The pipe on the oiltank is the vent pipe for the tank and not involved in any way with the crank case breather assembly...
WDM21s had the crank case breather located in the drive side crank case half just below the barrel base..Postwar engines from 1948 had it located in the timing cover...
In both locations the breather works in the same way...Internally a small Bakelite disc is trapped between the breather fittings...When the piston descends the resultant pressure pushes the (flap) valve disc of its seat and air is displaced from the crank case..
When the piston rises the partial vacuum created pull the disc back onto its seat, shutting the valve...This reduces the total amount of air drawn into the cases...
The process is the repeated on the next cycle...No spring is fitted to the valve..It functions only by air pressure and vacuum...
This reduces mechanical pumping losses created by moving all the air in and out of the crank case...
There are slight variations in the internal fitting that holds the disc and two basic versions of the valve fitted in the timing cover..That was altered to reduce oil losses through the breather. Actual breather function is the same for all types...Ian
email (option): ian@wright52.plus.com
The oil tank vent pipe is a two piece construction...A short rubber connector of the same dimensions as the ones in the engine oil pipes and a length of copper tube...
It goes basically, vertically downwards from under the oil tank and terminates just below the lower edge of the gearbox mounting plates where it vents to atmosphere...
At the lower end the copper pipe is clipped to the gearbox plates using a 'P' clip and a 1/4" cycle nut and bolt...
You will see the drilling for the 1/4" bolt in the gearbox plate just behind the rear gearbox mounting bolt...Ian
email (option): ian@wright52.plus.com
The crank case breather pipe is copper all the way...Cadmium plated originally I think...You can see the route it takes from the breather in this photo..It passes under the contact breaker cover and then turns down in a gradual curve between the back of the primary chaincase and the outer face of the gearbox plate on that side. It finishes just below the lower level of the plate and vents onto the road surface...Ian
email (option): ian@wright52.plus.com
That was mid June on the return trip from the Normandy D Day commemorations..
The umbrella is a great invention...Keeps you dry when it's raining and in the shade if it's too bright...
...Ian
email (option): ian@wright52.plus.com
...Ian It's quite the trick to open one when riding, much less keep it upright after that. I find they make the bike a bit unsteady, especially at higher speeds...
email (option): cas.vanderwoude@gmail.com
Holding one upright over 15mph can be tricky...but pointing one backwards does provide a useful boost to the M20s brakes... ...Ian
email (option): ian@wright52.plus.com
...Ian Just like in the races!
Imagine Ian the surprise of the salt flats people when you go there and at the end of your record breaking run reach for your umbrella to stop the bike!
...Ian It's quite the trick to open one when riding, much less keep it upright after that. I find they make the bike a bit unsteady, especially at higher speeds...
Higher speeds ?
Wm20 ?
email (option): bsansw1@tpg.com.au