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Hydralic -VS- Bi-metal plate tensioners

 
Old 02-05-2008, 12:25 PM
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--JR--
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Question Hydralic -VS- Bi-metal plate tensioners

I've been encouraged to upgrade my old bi-metal tensioner to a hydralic one when I do the timing belt.

I'm a little relicatant because a mechanical spring plate I would think to be more reliable then a static hydralic cylinder. Plus my 78 doesn't have the wiring to show a tension light should a problem arrise with the hydralic one.

Looked in the last two years of tensioner topics and didn't see any disscussions on this.

Thought's?
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Old 02-05-2008, 12:30 PM
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The 'hydraulic' ones aren't hydraulic. They both use bimetallic washer stacks to set tension. The 'hydraulic' version just adds oil flow to the block for better lubrication and heat transfer.
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Old 02-05-2008, 12:38 PM
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Jim bailey - 928 International
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There is no oil flow...only the oil you pour into the tensioner after it is bolted to the block. And the oil in the tensioner with the o-ring just acts like a shock absorber to control flutter. All the 928 tensioners are mechanical and actually are "detensioners". The only adjustment they make is as the washers get warm it loosens the tension. That keeps the belt from getting tighter as the aluminum engine expands. When you set the tension bolt and lock nut it never changes. There is no hydraulic 928 tensioner.
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Old 02-05-2008, 02:30 PM
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Originally Posted by --JR-- View Post
I'm a little relicatant because a mechanical spring plate I would think to be more reliable then a static hydralic cylinder. Plus my 78 doesn't have the wiring to show a tension light should a problem arrise with the hydralic one.
If by 'hydraulic', you mean a sprung/damped tensioner, like on the Porsche 944/968, they are self adjusting. They automatically reset up or down to the ideal range of tension. Unfortunately, when they designed the 968 tensioner system, they didn't bother to redesign the tensioner for the GTS.

It's the stock tensioner which supplies (in practise) a static tension, which leads to overtensioning, and reduces the life of the gears, and water pump bearing. But, most often, trouble with the 928 tensioner system isn't because of the tensioner itself. It's the weakness in the design of the rest of the parts, ie: weak shoulder bolt, plastic bushings, long offset tensioner arm, pulley w/small bearing, etc., which lead to belt tracking problems or loss of tension. Because of problems keeping the tension constant between hot and cold, and new to old belt, Porsch kept adding idler pulleys to try and control the belt.

In any case, AFAIK, it's highly unlikely that a '78 would suffer any valve damage from a timing belt slip or break.
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Old 02-05-2008, 02:34 PM
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Porken

Do you still sell that timing belt tensioner setup that you made? Looks alot easier to use than the factory stuff.
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Old 02-05-2008, 02:50 PM
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928fan4life

As I am not a Rennlist 'sponsor', I may no longer promote any 'products' I may or may not make, nor include a link to any 'commercial' webpage in my signature, so as not to offend paying 'sponsors'.

I'm cool with that.
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Old 02-05-2008, 03:34 PM
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928fan4life..............there are quite a few of us on the North side that have the non OEM tensioner installed with great results.

there is a web site somewhere; oh yeah:

http://liftbars.com/
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Old 02-05-2008, 04:06 PM
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PorKen can't promote his site here, but what I can say is that there is a rather informative site out there that discusses a hydraulic tensioner for the 928. Go to yahoo. Type in liftbars.com and you will find a link with information.
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Old 02-05-2008, 06:37 PM
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Good to know! I hadn't heard anything in a long time about this tensioner and I am wanting one.
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Old 02-05-2008, 09:13 PM
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Ok, now that we've established that the hydralic one is really more like a shock and there are aftermarket ones available... I am most interested in knowing about stock 928 tensioners only. The diference between the oil filled and non-oil filled versions. Is one really any better then the other?

Should I be worried about "upgrading" from one to the other if I'm doing a front engine re-and-re?

Thanks in advance!
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Old 02-05-2008, 09:39 PM
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They are all oil filled. The later ones which have bleed ports, and can be re-filled are better.

Note that there are a couple different tensioners, with different offsets, and matching tensioner arms. You cannot mix and match. There are a few threads on this.
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Old 02-05-2008, 09:47 PM
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Originally Posted by PorKen View Post
928fan4life

As I am not a Rennlist 'sponsor', I may no longer promote any 'products' I may or may not make, nor include a link to any 'commercial' webpage in my signature, so as not to offend paying 'sponsors'.
I never said that, Ken.

I have no problem with you 'mentioning' your tensioner, as it does not compete with a similar product sold by a paying Sponsor.

So there.

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Old 02-05-2008, 09:54 PM
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If you say you didn't say it, then OK...you da boss. I thought it was 'an offa I couldn't wefuse'.

I'm still gonna keep it cool, so it doesn't look like I'm getting a 'free ride'.

Fuhgedaboudit.
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Old 02-05-2008, 10:19 PM
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Just an FYI I just installed the second porkensioner in an 87 5 speed, works perfectly right outta the box,

thanks again Ken.

Now I have to do the 87 auto.
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Old 02-05-2008, 10:26 PM
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I'vd said this before...........Kens product advances what Porshe designed in the mid '70s.

For any folks that have modern m/cycles look at how they do the same; and have done for many years.
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