[T3] 72 FI timing question

["Jim Adney" <jadney@vwtype3.org>]

As Mike and I were finishing up our marathon engine swap, I got to 
the point of checking the timing. The 72 FI requires a different 
timing process because of the vacuum retard which its distributor 
has, but my question is:  

What is the timing supposed to be set to? (with vacuum hoses off, 
idle speed adjusted properly)  

The sticker ON THE ENGINE (original, from VW) says 5 degrees 
A.T.D.C. There used to be a separate sticker with a picture of the 
pulley, but this has disappeared.  

Bentley, and Without Guesswork say 5 deg B.T.D.C. and have 
pictures that are consistent with this.  

If I study the distributor advance curves carefully I find that it 
appears that all the advance graphs are given in distributor shaft 
degrees and RPM, while the chart for the 72 cars appears to be in 
crankshaft degrees and RPM. If I compare the 72 and 73 data 
presented there, it looks like all this is consistent with timing both 
to 5 deg BTDC.  

I have not checked my Haynes. I also need to look in the owner's 
manual to see if it has anything about this.  

Everything about this appears to indicate that the factory sticker is 
just wrong. The only thing I can think of is that either VW meant 
something different by the A in ATDC (like Ahead, or Advanced) or 
that it was just a bonehead mistake. This engine came out of a 
VERY early 72 production car, so I wonder if it is possible that VW 
corrected this mistake later.  

I'd love to move the timing from 5 deg BTDC to 5 deg ATDC as this 
would make for much better power and fuel economy, but this is 
such a big change that I'm reluctant to make it unless I'm sure that 
it won't damage something. The only way it could hurt something 
would be if I'm wrong about the 72 distributor charts in the Bentley 
manual being in crankshaft degrees and RPM. If I have to double all 
of these numbers, then this would result in too much advance.  

Russ, do you remember what you timed them to? The 72-3 pulleys 
have marks  |   |   | |, which are at -5,0,5,7.5. Is the correct mark 
the left mark or the 3rd from the left?  

Does anyone else out there have a 72 FI engine with the original 
sticker still on it? If so, I'd love to hear whether yours says ATBC or 
BTDC.  

Mike is happily back on the road, but he's going to call me in a 
couple of days to see what your verdict is. He has the tools to 
change all this on the road if it looks like a good thing to do.  

BTW, I've torn down his old engine part way and found a couple of 
things:  

The upper control rod for the air flaps had fallen out and wasn't 
doing anything.  

The metal air covers over the spark plug wires were both missing, 
so most of his cooling air was spilling out there.  

The metal cooling tin that guides the air on the underside of the left 
fan outlet was bent and fallen out of place, so the left bank was 
running even hotter. You may remember that his left spark plugs 
were running hotter than the rights. There were quite a few of the 
small cooling tin screws missing, so that they were poorly sealed.  

Keep in mind that this was not Mike's doing, he was just dealing 
with a typical engine rebuild/carb conversion coming from someone 
that didn't know type 3 engines well enough.  

thanks, and please let me know about the timing question....  

-
Jim Adney
jadney@vwtype3.org
Madison, WI 53711-3054
USA

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