Oil return pipe

Hello again folks
Thanks to all who pointed me towards information on possible electric starts upgrades for my newly aquired 1973 Commando 850. We shall see if the Alton upgrade ever gets to market!
As the battery on my new machine was sh@gged I decided to fit a gel cell from a Moto Guzzi (because I had an unused one on the shelf). Now this is a big beast and totally OTT (unless i go for an electric start of course) but measuring it showed it would fit in the frame if i could wriggle it into place....... Wow! I suddenly learned about Commandos - you need the arms of Mr Tickle to reach all the zillions of screws bolting every bit to every other bit and I ended up unbolting oil tank, removing air filter (hells teeth that's a good bit of design - NOT), battery tray etc. etc. After loads of swearing the battery went in, fits fine and everything was bolted back up......
And the oil feed question?
In doing all this I removed the oil pipe from the rear of the timing chest to the top of the oil tank and found that it has some sort of valve fitted. This looks like it is an addition as it's not mentioned in the Norton or Haynes service manuals.
The question is, what is the valve for? Is it a one-way valve? I assume it will allow breather to 'blow' into the oil tank but not 'suck' back?
Any ideas why this has been fitted?
Do I need it or should I just refit a plain pipe?

Next job is to sort out the rubbish ignition switch - Can't say I really feel comfortable with a 1970s Lucas ignition switch (with 5 positions!!!) mounted to sit facing forward into all the weather it can get..... Will simplify the whole job to have permenant lights and a simple ON/OFF ignition switch methinks.
Tony

tony.pattison said:

Oil return pipe

And the oil feed question?

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I hope you mean "Breather" pipe-and not the oil feed or oil return pipe/s because they are the pipes that connect to the oil junction block?

tony.pattison said:

In doing all this I removed the oil pipe from the rear of the timing chest to the top of the oil tank and found that it has some sort of valve fitted.
what is the valve for? Is it a one-way valve? I assume it will allow breather to 'blow' into the oil tank but not 'suck' back?
Any ideas why this has been fitted?
Do I need it or should I just refit a plain pipe?

Click to expand...

It's a one-way breather valve, which is a fairly popular modification, it's purpose-as you rightly guessed, is to allow air and combustion gases to vent from the crankcase when the pistons move downwards, but not allow air back in as the pistons rise, so it is supposed to keep the crankcase slightly below atmospheric pressure and thus helps reduce oil leakage and (according to some) may possibly improve power output a little. (If you use the forum search function using the term "breather valve" you should find a lot of information?)

tony.pattison said:

a 1970s Lucas ignition switch (with 5 positions!!!)

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Five positions? I don't think it's the right switch-as the correct switch should only have four positions in the following order (turning the key clockwise)= Parking lights---OFF---Ignition---Ignition and lights.

Hello again
Quite right I did mean Breather pipe. The pipe is the Engine Breather pipe in your picture.
I'll have a look on the site to track down more on this valve. I can sort of see that this could maintain a bit of -ve pressure in engine so help preven oil being pushed out of joints and gaskets but can't imagine how it helps power output? Is this a generally accepted improvement or is it one of these 'magic mods' to some and 'waste of time' to others?

You could well be right that the switch is 4 position and I may strip it to check it out - the detents are all a bit imprecise and it feels to have 4 positions and another 'almost' position. Not knowoing what the positions were supposed to do didn't help! I was also confused by having some lighting features on the ignition switch and then a toggle switch on the headlamp too - must have made sense to the chap who designed it but the idea beats me! Personally with 35 years on old bikes and 25 years as an Electronic Engineer I do really prefer to minimise the wiring on these old machines - might not be a purist attitude but it works for me.
Tony

Ah
It seems the valve on my machine is an XS650 flap valve. Bit of a tight fit with Guzzi battery but I'll re-fit it I guess. I will experiment with effects of having it in or out as I'm not convinced by the some of arguments I've reasd about this mod...

tony.pattison said:

I was also confused by having some lighting features on the ignition switch and then a toggle switch on the headlamp too - must have made sense to the chap who designed it but the idea beats me!

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Most motorcycles of that period (yes-even the Japanese ones!) usually had a "Pilot" position on their lighting switches so the headlamp could be turned off independently to the pilot and tail lamps and that is what the (71-on) headlamp toggle switch should do = switch only the headlamp on or off.

[The headlamp flasher is unaffected by the toggle switch position as the headlamp flash button is fed from a different supply (white) wire.]

tony.pattison said:

I will experiment with effects of having it in or out as I'm not convinced by the some of arguments I've reasd about this mod...

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Oh, really. Like which ones and why?

And yes, you just started another breather discussion. :mrgreen: