Can a leaking tensioner be the sole reason for loss of timing belt tension? - Rennlist Discussion Forums

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Can a leaking tensioner be the sole reason for loss of timing belt tension?

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Old 01-17-2012, 09:44 PM   #1
Captain_Slow
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Default Can a leaking tensioner be the sole reason for loss of timing belt tension?

The tensioner is leaking and possibly empty now. Because removing the timing belt is necessary to R&R&R the tensioner, I'll put in a Gates belt. The water pump and belt were replaced within the past 6000 miles. Don't know if the cam gears, rollers, etc. were replaced, or if any of these are contributing to the lost tension.

Thanks
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Old 01-17-2012, 10:06 PM   #2
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I believe it can be a factor. When I first changed my timing belt, I had to go back about 6 weeks later to adjust it, which is normal after the initial break in. About two months later the warning light came on again. I checked the level in the tensioner and it was too low. I filled it, and put maybe one or two turns on the tensioner. I never saw a warning light after that.

Check the fluid level first and fill it if necessary. Check the belt tension. Visually inspect whatever you can see with the cover off.
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Old 01-17-2012, 10:25 PM   #3
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Thanks JHowell,
I ask because searching the archives I found a lot of discussion about what whether the tensioner is truly "hydraulic", whether the oil is just a damper, heat transfer fluid, etc. One member wrote that they didn't have oil in the tensioner at all and it made no difference. But in my case the clean oil started leaking about two weeks ago but I wasn't sure from where. After some spirited driving this past weekend the oil loss increased. The tension warning light came on the following morning after start up. I turned off the motor, popped the hood, and found a lot of clean oil more to the front passenger side of the engine. The oil leak and the loss of tension coincide.
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Old 01-17-2012, 10:29 PM   #4
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Jon:

The belt tensioner is not hydraulic. There are bimetalic washers inside and the oil keeps them lubricated and transfers the heat.
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Old 01-17-2012, 10:50 PM   #5
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since you found a leaking tensioner 2 things can cause the leak a faulty boot clamp and a bad tensioner gasket.

So get these new parts, also i suggest to use Hondabond 4 on the new gasket ,
I know it has silicone ridges but it will soon be leaking if you dont use the hondabond.

Inspect the inner bimetallic washers for the correct position ref WSM

Then make sure to position the inner circlip on the new boot so the open end is pointing to the sky when its installed ,
install the tensioner then fill it with STP use a visene bottle with the tip drilled out, this prevents you from overpressuring the boot and blowing off the inner circlip.

If your waterpump isnt a new Laso I would replace it, reason being the WP if its a rebuilt you wont know it till the bearing slips again and then the belt will get loose,
I have replaced 2 in my car till I got the Laso.

I will bet you have a rebuilt pump.

Just loosing oil shouldnt let the tensioner turn on the light,

that said if you plan on keeping this car for 5 years start off fresh so you dont have to do this job again,
also make sure to replace the tensioner pivot arm bushings, Roger sells good tan versions as well as the new Laso pumps
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Old 01-17-2012, 11:02 PM   #6
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The oil acts a little like a shock absorber and helps dampen flutter BUT it does NOTHING for tension. Belts depending on the flavor stretch and when you romp on the motor with a somewhat loose belt the contact circuit for the "warning Light" may trigger.
However .." About two months later the warning light came on again. I checked the level in the tensioner and it was too low. I filled it, and put maybe one or two turns on the tensioner. I never saw a warning light after that." I can only hope that you ALSO checked the tension with a proper tension tool.
The "tensioner" is very misunderstood should actually be called a "slackener" as that is ALL it can ever do ! make the belt looser to compensate for the thermal expansion of the engine. The Bi-metallic washers get flatter as they get warm.
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Old 01-18-2012, 01:47 AM   #7
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Quote:
Originally Posted by brutus View Post
The oil acts a little like a shock absorber and helps dampen flutter BUT it does NOTHING for tension. Belts depending on the flavor stretch and when you romp on the motor with a somewhat loose belt the contact circuit for the "warning Light" may trigger.
However .." About two months later the warning light came on again. I checked the level in the tensioner and it was too low. I filled it, and put maybe one or two turns on the tensioner. I never saw a warning light after that." I can only hope that you ALSO checked the tension with a proper tension tool.
The "tensioner" is very misunderstood should actually be called a "slackener" as that is ALL it can ever do ! make the belt looser to compensate for the thermal expansion of the engine. The Bi-metallic washers get flatter as they get warm.
Excellent point.
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The longer I spend reading and seeing what people build and do to their 928s, the less I laugh these days.
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Old 01-18-2012, 01:49 AM   #8
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I have seen some notation about the tensioner being low on oil causing the light to come on. I'll look for this tomorrow.
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The longer I spend reading and seeing what people build and do to their 928s, the less I laugh these days.
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Old 01-18-2012, 03:19 AM   #9
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Low oil can allow more belt flutter, whcih can trigger a marginally-tensioned belt.

The 32-valve tensioners also use the movement from belt flutter to pump the oil around, getting the heat from the block into the tensioner (or "slackener" - that is truly the function) more quickly and ensuring that the oil in the tensioner doesn't cool off.
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Old 01-18-2012, 08:56 AM   #10
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or you could put a Porkensioner on there and this point is moot.
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Old 01-18-2012, 11:56 AM   #11
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Quote:
Originally Posted by jeff spahn View Post
or you could put a Porkensioner on there and this point is moot.
+1 : Thats what I did. My tensioner was toast and the guy that was the 'porsche repairman' wanted 2k to do the job. I did it myself < 500 in parts.
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Old 01-18-2012, 12:49 PM   #12
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Porsche says this in the MY83 Service Technique book:

"If the hydraulic damping fails because of insufficient oil, the toothed belt tensioning mechanism will function as the former system without damping."

That would seem to imply no great difference, at least with a properly tensioned belt. They also wrote:

"The different amounts of drive torque during a revolution of the camshafts produce oscillation in the toothed drive belt, which could cause belt flatter (sic) and in exceptional cases, when belt tightness is not sufficient, even a jumping out of the belt.

The new toothed belt tensioner has been designed to hydraulically dampen this oscillation in the toothed drive belt."

Now, oil was present in the earlier tensioner as well. It just did not have a hydraulic dampening function. AFAIK, Porche never stated what the purpose of the oil is, but most people suspect it may improve heat transfer to the washer stack. The washers are bimetalic conical washer that flatten in response to heat. This helps to maintain constant belt tension as the block and heads expand from heat. That part is covered by Porsche.

So, does loss of oil impede the temperature adjustment and overtension the belt? If so, does that actually stretch the belt or just accelerate wear on the gears from excessive tension? The belt is reinforced and designed not to stretch, but I did have one Conti belt lose tension progressively at about 25K miles, and it is true that my tensioner, like many others, was not retaining much oil at the time.
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Old 01-18-2012, 01:11 PM   #13
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Loss of oil is an epidemic. And, it causes at the very least what Bill points out above. But most tensioners also are damaged inside, meaning that the plunger does not slide smoothly along the inside of the tensioner body. This can effectively cause the system to permanently be unable to dampen vibrations.

As far as tension is concerned, NO, oil loss cannot realistically cause loss of tension. The factory tensioner is both a damper and a tensioner, two separate functions.
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Old 01-18-2012, 01:37 PM   #14
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If anything, lack of oil will make tension tighter as washers can't do their job properly when heat from block will not reach them.
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Old 01-18-2012, 02:35 PM   #15
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The very early slackeners are to be mounted with NO GASKET so heat tranfers from metal to metal contact of the block and housing. Later versions have a bleed hole to allow oil to contact the block and fill the open spaces in the webbing of the back of the housing which is why you must fill these after mounting to the block and use a gasket.
Liquids tranfer heat far better than air so the oil helps get heat to the discs faster. Porsche added the shock absorber disc when they added the belt tension warning light.
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