scavaging

On removing the drain/ filter at the bottom of the cases after running the bike up how much oil should be there ?
I have no routed my breather into the oil tank but the knowledge from the vintage meeting at the weekend is that I should look at the scavaging side first.
Comments please
thanks Chris

About 200 to 250cc is usual after shutting off. Did you get the one way valve sorted and did it make a difference?

If your motor has wet sumped you will find a lot of oil coming out of the breather tube. After a while that should stop and only the return pipe in the tank should be flowing oil. What does your's do?

Cash

oil covered bike!

Thanks for the advice.
I had hoped to get my mate to practise on it at Lydden on Sunday. However no sessions were run as everyone had raced on Saturday.
So !! I do not know if the one way valve has worked (I fitted it without the spring) I also dont know if connecting the breather to the tank has helped. I dont remember that much oil coming out of the sump when I drained it after Donnington. So the game plan is to run it up on the roller tomorrow, then drain it down. I then intend stripping out the oil pump & blowing out the return system. Have a quick look at the pump itself but replace it anyway. Clean out the sump filter & the pickup pipe connector. New seals gaskets & rebuild it all.
As to what has been happening. I believe that the timed breather was pumping oil into the catch tank with great force & getting past the crank seal.
It covers the bike in 4 laps ie about 8 miles at 6,600 revs.
Just a question of working my way through everything but as Snetterton is a fast track I dont want to waste my entree fee.
all the best Chris

I haven't been here for a while, so I don't know the whole story, but I have a race Commando.
I always drain the sump before a race meeting.
If it has wet-sumped, it takes forever to scavenge it back to the tank. If you ride it too soon, you'll have oil everywhere.

If it's any use, mine has a '72 motor and the breather is a 20mm diameter clear pipe that is fitted where the magneto used to go on earlier bikes.
The catch tank is in the seat hump, which is uphill all the way.
When the engine's running you can see a small "wave" of oil in the tube a few inches up from the motor, but it doesn't seem to move anywhere.


If you're having problems with it spewing oil out of the breather, I'd say either it's wet sumped or there is crankcase compression from worn rings.

Oh yeah. If you have routed the breather into the oil tank, you still need somewhere for the air pressure to go.
If the breather is 20mm hose, you'll need a 20mm exit vent from the oil tank otherwise you will be pressurising the oil tank and that won't help the scavenging.
Remember that in a Commando, the pistons travel up and down together, so the crankcase changes volume by 750cc, 7000 times a minute. That's a lot of air that needs somewhere to go.

I have a71 and I went over to the updated sump plug with the magnet and screen minus the screen, I do not trust that circlip.What I was wondering is that year sump plug further back in the crankcase, which would seem to me to always leave a bit of oil in the crank even after draining?Any other 71 owners out there?Any info much apprecco.

drain plug

Hi
thanks John
we have replaced the rings after Donnington.
I will get a drain plug / sump plug & drain down before I go out at Snetterton.
I will keep you informed.
all the best Chris

Right !

Stripped the seat off & ran up the bike for5 minutes. Plenty of revs.
When we drained the sump we found over 350cc of oil there. Removed the filter & mesh & ran the bike again 250cc this time.Filter was clear. The return flow looks very healthy back into the tank but maybe is not coping under full revs.No oil from the timed breather or the timing side breather The drive oil seal is not coping so I will replace that tonight. Just a coating of fine spray from the drive side pulley.Think I will change the pump as a precaution & I
will take my road engine with me!!
all the best Chris

If you want someone who knows Nortons, it's worth chatting to Cray Engineering in Faversham, Kent.
He mainly does BMWs now, but he really knows Nortons.

Hogan!!!

Hi John
Thanks for the info.
I ran the bike for the first time in 20 odd years at Lydden & matched my best times from 96 on my 8 valve bonnie.
I remember the track specialist was the awsome mr Hogan on a 1200 cray beemer! Ten odd years ago he lapped me easily in the race this year 10 triples did me!!

On stripping out the oil seal I found it had been turning with the crank so have araldited in the new one in. I have decided I will drain the sump before I race at Snetterton & take the spare pump along with me.
all the best Chris

We must have raced together at CRMC meetings. I raced with the CRMC from 1984 to 1999 when I came to Australia. First I raced my Commando then I built a BM with Jim Cray's assistance.
Sadly Paul Hogan died in a car accident a few years ago.
Do you recognise either of these bikes?