[V8] belt tensioners

[Scott Simmons]

As I said in my T-Belt post, the derlin bushing was perfect, but I 
replaced it anyway.

I know they're independent, I was stating that it appears that both have 
two tensioning devices.  The serp belt has a spring loaded tensioner 
(like most vehicles) that's bolted to a shock that seems to press 
against the spring load.  I found this to be curious.

The timing belt has a shock-operated eccentric roller and a standard 
eccentric roller.  A lot of T-belts are tensioned simply by one 
eccentric roller or one shock-operated roller.  I found the fact that 
this vehicle has two tensioners for the T-Belt curious.

Just wondering if anyone else knew why.

~SS

Buchholz, Steven wrote:

>... the timing and serpentine belt tensioners are completely independent.  
>
>For the timing belt, the roller on the eccentric pivot is used to optimize operation of the dynamic tensioner ... you adjust the eccentric to establish the proper operating length of the spring/damper.  The dynamic tensioner acts on yet another roller.  BTW, when you did your TB I hope you knew to check out the mechanism of the dynamic tensioner.  There's a "friction piece" that should be replaced.  On #344 I almost lost the timing belt/engine because the pivot mechanism for the dynamic adjuster wore through and was not tensioning the belt at all.  Fortunately the 5-speed heads have pins near the cam pulleys to keep a loose belt from jumping teeth on the pulley!
>
>As far as I know both belt dampers are intended to resist motion in both directions.  If your serp belt tension appears to damp in only one direction it may be bad.  Same would go for the TB damper.  
>
>Steve B
>San José, CA (USA)
>  
>
>>It seems as if the V8 has two tensioners for the timing belt and two for
>>the serpentine belt.  For the T-Belt, there's two eccentric rollers:
>>the one on the right bank and the one attached to the shock.    For the
>>serp belt, there's the spring loaded tensioner but it's bolted to a
>>shock of its own.
>>
>>What gives?
>>
>>I've done a lot of t-belts on 944's.  The early ones had a simple
>>eccentric roller.  It was extremely easy to time and tension the belt.
>>If a pulley was one tooth off, it took about 10 seconds to correct.  I
>>had a cam one tooth off and I had to adjust so much just to get some
>>slack.  The later 944's and a spring loaded roller, but it was still
>>easier than this.  Never got too involved in a 928's belt, but I know
>>they're regulated by oil pressure (as are 968's).
>>
>>How does the T-Belt shock-and-roller combo combine with the other
>>eccentric roller?
>>
>>Why does the serp belt need a shock that seems to act opposite of the
>>spring tensioner?
>>    
>>
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