Belt tensioning

[Paul Fraser]

I need to take off my belts next time I'm home to put on a belt to the aircon condenser on the 928, so I bought this gadget:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=160016851642&sspagename=STRK%3AMEWA%3ABIN

Probably reinventing the wheel, but FYI. Will post more once I get it.
PS He's got some useful web pages about 944 cam and balance belts as well.

 

[Hilux]

Personally I never can quite understand the 944 belt tension issue. I`ve built many an engine and always used the 90 degree twist method as a check regardless of pre sprung tensioners.

IMHO if the belt snaps (unlikely if changed as required opr unless oil contaminated) thats one thing but to jump a tooth or two requires the belt to become loose or stretched by miles. To stretch one of these belts to that extent means that it was over tensioned in my opinion.When you see how tight they are and measure the pitch its impossible to see how any belt can stretch that much. Much more likely is a loose belt `chattering` prior to the toothed pulley on the longest part of the run then jumping a cog or the mileage is considered as indication of age wheras time is also important.

Auto2000 have given up retensioning belts (unless asked) as they have never ever found one that after 1-2 thousand miles if fitted correctly needed it doing.

 

[TTM]

ORIGINAL: Hilux
I`ve [...] always used the 90 degree twist method as a check regardless of pre sprung tensioners.

Same here.
The spring that preloads the late 944 tensioner actually seems to apply the right tension on the T-belt as it can be twisted just 90° when the two bolts on the tensioner are untightened.
Once the two bolts are tightened the spring should not "work", suggesting it should not even soften with use/age ...

 

[tref]

I held a conversation with a member that tensioned his 944 T belt by the 90 degree twist method... then later in the same conversation told me how he rebuilt his cylinder head after the belt snapped.

The actual fitting the belts is no different no matter how you set the belt tension, so why not have the peace of mind of ensuring that it is objectively rather than subjectively measured?

Correct balance belt tension is very slack, I certainly couldn't get it right without some form of measuring device, and yes, I use the 90 degree twist method on pretty much every other car I have ever owned.

Over tensioning risks damaging bearings. Undertensioning risks damage from whip - Porsche modified the engines very early on to include a guard to limit this, presumably even at the correct tension.

The correct tool is also available from the club, and there are a few aftermarket ones about that could be calibrated against the official tool. I believe the one mentioned at the begining of this thread is well thought of.

Regards,

Tref.

 

[chris_boyle33]

I've only had to fit new belts to my '83 lux once. It doesn't have the belt tensioner thinggys the later models have. I've got to say i agree with Hilux here - the teeth on the belt are so massive I can't see it hopping anywhere easily.

I used the 9201 thinggy and was suprised how slack the belt was meant to be. I'll probably use the same tool next time too as its from the club and costs virtually nowt to loan. But if it wasn't available I doubt i'd be too upset.