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venting through magneto hole

i finally got my clutch on and the primary chain so kicked it over a few times by hand with the spark plug out to make sure the vent was working ( it is ) but i could here air escaping from what seems to be where the mag mounts ?? this cant be normal as im sure oil mist will come out too upon startup. can anyone comment on this

email (option): taybrig@shaw.ca

Re: venting through magneto hole

You shouldn't be able to hear air escaping from where the magneto adjoins the motor. There should be a seal behind the magneto pinion to stop leaks. If you're sure there's a leak here then a physical inspection's the only way to find out what's going on. Fortunately for you there's a lot of information on this forum & its technical section.

Re: venting through magneto hole

thanks for the reply, i was afraid of that, the magneto seal hole was out of round so i repaired it or thought i did with JB weld,
seems like ill have to go back in there and figure something out, i didnt realize there would be so much pressure there, and thats with the vent working and the spark plug out
the repair plate from bsa looks like it was mounted using 3 holes for screws but if it was attached from the outside then the magneto wouldnt meet up close to the case and the gear wouldnt go all the way on the shaft.
If it is attached from the inside then the seal would be further out on the shaft
how did it attach? anyone?

email (option): taybrig@shaw.ca

Re: venting through magneto hole

The repair plate goes on the outside and is 2.5mm thick which must be designed to not interfere with the location of the mag.

http://www.wdbsa.nl/download/Magneto%20Oil%20Seal%20Flange.pdf

I guess your problem would be, how to pick up the center of the hole and machine the cover in situ?

You might have to re-address the repair the way you have done it. If the seal is still firmly glued in the case and it's the right seal and facing the correct way. ie open side with spring facing outwards to the right, and centered on the shaft.....I can't think what can be the problem?

Ron

email (option): ronpier@talk21.com

Re: venting through magneto hole

Ron has a point here. If there is no oil leak, just leave it like that.

Re: venting through magneto hole

['I guess your problem would be, how to pick up the center of the hole and machine the cover in situ?...']

Accurately assessing the centre of the hole is the key difficulty in any machined repair made to the crank cases and the only way to do it without a jig would be to set up the magneto on the crank case with the drive gear correctly meshed, then remove the drive gear and clock off the armature using a dial gauge to find the centre.....Machining anything in situ I would regard as effectively impossible and a complete engine strip down is really needed prior to doing a machined repair...At the very least the bottom half of the engine would need to be set up on a milling machine...

I made a jig to pick up on the original centre of the hole prior to carrying out the repairs on a milling machine...
Often the boss into which the seal fits will have enough material left to machine it out to make it true to the armature again without breaking through the side of the boss...In that case it can either be machined to suit a seal with a larger outside diameter than the original or after machining, an aluminium sleeve can be fitted to restore it to the original dimensions...

One way that a repair could be made using 'liquid metal' or similar would be to clamp the magneto to the crank case with the gears correctly meshed, remove the drive gear and then have a piece machined that fits onto the armature and has an external diameter to fit the oil seal. The seal could then simply be fitted over that piece, pressed into the liquid metal and then be left in place until it sets...Ian

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

Re: venting through magneto hole

61264688736_B25FDAE9_33C0_4171_854A_817F920E3385

hope this pic works, so what i did was to wrap the seal in saran wrap and put the JB weld in the worn area and press the seal into it till it set then removed the wrapped seal and installed it as normal, it seemed to fit ok (spring toward oil side) and buttoned it up
but then the chuff chuff noise on turning it over, so today i removed the cover and gear and all still looks ok but im guessing that the air is venting round the outside of the seal so i siliconed it in place tonight and will see what happens....im still kicking myself for missing it when the engine was apart.....

email (option): taybrig@shaw.ca

Re: venting through magneto hole

well the small amount of silicone that i used has sealed it up..no chuff chuff anymore, but its still a bit from getting it running yet so time will tell

email (option): taybrig@shaw.ca

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