Hi all.

I have just bought a new magneto oil seal for my 1941 model and it is a very sloppy fit in the case, probably about 2mm too small. I have a couple of sets of BSA B31 cases and it fits these just fine.

Are there different size seals or is my case just worn ?

Regards

Tony

email (option): tony-wilkinson@sky.com

This is an increasingly common problem as the engines get older, largely caused by running with the magdyno straps loose and/or the gear mesh incorrectly set up....Your casings are worn as all the seals for these models are the same size...The problem with remachining the case for an oversize seal is the difficulty of picking up on the original centreline of the seal...
If the engine is together in one piece there isn't really a good way of solving it in my opinion, though other opinions may vary!!...If the engine is apart for a rebuild then remachining is possible...There are basically two ways to pick up on the centerline...One works IF the mag platform is unworn and could be carried out by a competent machinist...I made a jig to achieve the same thing which isn't dependent on the mag platforms condition...The mag platform will also need rectification to prevent further problems if badly worn (it should be completely flat under the magneto)...Ian...

email (option): ian@wright52.plus.com

I had this same problem and wondered if it Would be possible for someone like Mark to make up a template from a known good case.
Something like a plate that bolts to the mag mount and has a 90 degree piece with a small hole that a drill could go through at exactly the correct spot showing the centre

email (option): taybrig@shaw.ca

This is the repair procedure.
http://www.wdbsa.nl/download/Magneto%20Oil%20Seal%20Flange.pdf

If the recess for the seal is worn fairly round, I wonder if a seal supplier could come up with a slightly bigger OD? Maybe in the metric range??

Otherwise I've found JB weld to be an excellent material to use. It takes several hours to cure properly and sets like steel. So the seal, mag and pinion could be set up with a smear of JB round the perimeter of the seal and left overnight. Of course the next time the seal needs to be replaced, A proper engine strip might be required.

Ron

email (option): ronpier@talk21.com

The solution recommended by REME as posted by Ron isn't an easy one to carry out for various reasons, though it obviously does work if everything goes well...Of course, you still have to pick up on the correct centre of the seal before machining the crankcase to accept the piece and that's the difficult part...

The standard seal is 39mm OD X 20mm ID x 7mm thick...I generally use either a 40mm seal or a 42mm seal depending on the degree of wear present...Seals with these dimensions are readily available...Most cases can be repaired without resorting to REMEs extreme surgery which weakens the crank case considerably in that area..I've seen more than one that has cracked after the procedure (including my own on one M20)...That's why I came up with an alternative method.....Ian

email (option): ian@wright52.plus.com

Yes I thought it was probably wear in the case. I have managed to measure it and it appears to have worn fairly round. I have ordered a seal 2mm bigger and will gently relieve the hole to make it fit as it is really close.

Tony.

email (option): tony-wilkinson@sky.com

Many years ago I repaired my B33 the way Ron did. It is still working well.

email (option): ian.clare1@virgin.net

Hi Ian,

Thanks for that. So I have a couple of options now without resorting to drastic surgery.

Tony.

email (option): tony-wilkinson@sky.com

Just to be clear. I haven't had to use the JB remedy on my M20 as the standard seal still fits, but I have used loctite to try and avoid any future movement. My recommendation for JB Weld is based on other applications. Ron

email (option): ronpier@talk21.com

I repaired this problem with the engine together and in the bike with silicone gasket compound.

Put the mag back on the bike and set the gear mesh.

Tighten the strap.

Remove the gear.

Put silicone on the seal face and cases and push it in to the recess.

Put the gear back on and tighten the nut while silicone is still wet.

Once gear is back on, don't turn or move the gear at all!!!!! Especially don't back off the gear or the seal will move back away from the cases and you need to start over. Put the gear on in one movement and tighten the nut a little bit.

Have a beer and wait overnight for the silicone to set.

Then time the mag.


I did this to a B32 and it is still working after 20 years with no issues.

As an aside. My M20 worked perfectly with it's rebuilt mag for about 20 years, but suddenly stopped whilst on idle when I was closing the gate in my lane. I spent 1/2 hour trying to restart it by all the usual checks and measures, but arrive late at the rendezvous on a different bike.

There was no spark at the mag and when my guy opened it up, it was full of oil.....Culprit was a rock hard oil seal. Ron

email (option): ronpier@talk21.com

I have to repair my crankcases as someone managed to crack them around the magneto seal housing. I expect I’ll just weld them up and bring them back to standard. I have some photos of goldstar crankcase drawings and hopefully the position is the same. I want to make a tooling plate to allow for many other repairs. After getting that far, it wouldn’t take much to make a jig plate that could be shared around for finding the centre.

Mark

email (option): pes.sales@btconnect.com

In my case :) the hole was oval and i used the JB weld method thats still holding buy i had the problem of finding centre in order to place my seal, A plate would solve this, and after the plate was made all that would be needed to share would be the dimensions of it for those of us in far flung places like western Canada

email (option): taybrig@shaw.ca

Kevin, hence my suggestion of clamping the mag with it's pinion in place before the JB sets. It will naturally be in the right location. Ron

email (option): ronpier@talk21.com

I might be offering more than I can deliver. I was hoping that a simple jig plate could not only be used to find the hole center, but also assist in check the magneto height and ensure the correct mesh with the gears.
Treat this as a fantasy until I manage to do it.

Just a side note, if aluminium has been repaired with any kind of epoxy it's incredibly hard to weld afterwards.

email (option): pes.sales@btconnect.com

I should have checked the size first!
Enlisting the help of Anita I asked her to machine my welded crankcases.
Unfortunately, I hadn't checked the size of the hole for the oil seal.
Yes it was oversize and would not clean up.

I should have done this in the first place.
Casting flipped over and machined for a repair insert.
I'm just hoping that the BSA hole center matches the one the magneto was lined up to.
If it doesn't work options include making an eccentric repair insert or making an over or undersized magneto gear.



Mark

email (option): pes.sales@btconnect.com

I've made this up a few years ago, it worked o.k.
Not BSA but in general the same, see pics.

email (option): info@wetblast.nl

Looks good Vincent,

Mark

email (option): pes.sales@btconnect.com

Hey Ian,

I've been out of action for the last few years but starting to play catch-up on my M20 rebuilds. I've 3 oil seals that I've ordered over the years, I'm assuming from drags, and they all reference 20 38 10 (or 9.5). These are all too slack for 2 engines I'm trying to rebuild. A crude measurement of the rebate the seal is supposed to locate into the crank case is closer to 39 mm. Are you able to purchase a 39 mm seal and of so , do you have a part number? Ob should I be targeting the more readily available 20 x 40 x 7 mm seal, and of so can this be hammered into the space?

Glenn

email (option): glenn_mullan@postmaster.co.uk

If you have a local bearing and seal shop speak to them as they can probably order seals made to whatever size you need. We have had many made to size for various military vehicles we have which is much better than trying to force in an oversize seal. If you don't have anyone local we use Bearings and Belts, 1 Arkham House, Plough Road, Horley, Surrey, RH6 9JW 01342 844275. They can get any size seal made in metric or imperial.

email (option): m.gurr@yahoo.com

Thanks Mike! I'll check out some of my local suppliers first.

email (option): Glenn_mullan@postmaster.co.uk

Have the previous seals run slack in there due to a loose magneto Glenn ?

If so - the aperture & the area to site seal will now be oval

Thus might explain the slack seal

Jo’b

email (option): Jonnyob1atgooglemail.com

If the recess for the seal isn't too badly worn it is frequently possible to remachine the case for an oversize seal without breaking through the 'wall' of the boss that the oil seal recess is machined into...I made my setting up jig using a NOS set of crankcases as a template to determine the exact hole centre...Ian

email (option): ian@wright52.plus.com

Hi Ian
You did nice work on this before for me
A credit to your workmanship

Job

email (option): Jonnyob1atgooglemail.com

Thanks John..:blush: ...Ian

email (option): ian@wright52.plus.com

I did pretty much the same as Bruce. In my case the case was almost worn through. Never thought much about it, just packed silicon sealant round the felt washer and let it set. It's never leaked since. Folks overcomplicate things.

email (option): jeremy@clogmaker.co.uk

['Folks overcomplicate things...']

Not really, remachining the crankcase is a permanent and accurate engineered solution that makes any future oil seal change a straight forward job...

It's a different but better solution than various forms of 'glue' which IMO are only a temporary bodge to get you out of trouble until the correct solution is applied...I try to start from the point of 'best practice' wherever possible as there is a tendency to end up bodging everything if the easiest route is always followed...Ian

email (option): ian@wright52.plus.com

Hi John,

I the recess tor the bearing still seems to be round, so I'm guessing I just have the incorrect seal sizes. I've ordered a larger seal and hope this will fix the issue.

Glenn

email (option): Glenn_mullan@postmaster.co.uk

It rather depends how much time and money one wants to chuck at the problem. My mag has been off a couple of times since I bodged it seven or so years ago and I haven't had to do anything further.

email (option): jeremy@clogmaker.co.uk

Some of us simply.like. Proper engineering solutions and hate the idea that next time a routine task has to be undertaken, previous botches will mean a long term "Vehicle Off Road".

Surely the point of this hobby is to do it to the best of our ability ? If not, and we simply like gluing things then collages must be the way forward :grinning:

In terms of bodges this is a very minor and reversible one. If it fails to stop a leak one just tries something far more expensive and time consuming. The bodge itself leaves no mark on the cases and doesn't involve any moving parts. By all means spend time and money if you have both to spare. I just use my M21 as transport in the summer months. In the winter it gently decomposes under a sheet next to my workshop. It's never been 'restored' and to call it's rusty condition patina is rather stretching the term. Using the gearbox is rather like stirring porridge, it needs a gentle touch to avoid neutrals, having been abused for decades with a previous sidecar.
However it runs LEDs, a Triumph clutch, a top quality English made electronic regulator [none of that Far East garbage] & has had a complete engine rebuild of the internals. I expect it to happily make another 30 years, far more than I have left.
When I was at school and college the charm of the M21 was that it would run and keep running when pretty worn out; and worn out bikes were all I could afford. They didn't need constant attention and parts to keep them on the road. After a gap of some forty years I'm on my third one, so I suppose my attitude is atypical on this site. When I ride it I'm 20 again, just as long as I don't see my reflection....

email (option): jeremy@clogmaker.co.uk