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Timing belts vs chains?

Other than padding Tom & Ray’s bottom lines with required replacements at 70+K miles, why did auto engine technology go from timing chains to timing belts? I don’t think chains ever needed replacement and I have two cars with them. The other two have had to go thru the expensive surgery plus water pump replacement. What’s the diff?

That horse has been beaten to death. Here’s a 12 page discussion.

Water pump replacement is not required, either for a chain engine or a belt engine. It’s just that if you take it all apart to replace the belt, the added cost of the pump is small.

Timing belt engines are cheaper to manufacture. Anything to save a buck.

Timing belts arrived with the OHC, simpler to design and build with a belt. Some used chains in their OHC engines from the start (like Mercedes). They were not trouble free, either, the 3.8 l Mercedes V8 had to have its single-row chain and gear replaced with a double-row setup because of rapid failure, IIRC.

Read the post by PVT PUBLIC please.

Chains do need replacing…but not for at least 250k miles.

. If you keep a vehicle for 300k miles (like I do)…then replacing 1 timing chain could easily cost you 2-3 times the cost of the 3 timing belts you replaced.

. Timing belts are far easier to replace…and the average back-yard mechanic can do it an afternoon (depending on the vehicle). Timing chains are much more complicated because of lubrication. Many times you have to drop the oil pan.

But if you only keep your vehicle 100k-200k miles like most people…then a timing chain will be the cheapest.

In my opinion the real reason most manufacturers went to belts was manufacturing cost. It’s cheaper.

I think the real reason most of them have gone back to chains is sales. Consumers got sick of paying for the surgery every 60-70K and too many TB replacements resulted in problems. Too many shops didn’t take the time to properly time the cams and too many operating problems resulted. Too many customers, after having a problem after belt replacement, started walking away from cars with belts. Manufacturers took notice.

I don’t know this for a fact, but it’s also possible that variable timing valve systems were more prone to problems if cam timing wasn’t properly done, and belts exacerbated the problem.

In summary, belts were cheaper to manufacture up front but just too problematic in the long run.

To me its six of one, half dozen of the other. Good posts above about the advantages and disadvantages of each. One advantage for belts I don’t think got mentioned, belts have less mass, which makes them easier to move around the timing loop. This might show up as improved engine performance, especially during hard acceleration, due to less inertia.

Timing belts are not all bad.

It’s easier to assemble or remove a cylinder head with a timing belt.
A cogged timing belt is quieter than a timing chain.
A timing belt is more durable than a timing chain at sustained high RPMs.

I am still wondering why polyacrylic rubber timing belts can’t work. Polyacrylic rubber is very heat and oil resistant and has been used in industrial applications.

The overhead cam engine that were manufactured in the 1980’s had reliability problems, the chains would stretch and the chain guides wore resulting in a noisy chain. I could recognize a Mitsubishi engine as it came up the drive way of the service department by the noisy chain. The most practical solution at the time was to use timing belts.

Timing belts are very quite, Lexus used timing belts for 20 years, not to save money. As timing chain engineering improved manufacturers began using chains again.

Most engine made today have timing chains so I guess your question is; why did manufactures go from chains to belts 30 years ago?

Not all OHC engines of that time used one long chain.

My 74 Chevy Luv (Isuzu engine) used two short chains. Crank to a swivel gear…then a chain from the swivel gear to the cam. The chains were actually shorter then many V8 timing chains…It was however a little more difficult to align the timing marks.

Hands down…I would rather have a vehicle with a timing chain. It’s a no-brainer as far as I’m concerned.

I’ve done a timing chain before but I don’t think I’d tackle a belt. Just seems a lot more complicated and no room to work anymore.

Timing belts are much easier then a chain. No gaskets to worry about.

As for no room - that has nothing to do with belt or chain…but everything to do with engine configuration. My wife’s Lexus and my Highlander both have transverse mounted V6 engines…and both have chains. I won’t tackle that job

It seems a fair amount of heavy motorcycles use belt drives these day (if they dont use a shaft-maybe we could shaft drive a cam ?
One reason I bought a particular import one time was because it didnt have a timing chain(people were lax on maintenance around here and those things failed before 100k.It was fairly hefty ,messy job to replace the timing chain and all the ancillary components and believe me if the manus wanted too ,the belt replacement could even be made far easier,
Marketing gotta make money on repairs(maybe they will do the B&S thing stop requiring oil changes,when electrics hit en masse,they will have to be dumbed down enough to require fairly frequent service(cant have any 50 yr old electric motor driven vehicles running around that didnt require service.)