Engine breathing

Hi all - my 920 Mk2A is now run in (1500 miles) and runs a treat - one issue though:-

I removed the old air filter system a long time ago and fitted a single Amal Mk2 which I was never happy with - I have subsequently refitted 2 x Amal Mk1s - the bike starts and runs much better. Obviously the old engine breather system went when I fitted the single carb - I fitted a one-way 'clack' valve in the breather pipe from the crankcase to the oil tank - this has improved oil-leak problems (the engine is 100% oil-tight). I ran a pipe from the oil tank filler neck to the rear of the bike as the main breather - this works OK but I do tend to get a fair bit of oil dripping out of this when the bike is stopped after a run - the leakage does seem to vary from run-to-run. I gather that the the oil level in the tank has a lot to do with this and I try to not fill the tank above the 'low' mark on the dipstick which seems to help but I'm perplexed as to how so much oil finds its way up to the top of the tank (i.e. the filler neck). I also noticed that the filler-cap seal seems to be worn - I cannot make out what the material is - is it metal or rubber etc. - some oil seems to weep down the right hand front of the rear mudguard - I cannot see where it is coming from but suspect it could be the the filler cap - all other joints etc. seem bone-dry.

Any ideas ?

Cheers.

mwoo said:

I ran a pipe from the oil tank filler neck to the rear of the bike as the main breather - this works OK but I do tend to get a fair bit of oil dripping out of this when the bike is stopped after a run - the leakage does seem to vary from run-to-run.

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The filler neck stub should be connected to the crankcase breather outlet, the other stub on the top of the oil tank is the tank breather.



If you have the pipes reversed then it is understandable why some oil is being lost.

mwoo said:

I also noticed that the filler-cap seal seems to be worn - I cannot make out what the material is - is it metal or rubber etc.

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The cap gasket is normally cork.

[Edit] Also, there appears to be three versions of dipstick all of varying lengths with "H" and "L" marked at different heights.

Thanks L.A.B - I'll be damned - that's exactly what I've done !!! bugger !!!!!!!!!! - and I thought I'd covered all possibilities - - -

Cheers

mwoo said:

that's exactly what I've done !!!

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Well...you certainly aren't the first person to have done that!

I stuff some paper towels around the oil tank filler neck, and use them to wipe the dipstick. Then they catch the weepage that gets by the cap's gasket. The gasket has a tough job because that engine breather/return, especially with a reed valve, can throw a lot of oil right at the bottom of the cap.

As for the tank breather line, I made a catch can out of a black plastic 1 quart oil bottle; cut the neck off because it was too tall and to allow a nice sweep to the bend of the rubber line. With the catch can, in theory, I'm now able to check the amount of blow buy I'm getting after a hard day's running and compare that against any drop shown on the dipstick. Can't do that check if the blow by is going down the carbs or dribbling out the bottom of the air cleaner.

L.A.B. said:

mwoo said:

that's exactly what I've done !!!

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Well...you certainly aren't the first person to have done that!

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That's for sure.
I made exactly the same mistake. Some dripping from pipe when stopped.
Plumbed them the right way and problem disappeared.

Bob