If you came here expecting to find out where XSMike gets his breather, sorry. This is more to show what the insides look like.


All apart. I didn't know the reed valve came out. I thought it was glued in or something. I put a little air to the exit port and the reed valve popped out. Two M6 screws, Intake housing, Reed Valve, and Exit housing.


Reed valve back in the Exit housing.


Near the upper right of the reed valve you can see the drain hole I drilled. This will allow any oil that gets pushed up past the reed valve to drain back to the sump.


All assembled. The previous owner had added the barb fitting so I didn't have to.

The barb fitting was probably put in because the original pressed in part fell out, like it did on mine.

The early XS 650 PCV valves didn't have a spigot for the outlet, it was the flange only.

JimC wrote:The early XS 650 PCV valves didn't have a spigot for the outlet, it was the flange only.

That makes sense, it looks like an afterthought compared to inlet.

Just curious, aside form the stock breather hose, why do you need this or what are the benefits of the different breather?

britbike220 wrote:Just curious, aside form the stock breather hose, why do you need this or what are the benefits of the different breather?

Do a search and you'll find volumes of info on the XS 650 PCV valve and other breather valves for the Norton.

Ok, reading about it says more HP, no biggie for me to get a hp or two out of a bike I don't push anyway and helps stop leaks? I guess what I should of asked is what made people start putting these on in the first place, what leaks does it stop and though simple and cheap is there a real benefit to the average person? Oh and are there certain years of commando's this is better for. I just ask because I haven't had any out of the ordinary issues on my 73-850 in the last decade, but if it is something noticeably beneficial I'd put one on. The cnw breather seems like a lot of work and expense if there are minimal street gains. 16.00 bucks is a no brainer for some gain other than it looks cool. The posts I read seemed to talk a lot and not really define why, but I could have missed something in the posts I read, thanks.

I don't think you'll find many claiming extra HP from fitting a breather valve. Most, like me, fit them to cure those persistent irritating small weeps of oil.
Typical ones are the rocker covers, back of the barrel to crankcase and cylinder head pushrod tunnels.

Some engine don't show any of these, other have these and a few more which even the most meticulous rebuilds don't seem to cure 100%. A breather valve gives all the seals and gaskets an easier time saves the hassle of repeated strips and rebuilds chasing down every small weep.

britbike220 wrote:Ok, reading about it says more HP, no biggie for me to get a hp or two out of a bike I don't push anyway and helps stop leaks? I guess what I should of asked is what made people start putting these on in the first place, what leaks does it stop and though simple and cheap is there a real benefit to the average person? Oh and are there certain years of commando's this is better for. I just ask because I haven't had any out of the ordinary issues on my 73-850 in the last decade, but if it is something noticeably beneficial I'd put one on. The cnw breather seems like a lot of work and expense if there are minimal street gains. 16.00 bucks is a no brainer for some gain other than it looks cool. The posts I read seemed to talk a lot and not really define why, but I could have missed something in the posts I read, thanks.

Search "breather" and "comnoz".

Most common benefit is less inside pressure to blow oil out where ever. Less common is extra hp which would only show up at maxed out loads-rpms. To get best of this benefit open up the vents between sump and TS case volume and put in some sort of check valve. To exceed this put in exhaust extractor to pull stronger vacuum and maybe some extra oil smoke out the pipe too. As rpm increase the elastic nature of Brit cycle engines shows up to send waves of metal surf along seams.
Most common crank check valve is made by Krank and cost ~$90. For sure the reed valves look cooler but don't know if any advantage over inline type brake vent valves. Someday I'll put PSI gauge on and see what it shows with various combo's.

swooshdave wrote:Search "breather" and "comnoz".

Those search terms together provided an enormous amount of info, thanks Dave.

That valve is identical to the SAI(secondary air injection) reed valves on my Triumph. A lot of the Triumph guys take those off the bike, replacing them with blank-off plates, due to the 'popping' the SAI's cause on deceleration, especially if the exhaust is replaced or a different map installed on the ECU.

My $6.00 Motormite disk valve is still working fine after 10K miles.

Ya, I thought they looked similar, but the triumph ones do not have the backing plate with intake opening. I have three of them wasting away on the shelf in the garage from my daytona, but unless there is a backing plate they can't be used. I don't have a machine shop so out of luck.

britbike220 wrote:

swooshdave wrote:Search "breather" and "comnoz".

Those search terms together provided an enormous amount of info, thanks Dave.

Yeah, I have a feeling this thread will bloat to 5-6 pages before it's done.

oh ya at least, but this is where I got all of my answers, in the first few pages.........crankcase-breather-t3864.html