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

I have a 2026 with steel sprocket. Still sounds like I'm towing an air raid siren

Although a worn alloy rear sprocket does make a lot of noise it is a different noise to the bevel gearbox "scream".

Disappointing to hear that no solution will be found over the next 9 years

LMAO :-) Thanks for the chuckle!

Think might be a typo! or have i been asleep that long!!!!

let me revive this old thread ;-)

today i disassembled my BB in the same way as described in P964 post from 2017, because of undefined (rumbling) noises ....

I found everything ok. inside the box , so I'am afraid that the bearings of the pinion where the reason ...

As I understoud the bearing clearance of the tapered roller bearings will be adjust by the torque of the main (34mm) nut, holding the connection to the propeller shaft ...

Does anyone knows what is the correct torque her ?

Thanks
Thorsten

A picture is worth a thousand words

I'm not familiar with the M3W BB in how the pinion bearings are preloaded, but I can tell you this much.

"IF" there is a crush sleeve between the two bearings, there is a spinning torque setting for the pinion shaft. In the US it's in inch/pounds for resistance to turning. This torque for turning is controlled by the amount of pressure supplied by the pinion flange nut to compress the crush sleeve. I don't think in the case of the crush sleeve that a specific torque for the nut can be given as all crush sleeves will not compress at the same applied torque on the nut.

The other way is to shim the inner/outer pinion bearings. You add/subtract shims until under a certain flange nut torque you have again, the same turning torque on the pinion shaft. This is a trial and error setup that may take several attempts to get it correct. When completed there is a torque value for the pinion flange nut.

There could also be shims involved in how deep the pinion gear engages within the ring gear. All of this has to work together as a finite orchestra, one instrument off and the whole thing sounds bad.

I'm sure others here will give you more direct M3W experience.

Good luck with your rebuild.

Thono, I typed this up and just prior to posting read Dan`s contribution so thought to bin this, which may be all it is worth.... (-: BUT I thought to post it anyway..

as I have typed before I have not even sat in a M3W, let alone put a spanner to one, so I could be typing NONSENSE. I was passing time and wandered into the M3W section and read your post, and until someone who knows what they are typing about comes along I thought to share my thinking as I have nothing better to do at the moment.. (-:

I know not the entire set-up of the BB though the taper bearing assembly seems not a lot different to a wheel bearing set up where ideally there is no real pressure exerted on the bearings during assembly other than to endure they are fully seated with no play between them.

Overtightening the nut creates extra loading on the rollers and bearing faces, and would seem less than ideal, to avoid this there can be a tab washer or castellated nut and split pin involved to hold the nut from spinning and altering the initial adjustment once set..?

The method I have used in the past when replacing tapered WHEEL bearings, was to tighten the nut up enough to be sure that the new bearings had seated properly which is important, as an incorrectly seated bearing may in use end up seating it`s self and altering the vital clearance once in service...

Once satisfied the bearing are seated the nut is loosened back until play is evident then re tightened till no play was felt in the bearings at which stage the tab washer would be bent over a flat on the retaining nut. Or in the case of a castellated nut the split pin would be used to stop it from rotating, there have been other methods used over the years.

Admittedly it is relatively simple to check if the play has been taken up in a taper bearing set-up on a road wheel, as you can just grab the top and bottom of the wheel at the same time, pushing on one hand while pulling on the other then in reversing that process you then can feel if there is ANY play in the bearing. After adjustment I always checked that the hub was free to spin freely with zero resistance felt.

Looking at the pic of the BB bearing set up you posted it may be that a dial gauge is best used to determine if all the play is adjusted out of the assembly. Having typed that an overtightened nut would show no reading on the dial gauge, thus care must be taken NOT to overtighten the nut and some process of determining the bearings are free to rotate as opposed to being overloaded which would cause advanced wear over heating and rumbling prior to total bearing failure...? Given that there is a helical gear meshing with another, I suspect there may be a degree of play required in that assembly, and if that is the case then that play can perhaps be utilised to help determine that the the shaft can rotate freely to some extent...?

Whether any or none of this ramble is of any use whatsoever, I know NOT, just thought to give you something to think about Thono, while you wait till someone who really knows what they are typing about hopefully jumps in.

Just searching past threads for 'bevel box torque' I found this old thread where a complete box rebuild with new bearings is undertaken, with apparent success - it would be interesting to see if 4 years on if it is still quiet.
Bearing preload and torque settings are discussed.
I hope this is useful.
http://www.talkmorgan.com/ubbthreads.php/topics/268136/1