Burman Gearbox BA Gearbox Bearings

[ClassicBiker]

Well Doug has got his A Comet up and running. We still need to do some on work the electrics. The big concern at the moment is the BA gearbox is leaking 80w like the Exxon Valdez. So we thought we might replace the bearings with sealed bearings in the hope that might stem the tide. But we don't know the size of the bearings to see if we can order sealed ones. Does anyone know the size of the two bearings?
Thanks in advance.
Steven

 

[AndrewM]

These boxes were designed for semi-fluid grease, not oil

 

[Pushrod Twin]

Well Doug has got his A Comet up and running. We still need to do some on work the electrics. The big concern at the moment is the BA gearbox is leaking 80w like the Exxon Valdez. So we thought we might replace the bearings with sealed bearings in the hope that might stem the tide. But we don't know the size of the bearings to see if we can order sealed ones. Does anyone know the size of the two bearings?
Thanks in advance.
Steven

Are the Pre-War bearings same as Post-War? I have a couple of Post-War BAPs apart right now and would be happy to measure up for you. There is an output shaft oil seal kit available from Dragnfly which is supposedly an improvement over the grease seal, again for Post-War types. I discovered that the welsh plugs, which seal the shaft bores on my Post-War BAP, are not fitted squarely and grease was making an escape through them.
In spite of insistence from the staunch grease supporters, I believe that running them on oil gives superior lubrication. There are places where grease does not penetrate, even when hot, and wear is evident as a result. Even Burman conceded to using oil on the BAP & CP boxes about 1951 IIRC.

 

[ClassicBiker]

Thanks all for your input. I've passed it along to Doug. I'll let you know how he gets on.
Steven

 

[Pushrod Twin]

Thanks all for your input. I've passed it along to Doug. I'll let you know how he gets on.
Steven

Steven, As much for my interest as yours, I have done some research on BAP output bearings.
According to Draganfly's BA gearbox listings, the same bearing, Ariel part number, 3095-31, was used from 1931-52. I could not elicit any size information from their web page.

Ariel Motorcycle Spares And Parts - Ariel 4 Stroke - Engine & gearbox - Gearbox - All models - CP & BA gearbox - Draganfly Motorcycles

casings the position of the mounting bosses of the sq4 gearbox shell is different to the other models in order to move the gearbox sprocket further to the left. part no. description per model years 3000-35u shel

draganfly.co.uk

So I measured a NOS bearing which I recently received. It appeared to be a straight forward 1 1/2 x 27/32" until I looked more carefully at the numbers. The OD measured 2.8346" But wait, 27/23 is 2.8438" 2.8346" = 72mm!
The bearing is Metrinch! 1.5 Inch x 72mm x 17mm which confirms folklore that Burman had their own bearing sizes made.
It is marked SKF W3500A

But 1.5 = 38.1mm. or conversely, 38mm = 1.496" Is it feasible to take .004" off the sleeve gear or hone 0.1mm out of the bearing, and use a 38 x 72 x 17 bearing? I went looking for 38x72x17 bearing on the interweb. I'm not convinced that they actually exist, there are web sites that will sell you anything you ask for, but that bearing size does not pop up as an ISO bearing that I could see.

I would suggest that the best you are going to be able to do is use this seal kit, available from Draganfly or make your own adaptor ring, and buy the 1.75 x 2.25 x .25" seal.
Good Luck

 

[Comet Rider]

Steven, As much for my interest as yours, I have done some research on BAP output bearings.
According to Draganfly's BA gearbox listings, the same bearing, Ariel part number, 3095-31, was used from 1931-52. I could not elicit any size information from their web page.

Ariel Motorcycle Spares And Parts - Ariel 4 Stroke - Engine & gearbox - Gearbox - All models - CP & BA gearbox - Draganfly Motorcycles

casings the position of the mounting bosses of the sq4 gearbox shell is different to the other models in order to move the gearbox sprocket further to the left. part no. description per model years 3000-35u shel

draganfly.co.uk

So I measured a NOS bearing which I recently received. It appeared to be a straight forward 1 1/2 x 27/32" until I looked more carefully at the numbers. The OD measured 2.8346" But wait, 27/23 is 2.8438" 2.8346" = 72mm!
The bearing is Metrinch! 1.5 Inch x 72mm x 17mm which confirms folklore that Burman had their own bearing sizes made.
It is marked SKF W3500A

But 1.5 = 38.1mm. or conversely, 38mm = 1.496" Is it feasible to take .004" off the sleeve gear or hone 0.1mm out of the bearing, and use a 38 x 72 x 17 bearing? I went looking for 38x72x17 bearing on the interweb. I'm not convinced that they actually exist, there are web sites that will sell you anything you ask for, but that bearing size does not pop up as an ISO bearing that I could see.

I would suggest that the best you are going to be able to do is use this seal kit, available from Draganfly or make your own adaptor ring, and buy the 1.75 x 2.25 x .25" seal.
Good Luck

The BAP output bearing is indeed Metrinch.
Peter Barker had have some made a few years back, but I think he is out of stock now.
I managed to get one to rebuild mt Comet 'box , where I cannot use the normal seal due to damage when a chain snapped (Poor quality).
I am going to machine the kickstart, and gearchange shafts to take an o-ring to improove the chances of lubrication staying on the inside...

Neil

 

[A_HRD]

I can confirm that the BAP gearbox output bearing is 1.500" x 72mm x 17mm. It's 1.500" bore because that is the OD of the Driving Gear Sleeve. Consequently, the two should slip together as a nice smooth sliding fit. Why anyone would want to seek any other size I know not.

Decades ago, SKF sold this size to Burman (unsealed); they called it a W3500A. Naturally, as the use of Burman BAP gearboxes declined in the mid-1950s, SKF stopped producing that bearing. Subsequently, as the supply began to dry-up and bike restoration took-off as a hobby, people needed that very bearing. The requirement was fulfilled by a few enterprising bearing companies taking a stock metric bearing of the same OD and width, then boring them out to 1.500". And that's still where we are today, and that's why its so expensive to buy. Be sure to buy reputable donor bearings. (Don't even think about buying Chinese ones!). The VOCSC one is £135+VAT; but it has steel shields which pass oil.

I have one left of SKF manufacture 1.500" x 72mm x 17mm with seals in both sides; but it's destined for one of my projects. I recommend leaving both seals in place to keep contaminants out. The correct amount of factory grease is trapped inside and will outlast most of us!

Peter B

 

[vibrac]

Sorry but I think the real answer was at about post #2 use semi fluid grease nobody had sealed bearings for 70 years so why start now?

 

[Pushrod Twin]

I can confirm that the BAP gearbox output bearing is 1.500" x 72mm x 17mm. It's 1.500" bore because that is the OD of the Driving Gear Sleeve. Consequently, the two should slip together as a nice smooth sliding fit. Why anyone would want to seek any other size I know not.

Decades ago, SKF sold this size to Burman (unsealed); they called it a W3500A. Naturally, as the use of Burman BAP gearboxes declined in the mid-1950s, SKF stopped producing that bearing. Subsequently, as the supply began to dry-up and bike restoration took-off as a hobby, people needed that very bearing. The requirement was fulfilled by a few enterprising bearing companies taking a stock metric bearing of the same OD and width, then boring them out to 1.500". And that's still where we are today, and that's why its so expensive to buy. Be sure to buy reputable donor bearings. (Don't even think about buying Chinese ones!). The VOCSC one is £135+VAT; but it has steel shields which pass oil.

I have one left of SKF manufacture 1.500" x 72mm x 17mm with seals in both sides; but it's destined for one of my projects. I recommend leaving both seals in place to keep contaminants out. The correct amount of factory grease is trapped inside and will outlast most of us!

Peter B

Thank you Peter. A couple more questions; Just to confirm, this applies to Pre-War boxes as well? Any idea what size bearing the companies use to bore to 1.5", is 38 x 72?

 

[Pushrod Twin]

The BAP output bearing is indeed Metrinch.
Peter Barker had have some made a few years back, but I think he is out of stock now.
I managed to get one to rebuild mt Comet 'box , where I cannot use the normal seal due to damage when a chain snapped (Poor quality).
I am going to machine the kickstart, and gearchange shafts to take an o-ring to improove the chances of lubrication staying on the inside...

Neil

Thank you Neil. Is yours a Pre or Post War Comet? I also see opportunities to use an O ring in the gearchange system, but for the Post War kick start, there is a seal available which requires some careful boring of the case where the existing felt ring lives.