3.2 FSI BKH timing chain tensioner system

[54A4Avant]

So if you're familiar with the 3.2 FSI petrol engine in the C6 series you know the Achilles heel seems to be the camchain upper tensioner, which can fail after about ten years or so, helped by audi's long life servicing no doubt.

I've just replaced mine on bank 2 (passenger side on a UK car) and as called for in the fitting sequence I have hand cranked the engine through two revolutions to check it stays in time. I'm really looking for some input from people who know this timing chain system well please, as I have videoed the engine and chain through one complete revolution and it's clear that at three points in the cycle the tensioner piston pops back inwards with a loud click. My videos are below, first from overhead (you can see the tensioner arm on the right hand side next to the intake sprocket) and then a close up of the tensioner piston which makes it clearer what is happening. Both videos show one complete cycle of the engine and the engine stays correctly in time as cam locks and crank locking pin were able to be fixed in place both before and afterwards.

So.. is this normal or a problem?


Close up
Cam chain tensioner hand crank - YouTube (https://youtu.be/6Yrn_maILT0)


Overhead
Audi 3.2 FSI BKH Camchain tensioner clicking - YouTube (https://youtu.be/gsZAskvwDpE)

[54A4Avant]

So it turns out this appears to be normal behaviour, strange though it looks. I was assisted by a user on another forum who filmed his tensioner before disassembly and it seems to do exactly the same, dipping in and out as the engine rotates.

I suppose there is a valve which opens to charge the piston with oil and in the absence of oil pressure the tensioner just collapses down like this (hence the chain rattle on cars with failed tensioner piston seals).

So so on the basis the cams and crank are still in time after hand cranking it about four or five times over, I'm going to put it all back together and try starting it.

[dodonald]

Have you tried starting it, and did it all go well, let me know.

[54A4Avant]

Hi

i got it back together and started up. Briefly it went well, no rattle on start and vcds block 93 values of 0.0 and -0.4 on bank 2. Soon though, maybe 30 seconds after starting, it began to rattle. I've got it apart again and can see the piston on the tensioner isn't extended as far as it was and there is some slack in the chain, so not sure at present why that is.

Maybe the backplate didn't seal correctly and there wasn't enough oil pressure, or the chain tension wasn't even enough and the chain compressed the piston as it rotated so the ratchet mechanism compressed down. Only answers will come from taking it apart and checking the function of the tensioner ratchet, then maybe putting it back together to try again.

[54A4Avant]

Last weekend I swapped out the failed tensioner for a new one and got the car running ok following this. Still not entirely sure what caused the first tensioner to fail, but I cannot reset it - it will not compress fully.

Now the car car is up and running with 0.0/0.0 on vcds block 93 for bank 2 (which is the one I worked on), and to be honest its running so much smoother than before so I think the engine was marginally out of time. No more vibration at motorway speed.

I've seen Crasher advise against upper tensioner replacement as he says they fail again. This might be true, but I drive a very low mileage so I'm hoping it lasts a good few years at 4-5k miles a year.