timing chain service life

[440Magnum]

Chains are essentially a no-service item, if everything is well designed. Yes, there will be a small amount of timing shift as the chain stretches and the tensioners take up the slack, but it is very small and generally won't affect performance for 150k to 200k miles. That said, some engines have better timing chain systems than others. You almost *never* hear of chain problems on most cam-in-block (pushrod) engines, Cad Northstars, Chrysler 4.7/3.7 series, modular Fords (after a some early problems), etc. On the other hand, the gone-and-not-missed Chrysler 2.7 had a whole world of timing chain failure modes. Even the early Modern Hemi, even though it is cam-in-block, had an issue with premature tensioner failure. Fixed now, thankfully.

Belts are an OK way to time an engine if you can build it non-interference, so that if the belt breaks the engine just stops without hurting itself. But non-interference puts a lot of constraint on combustion chamber and piston crown design and is just not acceptable in the world of tightening emissions rules and the quest for more and more power from less fuel burned. Belts on an interference engine are S-T-U-P-I-D, and its unbelievable to me that most autmakers have actually produced at least one belt-timed interference time-bomb. Some (Honda) have built MANY such engines. But I'll never own another one after my wife's PT is retired. Just too much risk of a $80 part doing $2000 worth of damage.

 

[Donald]

Back in the days of my 289 Mustang, people never even talked about the timing chain. It was a non issue. But I guess they were too noisy so then the new modern advancement to a timing belt and a $500 repair bill every 75K-90K miles.

 

[440Magnum]

Originally Posted By: bullwinkle
That AGCO link is actually very educational, too-looks like the Ford reasoning behind the 5W-20 oil is THINNER is better-oil pressure builds more quickly on a winter cold start, less chance to snap off one of those flimsy plastic timing chain guides!


NIf you look at almost all the diagrams in the pictures Overkill posted (note the Ford 4.6 and Chrysler 4.7 in particular), you see two kinds of "tensioner." The curved pieces on the slack side of the chains are movable (oil pressure activated) tensioners that apply pressure to the chain to stretch it tight. The straighter pieces on the tension side are fixed and are more accurately "snubbers." The guides on the movable slack-side tenisoners that really press hard on the chain are only coated in plastic, the structure of the ones used in most engines is metal. The tension-side snubber may be all plastic, but in most cases they really don't do much other than keep the chain from fluttering a little bit and making funny noises as it re-engages the sprocket. They don't bear down hard on the chain. And the movable tensioners usually have a ratcheting mechanism that keeps some tension on them even with 0 oil pressure.

 

[440Magnum]

Originally Posted By: Donald
Back in the days of my 289 Mustang, people never even talked about the timing chain. It was a non issue. But I guess they were too noisy so then the new modern advancement to a timing belt and a $500 repair bill every 75K-90K miles.


I've said this before, but the late 60s and 70s were the worst period. The Big Three went to plastic GEARS on the cam in order to quiet the chain (except for high-performance engines like the Mopar 340 and 440), and the plastic cam teeth would wear down and let the chain jump time long before 200,000 miles. Ask me how I know.... :-/ That was my first really big car repair.

 

[eljefino]

BIL's 96 cavalier, I bought for $300 when he needed a car, chain sounded rough. Snapped 8k later at slightly over 200k. Had a nice diesel/ maybe-it's-the-lifters noise to it.

Saturns, and maybe other cars, with long OHC timing chains will start weeping oil at higher mileage. More surface area to gasket. A timing belt just has seals around the cam and crank shafts.

Am happy to not have one of those V-DOHC engines!

 

[JHZR2]

Originally Posted By: OVERK1LL
Originally Posted By: ARCOgraphite
More trouble with chains, tensioners, guides plus chains are tough on oil. Almost all engine problems I've seen lately have been Chain timing drive related. Belt is the way to go on OHC. The Short chain on pushrod V engines are OK but have median service life of about 3000 hours with silent nylon gear overmolds.


Explain the Modular then....... And most BMW and Mercedes engines.


MB single roller chains werent that great. Dual rollers like in the OM617 are fairly bulletproof.

The BMW M42 as an example has seen bad sprocket wear from the chain, causing all kinds of issues early on in some cars.

 

[OVERKILL]

Originally Posted By: JHZR2
Originally Posted By: OVERK1LL
Originally Posted By: ARCOgraphite
More trouble with chains, tensioners, guides plus chains are tough on oil. Almost all engine problems I've seen lately have been Chain timing drive related. Belt is the way to go on OHC. The Short chain on pushrod V engines are OK but have median service life of about 3000 hours with silent nylon gear overmolds.


Explain the Modular then....... And most BMW and Mercedes engines.


MB single roller chains werent that great. Dual rollers like in the OM617 are fairly bulletproof.

The BMW M42 as an example has seen bad sprocket wear from the chain, causing all kinds of issues early on in some cars.


That's why I said "most", LOL. There are always exceptions

 

[4x4chevydude]

Ive done more belt replacements than chains but belts are also easier to do....both serve the purpose one lasts longer the other is easier

 

[dparm]

Chains can stretch but there are tensioners to adjust for this.

On some early Audi 4.2 V8s, the chain guides could crack or even break. An easy but extremely costly repair (once the motor is pulled, lol). This was quickly fixed but the issue still remains on the older ones.

 

[The motor guy]

I didn't know an engine could have more than one timing chain/belt. My goodness.

 

[Spazdog]

Originally Posted By: bullwinkle
Every chain failure I've seen has been caused by either the plastic overmold on a gear or plastic guides failing.

or the tensioner failing.

Nissan KA24s usually give you plently advance notice that it is failing though. It rattles like [heck] on cold starts for quite awhile before it throws the chain.

 

[ARCOgraphite]

Originally Posted By: OVERK1LL

Explain the Modular then....... And most BMW and Mercedes engines.
My '98 3.2 M-engine had a timing system /VANOS failure. The Synthetic oil ate the guides and the chain was chewing through thur cover at 70K miles. None of you guys would have any manufacturer quality data on this. The manufacturers keep this in their vest pocket.

 

[mechtech2]

Originally Posted By: Cristobal
Back in the day timing chains almost always lasted until the motor was replaced, rebuilt, or the car got junked.


No way.
Timing chains were a bread and butter daily job.
Many older set ups were kinda crude.
Modern ones seem to have nicer rollers and construction.

 

[ARCOgraphite]

+1 always needed a T-chain (amoung other stuff) at 80-110K miles. Back in the 70's that was a ten year old car though. We drove less.

 

[OVERKILL]

Originally Posted By: ARCOgraphite
Originally Posted By: OVERK1LL

Explain the Modular then....... And most BMW and Mercedes engines.
My '98 3.2 M-engine had a timing system /VANOS failure. The Synthetic oil ate the guides and the chain was chewing through thur cover at 70K miles. None of you guys would have any manufacturer quality data on this. The manufacturers keep this in their vest pocket.


Note again, my use of the term "most"

Taxi and fleet Crown Vic's, Town Cars and the like usually run their entire life on the stock timing chain. That can be 700,000 miles.

I'm not saying they are all like that. But you are saying they all aren't. Clearly there is evidence to the contrary here.

 

[Dakota1820]

It's usually not the chain that wears out it usually the gear with nylon tips or the guided and tensioners. My Saturn has 190 and I had the valve cover off few weeks ago chain looked great and had 0 play. They can last forever. If it ain't making noise its probably ok. Usually they will make a raket before they fail.

 

[TooManyWheels]

Originally Posted By: mechtech2
Originally Posted By: Cristobal
Back in the day timing chains almost always lasted until the motor was replaced, rebuilt, or the car got junked.


No way.
Timing chains were a bread and butter daily job.


Thank you - That is what I remember also.

 

[Jeff_in_VABch]

Originally Posted By: Donald
Back in the days of my 289 Mustang, people never even talked about the timing chain. It was a non issue. But I guess they were too noisy so then the new modern advancement to a timing belt and a $500 repair bill every 75K-90K miles.


Although the price cany vary of course, I would say $500 is way low. OEM parts alone can cost that on some engines. You see some shops trying to save money by eyeballing the sprockets and not replacing them, only the chain/guides/tensioners.

 

[Hokiefyd]

Originally Posted By: motor_oil_madman
I didn't know an engine could have more than one timing chain/belt. My goodness.


I really like how Cadillac did the Northstar's setup (and how Chrysler did theirs, now that I see it). They used an intermediate timing chain to an idler shaft, then ran shorter chain runs off that idler shaft. Chain runs were kept short and chain whip was reduced. It requires more parts to engineer, but in my opinion, is a superior arrangement to one or two longer chains.

 

[OVERKILL]

Some of them use 3 or 4 actually. The BMW links both cams together with small chains, then has a larger one running from the one cam to the crank then up to the other cam.