Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Bevel Box Noise Survey

I was at the factory a little earlier today and went and found Mark to discuss this. I'll give Mark his dues as he stopped what he was doing and we went over to the workshop.

The belt tension guide might work but then we'd need to make sure they were all the same scale so we opted for the simple solution.
We looked at what parts were readily available but drew a blank given the weight needed.

I've got home thins evening and looked around for some weights and found the remains of one of the kids project trebuchet which had 4 x 2.5kg weights on it and a hook through the middle.

After a little bit of working it out I managed to suspend 7.5kg from the top of the belt and had a deflection of 3mm.

I rolled the car back and forth to take out any tension and then using a piece of masking tape marked the position on the splash guard.

I then placed an allen key on top of the belt and suspendend the weight either side of the allen key with two zip ties and measured the distance to the tape line.

My BB was fairly quiet but was too loose as it kept pinging the splash guide when driven hard. I think my belt is now too tight and has started whining under the new tension.

Does it all come down to belt tension?
When i had my MK 3 Cortina, correct tension in the timing belt was a 90 twist along the longest length.

Does it all come down to belt tension?
When i had my MK 3 Cortina, correct tension in the timing belt was a 90 degree twist along the longest length.

I don't think anyone knows but it would be worth ironing it out as a cause.

Thank you Mark for becoming more active. Just the feeling that someone is listening inspires my confidence. Thanks again.

Laurens, good evening.

No, the belts are not elastic in any way by design. But they are very stiff and hard to flex compared to other type of belts.

It's necessary to have consistent amount of force to "push" the belt to a given deflection that equates to the proper belt tension. What that force is in pounds and how much deflection is needed, is still up for debate on a M3W.

I will say that across the board on Harleys, it's 10# of force on the belt. But not all Harley belts get the same deflection. Touring bikes have one deflection and Softails have another amount of deflection, but all with the same spring force against the belt. And not all years of the same models have the same deflection.

All I'm saying is that "some" amount of force will be needed to keep everyone on the same playing field. Your index finger pushing up against the belt is not the same as my index finger pushing against the same belt. It cannot be subjective, it has to be a science.

In the case of the M3W, the front swingarm pivot point is close enough to the center of the BB that it will probably not matter if you're on the ground or freely suspended off the ground. The only issue with being on the ground is that if the car is under load in one direction or the other, that portion of the belt, top/bottom, can be slack or tight depending on the load. So probably to help it would be best to check this with the car cold and the rear tire off the ground. Also as Harley suggests, the belt tension should be checked in different parts of the belt as to take into consideration of any possible high spots on the pulleys etc. The tension is usually then set at the tightest spot.

I'm sure that it will be figured out soon and everyone can then do the same setup.

I hope I've not confused the issue.

Hi Mark,

I agree we need to add some scientific objectivity to the measuremnts but I don't see how I could use this method with the car on the ground. I suspect many of us don't have ready access to a lift.

Would it maybe be something MMC could ask the dealer network to join in with? I'd happily run over to my local dealer if they would measure the tension and report back.

I have always assumed that the centre line of the bevel box drive belt pulley is exactly on the swinging arm pivot point. Designing it to be close enough would be a pointless exercise when there seems to be no reason for it not to be exact (engineering tolerances aside), allowing belt tension to remain constant throughout suspension travel range.

When I changed the shocks I had the car on the lift and dropped the swinging arm low enough to remove the bolts from the shocks. Hanging down so low the belt was under tension but not extremely. So the pivot point is very close to the centre line of the box.

But to my opinion the belt tension will not bring the solution for our bevel box problem.
If the solution would be so easy it would be solved already for long.
Most of the boxes which having problems getting more noisy when hot and I don't see what this has to do with the belt tension.

Richard,

I only said "close to the centerline" because I've read here that it may not be exactly on centerline with the BB shaft.

But I do stand by my point, and that was that it's close enough to not make a difference in belt tension when the swingarm is up or down from ride height.