The Knowledge - Velocette Owners Club

#1237 Good point about the shaft seal. I'd not realized the size of the opening. I've intended to use a
reed valve from a airhead BMW. The valve is an aluminum disc approx. 25 mm in diameter with a reed
and stopped in the middle. The disc will be inserted in a aluminum cylinder turned up from some bar
stock and finished with a couple of barbed nipples for the breather hose. It will cost me about an hour of
time to build it and 7 bucks for the reed valve. The whole affair will be about 1 inch in diameter and 1
1/2 inches long. What did you use for your valve? I may be able to beat the size and buy one off the
shelf.
#1248 A few aftermarket companies make one way breathers, especially for Harleys. Try Spyke.com
for one. I've also run, with varying degrees of success, automotive PCV valves, smog (gulp) valves and
power brake booster valves. Bring your girlfriend to the auto parts store and have her find one that
blows a lot of air in one direction with least effort to open and nothing the other way. Sealing the
mainshaft is tougher. Only way I've found is to put the case in the lathe and open the hole out to 1.875
for a .188 wide lip seal. One could easily make a tool to do it in situ. I've heard of lubing the shaft and
squirting silicone seal in there to make a seal of sorts. Might work, might make a mess.
#1249 I have been using a breather intended for a certain American motorcycle for two years now. Its
available from www.dohertymachine.com. I don’t know if it’s worth installing, had quite a lot of work to
get it operating properly. One problem which is not finally solved yet is to plug the mainshaft breather
hole, haven’t found a reliable way to make a plug stick and it seems to work better when that hole is
plugged. Another problem is that there comes quite a lot of oil from the below mag breather outlet and
that must be taken care of somehow so now I have a hose from below the mag to the oil tank and the
breather valve is installed on the oil tank breather outlet. This tends to pressurize the oil tank so my
only engine leak is now from the oil filler cap. I still have problems with oil leaking from the gearbox into
the primary chain cover and eventually out from there in the usual places. Third problem is the sound,
the description oink oink is quite accurate. Have tried several ways of insulating the breather valve but
its still audible if You listen for it. It did cure the problem though of very small oil leaks from several
places on the engine especially after a hard ride but the system still needs further development.
#1255 Surely if a valve of this type is fitted it should be in the breather line from below the mag to the oil
tank? This would prevent tank pressurization due to the positive pressure required to open the valve
and consequently prevent leakage from the tank cap. The tank will still act as a separator/catch tank to
catch any oil returned through the engine breather and the tank breather will still work as intended and
vent only dry(ish) gasses.
#1257 I just happened to fit a drive side oil seal, because I use a Watson belt drive and oil always was
pumped into the primary drive up to the point when it exits through the felt ring after 200 miles. Now we
in Europe are strangled finding the correct diameter size seal. And the seal must be of tiny proportions
anyway that it can be fitted. The nearest solution was a metric seal with 35 mm inner diameter, and this
is not a proper shaft seal with an inner wire spring, just a lipped seal like for fork stanchions. For fitting
the crankcase has to me machined with a recess, in my case the top hat bush was the victim, and the
boss and recess of the primary sprocket as well to get it down to 35mm. I plugged the breather whole in
the crank and used silkone gasket on the slots in the sprocket facing the flywheel. To lubricate for the
rocking motion when the shock absorber is acting, I filled the inner recess in the sprocket with grease. If
the whole system works I can not say yet.
#1262 Thanks for info. I will try that this summer. I thought there would be a risk that the hose would be
filled with oil after the breather valve.
#1266 A little oil may collect in the pipe but it should be of no consequence. If there were no valve in
the pipe then any oil there would either lie in the lowest point of the pipe or drain back into the
crankcase when the engine is stopped, but if the breather adapter under the magneto is in the right
place then the amount of oil finding its way into the pipe is quite small, the main purpose is after all to
breathe gasses, not liquid. There is of course some liquid content but this is separated out in the tank.
The majority of this liquid is carried into the tank while the engine is running, and only a minuscule
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