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

[Joe Elliott <jee@xxxxxxxxxxxxxx>]

When people say that the Zat tensioner is fixed, they mean FIXED. 
(It is, of course, manually adjustable.)  It doesn't provide constant 
tension on the belt, it keeps the tensioner pulley in a constant 
position.  This means that as the engine expands, all the pulleys 
move away from each other and nothing compensates for this.  While it 
seemingly works, the belt is extremely tight on a hot engine, and (at 
least in one case!) floppy-loose on a cold engine.  This is rather 
unsettling on an engine that was originally equipped with a dynamic 
tensioner, presumably for a reason.

A non-hydraulic hydraulic tensioner, on the other hand, is "fixed" 
only in that it applies a roughly constant force on the belt.  It's 
still free to move when the engine expands and contracts, with the 
tensioning force provided by two springs.  Disabling the oil feed 
only prevents it from reducing the tension based on engine speed.

In lieu of having both tensioners in front of you, here are some 
pictures.  Image A shows the hydraulic tensioner.  The approximate 
path of the belt is shown in yellow.  The position of the tensioner 
pulley can change because the green part, upon which the pulley 
rotates, can pivot about the red cross.  It should be apparent that 
pressurized oil in the shaded red region will force the piston (blue) 
up, thus slackening the belt as oil pressure rises (in proportion to 
engine speed).  The belt tension is provided by two springs, one of 
which is highlighted in light lavender, the other of which is 
expertly illustrated in a darker lavender.  By disabling the oil 
feed, you no longer have pressurized oil in the red region, but you 
still have a dynamic, spring-loaded tensioner which can move to 
accomodate thermal expansion (and contraction) of the engine.  Image 
B shows the portion of the Zat tensioner that you buy from Tom Zat. 
You have to use the pulley and the green part from your old hydraulic 
tensioner.  Again it pivots about the red cross.  The position of the 
pulley is fixed by the bolt, highlighted blue, which you adjust upon 
belt installation to get the desired (cold) tension.
A) http://www.andrew.cmu.edu/user/jee/tensioner.gif
B) http://www.andrew.cmu.edu/user/jee/Staybelt.gif

Joe Elliott
'82 GTV-6



> This is mostly a question for Joe, but I figured I'd throw it out there for
> all to comment on.  Like Joe, I've reverted back to running the "old"
> hydraulic tensioner but in a fixed, non-hydraulic fashion.  I've been
> running this way for years now without issue.  When I first made the change,
> I was told it basically made the tensioner function like the Zat one.  I
> took it at face value and readily admit I didn't give it much thought.  I
> had just witnessed a 500-mile race engine destroyed by an equally new
> mechanical tensioner failure, and I was very interested in deploying an
> alternative solution.
>
> Joe now points out with some conviction that running the hydraulic tensioner
> in non-hydraulic mode as we do is a much better solution than the Zat
> tensioner.  I'm happy to hear that, but I'm not sure I fully understand why.
> Mind you, I've never seen the Zat tensioner.  I imagine with both of them in
> front of me, it would be a self explanatory, or a 30 second conversation at
> best.  Given that's not a reality, I'd be interested to hear in greater
> detail why this is.
>
> Signed,
>
> Curious George :)
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