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

["DAEGRIGG" <daegrigg@xxxxxxxxxxx>]

Dave,

Thanks for an excellent post.  After two bad mechanical (de)tensioner
experiences, I came to the same conclusion that "simple" works in this
application.  I modified a mechanical tensioner to bypass the spring and
apply a constant tension.  It works and that was 30,000 miles ago.

I read many and many well informed post on the digest.   The "correct"
adjustment procedure for the mechanical tensioner has been discussed ad
nauseum.  To me, it is clear that Alfa made complex what most other
manufacturers made simple - successfully.

Don

----- Original Message ----- 
From: "David Jarman" <jarmanhome@domain.elided>
To: <alfa-digest@domain.elided>
Sent: Saturday, September 18, 2004 9:38 PM
Subject: Re:[alfa] Zat Tensioner Vs. Hydraulic in non-hydraulic mode


> 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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