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Just musing over the issues here I wonder if the running in noise is not due to inaccurate shimming, which is inexcusable, but insufficient lapping in of the c/w and pinion gear teeth. This would explain the noise on a new box slowly subsiding.

I remember reading about a cammy (OHC) Velocette rebuild. The owner had fitted new helical gears to the camshaft drive. On starting up the gear noise was terrible. He then built an electrically driven rig for the gears at work, and when the boss wasn't looking ran it for several days under his bench with a mildly abrasive lubricant, until the gears became quiet. Re-fitted to engine and no further issues.

You could well be right, ISTR people doing something similar when rebuilding bevel-drive Ducatis.

If it is the issue, you can see how it might have come about: for the gears to be fully lapped during build would take time, and that might not have been something MMC were prepared to pay for or Quaife were prepared to do for free.

I'm still wondering why BMW and Moto Guzzi bevel drives don't make noise.

My understanding is that the bevel box itself is not particularly noisy. It is resonance and amplification by the panel behind the seats which causes the problem. This is also why it's typically most evident at a specific range of road speeds (in my case 60 - 65mph). If it were down to assembly tolerances I would expect it to be noisier over a much wider speed range.

The NVH mod for pre 2014 is supposed to improve this and 2014 onwards cars have this flexible mounting as standard.

Bear in mind that a worn alloy rear sprocket will scream and could be mistaken for BB noise. This is a separate issue cured by a steel or supermax upgrade.

I'll set up a survey to see if this is born out in practice.

So are cars who have had sound deadening material fitted to these panels significantly quieter ?

I haven't done the sound deadening but I have sealed the cracks, crevices and gaps. Significant difference. Less dirt and dust too. I'd suspect a Maybach without sound deadening would present more noises even.

I'm not trying to make the thing quiet. It's vicerality is one of its best characteristics! I just wanted to hear the exhaust better!

Richard,

To take your thoughts a bit further, maybe that's the black goo that was in all the early, maybe later BB's too. If it was a slight lapping and lube mix, that would explain the dark color and thickening.

But if that were the case, they should have informed all the owners to run in the BB lube for 1k miles and then flush and fill back up with normal lube.

But to leave that crap in there was inexcusable. I also remember a member in TX that had his BB seize up while his wife was taking her first drive. I believe it seized at around 60 mph. I'm sure that BB was just dry as a popcorn fart...

I'm really glad that the newer M3W's are coming in a lot quieter than days of old. Sounds like MMC is doing something right.

Well I certainly noticed some bevel drive noise on my K100 probably due to it quieter engine. Come to think of it quite a bit from a Guzzi as well. It was the finale to a factory visit in the late 70's. A brave tester wound a new Le Mans up to 90 mph on a rolling road, locked off the throttle and proceeded to climb onto the seat, finally standing on it

As Chris suggests though its location on an M3W attached to the chassis, close to your ear and cocooned in sound reflecting bodywork, amplifies the noise.

Well the BMW ones, on the post 2004 bikes up to the new WC ones fall to bits instead. Mine failed at 7k miles and I've seen them fail at 2k miles. In the UK there is a small industry developed in repairing them - its the bearings that go.

Quaife are a successful manufacturer of competition gearboxes where noise doesnt matter. I do wonder if they even know how to avoid noisy bevel boxes