back to chains. Wonder why?"

Easy! When cam belts replaced timing chains a tension idler was the norm. Chains are only noisy when there is any slack in the system. Modern timing chains use a PTFE block to force the chain inward over an elliptical path. As the chain RPM increases it generates its own tension, so remains ideally tensioned over the life of the engine.

Folks are slowly moving back to chains since they are still more expensive than belts. Modern variable valve gear is getting more expensive to replace if there is a (service missed) cambelt failure. BMW valvetronic mech failure would be a nightmare, hence the chain.

Personally I think the ideal road engine would never need maintenance, but I drive a diesel so may not count. ;-)

Mart

 

[Chumley]

Graviman writes:

"Funny how a lot of folks are going back to chains. Wonder why?"

No, I don't either. Of course, today, with cell phones, OnStar, GPS, the internet, great warrantys, ECU's, ABS, airbags, Homeland Security, HMO's, and Medicare, you can agressively charge out into the world knowing nothing with confidence, and do anything you want without worry, knowing that someone will quickly come and save you (at no additional charge) when YOU screw up.

Chumley (laughing)

 

[SMOKEY44211]

Amen to that one Chumley------Phil