Technical > Automotive > Timing Belt Problem

Timing Belt Problem

One possibility is if the belt had been installed loose it could have possibly jumped timing a tooth putting the camshaft out of time/out of sync, or a second possibility is if it were installed with the timing marks off one tooth (advanced or retarded), but it should have run bad from the beginning if that second possibility were true. You will not see a Timing Belt stretch, they either break or strip the cogs/teeth off the Timing Belt instead of stretching. Then there is the belt tensioner (manual or automatic) that can lock up its bearing and/or come apart throwing ball bearings into the path of the rotating Timing Belt of which neither is a good thing.

»www.underhoodservice.com/issue/a···id=46596

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Timing belts are a maintenance item on engines that have them, but what about timing chains? On most overhead cam engines that use a timing chain to turn the cams, there’s usually some type of chain tensioner or adjuster to keep the chain tight and to compensate for stretch as the chain ages. But on pushrod V6 and V8 engines, there is no chain tensioner to compensate for chain stretch. Consequently, after tens of thousand of miles, the chain loosens up, starts to make noise as it rattles against the front cover, and causes cam timing to retard. At this point the timing chain needs to be replaced.

The main cause of timing belt wear is heat — caused by both friction of the belt moving, as well as high engine temperatures.

On some engines, the valvetrain uses both types of drives: a timing chain and a pair of belts. Chevy’s 3.4L DOHC V6, for example, uses a timing chain to drive an intermediate sprocket that also drives two belts (one for each pair of overhead cams). This type of setup doubles your opportunity to service the cam drive system. You can replace the timing belts for preventive maintenance, and you can replace the timing chain if it has stretched or is worn.

When Parts Wear Out
Timing belts and chains carry a heavy load. They have to turn the cam with enough force to overcome the resistance of all the valve springs. Belts are made of synthetic rubber reinforced with tough fiber cords that provide tensile strength and prevent the belt from stretching. Chains are made of steel links connected by flexible rollers. While chains are more durable than belts and typically have a longer service life, they are also heavier, noisier and more costly to replace. That’s why belts are used on many OHC engines.

The main cause of belt wear is heat. As a belt wraps around and turns the sprockets, friction creates heat (this is in addition to the heat from the engine itself). Over time, this causes the rubber to lose flexibility, harden and crack. The cords inside the belt also weaken as the belt accumulates wear, increasing the risk of the belt breaking.
Timing chains, by comparison, are mostly immune to the effects of heat. But they do stretch as they age, which can cause rubbing noise and retarded valve timing.

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I don't agree with the "should".
It might be nice, but absent a specific request it isn't realistic to expect.

Paul Sweet:
In addition to what Dr Olds stated about it being installed loose, a loose or defective belt tensioner (depending on type), or foreign objects/debris can cause the belt to jump time. Missing or incorrectly installed covers can allow entry of such debris.

Based on your description the timing was right originally, and it was rectified by the second shop by correcting the timing. I do not have any difficulty believing that this is the cause of your most recent issue.
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The talented hawk speaks French.

reply to Paul Sweet
I would agree with Dr.Olds. Possible the Tensioner failed. Most cars today the tensioner is automatic by hydraulic or spring, years ago it was a manual adjustment. Usually if a timing belt is off a cog after installed the performance would be noticed right away. If the marks are now not aligned something went a muck.

reply to Paul Sweet
If this has the 2.4L, you should of had the tensioner, idler pulley and water pump replaced at the same time as the belt. If any one of those were to fail, that new shiny belt is garbage. I will agree with what the others have said, if it was off a tooth, you'd notice it right away, it would chug like it had performance camshafts.

If it were me, I'd have them replace the tensioner, idler pulley, water pump, crank seal, and cam seals. At least, that is what I had the dealer do when I had my SRT4 worked on. (Same engine but with a turbo.)
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