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How-to: Check cam timing

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).

- 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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