Re:[alfa] Zat Tensioner Vs. Hydraulic in non-hydraulic mode

["David Jarman" <jarmanhome@xxxxxxx>]

Having owned a 24 valve 164LS from new for six years, I came away from the 
experience with some definitive thoughts on the timing belt tensioner issue 
(aka "detensioner", as originally applied to the 12 valve V6 cars).  To the 
point, I feel the hydraulic unit sans oil pressure is the way to go.  If I 
owned a Milano or GTV6, I would most definitely modify the unit to use only 
spring pressure.  This approach accomodates expansion, and if spring tension 
is adequate, provides a fairly constant tension value throughout the rpm 
range regardless of engine temperature.

Our 24 valve engine abruptly stopped at idle one day, awaiting a stoplight, 
with 17,000 miles on the clock.  The timing belt skipped several teeth, 
bending almost all the valves.  The OEM thermostatic tensioner had 
inexplicably failed, allowing this to happen.  All was repaired on warranty, 
of course, with a new profile belt and new tensioner installed.   All during 
our ownership of the car, I remained well plugged in to the ARDONA technical 
service bulletins and the 164 FAQ site, following the latest information on 
the issue so as to (hopefully) prevent a reoccurence.  I even researched 
similar 24 valve V6 engines of other manufacturers, checking out tensioners 
at parts counters to see how Honda, Nissan, Opel, Toyota and others 
tensioned their timing belts.  Results?  I didn't find one successful 
aluminum V6 engine which utilized a complicated thermostatically controlled 
tensioner such as found on the Alfa V6.  I even spoke to mechanics who had 
done scores of timing belt/tensioner jobs, and none of them had run into 
anything more complex than a basic, spring loaded belt tensioner.

My conclusion was that Alfa engineers had wrung their hands needlessly in 
the beginning over the issue of tensioning the timing belt, and I contend 
that the V6 (12 or 24 valve) needs nothing more than a spring loaded 
tensioner, such as the hydraulic unit with blocked oil pressure to the 
detensioning piston.  After all, why in the world should this particular 
engine require a precise belt tension at low and high rpm, in hot or cold 
ambients, when all that is clearly necessary is to maintain a range of 
acceptable tension on the belt at all times?  If you talk with any 
applications engineer from any of the manufacturers of industrial 
synchronous belt drives, they will confirm that a range of tension is all 
that is required, even for variable speed drive configurations.  Besides, 
any timing belt/tensioner I have ever changed out has used a simple, spring 
loaded tensioner, regardless of aluminum or cast iron block.

On the other hand, perhaps it was the less-than-brilliant design decision to 
drive the oil pump externally, using the timing belt, which robbed the left 
bank cam sprocket of sufficient arc of belt contact, which in turn gave rise 
to the need to more precisely control the tension on the original SOHC Alfa 
V6!  We will surely never know the answer to that one, and if I were an Alfa 
power train engineer of that era, I certainly would not drag that skeleton 
out of the closet, either!   AFRA once assured me that there had never been 
a new part number, nor concurrent design change, to the 164 series 24 valve 
timing belt tensioner since introduction.  Amazing...

It was significant to me that, beginning with the introduction of the 
156/166 series, the V6 oil pump was driven internally as it should have been 
from the beginning, and the belt tensioners were completely redesigned.  
What I repeatedly asked for at the time, but never heard from our Alfisti 
friends and contacts abroad was whether or not those changes reduced the 
incidence of belt and/or tensioner failures.

David Jarman
Lexington, KY
'91 Spider
'94 Spider
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