Hitchcocks Forum

Hi All, I am newbe to the forum and Enfields. Can anyone please tell more more about what the rubber oil vent ? hose is for below the cylinder on my 350 bullet ? Also I am looking for a engine Haynes type manual, is there such a thing ? Thank you.

can you be more specific as to year precise model.

There are comprehensive parts diagrams here:-

http://accessories.hitchcocksmotorcycle ... ook-Online

If it's a pipe attaching to a backwards facing cast stub in the alloy of the crankcase just below the barrel on the left hand side, that will be the crankcase breather hose.



The piston goes up and down. As it goes down it draws fuel in or moves with the exploding fuel, as it goes up it compresses the fuel or expells the exhaust gas. There is also a space underneath it. As it goes down, it compresses the air in this space, as it goes up it creates a slight vacuum in this space. There is also a slight leakage of exhaust gas past the piston rings (some more than others where enfields are concerned).



If the area under the piston becomes pressurised, it will create resistance to the piston moving down, robbing the engine of power, it will also cause oil to start leaking by being forced past oil seals and gaskets. That hose is there to allow any excess gas pressure to escape. It will often (again, some more than others) carry some oil mist and combustion by-product gas/vapour but is mostly air. There is a non-return valve on the end of the hose to allow gas to escape out but prevent air being drawn in. The idea is to create a slight vacuum in the crankcase, this reduces "pumping losses" also helps keep things oiltight.



On multi cylinder bikes, this effect is minimal because usually one piston is up when another is down. On a large single cylinder bike, you effectively have a large and inefficient compressor under the piston.



What happens after that stub depends on the year and individual setup, it can vary between a simple short hose with a "duckbill" on the end that vents to the atmosphere to a more complex arrangement of catch cans and non-return valves introduced as environmental regulations became more strict.



Are you haivng a problem with it? It is normal for a small amount of mucky looking oily fluid to come out of the end of this hose if it's venting to atmosphere (if you held a bit of paper towel over it, it would be like breathng on a cold window). Some people take advantage of this and point the end of the hose at the chain as a kind of chain oiler. If it's pumping out a lot, it could indicate a problem with the engine or the routing of the hose.