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1972 Combat Oil pipe/crank breather pipe connection confusion.

Submitted by richard_chan on Mon, 05/06/2017
Forums
Commando

Hi everyone, Got my bike mostly sorted now with the help of a number of members here and in Germany. No more clutch slips since ATF changed and clutch cleaned. No leaks, no sumping. New front brake and all, so All good news so far... Since the bike is running as it should, I dug a little deeper to inspect all future possible leak and oil spots. I noticed an oil line coming off the oil tank is going somewhere that is not suppose to be? Or I could be wrong. Pls see below image. https://m.imgur.com/a/anwty The pipe from the oil tank circles in PURPLE is going down and under the battery, towards and attached to the Crank breather (here circled in BLACK https://m.imgur.com/a/KPwNJ ), The way it is attached it also very weird, from the crank breather using a larger pipe, then maybe 6 inches up, it then connects to some sort of connector, then connects a smaller size pipe up towards the oil tank. I'm a little confused as the schematic doesn't show this, in fact, on it shows a chain oiler or something. But if this set up isn't correct, then where is the crank breather pipe suppose to be connected to? Also, in the first image, circles in ORANGE, the breather pipe should be attached, but, mine has a rubber seal on it and it is closed off with no breather pipe going anywhere. Sorry if my writing is a bit messed up, I'm a little confused why the previous owner had done this or if this is all correct. Would be great if someone can shine some light on this. Thanks. Rich.

Submitted by john_holmes on Mon, 05/06/2017

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45 is the engine breather pipe, no idea why it's linked to fresh air when the other pipes are shown connected, it connects to 46 adaptor then to pipe 44 and finally to 47, 45 and 44 pipes are different diameters hence the need for 46.

23 is the oil return from engine to tank.

47 is the tank breather to the carb filter and connects to the oblong bit on the tank and then to the air filter assembly.

So the excess air exits the engine via the engine breather plus excess air in the oil return and both go into the oil tank, then the air moves out of the tank to the air filter.

What you have is not correct, cannot say why or if it works but some mods to the 72 cases close off 47 and take the air from elsewhere including the timing case and it could be going direct to the air filter.

The chain oiler connects to the little branch you see on the oil tank return pipe connection just above 23.

As long as the engine and oil tank have a route for the air to escape then air pressure will not build up, it is better for emissions for the excess air eventually to go to the air filter to be burnt inside the engine, but venting to the rear of the bike does mean you have a lower risk of any oil in the breathed air lowering the effective octane of the fuel as it burns in the combustion chamber.

My solution to the 72 issue is simple, fit a reed valve to pipe 44, shorten it suit and keep everything else the same.

Submitted by richard_chan on Mon, 05/06/2017

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Hi John,

Thanks for your reply and help again..

So what you're saying is... Schematics of Oil tank 45,46,44,12, is connected to the crank case breather, where I had a Black circle in the Crank Schematics. ?

23 is correct on my bike.

47 I have no idea yet, didn't check.

As for the oblongated bit - sorry, which is this?

Thx

Rich

Previously john_holmes wrote:

45 is the engine breather pipe, no idea why it's linked to fresh air when the other pipes are shown connected, it connects to 46 adaptor then to pipe 44 and finally to 47, 45 and 44 pipes are different diameters hence the need for 46.

23 is the oil return from engine to tank.

47 is the tank breather to the carb filter and connects to the oblong bit on the tank and then to the air filter assembly.

So the excess air exits the engine via the engine breather plus excess air in the oil return and both go into the oil tank, then the air moves out of the tank to the air filter.

What you have is not correct, cannot say why or if it works but some mods to the 72 cases close off 47 and take the air from elsewhere including the timing case and it could be going direct to the air filter.

 


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