Old style 5kq 'round' TB seized

[Bares, Vittorio]

All very good questions - and yes, I'm surprised at the failures as
well. The 2nd TB, I got from a lister, don't know very much about it -
but seemed to be just fine when I got it - have no reason to believe
otherwise.

What we are theorizing is potentially that severe heat from the turbo
and the manifold might be contributing to the failures. We were running
excessively lean to the point where the exhaust manifold was glowing
red. We believe the lean issue was a combination of the bad bearing in
the TB and a bad fuel pump setup.

I've spoken to a few other folks about this and I'm getting pretty much
the same answer - need to find a good TB (I think I'll disassemble and
lube prior to r&r).

When we took the shaft out of the TB, the needle bearings were all
rusty, there was wear on the shaft also. After some PB blaster, the
movement improved significantly - and yes there was a sudden pedal feel
change just before it seized.

So, while we're at it - I setup a dual/redundant fuel pump setup - each
pump being on a separate circuit and relay. However, with the assumption
that the check valves on the pumps would prevent back flow into the
non-running pump, all I did was 'T' from the gravity feed to the inlet
of each pump and then put the outlet of each pump also to a 'T' and into
the fuel filter. From your collective experience - should the stock fuel
pump check valves prevent backflow?

Vittorio -
 
-----Original Message-----
From: Louis-Alain Richard [mailto:laraa at sympatico.ca] 
Sent: Tuesday, May 27, 2008 9:59 PM
To: Bares, Vittorio; quattro at audifans.com
Subject: RE : Old style 5kq 'round' TB seized

Vittorio,

It's funny since I dismantled my round TB (stock WX engine from an
urQuattro) no later than last week. Indeed, there are needle bearings
but
mine were in good shape even if the car is an 1983. They are press fit
in
the TB, so rebuilding would need special tools but it is not impossible.

Let me ask you one stupid question. Are you sure the bearings were
faulty ?
There is, at least on my WX, 3 strong return springs so for a bearing
seizing so hard that it wouldn't move under all that backforce, it
surprises
me a bit. You should have felt it in the gas pedal before, unless you
are
really "lead footed"... :-)

In fact, a few years ago, one of the bolt of the air temp sensor on the
top
of the intake came loose and stuck the throttle partly open (while
stopping
at a red light !) I too looked at the TB itself, just to discover the
small
bolt preventing the complete closure of the butterfly. It is amazing
that
such a small angle of the butterfly can produce so much (unwanted)
power. 

To answer your original question : the easiest route would be to find a
known good used unit. And then, find the reason they fail (gas pedal
that as
no stop so all the driver's force is transmitted to the TB ? Bent shaft
?
Mud accumulation ? An old girlfriend that pour acid on your engine at
night
? Genuine bad luck ?...)

Oh finally, check if the springs are correctly installed. On my first
attempt, I thought I was right, but the return force was too weak, so I
checked another one I had and indeed, installing all the bits in the
correct
position demands good eyes, fine fingers, and patience. Now the cleaned
one
is very firmly sprung back on its stop and its motion is well
lubricated. I
can send you pictures if yours is similar to a WX unit.

Louis-Alain



> -----Message d'origine-----
> 
> Hi - we had a throttle stick wide open on the rally car this weekend -
> luckily it was the last thing that happened *after* we got her on the
> trailer.
> 
> Discovered that each end of the butterfly shaft has a needle bearing
on
> it. One of them seized right up and would not allow the shaft to turn
> freely. I believe this may have been the issue in a previous TB I had
as
> well...
> 
> Now, my quandary is what to do next - I can go buy another TB, but
that
> one is also going to be 20yrs old - and potentially have the same
issue.
> Can these be rebuilt? If so, does anyone have any leads? If not, any
> recommendations on what to do next?
> 
> Thanks,
> 
> Vittorio -