Upper timing chain slip?

[J-Lynch 0]

Hi folks,

About a week ago my vr developed this loud racket from the upper chain area.

The upper chain guide rail is often the cause of noise as its the most prone to failure and luckily there not too hard to get at, so.. I've set out to replace the upper chain tensioner guide rail and tensioner bolt.

Stripped down the intake and got the rocker off.

Turned the engine over a few times with starter to check oil was flowing up properly. All seems ok but do it again, this time the motor sounded like it was spooling up for 3/4 of each revolution, like it had no compression...

I could see it was still turning over, but each rev the chain was dropping slack between cam sprockets for a moment. It's like the rear camshaft is rolling forward a little, spring powered by the valve springs or something.

So I have set TDC with the timing marks on the crank pulley and cam shaft grooves ready to put in cam locking plate. These groves should now be horizontal allowing the locking plates to slide in, but there not quite there in the clockwise direction.(The cam rotation is behind)

It's only by half a cam sprocket tooth or so, I'm thinking it must be that the intermediate shaft sprocket has jumped advanced by one tooth.

Anyone know if it's possible to slip the int' sprocket back a tooth without removing the lower chain cover?

You can generate quite a bit of slack with the guide rail and tensioner bolt out so it does almost seem possible, if not bloody arqward!

Speaking of the guide rail I did find it in pieces broken down the middle fixture leaving the lower part free to flap about.

Anybody had this issue?

Most gratefully for any advice, anything to avoid transmission out job!

[coullstar 0]

If it still idles and revs smoothly Id say it was just the noise from the chain guide.

[J-Lynch 0]

Hi coullstar thanks for the response! before I took it apart it did rev nice and smoothly, however now it seems like the upper chain has slipped a tooth somewhere. The cam grooves that you use to lock up at TDC aren't quite horizontal. So effectively they have somehow become slightly behind the rest of the engine timing.

Will post pics when I get near a PC.

[coullstar 0]

Have you checked that piston No.1 (top left when viewing from front) is actually at TDC when the crank mark is used? Better to use that so you know for sure as mine is very slightly out. I know there is some slack in the chains when you take it apart even with the tensioner bolt in but not sure if there is enough even if the guide plate is gone. Saying that if its in pieces you will need to get the gearbox of anyway to replace the top plate so it looks like the box is coming off regardless.

[J-Lynch 0]

Haven't physically checked Cyl 1 for TDC but sounds worth checking. Should be able to do this through the spark plug port with a second pair of eyes.

I've fitted the new guide rail to correct as which only requires the top cover to come off. So this should have corrected any error in the taught side of the chain, however cams are still out of phase. (both behind by less that a camshaft sprockett tooth.

This is why I'm fairly sure athe intermediate shaft upper chain sprocket leaped forward by a tooth. Luckily there were only 2 large pieces still in situ which I got out no problem. So still hoping not to have the box off. ;). Otherwise :banghead:

[J-Lynch 0]

Here's what both the cam grooves are looking like when TDC is set by the crank pulley notch.

[mic_VR 3]

That's just chain stretch. Certainly doesn't look enough to be a tooth out.

[coullstar 0]

Are we talking out upper guide or the tensioner pad? Didnt think you could replace them with only top cover out.

Best way is to get a thin metal rod down the spark hole so you turn crank and see it at TDC for yourself.

[J-Lynch 0]

The upper guide rail was the part broken. You can easily remove and refit this, as the lowest fixture is a pin (green arrow) that the guide slides onto and the rest bolts up behind the upper chain cover.

 

(not my pic)

 

Sounds like a good way to check actual TDC, I''ll do this when the weather is better.

 

Mic, I hadn't thought of Chain stretch, but makes perfect sense as that would leave the cams lagging.

 

I did have it in my head that if the intermediate sprocket slipped past the chain there would be less of error/ lag in cams than if the chain slipped over the cam sprockets. Thought this would happen due to the smaller diameter of intermediate sprocket.

Thinking about properly, actually the effect of the int' sprocket slipping would be the same as the cam ones slipping. As all the sprocket teeth must be the same length as chain links. Can anyone confirm this.

If so, you must be right about not being a slipped chain because I have jumped the cams ahead one tooth, and they end up way too far..

 

Thanks guys

[vw rule 19]

Hello there,

 

no I doubt the chain has slipped because if it had then your engine would have run lumpy / rough,

plus like you have already said the grooves in the back of the cams would be out a lot more.

 

Half a tooth out on the cam sprocket is normal for most warn / stretched timing chains / cam belts.

Sounds like your chain tensioner is on the weak side,

and the issue you have with the incomplete chain guide where it's broken away,

this does greatly affect the tension on the top timing chain or any chain for that matter,

that doesn't have the full tension pressure on it.

 

A timing chain won't come off it's toothed sprocket,

not unless over half it's running area has detached it's self off.

What I mean here is that on most sprockets the timing chain,

only interlocks with half of the teeth on it,

so if only a quarter or less of the sprocket is covered by the chain,

due to a badly warn chain guide or badly warn sprocket teeth,

or if the chain had stretched that much that the tensioner just can't take out all the slack.

 

Normally if any of this had happened the chain/chains would be rattling like mad,

might even be hitting the inside of the chain covers.

Plus the chain would be hanging off the lower teeth where it goes round one of the lower sprockets,

this you would feel at the top of the chain near to the cam sprockets,

or each cam sprocket would turn independently due to too much chain slack.

 

The cam shafts should turn/rotate at the same rate,

half a tooth out is just wear which can course one of the cams to seem lazy,

i.e a slight delay until the second cam turns.

 

But like the other guys have said it'll be slight wear in your timing chain,

and the issue with the incomplete chain guide.

 

Check your service history to see when the chains were last replaced.

Most timing chains you replace every 80,000 to 100,000 miles.

 

Really and truly though you're better off replacing the lot,

well at least the two timing chains and all the chain guides complete with tensioner,

and the sprocket gears if it needs them.

 

If you just replace the top cam chain guide runner,

what's to say the lower crank chain or guide isn't on the weak side as well.

 

I know it's a pain in the butt,

but if it was me I'd have the gearbox out and check the lot.

 

 

Hope this helps.

 

Si

[J-Lynch 0]

Thanks for all the responses, I was kind of stuck in limbo thinking that I had slipped a sprocket tooth. Thanks to you guys I did not try to reverse this process which would definitely have left my timing buggered!

It was simply the noise of cranking the engine with no combustion that made me think the engine was free wheeling as in no compression. But it wasn't.

Dead surprised how much it sounded like noisy electric RC car though but sure enough got it back together and it fired up first time. Dreadfully noise gone!

Still have the chain rattle between 1000 and 1500 rpm engine is allot smoother and quieter in general.

Still haven't taken a pic of the broken guide rail, will post it up soon as I do.

[Roger Blassberg 0]

Did you change the broken top guide rail then? If "yes",was it possible without taking the gearbox etc out? Do you have a single or double row top chain?

 

Best wishes

 

RB

[J-Lynch 0]

Hi Rodger, sorry for the slow response. I did indeed, changed the broken guide rail and there was no need to remove the gearbox/lower cover etc. Mine has the early double row upper chain setup. The bit that looks tricky is that the thermostat housing slightly interferes with the guide when pushing it in but there's enough flex in it to get past it. Nothing serious just a gentle push does it and the lowest mount peg guides it in perfectly.

Ps. Anyone know the OE brand of these early double row chains? Noticed the tired(ish) chains I'm running are stamped Sachs France.

Any ideas?

Edited January 10, 2014 by J-Lynch

[J-Lynch 0]

This is the upper guide as fitted ! Notice the middle mounting hole has gone. The bolt was still fitted but the only thing it secured was the metal ring and a bit of plastic that should have been attached to the rail. Not surprising it made allot of noise.

[Kevin Bacon 5]

I could see it was still turning over, but each rev the chain was dropping slack between cam sprockets for a moment. It's like the rear camshaft is rolling forward a little, spring powered by the valve springs or something.

 

That happens if you crank it over without the tensioner bolt fitted, or if the tensioner bolt has failed and isn't pressurising.