Forum

[Mark M]

Just had a thought, the oil filler cap. This MUST have a small breather hole in it's top surface. It is tiny, only about a 1/64" but it makes a massive difference to the breathing efficiency. I built an early 500 Bullet and oil pissed out everywhere especially from the magneto drive seal until I remembered the need for the correct cap. Later Bullets and Twins (post 1955) had a cap with no hole, it is easy to fit the wrong one.

REgards, Mark

[Graham43]

Mark M, would this apply to the Electra X as well? Currently no hole in the screw on cap.

[Mark M]

Graham, no, the breather design is different and doesn't need the hole. Having said that I've used a spare cap with a hole in it on some late Twins (Connie, Mk1 Interceptor) which didn't originally have it and it helps them to stop 'sweating' oil (fine mist) as well so I'd say it might be worth a try if you're having problems!

REgards, Mark

[Tman]

Hi, a little update. It seems (though not 100%) that the oil was actually leaking out of the primary chaincase rather than the breather, and is due to a lot of oil being blown through the main bearing into the chaincase.

The engine breather pipe is clear and the two little disc washers are present in the breather body, the oil passage ways in the crankcase both to and from the two oil pumps have been blown clear, the little PRV/NRV in the mouth of the oil compartment has been removed, checked and appears to work well, the rocker pipe and passage-way into the head are both clear so I'm pretty sure the poor scavenging isn't down to any blockage or restriction.
Checking the oil pumps "discs" as the w/shop manual calls them, the feed pump (the one on the left) is poor when tested by the manual's suggestion of a finger over the hole and pulling out the plunger. There's very little resistance felt, unlike the scavenge disc which seems to be working as it should. This seems counter-intuitive to me. I can understand the visibly low rate of oil return to the tank if there's not much being pumped by the feed pump, but that doesn't explain why oil is being blown through the main bearing. Anyone have any thoughts before I spend £60+ on a (possibly unnecessary) new feed pump disc and plunger?

[Tman]

Revise that, on closer inspection it seems that most of the oil has come from the breather rather than leaked from the chaincase via the main bearing.

[Marko]

Hi Tman, my model G has suffered the same symptoms as yours; I've tried all the "fixes" I could think of. It used to pisss oil out of the crankcase breather (same set up as yours). It still blows oil out, not as much now , but if I do a 20 mile run the rear of the bike looks as if its been attacked by a lunatic with a can of chainlube (oil splattered all over the place). I've had an idea which i'm going to test soon (once I fix the evil constellation!): i'm going to re-route the path of the pipe from the crankcase breather to the oil filler "extension"... in essence making my own version of the Hitchcock bullet breather mod. Sounds daft but having to wipe the rear end clean after a blast does my head in, as, other than that, its a bloody nice bike that goes well.