Author Topic: A10, overpressure in the timing side?  (Read 974 times)

Offline FoxDK

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A10, overpressure in the timing side?
« on: 04.07. 2014 16:50 »

Hallo,

I previously had some problems with my BSA A10 from 1960, shoots oil into the magneto, which result in lack of spark  *conf*

When I had the magneto removed the other day, I noticed the buildup of air pressure inside the timing-house, when I pressed down on the kick-starter. The outer timing cover was installed, but the magnet was removed. I had a plastic bag over the hole where the magneto is mounted and I could clearly see the plastic bag was pressed in and out when I pressed down on the kick starter.

Should this occur?

Best regards,

Frederik

Offline a10gf

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Re: A10, overpressure in the timing side?
« Reply #1 on: 04.07. 2014 17:33 »
Quote
I had a plastic bag over the hole where the magneto is mounted and I could clearly see the plastic bag was pressed in and out when I pressed down on the kick starter.
Clever experiment  *smile*  but I guess the pressure will build up, then -should- get released, but the mag simmer ring should be able to withstand it and stop any oil from getting trough.

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Re: A10, overpressure in the timing side?
« Reply #2 on: 04.07. 2014 17:47 »
G'day Fox, the short answer is yes. With the rise and fall of the pistons the case pressure is either + or -. The timed breather only activates at a small portion of the cycle. So if your breather is engaged on it's peg properly with the right thickness cork, what you have got is normal.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Offline Resto-Rob

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Re: A10, overpressure in the timing side?
« Reply #3 on: 04.07. 2014 18:19 »
I have just fit a new seal to my magneto as oil was getting past. I found it very easy to do so no need to worry about the process.  I found with a tiny bit of heat (with the armature removed) the bearing race came out easily :)  oil was getting past due to a badly leaking oil pump seal filling the timing cover.
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Offline wilko

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Re: A10, overpressure in the timing side?
« Reply #4 on: 05.07. 2014 00:35 »
What about the insulating washer. No drama?

Offline Resto-Rob

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Re: A10, overpressure in the timing side?
« Reply #5 on: 05.07. 2014 06:41 »
No drama with the insulating washer. I fitted a new one.  The only difficuly was in re installing the bearing race, having to fight against the magnets! :)
When life throws you a curve..... lean into it!!
1953 BSA A10 Plunger
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Offline FoxDK

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Re: A10, overpressure in the timing side?
« Reply #6 on: 05.07. 2014 09:46 »
G'day Fox, the short answer is yes. With the rise and fall of the pistons the case pressure is either + or -. The timed breather only activates at a small portion of the cycle. So if your breather is engaged on it's peg properly with the right thickness cork, what you have got is normal.
Cheers

Thank You all for Your answers. That must be normal. The magneto have just been to service, and a new simmer ring have been fitted, maybe the old simmer ring was in bad condition.

Muskrat - How do I check that my breather is engaged on it's peg properly?


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Re: A10, overpressure in the timing side?
« Reply #7 on: 05.07. 2014 11:03 »
The breather passage is much smaller than the magneto mounting hole. I expect that makes a difference,

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Re: A10, overpressure in the timing side?
« Reply #8 on: 06.07. 2014 15:14 »
might be wise to blow through the breather line at the camshaft end with an air line as some old cork may be in there?

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Re: A10, overpressure in the timing side?
« Reply #9 on: 06.07. 2014 19:34 »
I'd use comp air from the other end. The exit hole/tube at the back of the cases.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Offline FoxDK

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Re: A10, overpressure in the timing side?
« Reply #10 on: 16.07. 2014 10:59 »

Ok, thank You  *smiley4* I will try to blow the breather line with comp air.

Regards Frederik