Noisy belts

[knightma]

I've recently changed the camshaft and balancer shaft belts on my S2 and notice the belts are noiser than before. They now make a wirring noise. I know it's not the alternator or power steering pump belts because I've since removed these and it made no difference.

The camshaft belt has the spring tensioner design. The manual states for the older manually tensioned engines they should be adjusted to 4.0 +/- 0.3 when new or 2.7 +/- 0.3 when old. It appears the manual doesn't quote a tension value that results from the spring tensioner but presumably it is close to 2.7, hence the requirement to re-tension after a few hundred miles. When I fitted the belt I rotated the crankshaft a couple of turns clockwise with the spring tensioner unclamped to remove any slack from the non-tensioned belt run between the crackshaft and camshaft. The spring tensioner was then clamped.

I don't have a belt tension gauge so the balance shaft belt was tensioned so that it felt similar to the camshaft belt. The manual states 3.5 +/- 0.5 for an 18mm balancer shaft belt. The idler roller clearances were then carefully set in accordance with the manual.

If the camshaft belt spring tensioner does result in a 2.7 tension value for the camshaft belt then maybe I've not put enough tension in the balance shaft belt. Does anyone know whether this wirring belt noise is a sign of an under tensioned belt? Also could I start the engine without the balance shaft belt in place to isolate the noise without doing any damage? As it only runs the balance shafts I think it would just result in a little more vibration and nothing else, am I right?

 

[SteveSJS]

Talk to Jon Mitchell - but I believe your balancer shaft belts are too tight.
Happened to mine when done by a local garage here in Cornwall - JM talked their guy through the procedure and everything then went quiet.
AFAIK they should be rather less than the Cam Belt - but do get some fully qualified advice.

HTH

SteveS

 

[berg944]

I believe your balancer shaft belts are too tight

I agree,

Unlike most cambelts that can be adjusted to 90' twist on the belt, the balance shaft belt could be twisted 180' when set with a gauge.

I don't believe you can over adjust a cambelt with the spring tensioner but they can stick.
I would not recommend turning the engine over with the adjuster loose as there is no ratchet, so no point!
set it correctly, tighten, turn the engine over and test again.

 

[knightma]

ORIGINAL: berg944

I would not recommend turning the engine over with the adjuster loose as there is no ratchet, so no point!
set it correctly, tighten, turn the engine over and test again.

The point is that the spring tensioner does not have enough force to turn the camshaft or crankshaft so if the tensioner is clamped without turning the crankshaft first there is a very loose section of belt between the crankshaft and camshaft which will mean the overall tension ends up far too loose. It's acheiving the same as what you say in the second sentence above, if what you mean by "test again" is unclamp and then re-clamp the spring tensioner after turning the engine over.

 

[carlmthompson]

My belts went quite noisy when I had them tensioned a couple of years ago (local specialist Tom Ferguson who is well versed on 944's and older Porsches here in Newcastle)
The noise died away after a few hundred miles of use.

 

[berg944]

spring tensioner does not have enough force to turn the camshaft

Move the tensioner with one hand while checking there is no slack with the other hand, let go and tighten up.

You need to check tension with the cam timing 1 1/2 teeth anticlockwise, but don't turn the crank pulley anticlockwise or the tension is on the wrong part of the belt!

Mike[:'(]

 

[knightma]

ORIGINAL: berg944

You need to check tension with the cam timing 1 1/2 teeth anticlockwise

Mike, thanks for the reply but I don't know what you mean by the above. Please can you elaborate, 1 and a half teeth anticlockwise of what?

 

[berg944]

I think you should set your tension again before running!

Tension is not set at TDC but 10' anticlockwise on the camshaft (1 1/2).

Get all the timing marks aligned then turn the cam pulley anticlockwise 1 1/2 teeth, this will keep the tension in the correct place.

If you try to set tension at TDC the valve springs will put tension in the wrong place on the belt.

http://www.clarks-garage.com/ Go to Garage shop manual and Read section on camshaft timing.

Mike[:'(]

 

[knightma]

ORIGINAL: berg944

Tension is not set at TDC but 10' anticlockwise on the camshaft (1 1/2).

Porsche state in their manual that the spring tensioning procedure is carried out at TDC, still what do do they know!

 

[berg944]

Porsche state in their manual that the spring tensioning procedure is carried out at TDC

Good job you were wise enough to realise it was wrong.

I learnt the hard way with a manual tensioner. I did not replace the adjuster stud, also not mentioned in the manual. Belt tension was perfect .........right up to the moment the stud broke[]

Mike[:'(]

 

[knightma]

I think it won't make much difference what position the engine is in when the tensioning procedure is carried out. What will make a difference is how much tension is in the belt between the camshaft and crankshaft when the spring tensioner is clamped (I realise this will to some extent depend on engine position due to valve spring loads on camshaft lobes though). As these two shafts don't turn freely due to friction, the tension in this part of the belt can be set independently of the spring tensioner section. If this section is pulled very tight the overall belt tension will be on the tight side and vice versa. This is where I require some helpful advice, during the spring tensioning procedure, should this portion of the belt be pulled tight (and if so how tight) or just be set with zero tension (but no slack)?

 

[sawood12]

Surely if you overtighten the belt the tensioner can't un-tension the belt to the correct tension can it?

 

[berg944]

when you turn the camshaft 10' (plugs out) then let go, the only tension on the belt will be the friction from the crank (very little).

After locking the adjuster check with a belt tension tool.

Mike[:'(]

 

[knightma]

Thanks Mike, I'll carry out this procedure, I don't have a belt tension gauge so I'll just trust the spring tensioner gives the correct result.

Any advice on tensioning the balance shaft belt? How should the tension compare with the cam belt? The manual states 3.5 gauge units (compared with 2.7 for the spring tensioned cam belt) but at that tension there is no way I could rotate it 180° with my fingers. In fact to rotate it 180° the belt would actually need to be loose. I'm a little confused as everyone is suggesting the balance shaft belt should be looser than the cam belt but this is not what any of the manuals are saying (Porsche and Clark's garage).

 

[berg944]

The balance belt is slacker than any cam belt I have done, this is probably your

wirring noise

I think you should hire the clubs belt gauge, using new belts with appropriate manual settings.

let us know how you get on.

Mike[:'(]