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

Seem mad that they have to make the induction noise reduced! for euro4 ! i can't hear my induction over the howl of the bevel box!so why should we pay to have it made to do what it should already do!

During the Jungfrau Treffen I had an interesting discussion with R1NGA about the bevel-box problems.
During this discussion I got an idea which I told R1NGA about. He crabbed his head and said: "Hmmmm, perhaps your correct".

Let me explain my thinking

Many times I wrote that the bevel-box of a BMW motorcycle make almost no noise. Is this a different construction or it it something else ?

Let's compare the two bevel-boxes.

The rear wheel of a BMW motorcycle is directly coupled to the big crownwheel in this bevelbox.
So if the rear wheel makes one turn the crownwheel also makes one turn.
Let's assume the rear wheel tyre has a circumference of 2 meter. When driving 100 kilometer per hour the wheel rotates 14 times a second.
So also does the crown-wheel in the bevelbox of the BMW.

With our M3W the front sprocket of the final drive belt is coupled to the crownwheel.
When the rear wheel rotates once the front sprocket (and the crownwheel) rotating 2 times (due to the difference in size of the final drive belt sprockets)

So instead of rotating 14times a second like the motorcycle crownwheel
our M3W crownwheel need to rotate 28 times !

So our M3W bevel boxes need to rotate double as fast at the same road speed compared to the BMW motorcycle or any other motorcycle with a bevelbox.

Can this perhaps be the cause (or one of the causes) of the problems with the screaming bevelboxes ??

Good thinking Laurens! but why are some quiet some noisy?they all the same crown wheel size!

The difference with respect to a car is that the final reduction at the output of the tapered torque 1/2 for the three wheels and 1/4 for the four-wheeled cars, in addition the tapered torque does not drive the wheel directly, noise is very variable with equal speed aven function of the adjustment of the tension of the belt, I think that with a trapezoidal belt many problems of noises disappear.

Given that there are quite large variations in "performance" across the bevel boxes fitted, it's apparent that an improvement in production quality is required in the first instance.

Super-finishing the gears at the production stage isn't too expensive.

Combine this with closer attention to alignment and tolerances and there's no reason that there shouldn't be an improvement across the board.

It's a very simple gearbox, and assuming it's fit for purpose in the first instance, the problems should be easily solvable at the production stage.

It would be normal practice to include noise limits in the specification. I wonder if Morgan did so ?

Has there been any improvement on more recent cars or it still the luck of the draw whether you get a quiet one ?

Mines a 2016 still noisy at anything over 55mph..

Below an excerpt from an email which I received a few months ago from MMC.

"All I can tell you at present is that there is more than one company currently working to reduce the bevel box noise, I guess if it was easy someone would have done it by now and made a small fortune!"


What I also heard from one of the participants during the Jungfrau Treffen, someone who has close contacts with MMC, is that as soon the bevelbox is on a test bench the noise is much less.

Looks like our M3W's are acting like a guitar and the smallest sound which goes in, comes out loud.

Or the test bench is missing something!

While we are in full blown speculation mode I would to throw another theory into the pot.
We all know the drive is very lumpy with big torque spikes many thousands of times a second at speed.
With the compensator not acting as a Cush drive ( another story ) the poor old bevel box is getting hammer blows on the input in audio frequencies.
So I my theory is the bevel gears are bouncing off each other with each torque pulse so making the noise we love and hate. There will be many factors which will make this better / worse which is why we see so much variation : like belt tension , oil temperature , compensator wear, rear wheel pulley wear, Inclusion of NVH kit etc etc
Just a theory

Im sure it resonates forward through the driveshaft.