1968.. Crankcase mods

Adding holes to timing side may not be the best idea now. Perceived wisdom is to leave well alone there but to add a drain hole at about 7 o'clock from oil pump. Apparently, and I'm only going on tests done by a US tuner, the timing chest fills with oil that is churned into a froth by the gears and cannot escape until the engine stops. He made a see thru' cover insert to view what was happening on a running engine. Adding the lower 1/4" drain keeps the oil at an acceptable level. Removing metal from drive side wall around the drain/filter may not be necessary either. That was part of the 'Combat' improvement, which had the pickup originally at the front. You have the 'correct' original rear pickup position and nice big filter/drain.

On the breather front adding a larger one way valve (Norvil) is usually helpful but would this conflict with the timed breather? I don't know. I guess if there is enough pressure to open the valve via the timed breather then preventing reverse suction can only reduce reliance on it.

You should get on the 'Access Norton' site and do a search on breathers, theres a lot of stuff there........

http://www.accessnorton.com/norton-commando-f1.html

I did away with the timed breather and drilled through the timing side crankcase and fitted a breather where "your" points mount. The Yamaha XS650 breather works well there. Jim Comstock recommends the hole at 7 oclock to the oil pumpand whilst I haven't done this mod I think it would be a good idea. with your points mounting being behind the timing side, I'm not sure how you could fit a breather without it looking untidy.

The Yamaha XS650 breather valve is similar in construction to the CNW item with reed valves. you would just need to work out where to fit it. That is the hole that Jim Comstock uses to prevent the timing cover flooding. Your timing cover might not suffer from that with a chain drive to your points mounting. Try www.xs650shop.de for a Yam breather it should be cheaper than the Gucci CNW item

Yes it is the RED hole. I meant to attach that. Was going to do it on mine when I put the std cam back this winter but I forgot. It is supposed to be possible assembled but theres a lot of wall to get thru on my 850 cases, maybe a little less on early 750's. Even so its a substantial risk, minimising swarf ingress etc. Not sure why Access is blocked in ME. It's an American site of course run by a Brit from Essex but there a plenty of US sites available over there. Where are you exactly?