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

Hi Planenut
We have put a few km on the rebuilt bevel box, and it is almost getting hot ( cold and wet how its mostly been )
We, especially the missus, are extremely happy that the "scream" at 50 to 60 mph has gone and stayed away.
The box is still a bit noisy at town speeds ie 30 to 40 mph but is very tolerable.
Overall very happy with the progress.
However I am now keen to get the box out and review the contact points to see if they have changed much. I fancy that there is room for improvement after this bedding in. Cant be arsed to wait for a 1000 km! To see if it improves.
Now done it once its not so arduous to do it again.
I do believe this is an iterative process and would like to perhaps rig up a test bed set to the "noisiest" rpm which i think is around 2000 rpm of pinion? Ie 60 kph

I rationalise the "scream" as a harmonic of the main gear teeth impacts . The reduction in the roughness of the metal surface ( lapping and super finishing) appears to have dealt to that.
Remaining noise is the actual teeth impacts. Noisey when loaded but quiet when at that mid point of no load on accel or decel. This noise grows with rpm to a max then reduces with higher rpm.possibly due to frequency? Hence me having another look at the contact patterns and gear positions.

Was it worth it.
Absolutely. SWIMBO is much happier on longer trips which means we might be doing some runs if summer gives us more than a couple dry days in a row!

Thanks for the interest

I used to run a factory making gears for aerospace applications and i cant assure that the science of getting the correct contact pattern is both highly skillfull and time consuming. Even with the best equipment available.
Good luck with your development.

Do you really think it’s speed related? I think it’s RPM specific... right around 3,500. So, more likely to hear it “ in town” at lower speeds than at higher speeds where wind noise takes over.

Mine is definitely speed related and not RPM related. Noisy between 45 and 60 mph no matter what rpm

Hi
I do agree with you that it is not engine rpm, but the rpm of the pinion gear hence speed related!! The pinion rpm determines the tooth impacts which determines the " noise "

My theory is that The noticable noise increase and decrease i think is due to the Frequency of the noise as when you are going faster the impacts per min increase hence frequency increases. Certain frequencies are more annoying than others?

Again theory, but probably the NVH mount is designed to minimise the frequency being picked up by the chassis etc.

Anyways, happier than the last 5 years, but still want better!

More a hobby than anything else, especially as retirement looms!

When mine was rebuilt with new chassis & centa compensator it "gained" (or was imposed) the NVH mount. The bevel box was no quieter just different. Previously it was loudest 50-55mph & disappeared above 60mph. Now it loudest around 45mph & still disappears above 60.

Tim

Nigel- Keep the good bevel box news coming!

I just changed my gear oil and now I am hearing more noise than before. Previously I had slightly overfilled using 15 ozs. This time after draining I went to the overflow level plug adding about 8 ozs. total. I will add more now since that seems to slightly soften the clucking and screaming.

The best news is the weather here is to good to pass up. I won't be doing anything with the bevel box until a little more winter sets in.

Episode two!

Have now had another look at the contact pattern. I felt there should be room to improve.
Getting box out is quick ( about an hour ).
This time i didnt strip the bevel box, but simply removed the eight screws holding in the crown gear complete with sprocket. Again quite quick.
Checked the contact pattern as is and whilst it looked OK i felt need to improve.
After checking the "ideal" patterns from the interweb decided to try moving pinion further in towards the gear.
On my box there is a gasket between the pinion arrangement and the box, so i removed this to allow the pinion to sit further in.
Re did the contact pattern and it was an improvement. Pattern was more central and spread over most of the tooth surface.
Backlash " felt" to be a fraction less than before, but still obvious.
Reassembled and tightened and put back into car. This is more difficult than removal due to the position of the two front bolts. The nuts are hard to spanner . Damn near impossible to do it single handed.
Anyways, first tentative run was promising indeed, the noise at 30 to 40 mph was all but gone. All other speeds were similarily quieter too.
Before risking it on the motorway, went round all the nuts and screws and retightened, checked for any oil seepage without the gasket and made sure belt wasnt trying to escape from sprockets.
Tonight, the missus and i ventured out for a quick blast around the neighbourhood and onto the motorway.
In short, Everything was better than the last setup. Absolutely no screaming and an order of magnitude quieter at urban speeds. Yeh !

Her indoors is happy. Yeh !

Should the weather be kind this weekend then will go to Ardmore airport to the Armistice air show. This will allow me to get a few km under the belt and see how it all settles in.

Fingers crossed all remains stable for a good while. But then what will i do ??

Good to confirm that setting the gear contact up correctly does make a difference to the noise from the bevel gearbox. I think this will be a job for the winter on my car as the bevel box screams at anything much over 60 mph once the oil is warm. Thanks again for all the info and feedback.

I did not read the whole thread so I do not know if you run the original alloy spocket or a steel spocket. The key difference on reducing running noise on my 2013 M3W was the exchange for the steel version.
Most of the noise was not caused by the bevel box but the belt drive...