Crankcase breather 1975 850

Follow this linkto the Technical section:

http://www.nortonownersclub.org/support/technical-support-commando/crankcase-breathing

I'm not sure of a UK supplier but you can get the XS650 valve from Heiden Tuning in the Netherlands.

http://www.xs650.biz/p/28/2501/mo8-cg|txt=*breather*/%2315-0677-reed-type-pvc-valve

There has been much discussion on the Commando forum and it has been suggested that these work best directly from the crankcases. If fitted in line from the timing cover they can cause higher oil levels in the timing chest by drawing the oil in there and preventing it from flowing back.

I've got one on the shelf and am still debating whether to fit it. I don't have an oil leak problem. A late 850 in good mechanical condition shouldn't as the joint faces had been beefed up by then.

I have used the Norvil type for 8 years and it works well but I do get a lot of mayonnaise in the line just before and after the valve, even after long hot runs. It needs cleaning every 2-3 months though that does not seem to impair the function even when full of sludge. The type that comes off the cases has been proven to be the best in a series of tests done by a US tuner Dave Comstock (same guy who is building FI systems for Commandos. Its not cheap but is available from Colorado Norton. The Norvil is just a chunky old brass valve used in Marine water systems.

I got one from A dealer in Germany, his website is xs650shop.de click on the union jack for english and then engine parts. cost 13 euros plus p&p came to 19 euros including tax. It's a good piece of kit and I mounted it on the front of the battery tray where the air filter used to be. (before I fitted a single carb and smaller filter) The CNW looks good but is expensive, probably got similar bits inside.

I use the standard set up on my MKIII, along with full synthetic oil. It still blocks with emulsified oil but nowhere near as bad as it used to. It easy to tell when it needs doing - with the black box airfilter you will see either emulisfied oil or water resting in the left hand intake when bike has stood for a while indicating its not blocked - if you cant - clean it out as it most probably needs doing, also remember to clean the pipe back to the oil tank.

Previously wrote:

I got one from A dealer in Germany, his website is xs650shop.de click on the union jack for english and then engine parts. cost 13 euros plus p&p came to 19 euros including tax. It's a good piece of kit and I mounted it on the front of the battery tray where the air filter used to be. (before I fitted a single carb and smaller filter) The CNW looks good but is expensive, probably got similar bits inside.

David, thanks for the link, I have ordered one myself today. Tell me, how have you terminated the outlet side of the valve? I have a mikuni single-carb setup that I am about to fit after my recent re-build. Where have you vented it to? Peter.

Previously wrote:

Previously wrote:

I got one from A dealer in Germany, his website is xs650shop.de click on the union jack for english and then engine parts. cost 13 euros plus p&p came to 19 euros including tax. It's a good piece of kit and I mounted it on the front of the battery tray where the air filter used to be. (before I fitted a single carb and smaller filter) The CNW looks good but is expensive, probably got similar bits inside.

David, thanks for the link, I have ordered one myself today. Tell me, how have you terminated the outlet side of the valve? I have a mikuni single-carb setup that I am about to fit after my recent re-build. Where have you vented it to? Peter.

My pipe goes to the top of the Fastback tank and a further pipe from the tower part of the tank goes to the back of the bike and vents to atmosphere. I don't think it's worth routing that back into the air filter.