Forum

[PO51UHD]

Firstly apologies to Connieowner for hijacking this topic!

Mark - many thanks for your kind words about my RealClassic articles! The bike's going well thanks, but I confess I haven't put many more miles on it yet this year. I've also fitted rearsets (home-make from scratch) which work really well, and am contemplating ace bars to complete the look!

I certainly agree with your suggestion about an additional catalogue for twins - will write to them forthwith to reinforce your suggestion - and thanks for the info on rocker feed 1:4 pipes - I've not seen that!

Regards Stephen

[Tim NZ]

There is a simple reason why the breather vent of the drive side of the crankcase below the LH barrel carries oil: centrifugal force. Most of the oil in side the crankcase is initially being spun to the outer surfaces.


Which is why the central crank-shaft breather does not see oil migrating into the primary chain case.


Another contributing factor why there is an excess of oil present at the LH case breather is due to the crank case return pump having to deal with around 25% more oil than it is supposed to, more so with the connie.


The rocker oil supply that drains down the tappets and into the cam tunnels is able to enter the crank case proper via the oil drillings in the lower half of the barrel liners. Worse with the exhaust cam as the camshaft tunnel is flooded (to reduce cam wear) and the unwanted oil drains straight onto the spinning crank through both case ‘cam tunnel windows’ that open to the barrel liners.
With the Inters this was all alleviated as the cam tunnels are sealed off from the crankcase, with the inlet cam tunnel draining direct into the oil tank, and the exhaust tunnel and timing side draining to the sump, and both sides of the oil return picking up from the crankcase. Plus, their breather from the LH case which goes into the top of the oil tank is also vented to atmosphere.
The simple fix that I apply to the twins breather is to fit a post 2004 Bullet catch-can inside the tool box, a circa 1957 ‘open’ vent off the LH crank case, (it is intended to have a simple ‘duck-bill breather hose attached) The vent is connected up to the catch-can, via a 7/16” hose. The fume/steam/condensate is vented directly out the rear of the bike, and the oil mist in the fume is trapped and collected in the lower half of the Catch can, where it is free to drain back either into oil tank where the case is machined for such, or in the case of the earlier motors, into the fitting screwed into the back of the oil filler neck.


One could fit the Inter Oil tank breather fitting, but I prefer the larger and simpler 1957 vent with the 7/16 hose, as it reduces the velocity of the fume and allows the oil to separate easier.