Correct. An OEM timing chain only requires replacement when it gets stretched out. Typical service life of the OEM "laminated" chain runs 250-500Kmiles, with an extreme short of ~200Kmiles, and an extreme long of ~900Kmiles. You can probably double that for a "roller" chain.
A "laminated" chain has links that are built-up from plates, while a "roller" chain looks rather like a bicycle chain (there are "single rollers" - single row - and "double rollers" - two bicycle chains side-by-side. The "single roller" is far more common, and has effectively replaced the "laminated" chain.)
I flatly refuse to buy a vehicle whose engine has a belt-driven camshaft.
"Priceless", :rtft: I hate interference motors....loved my '03 Miata and '99 Solara 4cyls which were both non-interference, no worries but, I changed the Yota at 88K when the slightest "weep/drip" was noticed at water pump....note that CA mandates 105K mile changes, often on SAME timing belt PN due to state regs of 100K mile warranty issues...so go figure the SAME car belt is 60K, 90K out of CA but, 105K IN same state, same belt too! :cheers2:
Have the later models cars finially all gone to 100K+ mile intervals??
With Interference engines the valve will come in contact with the piston if the engine gets off timing, ie timing belt/chain breaking. So if the piston is at the upstroke and valve is open +Crash+ Bent Valves. My understanding in Non-interference engines there is enough room so the valves and pistons will not contact even if the timing goes.
I wasn't aware the 3.8 was a interference...I'm not sure what indicates an engine being one or the other? I assume efficiency and the need for higher revs
Free wheeling engines can also have catastrophic failure if belt breaks. This would mainly occur in high rpm situations. Some motors have good chain and guide designs where both will last as long as the motor. Others have design not so good where the guides will wear out and come apart causing chain to have slack and allow motor to destroy itself. Most all chain drive motors have a tensioner that is controlled with oil pressure. As chain stretches tensioner can keep constant pressure on chain to compensate. With this being said you can see how using a good quality oil and performing scheduled oil changes is critical on these motors. All chain drive motors I have ever worked on give a very early warning before a tensioner fails or a guide. If it gets to the point of engine destruction then the driver must have just turned the radio up and ignored the early warning noises.
Timing belts definitely had a bad reputation but as technology improves, so does belt performance, materials and longevity. Remember when fuel injection first came out and it was viewed as the worst thing ever?
I remember as a kid being really torn between timing gears or a timing chain on my 351W so that's proof that I've certainly come a long way. The truth is, modern motors with timing belts have better mileage, less parasitic drag, and the belt helps to damp valvetrain action a bit for a smoother running engine.
I'm truly amazed at the Pentastar V6 which is why I bought two vehicles that both have them. It's a workhorse of a motor and has a great feel to it. If it came with a belt vs a chain, would that have stopped me from buying it? Nope.
Yea but in non interference (freewheeling? Never heard that one before) engines the combustion chamber is either A) HUGE with a related low power output or B) Above the valve like in a briggs and stratton or Flathead. Even the Dodge Hemi will touch valve to piston with a broken chain!
The primary reason for belts is: they can be used externally. A chain requires oil and thus gets buried in the crankcase behind the water pump etc. And on a OHC or DOHC chain drive - the chains are so long even the slightest stretch can retard the valve timing as much as 2degrees!
A belt can be changed in ~30 minutes with no loss of coolant or oil. A chain takes about 7 hrs (to do it correctly) and requires draining and filling the radiator, the oil and disposal of both...
The secondary reason is (believe it or not) they DON'T stretch. That is until they wear out which occurs faster than a chain towards end of life. A chain wears from day one. If it stretches .005 - in 200K miles - that was at a rate of .005 divided by 200K AND any gain never left (ie if it stretches .002 it STAYS stretched .002).
A belt will have ZERO stretch until around 45K and may gain .003 by 90K. It CAN get stretched momentarily under hard acceleration - but returns back once inertia is more equal between crank and cam gear. Like a rubber band returning to its shape after use.
As a machinist I prefer chains. Even though on a OHC or DOHC if you surface the head - you have moved the cam closer to the crank and that is then "made up" by the chain - resulting in retarded valve timing. A lot of rebuilders forget this as two degrees does not make it run bad - just lower economy and lower power but compared to the pre rebuild it is BETTER so overlooked!
As a consumer I prefer belts - (and have even belted some chevies for drag racing) just MUST do the maintenance on time!
Whenever I have seen an interference engine with bent valves - it was NOT because of "a broken belt". It was because of failure to perform scheduled maintenance. THEN the belt broke! I have never seen an engine come in with all of the valves bent a broken belt and less than 40K on it. I am sure there are some, but VERY rare.
Wow good stuff, thanks for posting. Totally didn't even think about machining affecting the distance and causing the timing to be off. You learn something new everyday!
Daewoo cars were bad about braking belts before their scheduled replacement and they would destroy themselves. Then they went out of business probably a contributing factor.
The parent company went out of business, but Daewoo Motors is now GM Korea. I'm not sure if they still rebadge anything for the US market, but the previous generation Aveo was a Daewoo.
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