Some contributors have advocated sealing the end face of the dynamo against the crankcase. Don't do it! The Primary Chaincase needs to breathe. Ask Hugo Myatt about the consequences of applying sealant.
Rapide Oil Leak - Help Please
- Thread starter youngjohn
- Start date
On my bike with a 'Walkernator' I totally seal the dynamo replacement to the back of the crankcase casting but I have a small breather fitted to the filler cap. All the other bikes to which Walkernators are fitted are also fitted with a totally sealed system and in fact I provide a large 'o' ring to fit into the cone to take up some of the space which would otherwise have to be filled with sealer. If we do not do this then oil pours out of this joint despite the oil thrower. I do not know what happened to Hugo's bike but it does not happen to them all so a bit more information might help us all here.
I agree with Norman, total sealing of alternator drive (or generator) to casing is the way to go. The only breather on my primary case is a .125" hole drilled through an alloy plug that is driven into the tunnel for the left hand kick start shaft. Any pressure escapes easily around the right hand quadrant shaft, and any oil mist keeps the selector mechanism lubricated. An occasional oil drip appears below the selector cover, but that is ok in my book, and is ignored.
John.
John.
Surely unless you have sealed main bearings any pressure that builds up in the Primary case would blow back through into the crankcase. My "D" doesn't have a breather in the primary case although there is n occassional drip the the kick shaft tube.
That's exactly right John. I was assuming that we were talking about sealed main bearings as the primary breathing would not be an issue otherwise.
What happened to Hugo's bike was written up in MPH a long while ago. He was puzzled by the fact that his gearbox was getting pressurised, thinking at one stage that there might be a blow-through from the flywheel section of the crankcase. In fact, sealing the dynamo prevented the chaincase from breathing so pressure coming through the drive-side main bearings was being forced past the oil seal on the clutch shaft which, after all, is meant to keep oil in, not out. The method used by Hugo to confirm gearbox pressurisation is best left to him to describe.
Hi all,
I'm just catching up having been off-line for a few days. The following is a summary of the MPH article Len refers to.
Having had my Rapide engine rebuilt by a Vincent specialist (Not the one who did my girdraulics!) I decided to make the primary chaincase completely oiltight with particular attention to the dynamo drive. I succeeded 100%. Not a drip. However the following phenomena happened. The oil in the chaincase vanished and the oil in the gearbox rose dramatically. The were lots of suggestions e.g tightening the crankcase halves, a porous wall between gearbox and sump, mistimed breather etc., it was none of these. I purchased a packet of condoms and after taking off the gearbox oil cap and removing the dipstick I pushed a condom over the gearbox oil filler (I don't remember how I explained away the remaining two). I rode the bike for less than a quarter of a mile. I was amazed how much a condom can expand. It ballooned up to such an extent that it forced my foot off the footrest, which says a great deal for the manufacturers claims. Anyway it proved that the gearbox was being drastically pressurised. The Prof came up with the answer. When the engine had been rebuilt the drive side outer main bearing had been fitted with a sealed bearing but with the inner seal removed. The outer seal was working as a diaphram flap valve that opened when the pistons descended allowing pressurised oil/air into the chaincase but neatly closing when the pistons ascended. The result was that at every down stroke the chaincase became more and more pressurised eventually forcing the oil/air though the gearbox bearing seal and into the gearbox with dramatic results.