Ajs 350 16m 1948 Crankcase breather

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Ajs 350 16m 1948 Crankcase breather

Postby got2BaSBT » Sat Apr 25, 2020 10:52 am

Morning everyone, my 16m is a little bit smokey when warm, the oil level is correct and it has the correct oil. Am I right in thinking there is no breather other than through the main bearing seal into the primary case. If so has anyone ever fitted a breather to theirs?
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Re: Ajs 350 16m 1948 Crankcase breather

Postby ajscomboman » Sat Apr 25, 2020 11:11 am

The breather is not linked into the primary case. Just behind the case on a boss by the bearings there is a taping for a brass male/male fitting which the breather pipe is attached. If you are able to lay on the floor and look at the crankcase in that area you should be able to see the pipe and when running you can feel the air pressure pulse out. Alternatively you can use a clear hose and use it like a water level and watch the fluid move with the stroke of the engine. If it doesn't let any air out then it's blocked and this will cause smoking or engine leaks as pressure is building in the cases.

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Re: Ajs 350 16m 1948 Crankcase breather

Postby SPRIDDLER » Sat Apr 25, 2020 11:33 am

Breather - crankcase marked.jpg
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Re: Ajs 350 16m 1948 Crankcase breather

Postby pkr87 » Sat Apr 25, 2020 3:22 pm

I have just put the original engine back into my 16MS after replacing the broken big end. When I started it that breather was pumping oil so I fitted a pipe to feed it into the oil tank. I obviously can't give the bike a proper road test but after a quick run round the field everything seems to be OK so hopefully I can leave well alone.

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Re: Ajs 350 16m 1948 Crankcase breather

Postby ajscomboman » Sat Apr 25, 2020 3:30 pm

pkr87 wrote:I have just put the original engine back into my 16MS after replacing the broken big end. When I started it that breather was pumping oil so I fitted a pipe to feed it into the oil tank. I obviously can't give the bike a proper road test but after a quick run round the field everything seems to be OK so hopefully I can leave well alone.


Be careful, I've just had a single in the workshop that has had the same mod done. I disconnected the pipe and never had so much emulsified shit come out a breather pipe, ever! I trimmed it back to standard and told the owner and showed him what came out.

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Re: Ajs 350 16m 1948 Crankcase breather

Postby pkr87 » Sun Apr 26, 2020 6:27 am

ajscomboman wrote:
pkr87 wrote:I have just put the original engine back into my 16MS after replacing the broken big end. When I started it that breather was pumping oil so I fitted a pipe to feed it into the oil tank. I obviously can't give the bike a proper road test but after a quick run round the field everything seems to be OK so hopefully I can leave well alone.


Be careful, I've just had a single in the workshop that has had the same mod done. I disconnected the pipe and never had so much emulsified shit come out a breather pipe, ever! I trimmed it back to standard and told the owner and showed him what came out.

Thanks for your reply. The original engine has been lying in my shed for 4 or 5 years and the bike had a 500 engine fitted which I did not like. So I found all the bits and rebuilt the engine with the original piston and rings ,which are free in their grooves. When I started the bike it ran beautifully, no smoke or rattles but it was pumping oil out everywhere including out of the breather pipe. My thought was that at least it goes and when we get back to the 'new normal' I could whip the barrel off and sort out the piston and rings.Even a re-bore perhaps

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Re: Ajs 350 16m 1948 Crankcase breather

Postby Dave T » Sun Apr 26, 2020 11:57 am

Two questions.
1:How long did it pump oil out for? Could it have been the sump too full after "wet sumping" and after the oil had returned to the tank it would have stopped but you didn't give it time?
B: Do the rings need time to bed in? After my last rebore my G80 "pissed" a big puddle everywhere but after a tankfull of fuel used it reduced and eventually stopped. Completely, I was very impressed as I thought"this is going to go on forever!"
Old bikes eh?
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Re: Ajs 350 16m 1948 Crankcase breather

Postby pkr87 » Mon Apr 27, 2020 5:39 am

Dave T wrote:Two questions.
1:How long did it pump oil out for? Could it have been the sump too full after "wet sumping" and after the oil had returned to the tank it would have stopped but you didn't give it time?
B: Do the rings need time to bed in? After my last rebore my G80 "pissed" a big puddle everywhere but after a tankfull of fuel used it reduced and eventually stopped. Completely, I was very impressed as I thought"this is going to go on forever!"
Old bikes eh?
Have fun, Dave.

The engine is unlikely to have wet sumped as it was only filled with oil when I fitted it into the frame. I did not run the engine for long with it pumping oil. I fitted the breather pipe and then finished assembling everything. The only ride I could do was around the garden and there do not seem to be any leaks. The 500 engine was a bit of a mystery, in the 16MS it was harsh, difficult to start and vibrated like mad. I did use it in another bike and it was not too bad, but the original 350 engine back in it's proper frame seems much more friendly. I am really looking forward to riding the bike now because I have tended to leave it in the shed as it was not a nice bike to ride, I think it just did not like me.

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