Hi Gents
I am throwing oil out at the magneto at an unacceptable rate. It started a few weeks ago at a small rate and has got progressively worse.
I don't have a seal behind the timing gear and cannot really see how it would fit. The mag shaft is not completely concentric with the timing case opening.
Does one normally have a seal and is it normal to leak if there is no seal as it never used to leak?
Possible causes could be return oil not returning fast enough to the oil tank or engine not breathing adequately. I have a manual anti-wet-sumping valve so I don't think that is the problem.
Is this a common problem and what are the normal remedies?
I will be grateful if someone can give me some pointers on where to start looking.
email (option): pvlietstra at gmail
There should be an oil seal fitted into a recess in the crank case located behind the magneto drive gear...The seal should be a light press fit into the cases and when fitted the inner diameter runs on the shoulder on the back of the mag drive gear to create the seal...A modern oil seal replaces the original and fairly ineffective rubber and fibre unsprung seal...
Wear/corrosion on the gear shoulder can detrimentally affect the effectiveness of the seal causing a leak...Also, if the bike has been run with the magneto straps loose the resulting movement of the mag can wear oval both the recess that the seal fits into and the hole through which the armature spindle passes...The resulting loose seal can cause an oil leak there as well..
The magneto platform on which the magneto sits will also wear if the bike has been run with the mag. straps left loose for an extended period. The platform should be completely flat...If this is worn or the mag has been badly shimmed for gear mesh, or carelessly positioned in relation to the seal when the straps were tightened, the magneto armature (and thus the mag drive gear shoulder) will be off centre to the seal...That can be the source of another leak...
So you will have to remove the magneto drive gear and the magdynamo to check all these points...If the recess for the seal is worn, but not too badly, it is possible to glue the seal in place..If the wear is worse a repair is possible but the engine will have to be removed and stripped to carry it out. If the mag platform is badly worn this can only be repaired with the engine out, though it is not necessary to strip the bottom end in either case if you can get the work done by a local machine shop...Ian
email (option): ian@wright52.plus.com
Thanks Ian for your comprehensive reply.
I measured the recess and it is slightly overall. The mean diameter appears to be 40mm.
The timing gear shoulder is 20.4mm
Would a 40x20x7 seal fit or is this an imperial size?
email (option): pvlietstra at gmail
There is a REME modification for a worn mag seal area.
http://www.wdbsa.nl/download/Magneto%20Oil%20Seal%20Flange.pdf
But Darren Wrudd from this forum should be able to help with a correct seal at....
john-fenwick@btconnect.com
Ron
email (option): ronpier@talk21.com
38x20x7(or8)
Is the normal one who can installed.
Roy
Roy is correct but the oversize seal may get you out of trouble without machining the case or resorting to 'glue'...They are cheap so I would get both and experiment a bit....Ian
email (option): ian@wright52.plus.com
Thanks all for your comments and help. I have examined the seal housing and it is oval. A 38 seal will rattle around unless I glue it in place. I may have to grind a bit to get a 40 seal to fit. The mag platform slots are also worn, so the mag pulls to the side. It also rocks a bit. This does not affect the gear meshing but the seal won't be happy.
So my plan is to get the mag to sit firmly on the platform, on the correct center-line and without sideways movement, then shim to get the right gear mesh.
Then I can experiment with seals, failing which I make up the external screw-on seal flange (drawing 65-2136). I have a few thoughts on modifying this slightly to make it easier to make and fit. This is the subject for another post and if it comes to that I will keep you posted.
email (option): pvlietstra at gmail
On my B33 the hole that the seal sat in was worn. I made sure that the mag-dyno was sitting right, then I smeared J B Weld around the seal and pushed it into place. Once this was set I was able to use the bike without oil leak. That was done about 10 years ago.
My bike came to me with a wobbly mag, which allowed oil to blow all round and into the mag itself. I idiotically overtightened the mag strap and broke it. When I finally got round to fixing it properly I used gasket paper under the mag and cut an extra piece for under the outboard end to get the mag shaft to line up properly with the engine seal. I can take no credit for this, I was advised to do it. Anyway it worked.
The magneto was wobbling on it's centre by the way and the seal housing was worn unevenly but fillable with a tiny bit of non hardening sealant. I think the case had been welded
email (option): jeremy@clogmaker.co.uk
The problem with completely machining away the recess for the seal to do the REME mod is accurately locating the correct centre of the newly machined hole into which the brass/aluminium seal holder will fit...
I made a jig for doing this job using a NOS set of crank cases to determine the correct location of the centre...
Another way which might determine the centre accurately enough would be to clamp the mag in place and then fit the mag gear...After adjustments to produce the correct gear mesh and with the mag straps fully tightened the gear could then be removed and the outside diameter of the magneto shaft clocked true...
This would require half the crank case to be mounted on parallel blocks with the mag attached and to be clamped to a milling machine table I would have thought...Obviously once the shaft is clocked the crank cases can't be moved in relation to the milling machine spindle..Ian
email (option): ian@wright52.plus.com
To find the center, I plan to fit the mag, mesh the gear, strap down and then remove the gear. I will machine a dummy sleeve to fit snug on the mag shaft and with the correct OD for the mod cutout. I will mark out around the OD of the dummy sleeve.
email (option): pvlietstra at gmail