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Pre-unit singles Mag oil seal dimensions/number? #348234
12/16/10 1:36 am
12/16/10 1:36 am
Joined: Oct 2007
Posts: 1,516
Auckland NZ
Ignoramus Online content OP
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Ignoramus  Online Content OP
BritBike Forum member
Joined: Oct 2007
Posts: 1,516
Auckland NZ
Anyone know, or have an oil seal they can give me the dimesions of or have an oil seal that they know the seal number of? (dont mean the BSA part number but the modern seal number)

Im talking about the oil seal that seals on the magneto pinion sholder and is pressed into the inside of the timing chest on B33/1 M20 ect

Have measured an old case which is chewed out on that diameter, looks like it wants to be 40mm?, the OD of the mag pinion sholder is around 20.5mm....it probably isnt a metric seal but nothing would surprise me maybee its 40x20x6?

thanks guys
and merry Christmas to all!


"There's the way it ought to be and there's the way it is" (Sgt Barnes)
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Re: Pre-unit singles Mag oil seal dimensions/number? [Re: Ignoramus] #348280
12/16/10 11:23 am
12/16/10 11:23 am
Joined: May 2004
Posts: 3,570
Sydney Australia
B
BSA_WM20 Online content
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BSA_WM20  Online Content
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B
Joined: May 2004
Posts: 3,570
Sydney Australia
It is an oil seal but not as you know it .
The original unit is a thick rubber ring.
The logic behind it is that the shaft is seldom Concentric with the hole in the case so the thick rubber ring can be distorted a bit and still ( not ) seal properly.
You can buy them NOS from Russell Motors in the UK .
OTOH get a non steel backed oil seal to fit the shaft and glue it into position, which is what I did.

Before you do this replace the round pins in the bottom of the mag with some semicircular ones so it can not move and pack out the bottom of the unit to get proper meshing of the pinion


Bike Beesa
Trevor
Re: Pre-unit singles Mag oil seal dimensions/number? [Re: Ignoramus] #348368
12/16/10 7:56 pm
12/16/10 7:56 pm
Joined: Oct 2007
Posts: 1,516
Auckland NZ
Ignoramus Online content OP
BritBike Forum member
Ignoramus  Online Content OP
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Joined: Oct 2007
Posts: 1,516
Auckland NZ
Trevor said"
"The logic behind it is that the shaft is seldom Concentric with the hole in the case "

that makes sence, I realised i would need to shim the mag height to get minimum backlash, but still some clearance in the gear, but hadnt thought as far as that effecting concentricity.

Sounds like the glue in position fix is a good one....what glue did you use ....5 minute araldite is what springs to mind, or maybee even some of that flexable silicon/"mastic" sealer the builders use as a substitute for propper joinery skills....will try some and see if it sticks to rubber.

cheers


"There's the way it ought to be and there's the way it is" (Sgt Barnes)
Re: Pre-unit singles Mag oil seal dimensions/number? [Re: Ignoramus] #348391
12/16/10 10:23 pm
12/16/10 10:23 pm
Joined: Aug 2001
Posts: 1,862
Elko, Nevada USA
dave - NV Offline
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dave - NV  Offline
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Joined: Aug 2001
Posts: 1,862
Elko, Nevada USA
The magdyno or magneto mounting system on the pre unit BSA singles is a good example of why their industry failed. Crude beyond imagination. JFC...

Anyhow .. I too have dealt with the goofy magdyno shaft/seal missalignment issue. One thing that can be done to help is to shim the base of the magdyno against the mounting strap to keep the mag from moving too far forward on the platformwith a strip of ~ 60 thou alu.

The most elegant fix for the missaligned seal issue was devised by a GSr I know. He made a reducing ring with a offset bore that tightly fit in the case relief. He then found a smaller OD lip seal that fit. I must do this, "One of these days". aarrgh

The OEM seal was 5 mm thick. However I've not found this size to be available and have had to use a thicker 7 mm seal which just barely has clearance to the face of the mag drive gear. If anyone knows a source for the 5 mm thick seals, I would sure appeciate the info. I'm using a 20 x 38 x 7 mm seal now.

Be sure to shim the mag base for sufficent clearance to prevent overloading the mag bearings. BTDT.
I now use Jerry Meadows', the GSr in Reno, designed 'peel to fit' alu mag base shims. Nice.


dave - NV
Re: Pre-unit singles Mag oil seal dimensions/number? [Re: Ignoramus] #348502
12/17/10 11:49 am
12/17/10 11:49 am
Joined: May 2004
Posts: 3,570
Sydney Australia
B
BSA_WM20 Online content
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BSA_WM20  Online Content
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B
Joined: May 2004
Posts: 3,570
Sydney Australia
Slow set epoxie resin.
The 5 minute stuff gets a bit soft at 80 deg C and me thinks the carby boiler gets a lot hotter than that.
Peter Scott sells the 1/2 moon locating pegs if you have trouble sourcing them on the other side of the pond.
When he rebuilt my mag he fitted them and then I cleaned out the muitalated holes in the case, filled then with Davcon, ( which now that I think of it is what is holding the oil seal in place ) then set the maggie in the cases perpendicular to the timing gear train.
When it had set I removed the maggie and shimmed it so now it is held square by the pegs and to the correct height with brass shim stock.
And what do you know , it no longer screams blue murder whenever I give it a belly full of fuel and the maggy has stopped eating bearings.
More fiddeling about that I would normally do but well worth the effort.


Bike Beesa
Trevor
Re: Pre-unit singles Mag oil seal dimensions/number? [Re: Ignoramus] #348612
12/17/10 9:12 pm
12/17/10 9:12 pm
Joined: Oct 2007
Posts: 1,516
Auckland NZ
Ignoramus Online content OP
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Ignoramus  Online Content OP
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Joined: Oct 2007
Posts: 1,516
Auckland NZ
thanks guys ....its obviously going to be more shagging about than i thought but at least now I have a fair idea what Im up against.

I had wondered how that piss poor location method of the slots in the case and a strap was supposed to locate anything accuratley

Must say im leaning towards Daves ecentric bush idea containing a std seal and set in so the shaft is Concentric, I had actualy thought of that but then thought no thats just being silly, but the more i think about it......

Trevors epoxy resin method will definatley be the go for another set of cases which has the seal diameter chewed out so you couldnt press anything in those ones anyhow.

The job is away off yet but just trying to get an idea of what Im up against so I dont end up rushing it at the last minute.


"There's the way it ought to be and there's the way it is" (Sgt Barnes)
Re: Pre-unit singles Mag oil seal dimensions/number? [Re: Ignoramus] #348855
12/19/10 10:46 am
12/19/10 10:46 am
Joined: Sep 2006
Posts: 144
Peterborough. UK
LJ. Offline
BritBike Forum member
LJ.  Offline
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Joined: Sep 2006
Posts: 144
Peterborough. UK
I'm in the process of replacing my magneto seal on the pinion as well. (B33) There really was a lot of oil coming out between the case and magneto, amazing really as there is no oil feed higher up than the cams within the timing case. I also found that the breathing mechanism was fairly well blocked, so it might also be a good idea to check this to stop the engine from trying to breath out of bad oil seals. Just my tuppence worth...

By the way, my new oil seal from Draganfly is a THK 4379 sc150 081 25 2 See picture below to make sense of all that. lol The knackered seal is on the right. Cant you tell its cold here! Cheers.



LJ.
*******
1940 BSA M20 500cc Girder/Rigid- In Bits!
1947 BSA M21 600cc Girder/Rigid-Green
1949 BSA A7 500cc Girder/Plunger Star Twin-Black
1953 BSA B33 500cc Teles/Plunger-Maroon
1961 BSA A10 650cc Golden Flash-Blue
1961 BSA A10 650cc Golden Flash-Red
Re: Pre-unit singles Mag oil seal dimensions/number? [Re: Ignoramus] #349087
12/20/10 6:53 pm
12/20/10 6:53 pm
Joined: Oct 2007
Posts: 1,516
Auckland NZ
Ignoramus Online content OP
BritBike Forum member
Ignoramus  Online Content OP
BritBike Forum member
Joined: Oct 2007
Posts: 1,516
Auckland NZ
LJ thanks for that ....will see if i can get a seal localy and fit it and see if the mag pulls it out of round when ive packed it into position for gear clearance....its on a project motor so a bit of shagging around isnt such a problem even if I fail to get it right and have to re do it.


"There's the way it ought to be and there's the way it is" (Sgt Barnes)

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