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Late Jubilee crankcase breather

Submitted by dennis_thompson on Wed, 22/08/2018
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Light Twins

The question is does my 1964 Jubilee have a crankcase breather?

I see nothing on the crankcase behind the cylinders and below the carb that looks like a breather connection.

I do have a breather connection on the primary chain case above the clutch.

I am worried about pressure build up in the crankcase as I have oil leaks already and I have not run the engine yet.

Many thanks,

Dennis

Submitted by patrick_mullen on Wed, 22/08/2018

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The crankcase breather is above the drive sprocket behind the primary chain case and connects via a rubber tube to the oil tank. I just happen to have an engine sitting on my bench at the moment.

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Submitted by dan_field on Wed, 22/08/2018

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Whoa, your cases have had a mishap! But thatâs a pre 63 breather the 64 and on breather was on top of the cases, Iâll take a pic. Back in a mo ..... the breather is the copper pipe above the gearbox sproket

Submitted by dennis_thompson on Thu, 23/08/2018

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Thanks but mine is like Patrick's so it may be a pre-64 engine.

Presumably, the breather on top of the primary chain drive casing is somehow connected internally to the crankcase to vent that as well? If not how does the crankcase actually breathe?

Dan, are you sure your copper pipe is not a chain oiler using mist from the oil tank vent?

Regards,

Dennis

Submitted by ulrich_hoffmann on Thu, 23/08/2018

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Dennis, open up the primary chain case an see if there is an internal connection from that hose into the crankcase, but I doubt it, there is not much space behind the clutch.

Submitted by dan_field on Thu, 23/08/2018

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I think thatâs a home made breather for the chaincase, on a pre 64 engine the breather is just above but behind the gearbox sprocket, the copper pipe screws into the crank case. If the pipe isnât fitted youâll find it hard to see it without taking the chaincase off unless the engine is out of the frame.

I think mine (post 64) is a breather but will check in the morning, if you look closely you can see the lump running to the back of the crankcase. The manual seems to be silent on the matter.

Dan

Submitted by patrick_mullen on Fri, 24/08/2018

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Andy S has for years recommended moving the breather to the top side of the crankcases just behind the left hand barrel. I definitely agree with this practical suggestion as the original threaded hole into the crankcase on all the ones I have seen is completely inaccessible unless the outer primary case is removed. Exactly what shape the original pipe was is a good question as I have seen several different versions.Most (early ones at least) seem to be shortish plastic pipes only a few inches long. So connecting on the rubber hose which goes to the oil tank is about impossible unless it is connected up before putting the engine in. I have also seen a longer copper pipe used but the one example I knew was chromed and not very long either.

I have never seen a breather connected to the primary casing before and can't see how it could work. Unless the threaded hole behind the drive sprocket has been blocked up the engine will still breathe through this but would probably blow some oil out around the drive sprocket.

Patrick.

Submitted by dennis_thompson on Fri, 24/08/2018

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After looking at Dan's photograph I examined that position more closely on my Jubilee and found that an 8mm hole had been filled with Plastic Padding or some similar material that looks exactly like aluminium which is why I didn't spot it before.

I was able to drill this out after taking the battery box off and I have now glued a new copper pipe into the hole. I checked that the hole was clear and it looks to go into the crankcase.

I will use a 'Y' piece to connect the new pipe in line with the pipe from the chain case breather and run them both back to the oil tank.

There are two stubs on the oil tank but someone suggested on this forum that the larger stub is for a chain oiler so I will join the two breather pipes to the other, smaller stub.

Dennis

 



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