164 ABS Fixed!, Head Rebuild Next?

[Talfieri61@domain.elided]

Hello All, and Happy New Year!

I am new to the discussion forum, although I have benefitted for some time 
now from the archives and ongoing echange of ideas.  Thank you all for your 
valuable comments.

Two years ago I bought my 164L in somewhat ragged shape from a car lot.  It 
had many electrical problems and a few unpleasant aesthetic defects, but it 
was mechanically sound and had no major body damage.  I got what I consider a 
good deal -- I don't think the dealer knew what they had, or at least didn't 
appreciate it.  I have taken the car on a few road trips, and have been 
steadily restoring it. 

I finally fixed all of the electrical problems, the most difficult of which 
was the failing ABS.  Before delving into the problem, I knew nothing about 
ABS in general.  But with a background in electronics I figured I had a 
chance at diagnosing the fault. In an effort to understand the ABS, I opened 
the Bosch electronic control module and made a partial schematic of the 
circuit (input and output stages).  To keep this brief, I will just say that 
what I found was that it is critical for the signals coming from the 
electromagnetic wheel sensors to be of sufficient and equal amplitude for a 
given speed of wheel rotation.  If either of these conditions are not met, 
the ABS control module will disable the ABS after the car travels just a 
short distance, as evidenced by the ABS warning light coming on.

On my car, the signals coming from the rear sensors were weak -- especially 
the driver's side.  To increase the signal strength, I filed down the sensor 
mounting on the left-rear strut.  It was hard work.  I spent considerable 
time taking off just 1/32 of an inch, but it was enough to make the signal 
amplitide of the left rear equal to the right rear (observable with a digital 
oscilloscope).  I was disheartened, however, when I drove the car, and the 
ABS light still came on.  I then decided to see if I could increase the 
amplitude of both rear sensors to match that of the front sensors, which I 
found to be about three times higher.

Using a fine-tooth flat file, I fashioned two small square bars out of an 
iron nail - one for each sensor.  Then, I bonded these onto the tip of each 
sensor using JB-Weld epoxy (JB weld has iron in it).  With all four wheels of 
the car off the ground, I repeatedly installed the sensors and spun the 
wheels while measuring the signal.  I then filed the sensor tips as required 
to achieve the desired amplitude. When I finally achieved the same signal 
strength on the rear sensors as I had observed on the front, I found that the 
clearance between the sensor tip and the phonic wheel was about 1/16 inch.  
This repair did indeed restore the operation of the ABS.

One detail I did not mention was that I had also replaced the left-rear hub - 
not because of the ABS problem, but because the previous owner had left off 
the dust cap, causing bearing wear to the point that the wheel made noise and 
there had considerable play.  Had the hub not been replaced, I do not believe 
the sensor repair would have worked.  The signal from that sensor would have 
been erratic, and likely caused the control unit to disable the ABS, although 
for a different cause.  For this reason, if anyone is experiencing a similar 
failure, they would we well advised to check the condition of their hubs as a 
start.  I hope this helps someone.  If anyone needs more info, feel free to 
e-mail me.

My second topic is one in which I do not have much expertise, and would 
appreciate some feedback.  Some months ago the car began running rough.  It 
seemed as though one cylinder was not firing.  I tried various tests to try 
to diagnose it.  One thing I did was to disconnect each plug wire, one at at 
time and try to start the car, thinking that the engine would run 
none-the-worse when the bad cylinder was disconnected.  But the engine would 
no longer start once I began doing this.  Even after reconnecting all the 
plugs, it never started again.

I finally decided to start taking things apart.  With the six intake pipes 
removed and the fuel injectors disabled, I observed the valves while my wife 
turned the engine over.  I noticed with a great sense of dread that the 
valves on the back head were not fully closing.  I am wondering if somehow 
the cam on that head got out of sync and crashed the valves.  But the timing 
belt remained tight, and none of the teeth are missing.  In fact, both the 
tensioner and belt are fairly new.  Is it possible that somehow the cam 
pulley skipped position?  I remember that while turning over the engine I 
heard a loud pop a couple of times, but had no reason to think it was 
anything of consequece.

Whatever the case, I suspect that I will have to pull the head and have it 
rebuilt.  I did this operation on my Nissan a few years ago, but I'm not an 
experienced mechanic, and I don't know what to expect with the 164.   Here 
are a few rapid-fire questions:

       1) Can the rear head be removed without dismounting the engine?
       2) Do I need any of the special ALFA tools referred to in the service 
manual, or can I " improvise?"  
       3) Can any machine shop not experienced with ALFAs do this work as 
long as they have the specs, or is a specialist recommended?  Who?
       4) Where should I go for parts (valves, gaskets, etc.)?

I would appreciate any advice or pointers anyone can offer.

Thank  you,

Tom Alfieri
talfieri61@domain.elided
1991 164L

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