GregBBRD

Only one way to find out. Run it and see.

ROG100

Hi,
Just got back to Minneapolis from the far North of ND and was able to log on.
I wonder what the 944 guys do with their RTB?
I will also talk to Gates and see what they have to say.
Roger

M. Requin

Ah ha! I didn't know there is a calibration standard for the 9201. That makes my comment irrelevant. On the AF thing, I'll have to do some digging, but I think the values are available. And again, if you take a look at the theory of the frequency of a vibrating string, you might be surprised at what does, and doesn't, affect the frequency of vibration. Thanks for the info.

danglerb

If the racing belt doesn't stretch, maybe the safe operating window is a slightly lower amount of tension? Likewise higher levels of tension might pose more of a hazard, also pointing to shifting the tension range lower.

I don't think its likely to slip a tooth or break, but there may be situations where the tension could be great enough to damage other parts of the system.

Given the unknowns I think I would like to see how well it works on a noninterference motor and with a porkentensioner, before using it on a interference motor.

danglerb

Its not a unique type of tool, same sort of thing was used in old tape drives and all sorts of other applications to measure tension. The calibration is with metal strip with a known spring value, but that would not compensate for changes in the belt characteristics. Its a calibration of force vs deflection, no way to know how much of the force is from belt stiffness and how much from tension.

jon928se

Re -read my earlier post.

Keep the extremities of the belt straight (as if it was tensioned) then use the 9201 in the normal way - that will give a reasonably accurate indication of how much the bending stiffness alone of the belt affects the tension reading. NB the bending stiffness of the belt won't change when it is tensioned. I will try and dig out an old normal Gates belt and try and "measure" the bending stiffness with a kempf gauge.

GregBBRD

Great idea. They should know!

ptuomov

When my current engine blows up, the next one in the garage has both Porkensioner and Roger's racing belt. I agree that there's just one way to find out about that combo. Once I cross that bridge I'll report back.

I haven't personally set the cam timing on a single 928 engine yet, so the following goes with a huge caveat:

I though the different timing between banks was for thermal expansion of the block and not stretch of the belt. "My" logic was that aluminum block is going to expand a lot and that had to be accounted for with different timing between banks.

Belt stretching and the block expanding are basically the opposite effects. I am thinking this thru in my head now and I think that if it were the belt stretching, one would advance the passenger side bank relative to the driver side. To compensate for the thermal expansion of the block, one retards the passenger side bank relative to the driver side. Does that make sense? I am sure I got the directions mixed up in my head with 50% probability.

cpayne

May be sooner. I was driving today tensioner light came on.
Stopped and turned the car off. I waited a while and started it up. The idling was bobbing up and down from zero to over 1000. The memory for tensioner didn't turn the light on. Started home and about 10 minutes into the drive the tensioner light came on, but the loping stopped. Got it home and parked.
Only 70 miles on it since the TB change.

M. Requin

Actually, this sort of tool is even used to measure tension on standing rigging on sailboats. What I didn't know was that the 9201 had a calibration standard. But thanks anyway!

jon928se

I 'ld forgotten about that, and I was using a Loos gauge on Saturday.

But like the 9201 and the kempf tool they all bend the tensioned "thing" they are measuring by virtue of the deflection they impose. This doesn't matter as you are always comparing like with like ( the same object bending through a fixed angle) so the error from bending is always constant and fixed.

That also why you can't compare the rig settings on a boat with rod rigging to an identical boat with dieform wire rigging.

jon928se

A data point. A 9" length (my guess at the length from tensioner pulley to Cam pulley) of used Porsche belt with both ends prevented from rotating but free to move longitudinally ie no tension does not register on the kempf gauge when deflected (twisted) through 90 degrees. From memory 90 degrees is approx how far the belt twists when checking it on the car.

Thus the bending stiffness of stock belt is probably negligible in so far as it affects tension readings using the kempf gauge.

A repeatable test for someone with the GRBelt. It takes 600 grams of force to bend a 3" length of Porsche belt through 180 degrees . Mark two points 3" apart on the belt, support the belt on scales at one of the two points, zero the scales, then bend the belt over pushing down with a finger until the second point very nearly touches the 1st. A whole belt weighs approx 250 grams and you may be supporting 1/10 of the weight of the belt on the scales - ie 25 grams this is an insignicant error as we are looking for orders of magnitude difference.

Landseer

Lovely.
Let's pull that cover tomorrow and see what's going on.
Maybe both of them.
We torqued those cam gear bolts to 45 ft-lb. The bolts were dry and as torque was approached, it moved. Could a cam shaft snout have broken?
We tightened the belt to the top of the window and the locked-down the tensioner bolt with the lock nut.
https://rennlist.com/forums/928-foru...e-driving.html
Turning car off clears the belt light. Then it takes a couple minutes of running to re-light.

jon928se

Thats normal - TBelt tension warning circuit doesn't start working until engine has been running for 2 minutes.

Landseer

But we just installed this belt and new camgears.
This has me concerned.