I have a lovely Norvin with a standard spec Rapide engine finished in black.
After a particularly hard ride over the mountain on the IOM with Glen English on my tail, on a Commando, (with his wife on pillion),the poor 66 year old motor started to weep.
Nothing from the top end, just from a few secret places hidden under the engine. Very difficult to source as the motors painted black but I have a strong suspicion it could be from the vertical crankcase joint.
I have only 1 breather on the rear inlet valve cap and the standard timed engine breather.
After all the years of research and prototyping of breather solutions for this kind of problem there must be an agreed "industry standard" remedy but for the life of me I can't find it on the web.
There seems to be multiple solutions suggested ranging from moving the breather pinion 2 teeth to fitting elephant trunks to the points cover.
Does anyone have a tried and tested solution or should I just rebuild the engine in standard trim and hope for the best?
John.
When I first received my Comet it leaked oil from almost every pore and it almost gushed out of the breather. Months and months went by as I tried just about every breather type and configuration known to man, but still the leaks and oil use persisted. All accessible gaskets were also replace – some more than once, but to no avail.
After many hard learnt lessons and a finally a failed big end bearing I eventually stripped the motor right down followed by a bottom up rebuild; new mains, new big-end and new small end bearings, new muff and liner, new piston and rings, new cam, valve seats and guides, new valves – the list was never ending! When it came to reassembly of the motor I sparingly used Loctite 510 on all joint and gasket faces, allowing well over 48 hours for it to cure. During the rebuild I located the required parts and installed an ‘original’ timed breather; though I did follow the advise of Phil Irving in “Tuning for Speed”, which was:
“
Better breathing is obtained by Filing across the breather valve sleeve till the slot is a full 3/8” wide then rounding the outer edges of the flat so the outgoing air has a clearer passage; the edges of the slot should be left sharp to act as oil scrapers. Replacing the external banjo and pipe with a straight union and a large bore pipe running upwards and rearwards also helps.”
In my case I did not use a straight union, but rather a conventional hi-flow banjo. The other aspect I was careful about was breather positioning and timing.
Combining information from Irving, Richardson and Stevens I learnt that the breather spindle needed to be installed in my Comet with the breather spindle slot pointing downwards. In twins the slot in the spindle should be pointing forwards directly towards the top magneto stud.
With the spindle correctly installed and with PEI’s mods made to the breather valve sleeve (in fact in my Comet I may have made the slot a whisker wider than Phils’ recommendation), I rounded and polished all of the faces of the breather valve sleeve and made sure that both the edges of the opening in it were knife sharp. I then timed the breather so that it was closing at or just after bottom dead centre; on my Comet this meant it was opening at around 24 degrees after top dead centre. On a twin, you should set the breather timing so that it closes at 30 degrees after bottom dead centre of the REAR cylinder.
I ran-in the rebuilt motor with considerable care and can report, now with over 10,000 miles on the rebuilt motor it remains oil tight and oil consumption is so low as to be almost impossible to measure.
As to the breather hose – I followed Phil’s’ advise about a large bore hose running from the breather outlet banjo upwards till it touched the bottom of the fuel tank, then it arches downwards, behind the battery where it exits into my home made catch tank (made from a small discarded plastic juice bottle). 1,000 miles of spirited running see’s around 2 teaspoons full of milky emulsion in the bottom of the catch tank.
The only downside to all of this is that I no longer have a constantly refreshed film of oil covering most of my bike, so I need to be a little more diligent about chain lubrication and drying the bike off after rain and washing.
