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Problem: Broken timing chain tensioner

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timing chain problem "Cullen Foresman" <csf01@msn> Thu, 1 May 2003 16:07:42 -0700
Re: [gti-vr6] timing chain problem "Bob Tillman" <bobt@p-vector> Thu, 1 May 2003 19:48:24 -0400
Re: [gti-vr6] timing chain problem "Cullen Foresman" <csf01@msn> Thu, 1 May 2003 21:28:17 -0700
Re: [gti-vr6] timing chain problem "Bob Tillman" <bobt@p-vector> Fri, 2 May 2003 01:34:17 -0400



From
From: "Cullen Foresman" <csf01@msn>
To: <list@gti-vr6>
Subject: timing chain problem
Date: Thu, 1 May 2003 16:07:42 -0700
 
About a week ago my '98 gti-vr6 almost died while I was driving right
as I shifted and ever since I haven't been driving it because it
has been making what appeared to be really bad timing chain noises,
as well as having a rough idle and obviously reduced HP.  So today
after exhausting every simpler possibility (and discovering I needed
new plugs and wires in the process) I finally pulled the valve cover
and found I could move the top chain about 1.5 cm with my finger.
It doesn't seem like that's enough slack in the top chain to be causing
as much noise and performance loss as I'm experiencing, but I've never
worked on a DOHC before. I haven't checked the bottom chain yet (any
advice on how to do that?).  I ordered a Bentley manual but it won't be
here for another week or so and I want to get my baby running as soon
as possible so I'd appreciate any specs or anything any one might be
able to provide. Does anyone know about this or has anyone experienced
this type of timing chain problem in a distributorless vr6?Get more
from the Web.  FREE MSN Explorer download : http://explorer.msn.com



From
From: "Bob Tillman" <bobt@p-vector>
To: "Cullen Foresman" <csf01@msn>, <list@gti-vr6>
Subject: Re: [gti-vr6] timing chain problem
Date: Thu, 1 May 2003 19:48:24 -0400
 
Hi Cullen -

If all you did is take off the top (plastic) valve cover, you should *not*
be able to move the timing chain at all with your finger!  It sounds like
the upper tensioner has failed, perhaps.  You're correct in not running the
motor!  It's possible that the cam chain has skipped a tooth or more.

The upper tensioner "shoe" is pre-loaded by a spring-loaded plunger in the
form of a large bolt which screws into the back of the upper timing chain
cover.  It looks like a fairly large bolt (19mm? 21mm? Don't remember the
exact size) with an aluminum crush washer under it.  You can try removing
that, and see if the tip of the spring-loaded plunger still works OK.  It's
conceivable (but unforunately not likely) that that's the only thing that's
wrong; if so, you've lucked out because that's the only component that's
easily replaceable.

However I'd recommend that you at least take off the whole upper timing
chain cover to have a look.  You'll have to remove the coil pack and un-bolt
the aux coolant pump bracket, as well as the tensioner "bolt" mentioned
above.  The cover is held on by a number of allen-head bolts on the side of
the cover, as well as two easy-to-overlook allen-head bolts that screw up
from the bottom.  Once that cover's off, you can have a look at the upper
chain and the tensioner shoe.

Unfortunately replacing the upper chain and shoes requires removal of the
tranny, clutch, and flywheel!  It goes without saying that the getting at
the lower chains/tensioner/shoes requires removal of the
tranny/clutch/flywheel too.

Such an operation is not for the faint of heart!  I'll leave it to you to
decide how deep you want to go on your own, vs. taking it to a mechanic.

Good luck,
- Bob T.
  '96 GTI VR6 (been there, done that ed.)



From
From: "Cullen Foresman" <csf01@msn>
To: "Bob Tillman" <bobt@p-vector>, <list@gti-vr6>
Subject: Re: [gti-vr6] timing chain problem
Date: Thu, 1 May 2003 21:28:17 -0700
 
OK, so I removed the upper timing chain cover and remarkably everything
that I could access seemed to be in remarkably good condition,
including the tensioner "shoe" which has virtually no visible wear
and the chain itself (although I don't really know what to look for
to identify a bad chain, there where no obvious problems), even the
spring-loaded/hydraulic bolt device that actuates the upper chain
tensioner still has some spring in it, but it is very easy to push
in the spring and I could effortlessly screw it in/out by hand once
it was initially broken with a wrench.  I suppose I shouldn't have
expected too much damage seeing as that the car only has 60,100 miles
and based on what I read in the archive timing chain problems don't
usually tend to show up until at least 100k or so.

So now I just need to find out whether or not the spring loaded
bolt/plunger thingy is broken, it seems that it would need to be
much stiffer in order to properly tension the chain.  Hopefully its
shot because if that isn't the problem I can't imagine what is.
Has anyone else heard of these going bad this early?



From
From: "Bob Tillman" <bobt@p-vector>
To: "Cullen Foresman" <csf01@msn>, <list@gti-vr6>
Subject: Re: [gti-vr6] timing chain problem
Date: Fri, 2 May 2003 01:34:17 -0400
 
I've never heard of the tensioner bolt going bad, but I'm sure it's
possible, and that does indeed sound like the problem with your car.  I'd
say go to the dealer and get a new one.  While you're at the parts counter
(before you pay for it;) try to depress the plunger on the new one.  I'm
guessing that its a *lot* stiffer than your old one - if so, pay the man and
fix your car. ;)  Don't forget to get a new crush washer for it too.

I think the Bentley has a procedure for "bleeding" it too, as it's fed by
pressurized oil.  Don't know if that has any effect on its "springiness".
I'll have a look in it tomorrow, if you'd like.

And I'm sure you're already thinking it, and I'll confirm it: you'll have to
check the cam timing before you button it up too.  It's easiest to do
*before* you re-install the upper chain cover.  There's a special tool that
VW has for checking the timing, but you can probably use a piece of an old
wooden yardstick or something about that thickness to fit into the slots
machined intob the ends of the cams opposite the sprockets.  Here's what I
recall of the procedure:

- Turn the crank to Cyl #1 TDC.  #1 is the furthest *left* as you're looking
at the engine from in front of the car (furthest from the transmission).  I
don't recall offhand if it's the front bank or the rear bank, but you should
be able to determine by eye which one is on the end.  I do a rough TDC
measurement by pulling out spark plug #1 and sticking a long screwdriver in
the plug hole to "feel" when the piston is at TDC.  Use a large wrench on
the nut on the crank pulley (I want to say 24mm, but I'm probably wrong) to
turn it.  When doing gross crank movements, always turn in proper engine
rotation (it happens that it's the same direction as the wheels would turn
when the car moves forward).

- Once you have rough TDC, do the fine alignment.  There should be a rubber
plug on the top of the bell housing; pull out that plug, and do the old
"line up the pointers" trick (a "pointer" stamped into the clutch housing
should line up with a "pointer" cast into the bell housing at TDC).

[ Here are a couple of pics of aforementioned rubber plug:
Pic 1
Close-up
]


- Check the slots in the ends of the cams.  They should be exactly parallel
to the machined horizontal surface at the top of the head.  Note that the
slots don't exactly pass through the centerline of the cam; they should be
turned so that they're slightly *above* the centerline.  If they're *below*
the centerline, turn the crank one full revolution and realign TDC.

- Now you should be able to slide a piece of wooden yardstick (or the VW cam
alignment tool if you've got one!) into the slots in the cams, and it should
be parallel to the top machined surface of the head.  When doing this check,
make sure that all slack in the chain is at the *tensioner* side, and that
the front side is taut.

- Now, reinstall the upper chain cover and thread in your new tensioner bolt
(and crush washer).  Remove the alignment tool from the cam slots, and turn
the crank two full revs.  Align TDC, and re-check cam timing with the
alignment tool.

BTW the Bentley specifies a specific adhesive to use when installing the
upper chain cover.  You could probably use some kind of Permatex RTV-based
gasket sealant instead.

If you do need to change cam timing by a tooth or so, it's best done with
the top chain cover removed (which means the tensioner bolt is removed too).
It's not totally necessary to remove a cam sprocket, as you *can* wrestle
the chain by a tooth at a time if necessary with the sprockets installed, as
long as the tensioner isn't loaded.

Good luck!

Cheers,
- b



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