fn_42

Forgive my ignorance here, this is my 5th car but my first non-inline engine =)

I was trying to get the engine to TDC to verify that it's timed right (getting a P0022) when I noticed that the top end of the timing belt is pretty slack... I can deflect it maybe 1.5" below the rollers. Is this normal with the engine off?

fn_42

I understand that once the engine shuts off the cams might move a little depending on how the valve springs are pushing back. But it seems like the tensioner should be strong enough to resist creating slack when this happens?

123quattro

No, it shouldn't have that much slack. I wonder if the tensioner failed, or came loose? That could definitely let it jump timing.

fn_42

Thanks! I thought so, just wanted to confirm

knowing this car the tensioner is probably just not there at all... got it from a scrapyard, they promised nothing was taken off but I've found other bits missing

silverd2

It is totally normal to have lots of slack (at rest) in a correctly tensioned belt on the 40V engine (cam lobes, etc...). If you push on the span below, however, it should be as tight as a piano spring (they are VERY tight, by the way).

If it's loose on the top and bottom of the belt loop, you got a problem.

There is only ONE way to check the tension on a 40V motor motor and it ain't by pushing on a belt. The tensioning damper (parts must be removed to access it) should have, ideally, 5mm of extension on the piston...8mm at the very most (with wear)...if it's 4mm or less, it's WAY too tight.

So, if you have a loose span at the top (as in your photo) and very tight on the span below, all is normal...ALL belted V8's do this, especially the 40V Audi engine.

123quattro

When I did my A6 4.2 it was decently tight on the top and bottom. That doesn't look right to me.

fn_42

here's a few pics of bank 1, sorry it's a bit awkward to take pics of

I'll measure the tensioner when I get a chance. It just feels like it's too loose to me

You're correct silverd2 this was "at rest", I hadn't tried spinning the crank yet to get it to TDC

fn_42

The bottom part of it is pretty tight by the way as expected

silverd2

Looking at a photo and being there are 2 very different animals. What we don't know (yet) is how tight the lower span was at the time of the photo....probably super tight and shifted to that position due to valve spring tension, warm engine at shut off and good circulation.

Every time I've done timing belts (many times on V6's and V8's, including my present cars) all is evenly tight upon completion, BUT (as in your photo) the engine is cold, oil not fully circulated...no reason for anything to have moved yet.

Believe me, this is a very common observation that scares people (myself included) the first time they notice it...my first time on a V8 was one of my P-928's (5 liter)...same thing.

If you've driven your 4.2 A6 and it's sat for at least a half hour, I would be shocked if you didn't find a very loose belt span above the cams and a super tight one below them, or visa-versa.
...Very common phenomenon in V engine with belts, especially with multiple cams and valves like our engines...a whole lotta accumulated spring tension in the valve train to push things to a "rest" position after shutting off a hot motor.

This has been discussed at length in many, many threads on Quattroworld and here on AW.

I'd still like to hear from the original poster here about the rest of the belt's tension. One quick test, is to hand turn the engine a full rev CLOCKWISE ONLY with a wrench on the center bolt of the crank pulley...All should fall back in to uniform tension all around for the time being. IF the engine is warm and well lubed at the time, you very likely may be able to watch the belt loosen at the top right in front of you...sometimes in one visible shift of one or both cam belt pulleys (a couple of degrees turn).

Cheers

silverd2

Yep, as expected.

For peace of mind, try hand turning the motor a rev or so (even less will do it) or even run the starter a second....all should fall back into uniform tightness all around at first.