Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Lucas MO1 Magneto

Hi all,

I am currently restoring a Lucas MO1L Magdyno and was hoping someone on here could help me with some information about the drive gear equipment.

I believe that the hub (Item A in the diagram, Lucas Part No. 463121) drives the magneto armature and points assembly by being 'clamped' to the fibre gear by the friction plate (Item C in the diagram, Lucas Part No. 463112).

This acts like a clutch, with the pressure for the friction drive being applied by the star shaped spring (Item D in the diagram, Lucas Part No. 463114).

The fibre gear is driven by the dynamo gear, which in turn is driven by the engine timing gear. The drive from the engine is done by various methods of sprockets and gears depending on the bike model.

What I am interested in is the actual magneto armature drive components.

I have bought a brand new fibre gear from Rex's Speedshop but the inside diameter of this gear (where the 463121 drive hub fits), has a slightly smaller inside diameter than the original, so the drive hub will not locate into the fibre gear properly. I can get round this by machining the fibre gear to fit and this is obviously going to have to be absolutely Concentric with the hub centre and have minimal clearance. I would imagine that the fit would need to be size for size in order for the fibre gear to be absolutely Concentric with the armature drive shaft?

The inside diameter on the opposite side of the new fibre gear is also slightly smaller than the 463112 friction plate, so I am going to have to do modifications for that too.

I am assuming that, as long as the fibre driving gear is located on the armature drive hub concentrically, the clearance for the friction plate is not so critical?

My original friction plate is in pretty poor condition, so I think I will make a new one. What would be the best material to use? I have access to an abundant stock of stainless steel, but I'm not sure if this is a suitable material?

Would anyone be able to give me any advice on this and also how can I find out (is it possible to?), the actual dimensions of these components? The thickness of the 463112 friction plate is one I would really like to know.

Thanks, Kev E

I think the magneto is actually driving the other bits to drive the dynamo, not the reverse. The mag armature is driven by the gears/sprockets in the timing case and does not need the other bits to rotate.

As for the bits that drive the dynamo I would agree that they need to be mounted Concentric to the mag armature shaft as the fibre gear needs to mesh correctly with the small gear on the dynamo armature. I do not have an M01 mag apart for measuring the bits but if is obvious that the fibre gear position needs to be fairly exact in all respects so that it does not rub against the mag housing or less likely the end cover (#1). In a correctly assembled unit the fibre gear is very close to the mag housing so any manufacturing of any components must be very accurate.

Hopefully another member with have some measurements for you.

Gordo

Hi Gordo,

I have obviously had a senior moment.

The magneto armature drive shaft that carries the magneto fibre drive gear is indeed driven by the engine, which in turn drives the dynamo gear.

The linear position of the fibre gear and its alignment with the dynamo gear inside the magdyo drive cover is fixed by the position of the fibre gear drive hub on the taper of the armature shaft.

I’m concerned with the inside diameters of the recesses in the fibre gear. The recess on one side locates the fibre gear on the armature drive hub and the recess on the opposite side houses the friction plate. The thickness of the friction plate has no bearing on the linear position of the fibre gear and as such is not that important. I would like to know what it should be though, as it will have some effect on the pressure applied to the slipping clutch function when the star spring securing nut is tightened up.

Cheers,

Kev E

Kevin

Thanks for the clarification.

Clearly with only BSA and Ariel Magdynos in my shop I have never seen such a M01 Magdyno arrangement.

That would mean that if the dynamo clutch ever slips the ignition timing would change. Could you post a photo of your mag so I can see what you are working on.

Gordo

Hi again Gordo,

Although I own a couple (one and two thirds would be more accurate) of BSA A65’s the magdyno I am working on is from my 1955 Royal Enfield 350 G2 Bullet.

I believe the same MO1L magdyno was fitted to some BSA B & M models from 1950 to 1962?

They’re essentially the same units but with different drives. Some from chains and sprockets, as opposed to gears like on my Bullet.

My MO1L magydyno is currently stripped down to its component parts and the magneto armature is away being rewound.

I will take some photos for you as soon as I can, but in the meantime I’ve attached a screenshot of the MO1L exploded diagram for BSA models.

Cheers,

Kev E

The timing can't change as the hub is keyed to the shaft and the drive gear is held on the taper.
I have seen many MO1 magnetos and they all are as shown, excepting the pick-up position which is on the barrel side on Nortons and Ariels.

Yes you’re right, the drive gear hub is held on to the armature shaft with two keys and the timing gear or sprocket is held on by a taper.

I believe the slipping clutch that sandwiches the fibre gear is a shock absorber device designed to protect the fibre teeth, that drive the steel dynamo gear, from being damaged at peak loads. It has no effect on the ignition timing if it slips.

Cheers,

Kev E

Kevin: I think we are all on the same page now. The mags I have are like the one shown above. My Ariel has a chain sprocket in the timing case on the mag shaft the BSAs have a gear on the shaft for driving the mag.

For Trevinoz my timing change question above was only if the dynamo was actually driving the mag through the 'clutch' apparatus which is not the case.

Gordo

Kevin,
The star shaped part is a spring (spring steel) and provides the necessary pressure on the fibre wheel to drive the dynamo
There is a Lucas service sheet that shows how much pressure is applied to the spring
Without reading through this long thread I think it is included
https://www.britbike.com/forums/ubb...g-a-rotating-armature-magneto#Post446733

Ask Priory Magnetos for a new star spring, He is very helpful 01625 265185

John

Hi John,

I'm not sure if you fully understood my question. I know what the star spring is for and I have a brand new one already.

My question was about the inside diameter dimensions of the recesses on either side of the fibre gear and the thickness of the friction plate. Also what would be a suitable material for the friction plate?

Cheers Kev E

Hi Kevin
Oops I picked you up incorrectly
The steel friction plate is hardened from memory ?
Its probably easier to order from Andrew at Priory than make one ?

John

I'm not sure what it is you're trying to do, and your question isn't as well-defined as you might think it is, so I spent more time dragging the box off the shelf from underneath other boxes than I spent measuring.

The first photograph shows what I think are the two parts you are asking about.



The "major" ID of the fiber gear is 2.755", but the OD of the 0.036"-thick plate is smaller, at 2.560". The reason is seen in the second photograph, that shows there's another ID lurking inside the major ID.



The third photograph shows the metal plate fits inside that smaller recess.



As for the other side, the 2.767"-OD, 0.100"-thick driving plate is a sliding fit inside it, with the top of the plate level with the face of the gear when it's in place.



I hope this is the information you're looking for. If you're going to all this trouble because of a badly-made aftermarket part, you have my sympathy.

And, you're not alone. Poorly made replica parts are common in this hobby and others too and we all have to deal with it. Hopefully you have your original parts so you can refer to them, make careful measurements/comparisons as needed to solve the problem.

Hi Magneto man, those are exactly the parts I’m taking about and the dimensions you’ve given are very helpful.

I will compare them to what I have and let you know the outcome as soon as I can.

Bit tied up at the moment with a poorly 90 year old dad who going downhill rapidly with a terminal illness. He gave me the bike that the magdyno is from when I passed my test back in 1973.

Cheers,

Kev E

You have our sympathies for your poor father, Kevin. On the other hand, he sounds like a cool guy to have given you that bike almost fifty years ago, and you are doing him proud by restoring it.

Good luck in the coming days and weeks.

Thank you

This thread has reminded me of when I worked on the magneto on my Ariel VH Red Hunter. The pressure on the fibre gear wheel exerted by the star shaped spring is important. My Ariel was improperly assembled or was out of adjustment as instead of slipping the pressure plate the spring was slipping/turning against the pressure plate, and had worn a groove around the pressure plate, almost all the way through. I have seen other used magnetos of this type with this same worn groove. I don't recall what, if any, adjustment to the spring pressure there was to be had, but the idea of a slipping "clutch" in the drive to save the fibre teeth of the gear wheel was a common problem. Velocettes have a reputation of stripping all the fibre teeth off their magneto drives, and they dont have a "clutch".
Some of these owners resort to changing the fibre gear wheel to a steel one. Personally, I think the whole design is flawed. It says a lot to keeping an eye on the magneto bearings to keep it seize free.
Fullminator

Hi all,

Update on this thread. I emailed the guys at Rex's Speedshop who told me that they have never had a problem with the fibre gears they sell.

I found a new drive gear hub on eBay, which looked in exceptionally good condition and was at the right price, so I bought it.

When it arrived I measured the OD and it was exactly the same as my original, so I now had two drive gear hubs which would not fit inside the recess in the fibre gear.

Conclusion: - Either I am very unlucky and have the only two drive gear hubs in the world that are too large on the OD, or the guys at Rex's Speedshop are telling me porkys?

Anyway I rectified the situation by machining a soft jaw chuck in one of our lathes to take the fibre gear and then machined the recess in it to suit the drive gear hub and all is good now.

Unfortunately my dad passed away on Friday March 4th. It's sad that he wont get to see the Bullet when it is finally back on the road but he had a good innings and passed peacefully and comfortably at home with his family around him.

Cheers,

Kev Ev

Another problem with some of the fibre gears is the outside diameter. I have had to machine a little off some.