BSA Owners' Club Forum

The BSA Workshop => Singles => Topic started by: BeenyBoy on 19 October, 2017, 14:51:32

Title: B31 Magneto oil seal
Post by: BeenyBoy on 19 October, 2017, 14:51:32
Hi guys

Partway through a B31 rebuild and come to refit the magneto; I've put a new oilseal in the housing - my gut instinct says spring/open side  to the inside- ie towards the pinion or into the timing chest...  but when I've peeled the old seal off the pinion its fitted the other way round- ie spring towards the magneto.

Which is correct ?

 :)
Title: Re: B31 Magneto oil seal
Post by: BeenyBoy on 19 October, 2017, 17:26:55
OK... I reckon the seal was originally put in the wrong way round so I'm going with my instinct on this one. However I am concerned that the mag doesn't sit very well on the crankcase "plinth" and actually rocks.... This cant be right surely ? It will clamp down with the strap but....

any thought appreciated
Title: Re: B31 Magneto oil seal
Post by: DEAN SOUTHALL on 19 October, 2017, 20:24:55
You are correct, the seal should be fitted with the open (spring) side facing into the engine. The way I always confirm which way to install seals is to have the open side facing the higher pressure side. That way the pressure will tighten the seal.

Have you checked the location studs under the magdyno as a source of the 'rocking' ?
Title: Re: B31 Magneto oil seal
Post by: ANDY HIGHAM on 19 October, 2017, 21:31:55
As the breather system is designed to keep crankcase pressure below atmospheric pressure, that would suggest the seal should be fitted spring out. I fitted mine spring in
Title: Re: B31 Magneto oil seal
Post by: BeenyBoy on 20 October, 2017, 09:52:43
Thanks Dean... There are 2 studs diametrically opposite on the base of the mag and 2 threaded holes on the other diagonal. With the studs seated in the recess in the crankcase it still doesn't feel secure- its "wobbly".. Should there be bolts in the threaded holes ?
Title: Re: B31 Magneto oil seal
Post by: BeenyBoy on 22 October, 2017, 09:55:01
Just to close this one off:
The general consensus is that the oil seal should be fitted with the spring towards the inside
The problem with the mag rocking on its base was a simple one- there were only 2  locating studs; one of which was had be badly home made and was slightly too long- stopping that side of the mag from seating correctly. Made 3 new studs of the correct length..problem solved. "Jobsa guden" 
Title: Re: B31 Magneto oil seal
Post by: ANDY HIGHAM on 22 October, 2017, 13:00:58
You may need shims to ensure correct mesh between idler gear and magneto gears
Title: Re: B31 Magneto oil seal
Post by: BeenyBoy on 23 October, 2017, 09:57:33
Thanks Andy...I'll shim it up to give just a hint of back-lash as per the manual