Forum

[stinkwheel]

I think the hole between the crankcase and oil tank might have been slightly enlarged when it became the main breather hole, maybe someone could confirm?

Those aluminium diesel fuel non-return valves work fine. I have dynamically tested one with the engine running and it flows more gas than a duckbill and in one direction only.

[windmill john]

More of a hypothetical question. When the piston is descending, it seems such a small hole to take that pressure (might explain some leaks).
The question, what is the down side of that hole being, say, twice the size?
The size could be to maintain a specific pressure in the crankcase possibly...
A bigger hole may allow to much oil to move between tank and crank!...


Actually a second (bonus) question.... how would you tell if you’d need a rocker breather? i.e. what signs?




John

[Wheaters]

Having asked a few questions and thought about this some more, I’m not sure a rocker cover breather is needed on these engines.

Pressure in that area will also pressurise the timing side and actually help return oil from the top of the engine to flow back through it and onward to the reservoir. Fitting a rocker breather might cause an excess of oil to build up, bearing in mind that crankcase gases vent back to the reservoir from the opposite side, which will oppose that flow, especially when the catch can begins to block up with oil emulsion, preventing the breather on the reservoir from working as advertised.

The oil level on the dipstick seems to vary a lot on these engines as it is! Unless the sometimes “temporarily missing” oil is in the crankcase, it can only be in the timing cover.

I think that without a definitive answer from the factory, we will never be sure.

[stinkwheel]

That "return" stub on the timing chest is effectively a rocker breather. There is a direct connection between the top end and the timing chest, that's how the oil gets back down. You could attach a hose, stick it in a glass of water and see if any bubbles come out when you run the engine.

[Wheaters]

I understand that there’s a duckbill one way valve designed to prevent return flow up the timing cover “breather” pipe.

My 350 Electra doesn’t have a timing cover pipe, btw.

[stinkwheel]

My 350 has one but it's just a brass stub going into the timing chest. There was a one-way valve built into the "return" hose from the catch can. I stuck a breather on the end of it just for fun to see if it reduced the amount of oil finding its way past the valve guides. Not had anyone to follow me to check for puffs of smoke on the overrun yet . It doesn't breathe anything noticeable out.

[stinkwheel]

I say "brass" stub. it's brass coloured, probably yellow passivated monkey metal like all the other fittings, didn't look that closely.

[Wheaters]

In view of the latest government statements I decided it was the day to put a few miles on my 350. After about 55 miles I’m pleased to say that the removal of the catch tank has caused no problem; I was cautious about the low routing of the single breather I’d fitted via a one way flap valve, exiting over the lower run of the rear chain. I wanted to ensure there was no sign of oil blowing out from the reservoir. There was none, the end of the pipe had only a small trace of oil emulsion. The oil level on the dipstick is sitting higher than before so it does appear that the return oil flow from the timing side has improved by ditching the catch canister, allowing improved venting.

The bike pulls really well on the 18/42 final drive gearing. I’d say it’s never run better and it sounds glorious.
The 5 speed box at last changes up and down perfectly since I fitted the lever return assist spring mod.
The spark plug colour is just about perfect, slightly richer than stoichimetric, I reckon.

A good day all round.