Breather pipes crank to oil tank/ air filter

Combat breather I take it? Yes follow the diagram for the breather to the filler tower but whatever you do don't feed the lower pipe (in the tank top section) into the aircleaner stub. It will just make a big mess and drip on the engine/gearbox etc. Fit a small bottle in the battery tray somewhere and take the overflow breather into that. It has to be emptied of water/emulsified oil now and again but it keeps things a bit cleaner.

If you have a breather from the LH crankcase, I'm guessing it's from the timed disc on the end of the camshaft. If that's the case then you would not normally have a further breather in the back of the timing cover. If you have a breather in the back of the crankcase then you would not normally have a breather on the end of the cam. These breathers normally feed into the top of the oil tank and then the vapour tower (the cylindrical pot on the top of the oil tank)breathes into the air filter. As Keith says this can lead to oil contaminating the air filter unless you have very little blow-by and only half fill the tank. If you have the confidence in your rebuild and only intend doing short journeys, then half filling the tank will get the oil up to working temperature and tend to evaporate any condensation build up in the system. Filling the tank will reduce the space for breather gasses and will tend to pass more oil mist out the final exit breather.

Previously andy_withers wrote:

Thanks for the inform

Have both breather on bottom of crankcase which is unique to the 72 model? and it looks like modified breather going into the back of the timing case side.

I've connected the timing side one to the oil tank, any ideas what to do with the breather on the bottom of the crankcase, currentlystuffed with rag?

The breather at the lower left crankcase is the original and goes to the oil tank just below the filler cap (lid). The additional breather on the timing cover can go anywhere you like.

I should say that the two breathers may not work well together. Its a bit complicated and I don't properly understand it but they do seem to conflict with each other. Probably why one is blocked. I had that arrangement on my Combat, modded by the previous butcher/owner. It never was happy till I blocked the front oil pickup and opened up the rear pickup as per pre 72 and post 72/3. It then blew up thanks to a pattern N****l rod bolt. Have you had the cases modified as above? It is worth it even though many say they have never had issues with the 'Combat' oil return design. The fact that Norton returned to the earlier design from 73 suggests otherwise.