Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Final drive belt jumping survey

Hmmm... wonder if what we need is some transducer sensors wired into a logging device. Attach transducers to BB, clutch assembly, Centa housing, and compare the results on an acceleration clank. Biggest and earliest jump in the sensor indicates the source*. Anyone know any Uni Engineering departments?

* there can't be many options: Centa, clutch, BB, belt, wheel/suspension. Phil's chain drive removes the belt but its possible there are more than 1 clunk sources...

How do you film a CLONK?

I could be all wrong here, and probably am, but I still cannot see how the belt is jumping the sprocket, drive or driven.

The new Harleys are only running a 25mm wide 14mm pitch Polychain type belt, same profile as the M3W.

With only 25mm wide and with passengers, a full dressed touring Harley can weigh in at around 544kg to 590kg.

Some with hopped up motors pull wheelies with a fully loaded Harley and only a 25mm wide drive belt without the belts jumping.

That is WAY more force necessary than to just spin a back tyre on a M3W.

So how do they jump on a M3W?

Again, I'm probably wrong, but I just don't see it happening.

I would have to agree with Dan, that belt would have to stretch a lot, there is very little stretch available in that type of belt. Other option is deflection of the structural components, but I don't think the forces are great enough to cause that. We could do some simple torque calculations to estimate the forces involved.

Inge, stretch in a Harley belt is call a break...

These belts do not stretch, they are literally as tough as chains, hence the Gates name of Polychain for their belts.

Harley uses Gates belts, but they are made to a slightly different level as retail available belts. Other manufacturers such as Falcon make replacement belts for Harleys. In the case for Falcon on the newer touring Harleys at a pitch length of 139, they don't stretch, they just break after a couple thousand miles.

The way the rear swingarm is made and the BB mounting, I don't see anything there that's going to bend under load enough to cause any issues.

I'm not sure how much compression the older Harley compensator system has, but the one I have at home shows extreme wear on the crowns for the three ramps. IF one was worn enough, I could see it jumping ramps, but it would probably sound more like a machine gun going off for a few quick shots. I don't see it just jumping one third rotation and stopping without hitting several before stopping. This is IF it has enough wear to allow this to happen.

I'm sure that some here have the Centa comp and still gets this "jump" sensation too.

Back to the belts, break not stretch.

This maybe the cause of one of my "clonks"

What are we looking at?

The barrel has tell tail marks were it's hitting the frame tubes.(see arrow) only hear the noise when accelerating hard(ish) from standing.

Most all automotive motors torque to the right when under load. If something is too close when the motor rocks on its rubber mounts, it's going to hit.

In the mid to last 60's, Chevrolet had issues with left side motor mounts. They would break and when the throttle was hit, the motor would rock up off the mount and due to the mechanical linkage to the carb, the throttle would go wide open. This just created a BIG problem.

Chevy's fix was a steel cable from the frame to the left front exhaust manifold bolt. They also came out with a new style motor mount which had a steel plate in the middle that would not allow the motor so shift very much even if the rubber broke loose from the steel mounts.

As far as the right cylinder hitting the top of the front frame rail, it looks like a little grinding is in order.

Good catch there Elcyd...

Love that story about the 60s Chevys Dan