[alfa] V6 hydraulic tensioner

[Olga Immel <immels@xxxxxxxxx>]

I recently reverted to the oil-fed hydraulic tension on my 1991 164b. 
(There is not one flat spot on my driveway and I was worried about 
possible belt slipage if the car would roll backwards while in gear).  
Before doing the operation I read what seemed like reams of paper on 
the subject.  The beauty of the oil-fed tensioner, in my opinion--and I 
say this based on my observation of the tensioner and belt while the 
engine was running at various speeds--is that it "applies" a very 
important viscous dampening effect to the adjusting arm.  If you 
recall, this tensioner has a pretension spring, and a regular one, both 
rated at 22lbs.  The pretension spring  (also in my opinion) basically 
deals with the problem of a new belt: within days the belt will stretch 
(not to mention in 30K miles), as anything made of rubber and thread 
will do. So, in effect, that pretension of 22lbs disappears pretty 
rapidly.  This is why Fred Di Matteo recommended setting the tension of 
a new belt so tight so you could "strum" on it. Now this is where the 
regular spring does its thing, from day 2, to day 730. Many people have 
pointed out the various (and contradictory) effects of "tight" and 
"loose" spots in the moving belt, thermal expansion, and changes in the 
viscosity of the oil, but no matter the scenario, the one thing that 
the oil-fed tensioner will have is a dampening effect (it can't change 
the 22lb of pressure of the spring, it simply gives it a steady hand).  
Now to my observations: at idle, when the dampening effect is the least 
(with warm engine and thin oil) the hydraulic rod/mechanism tends to 
move a lot, with the 22lb spring "adding" tension when the 
moving-flexing belt requires it.  At 3,500 rpm the "jumpy" movement of 
the rod now smoothed out--the power of hydraulics.  At faster speeds 
even more so.  Despite the problems of possible oil leakage with age, I 
maintain that the oil-fed tensioner is an excellent and novel design 
which and adds stability to belt tensioning that no other design can 
do. And anyone who compares the quality of the casting of the units 
(Alfa versus cheap modern replacements,  (including Zat, which I have 
also used) will conclude that you are much better hands with the 
original Alfa design (again my humble opinion).  --Steven Immel
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