[Closed] Cam belt tensioner track world

I'd get the garage that fitted the kit to quantify "faulty tensioner" It sounds like the belt has skipped a tooth. This may or may not have been enough to result in a valve/piston interface. At a minimum I'd be asking for a new belt & tensioner as the belt may have been damaged, plus a compression test on all cylinders. The garage might have a borescope to have a look through the plug holes if it's a petrol engine to see if there's any witness marks on the piston crowns. If the compression is low then further investigation is probably going to reveal at a minimum some bent valves.

Some engines will run with the valve timing slightly out. You might have got off lightly.

Thanks Davesport. It’s a VW bkd diesel. They are saying they will replace the whole timing belt kit and that it hasn’t jumped a tooth so the timing is unaffected.

My concern, which I have told them is that if there is no tension on the belt that this could affect timing slightly causing damage even if it is not as bad as a bent valve/ chipped piston.

Easy to establish if the belt had skipped a tooth - apart from the fact the engine would most likely be toast already if it did. If the timing marks would no longer line up. The belt wont stretch. They may be rubber but the structure of the belt is inside the rubber and is the chords within the belt. The tension on the belt is mainly to stop the belt from slipping under high engine rotational accelerations. The actual belt tension is not that great anyway.

The last thing you want to be doing is to start removing the head...just asking for trouble and totally and utterly pointless and unnecessary. If damage has been done then you'd know. the engine cannot run properly with a bent valve - it would sound awful, would run terribly and you'd be getting all sorts of smoke and crap coming out of your exhaust. So as long as the timing marks line up you'll be good to go and just put it down to good luck ensure it gets tensioned up correctly and crack on.

I've done many a timing belt on cars over the years and never used a tensioner tool. I've just twisted the belt through 90 degrees at the longest free section of the belt and tensioned so it can just turn through 90 degrees without putting in a huge amount of effort. Never had an issue using that method and the variability in actual belt tension must be massive, so obviously not that sensitive to belt tension.

As others have said, removing the head is unnecessary and you wouldn't do it unless necessary. Compression test should show up any issues and you could also stick an inspection camera into the head if you wanted to check the pistons.

But I would question why the engine stopped. Did the engine throw up an error when the camshaft and crankshaft sensors detected a problem with the timing? On my engine, the toothed side of the belt drives the high pressure diesel pump, and the smooth backside of the belt drives the waterpump. Presumably the water pump is untoothed so that if it seized, or the coolant freezes, the belt will skid over the water pump pulley rather than shred itself and wreck the engine. This also means a loose belt may cause the waterpump to stop and cause localised overheating of the engine that the temp sensors would not detect.

Check how your waterpump is driven.

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I'll bet the threads for the tensioner stud in the cylinder head let go , subsequently letting the tensioner release the belt .
It is a very common occurrence . repaired by fitting an insert in the head to repair the threads .

I have done a couple of these on my BKP engine. The tensioner has guide marks on it so you know the tension is right. My guess is that either stud threads have failed or that they didn't tighten the nut up properly.

If it had skipped a tooth I don't think it would run well. My engine has a camshaft position sensor and a crankshaft position sensor, so with insufficient tension in the belt the slack could cause these two to become out of sync, and the computer might notice this.

When you do the change (properly) you lock the crankshaft and both camshafts in position, so if it has skipped this wouldn't stop it being set up properly a second time if procedure has been followed. It's also easy to identify if it's skipped.

A known issue for some VW vehicles. Might not apply to your vehicle though:

https://www.gatestechzone.com/en/news/2019-12-t43245-adjuster-crack-during-installation

Thanks all

Honkiebikedude and molgrips - it was put in with a helicoil so should not have happened. They have said the tensioner spring has failed.

Marks - they are familiar with this engine and did the previous cam belt.

Spooky - I as7me they will have tested compression and will speak to them on Monday. The car just stalled like a fuelling issue as I lifted off the throttle and started to break going dow a slip road. I think the water pump is toothed but will check that out. Thanks

wobbliscott and molgrips - they have said it has not skipped, just to confirm the tension on the belt won’t affect timing, only it’s position on the toothed drive will?

Thanks again

Looks like fitting error to me, but they're just covering it up by saying the part failed.

just to confirm the tension on the belt won’t affect timing, only it’s position on the toothed drive will?

I am not a pro by any stretch, but I think your engine is similar to mine. The crank pulls the timing belt over the cams, and this is the 'tight' side as in it's always under tension when the engine's turning but the tension would vary with each combustion. The tensioner is on the return side i.e. the slack side. Without enough tension, I'd imagine the belt would be tightening and loosening off as the engine turns which could affect the timing *slightly* and the engine might pick it up, but it wouldn't damage anything. IMO if you didn't hear loads of loud clanging noises then the mechanical parts are all ok. But I'm no pro.

Molgrips - no banging or clanking, sounded a bit deeper and smoother if anything, more like the common rail version of the engine in my wife’s car.

The cam position sensor packed 3-4 years ago and it refused to run, completely dead like a flat battery.

Hopefully no damage has been done.

I wouldn't start stripping the head off, you're letting yourself in for another world of trouble. Get the belt put back on correctly and see how it runs. They either run right or don't.

Throw a new belt and tensioner on it.

Compression test it.

We used to fo that even on engines that the belt had gone on so we could check compression before we stripped them.

If its just the tensioner as above it pulls the slack on the non driven side of the belt.

I'd be surprised if its a duff tensioner though to be fair.

Thanks again all. I will find out tomorrow if damage has been done when they put the new kit on.