Belt tension

[vince944red]

I've a 944 2.5 86 NA registered Feb 86. Oval dash.
It has the water pump update kit and Gates belts, eccentric tensioner, no spring tensioner too early
I'm confused about the reference values for new belts tension on first install

If I look in the w/s manual it says one set of values - page 15.3 cambelt 4+/-.3 New, 2.7 used. Page 13.3 Balance belt 2.7+/-.3 new or used. It does not mention the new style belt 18mm width

If I look in clarkes garage he says a set of different values ( 4mm for camshaft with 2.7 when used (same as w/s man) and 3.5 for balance belts) he then gives 2.7 for the 15mm wide balance belt and 3.5 for the 18mm one with no values for 'used'

Also I read the balance belt always feels looser than the cambelt and should not be the same tension as the cambelt

Any wise advice? does the used balance belt have a 2.7 tension even if 18mm wide after 1000 miles?

The belts sound noisy ie whine but I believe thats always true of new belts and settles down after re-adjustment after 1000 miles?

 

[barks944]

I always use the 90 degree twist method for cam belt tension. I keep increasing belt tension until I can only just twist it 90 degrees. I increase the belt tension gradually as if you over tighten it will still bend 90 degrees from my experience. Me and my dad have done 3 cars and covered lots of miles like this and have never had a problem. I always do the balance belts by feel, they are much slacker than the cam belt. I don't put much tension on them at all or they get noisy. I can't really explain what I do here as its just my own preference.

 

[JamesO]

+1 on the 90 degree twist method myself, I have done 3 944 belts this way and had no problems. Although it's your car and your risk.

 

[ChasR]

AFAIK, the balance belt can be adjusted using feeler gauges via checking for clearances between the belt and the rollers.

 

[vitesse]

I used the 90* method on the 924S & yes the slight whistle of new belts on old pulleys does decrease over time,on mine because the new balance belt was the wide one replacing a narrow old one,so that part of the pulley had not been used before.
I was told that the balance belt is 180* quite a bit looser-can anyone confirm this figure as a good guide?

 

[ChasR]

I would personally never test the belt via 180 degrees. When I checked the belts on the new engine (they were a little tighter than the belts on my old engine (not surprising considering the belts on the old engine were 5 years old and had over 20,000 miles on them)) I could barely turn the cambelt through 90 degrees, with the balance belt just beginning to tighten up at 75 degrees (these belts were changed however).

As said though, I don't recommend sorting the belts out this way. The feeler gauge method is something quite a few specialists use and what a number of enthusiasts do too I believe. I'll need to dig up the figures from somewhere. Hell, I even remember there being a diagram showing where to check!

EDIT: It seems I have yielded some information. But if you are really stuck, just take the slack out of the balance belt, and take it to a specialist for them to check it (doesn't take long at all).

http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/404963-remove-crank-pulley-replace-cam-belt.html

 

[vince944red]

Answering my own questions:

http://www.rennbay.com/belttutorial.html
was good enough for me! thanks for the twisting advice, as pointed out its very imprtant the twist is not taken as correct tension as overtight also gives the same twist pretty much, you have to do it as you increase the tension in steps from too low towards teh right tension, so importna tno to delude yourself you are right for an engine you've not set up yourself