Questions? Looking for parts? Parts for sale? or just for a chat,

The WD Motorcycle forum

WD Motorcycle forum
Start a New Topic 
Author
Comment
Magneto oil seal

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

Re: Magneto oil seal

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

Re: Magneto oil seal

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

Re: Magneto oil seal

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

Re: Magneto oil seal

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

Re: Magneto oil seal

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

Re: Magneto oil seal

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

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

Re: Magneto oil seal

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

Re: Magneto oil seal

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

Re: Magneto oil seal

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.

Re: Magneto oil seal

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

Re: Magneto oil seal

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

Re: Magneto oil seal

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

Re: Magneto oil seal

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

Re: Magneto oil seal

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

Nieuwe pagina 1