Inlet valve causing no compression

[acealfa]

Currently looking at a family members 2.0Tfsi Audi TT that started misfiring after a run down the motorway. Turns out it has no compression in cylinder 1 so whipped off the inlet manifold to have a gander at the inlet valves & noticed they are all carboned up except 1 valve is clean. I'm guessing it's stuck open & the fuel has cleaned carbon build up off.

Does this sound correct & if no any ideas what would have caused it? My next step is to check the timing isn't off in case it's bent the valve but would have thought codes would have flagged up.

[stevieturbo]

Is the history known ? massive over rev at some point ?

When taking it apart, definitely pay close attention to the valvetrain, and rotate the engine to see if there is anything there that may be holding it open, or maybe it's just bent. Just trying to identify as straight

[acealfa]

It's well looked after, creeping up to 100k though but mainly motorway. As far as I know it just went. Going to turn engine over tomorrow probably see how it reacts

[Jordie Barretts sock]

I've had a couple of interference engines snap cambelts in the past. Neither one produced any warning lamps or codes.

Can't help with this one but I bet that valve isn't straight.

[GreenV8S]

Your theory seems reasonable ie that the valve is either bent or stuck partially open. That would imply you also have a dead cylinder, and probably lots of fault codes. A leakdown test might confirm the theory. Just cranking it over on the starter might confirm you have no compression on one cylinder.

[stevieturbo]

pointless cranking it on the starter when you already know there is a problem.

You need a visual on the valvetrain and turn over by hand

[acealfa]

GreenV8S said:

Your theory seems reasonable ie that the valve is either bent or stuck partially open. That would imply you also have a dead cylinder, and probably lots of fault codes. A leakdown test might confirm the theory. Just cranking it over on the starter might confirm you have no compression on one cylinder.

I did perform a compression test but not a leak down. Either way head would be coming off. Just glad it now looks like a valve rather than a piston.

Going to turn the engine later by hand 👍🏻

[GordonGekko]

Out of interest, what is the cambelt history?

Had an Audi A6 belt jump near Dover, the valves touching the pistons was audible- it still ran and got another 200 very careful miles back home.

[President Merkin]

Weird that only one valve shoud spontaneously bend though, assuming that's what it is. If a belt goes, you'd expect all of them to become damaged. What would cause that?

[GreenV8S]

GordonGekko said:

200 very careful miles back home.

I don't think there's any way that running an engine with valve/piston contact could be considered careful. There's really nothing you can do as a driver to prevent sudden catastrophic failure other than switch the engine off.

If you're willing to take that risk to avoid being stranded that's a call only you can take, but by running the engine you're essentially just rolling the dice.

[acealfa]

GordonGekko said:

Out of interest, what is the cambelt history?

Had an Audi A6 belt jump near Dover, the valves touching the pistons was audible- it still ran and got another 200 very careful miles back home.

It's chain driven. I don't believe timing as jumped but could be wrong. My guess at the minute is valve spring broken so piston has whacked the valve and bent it.

[GordonGekko]

GreenV8S said:

GordonGekko said:

200 very careful miles back home.

I don't think there's any way that running an engine with valve/piston contact could be considered careful. There's really nothing you can do as a driver to prevent sudden catastrophic failure other than switch the engine off.

If you're willing to take that risk to avoid being stranded that's a call only you can take, but by running the engine you're essentially just rolling the dice.

Try contributing something constructive that may help the original poster.

The experience I had was just as said, and driving carefully means 6th gear; 55mph. Once home the car was scrapped as it had 15 other annoying faults and life is too short to worry about a disposable car

[acealfa]

Broken valve spring! I was able to move valve up and down with my fingers

https://vimeo.com/879868048

I’m going to try and fit a new spring without removing head by pressuring the cylinder which should confirm valve is ok

Edited by acealfa on Tuesday 31st October 16:55

[President Merkin]

Sweet. Now where are the valve collets?

[GreenV8S]

GordonGekko said:

Try contributing something constructive that may help the original poster.

I already did. And the post your objected to also helps anyone else in a similar situation understand how risky it is to continue running the engine when there is a problem with the valve train.

[stevieturbo]

no video ?

[acealfa]

stevieturbo said:

no video ?

Sorry, crappy hosting.. https://vimeo.com/879868048

[stevieturbo]

Very odd, on a standard car stuff like that should usually outlast the car !!

Hopefully it hasn't bent the valve and you can get away with just the spring

I think it's being quite hopeful though

[acealfa]

After doing a quick search it seems there’s a few others with same issue in these Audi 2.0 engines

[HJG]

Valve spring failures are rare on any engine but in my experience no spring manufacture can guarantee complete lack of inclusions even with the cleanest steel wire. Springs are under a hugely demanding duty cycle with high cyclic loading.
Very unfortunate for you.