Series A Twin Breather

[billirwinnz]

My 1936 A Twin has the oil tank breather connected to the front crankcase breather. The catch bottle of 250ml fills in about 200 miles and I'm assuming that oil from the tank in addition to crankcase oil is finding its way there. I see in the club A Twin parts list that there is no sign of an oil tank breather.

Does anyone else have this setup? Does the oil tank need anything more than a hole in the cap?

Cheers Bill

 

[Robert Watson]

I'll have to go and investigate what I did. The oil tank did come with a small tube that goes up from the bottom and ends up near the top of the oil tank. I think mine was originally plugged and then I switched tanks, and then I switched back having got the original tank repaired and seem to remember putting a piece of rubber tubing on this breather, but that was a few years ago and it might not have happened that way. I'll look tomorrow and let you know.

I do know that with such a small capacity I do fill the oil tank well up and get a bit of leakage around the oil cap .........

 

[Marcus Bowden]

Bill me handsome, Old Harry oil tank breather is a small bore pipe under the tank and is lead through the coils of the hire springs down to the rear chain area Have never actually measured what come out of it, I too use to suffer from oil around the filler cap so brazed on a large bore pipe lead down to a small pill bottle on top of the mag but never more than a couple of thimbles full. As the scavenge pump is twice that of the supply there must be a volume of C/case gases to the oil tank. My metering screws are removed from the rocker feeds as it is a small orifice (primus stove cleaner size) my two head breathers were lead to a catch tank but a little ugly so blanked them off and removed the coffin lid and fitted the coffin box and a ball non return valve (NRV) and the elephant trunk make a bit of a noise at the back of the bike so thinking of a read valve next time I find some thing suitable. If one has a large enough cavity box then the oil and vapor will separate then lead the drain line down to the crank case bottom through a hose with a 6" trap so the C/case pressure doesn't blow it back. Robert W told me this trick when I had an abundase of oil coming from the mag drive cover with the felt seal not good on front cam. Now has a lipped Gaco seal.
Take my coffin box off and have a look for your self Bill.
Will it be ready for the November riders rally ?
bananaman

 

[billirwinnz]

Hi Marcus
I'm reluctant to go the coffin lid breather way but will if I have to as it doesn't involve any non-reversable changes. I assumed that your setup would be effective but non-standard so I didn't investigate but I will tomorrow.
I'm planning to ride the twin to our annual "Dunvegan Run" in Dunedin in 2 weeks time but don't want to be having to drain the breather bottle every couple of hours.
I plan to take the TTR to the Riders Rally. I should have enough miles on it by November to be confident in its reliability. It was oiling plugs due to the cylinder oil feed being above the oil ring so I decided to fit a modern CP piston and rings from Neal which has just arrived.
I'll ride Harry for you before you get here.
Cheers Bill

 

[billirwinnz]

Robert and Marcus

After inspecting Old Harry which didn't have any obvious oil tank breather, I plugged the tube between the oil tank breather and the front crankcase breather. After 110km of open roads and hills there was no sign of the oil tank pressurising and there seemed to be less oil being lost.

Cheers Bill

 

[Marcus Bowden]

Just goes to show that what works for one bike doesn't necessarily work for another, yours is indicating that there is little blow by the pistons , good sign.