What Happens if a Timing Belt is Put on/Adjusted Wrong?

Y2KBuggy · September 5th, 2011, 10:50

What happens if a timing belt is put on or adjusted (or whatever else is done to the timing belt when it is changed) wrong? Does it always happen right away, or could it take a 5K miles or a few months? What parts of the procedure are the most likely to be done wrong? Which parts are the likely culprits to cause problems? What parts are likely to end up damaged/broken?

Thank you.

ymz · September 5th, 2011, 10:56

Best case: nothing much will be noticed... ever...
Worst case: engine will self destruct any time over the next 20,000 miles or so...

Why do you ask?

I see that you're conveniently (NOT!) located midway between two of the finest TDI experts known to us... only about 2-1/2 hours away... any reason you wouldn't make the effort to have one of them do the job?

Yuri

RT1 · September 5th, 2011, 11:03

Depends on how "wrong" it is. The worst case scenario is on start-up the pistons deliver the kiss of death to the valves. Depending on the depth of the valve protrusion at the time of contact it can ding the top of the piston or smash a divot into it. That's not fatal, but at that point all threads on the subject say stop engine, pull head and send it off for a valve rebuild. If you don't ,the weakened valve stem can break, valve gets sucked into the cylinder and that's the end of the engine.

Y2KBuggy · September 5th, 2011, 20:11

Could a timing belt problem cause the timing chain in the upper part of the engine (if such a thing even exists) and/or the cam shaft to break? Or is this just part of the sequence of events that leads to the valves getting smacked? Would any of this cause the serpentine belt to break and disappear?

Thank you.

2jettasinthedrive · September 5th, 2011, 20:19

There is no chain. The belt or one of the other components could fail and allow the belt to slip. The tensioner came apart on mine after 63000 miles. I found a crack in it. I bent 2 valves and got all fixed up to the tune of 1800.00.
The serpentine belt can break for alot of reasons and drop on the roadway never to be seen again. Cam shafts usually do not break when these things happen.

Corsair · September 6th, 2011, 05:26

Sounds like there's some history- perhaps a timing belt job in the past, and maybe recently encountered a bad engine failure, and maybe suspect or wondering if the recent failure could have been caused by past work ? Recommend post the history (and specifically which car it is, and the mileages when various things occurred...) and share your thoughts- that may put others in a better position to offer feedback.
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Without knowing much specific, my 0.02 in general- yes it is possible that previous substandard work could cause issues in the future, even several thousand miles in the future. There's more than one possible scenario for that. Unfortunately, it's difficult / impossible to prove concretely that past work was the sole cause of future issues, so it's very difficult to pursue for reimbursement etc. Sometimes you just have to lick your wounds and call it "cost of wisdom" etc.
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I'm more familiar with the older (ALH) series, not so much the newer (2005). Did the newer ones contain a balance shaft module that was known for having issues that could destroy the internals if it failed ? ie. I'm trying to suggest that it could be possible that previous work was all done correctly, and something else may have occurred, causing the bad failure. Again- need more specifics about history and what actually happened. Sounds like you might have to invest some labor to take things apart, to reach a more specific diagnosis of what has failed. I'm making lots of a-s-s-u-m-ptions here......

halocline · September 6th, 2011, 05:29

I also wonder why you're asking. The basic situation is that the timing belt determines the timing relationship between when the valves open down into the cylinder and when the pistons come up; if the belt is installed wrong or slips, this timing gets screwed up and the valves and pistons hit each other, causing engine damage. Because the clearances are so tight on TDIs, it's important that the belt is adjusted very accurately. If it's just a little off, the valves might just barely hit the pistons, which you would not notice for a while, but eventually will cause the valves to break. Is that what you're asking?