Breather for early model

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Feb 26, 2008
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I have just got 1971 Commando project, and have a couple of questions about the engine breather. The bike originally had the timed breather on the left hand end of the camshaft but this has been blanked off and has a breather hose coming from the blanking plate over the inner rear of the timing cover, the hose then travels up to near the oil tank and a T junction, one branch of the T goes to a dome on the oil tank the other to a small plastic bottle in the right side cover. The bike by the way has the central oil tank. I can't seem to find any information or pictures anywhere on these oil tanks, the later one seems to have the breather from the engine dumping into the top of the oil tank and then another hose running from above oil level to the air filter. I can only think that my tank at some stage had another hose coming out, as there is now a way in for the breather through the dome but no means for the tank to breathe.

On my tank near the dome there is evidence of welding at some time, have they for some reason taken the breather hose off that goes to the air filter or were they just fixing a crack or whatever. Any information on how the breather arrangement was on these central oil tanks would be much appreciated. From what I can see by reading the posts here relating to engine breathing, the best set up seems to the the latest type fitted with a flap valve from a car brake booster, running to a catch can. I think I'll go with this arrangement if there are the holes drilled between the crankcase and the timing case, I'll pull the outer timing cover off and see if there are, if not I am thinking of recommisioning the original timed breather, and running it to catch can. Any advise here would be welcome.

Is the dome an oil seperator? It might work quite well you'll only know if you try it out.

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