Installed CNW Comstock reed valve breather off timing chest

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I installed a CNW/Comstock reed valve breather on my P11 timing chest in place of my hack job PCV breather. I'm hoping the CNW reed valve breather works better somewhere in the power delivery.

First and foremost the CNW reed valve breather is not designed to be installed off the timing chest like the 850 breather. It is designed as a bolt-on replacement for the breather on 72 Commando cases. To install it on my P11 I had to make a mounting plate/cover to go over the magneto hole in the timing chest. I started with a 6x12" piece of 1/4 aluminum flat stock. I used the gasket for the magneto to layout the 3 holes to mount the plate. I kind of faked the shape of the cover and made it large enough to mount the CNW reed valve. Matt sells the reed valve, reed cage, and top cover with the 3/8 hose connection without the piece that bolts to the 72 Commando crank case for crazy persons such as myself that want to install the reed valve off the timing cover.

Before you ask, the Comstock sump breather does not clear the cross members under the P11 frame, and I have a 2S cam that does not support a timed breather off the end of the cam toward the front of drive side crank case.

My timing case originally had a unthreaded hole at the lowest magneto mounting location. Typically the magneto gets a bolt through that hole from inside the timing chest. I threaded it for a 3/8-16 bolt I could wrench in a fastener from the cover side. Sinful I know, but I like easy, and did not want to take the timing cover off every time I come up with another idea for a breather.

The two holes into the crank case already in the timing chest were enlarged and one additional hole was added. Unfortunately, I did that around 1988 and can't find my notes yet. I think the idea was to make holes like what the 850 had in it. It is what uneducated people like myself were doing back then, before somebody decided it wasn't a good idea and plugged those holes

This is my old breather. Yikes, it did work though.

247P7562s.jpg


Old magneto hole cover.

247P7574s.jpg


Once I got the cover the right shape and could mount it, I laid out the 4 holes for the reed valve, drilled and tapped them. I also determined where the port into the timing chest would be for the reed valve. Matt provides a diagram for layout of two 3/8 port holes for the reed valve for people doing what I am doing. I changed it a little and made the port oblong and blended a taper on the port on the inside toward the center of the chest only. The side of the port closet to the tail end of the timing chest is not tapered. It's a flow theory, and probably about as useful as polishing rocker arms.

New cover and mounting plate for CNW reed valve getting hacked on.

247P7580s.jpg


Before deburring.

247P7590s.jpg


I don't have a machine shop in my garage. I did most of the work like a caveman would do it. It took me all day. I have not started the bike up yet, but will tomorrow.

The reed valve quacks like a goose kicking it over if the hose to the oil tank is off. With the oil tank connected to the reed valve outlet, it's quiet enough.

Tomorrow I'll report on my impression of how it works, and if it changed the tune at all.

Installed cover plate/CNW reed valve breather mount.

247P7596s.jpg


Installed CNW reed valve

247P7597s.jpg


Don't forget to open that shut off valve before starting the engine.

247P7602s.jpg
 
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Neat installation. I fitted a Reed vavle in the same place on my Commando. The valve I used was half a Hinckley Triumph sai valve, just hack sawed and bolted to the crankcase. Most egr valves can be modified in similar ways and some of the yzf egr valves can just be dismantled and the reed valve half bolted directly to the case. Same result less $$.
I picked up on the use of the Triumph sai valve on this site (Grandpaul?)
 
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Neat installation. I fitted a Reed vavle in the same place on my Commando. The valve I used was half a Hinckley Triumph sai valve, just hack sawed and bolted to the crankcase. Most egr valves can be modified in similar ways and some of the yzf egr valves can just be dismantled and the reed valve half bolted directly to the case. Same result less $$.
I picked up on the use of the Triumph sai valve on this site (Grandpaul?)
I like saving money as much as the next guy. I didn't pay the list price for the complete CNW 72 Commando reed valve solution, but it wasn't nearly as affordable as a modified SAI or YZF egr valve. Basically I paid for a clean compact install. Plus I like Matt's attitude, and support. I pondered many solutions, but the CNW Comstock version of reed valve made sense to my inner aesthetic side. Having had a few email conversations with Matt, I knew it would work as good or better than anything else being used. I got in my hack sawing, filing, grinding, and drilling making the magneto cover/mount. :)

Time to put on my big boy pants and boots, start it up, and go for a ride.
 

APRRSV

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I installed a CNW/Comstock reed valve breather on my P11 timing chest in place of my hack job PCV breather. I'm hoping the CNW reed valve breather works better somewhere in the power delivery.

First and foremost the CNW reed valve breather is not designed to be installed off the timing chest like the 850 breather. It is designed as a bolt-on replacement for the breather on 72 Commando cases. To install it on my P11 I had to make a mounting plate/cover to go over the magneto hole in the timing chest. I started with a 6x12" piece of 1/4 aluminum flat stock. I used the gasket for the magneto to layout the 3 holes to mount the plate. I kind of faked the shape of the cover and made it large enough to mount the CNW reed valve. Matt sells the reed valve, reed cage, and top cover with the 3/8 hose connection without the piece that bolts to the 72 Commando crank case for crazy persons such as myself that want to install the reed valve off the timing cover.

Before you ask, the Comstock sump breather does not clear the cross members under the P11 frame, and I have a 2S cam that does not support a timed breather off the end of the cam toward the front of drive side crank case.

My timing case originally had a unthreaded hole at the lowest magneto mounting location. Typically the magneto gets a bolt through that hole from inside the timing chest. I threaded it for a 3/8-16 bolt I could wrench in a fastener from the cover side. Sinful I know, but I like easy, and did not want to take the timing cover off every time I come up with another idea for a breather.

The two holes into the crank case already in the timing chest were enlarged and one additional hole was added. Unfortunately, I did that around 1988 and can't find my notes yet. I think the idea was to make holes like what the 850 had in it. It is what uneducated people like myself were doing back then, before somebody decided it wasn't a good idea and plugged those holes

This is my old breather. Yikes, it did work though.

247P7562s.jpg


Old magneto hole cover.

247P7574s.jpg


Once I got the cover the right shape and could mount it, I laid out the 4 holes for the reed valve, drilled and tapped them. I also determined where the port into the timing chest would be for the reed valve. Matt provides a diagram for layout of two 3/8 port holes for the reed valve for people doing what I am doing. I changed it a little and made the port oblong and blended a taper on the port on the inside toward the center of the chest only. The side of the port closet to the tail end of the timing chest is not tapered. It's a flow theory, and probably about as useful as polishing rocker arms.

New cover and mounting plate for CNW reed valve getting hacked on.

247P7580s.jpg


Before deburring.

247P7590s.jpg


I don't have a machine shop in my garage. I did most of the work like a caveman would do it. It took me all day. I have not started the bike up yet, but will tomorrow.

The reed valve quacks like a goose kicking it over if the hose to the oil tank is off. With the oil tank connected to the reed valve outlet, it's quiet enough.

Tomorrow I'll report on my impression of how it works, and if it changed the tune at all.

Installed cover plate/CNW reed valve breather mount.

247P7596s.jpg


Installed CNW reed valve

247P7597s.jpg


Don't forget to open that shut off valve before starting the engine.

247P7602s.jpg
Hi Schwany,
What are you using for ignition with the mag/distributor no longer there?

Ed
 
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Hi Schwany,
What are you using for ignition with the mag/distributor no longer there?

Ed
I am using a two wire Lucas 120W alternator, Antigraity 401 LifePO4 battery, TriSpark MOSFET reg/rect, Boyer MkIV ignition, dual epoxy filled coil, Autolite APP3923 plugs, and MSD plug boots. The Boyer EI is on the timing side of the 2S cam in a modified Commando timing cover. The original battery box was gone when I got the bike, and I wasn't doing a restore. I made a ground plane out of thin aluminum flat plate stock that is mounted behind the battery cover and mount the battery, reg/rect, and EI box on it. I run a #10 ground wire from that plate to the rear gearbox mount on the timing side.
 
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Went for a ride. Mellow and a little better down low short shifting on surface streets with traffic lights. Seems smoother going slow, and idle may have improved a little. Acceleration was good, but I have to do one more test to see if the top end is still there. Probably is. I didn't get on the HWY to find out.

Catch can (stock it would be a chain oiler) at the end of the oil tank breather exit pipe hose run had a little more oil in it than usual for a 18 mile put put ride. Need to get on the HWY see what happens at higher speeds.

No leaks. No complaints. I have to run to the hardware store and get some 1" 1/4-20 stainless button head Allen bolts. The standard 7/16" hex head bolts securing the valve body are not my bag baby.
 

mdt-son

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Hi Schwany,

Would there be sufficient space between crankcase and gearbox to install the breather at the rear of the crankcase as this is the recommended location? I am toying with the idea of installing this breathers on a G15, in addition to the Mk3. i will then remove the timed breather.

-Knut
 
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I installed a CNW/Comstock reed valve breather on my P11 timing chest in place of my hack job PCV breather. I'm hoping the CNW reed valve breather works better somewhere in the power delivery.

First and foremost the CNW reed valve breather is not designed to be installed off the timing chest like the 850 breather. It is designed as a bolt-on replacement for the breather on 72 Commando cases. To install it on my P11 I had to make a mounting plate/cover to go over the magneto hole in the timing chest. I started with a 6x12" piece of 1/4 aluminum flat stock. I used the gasket for the magneto to layout the 3 holes to mount the plate. I kind of faked the shape of the cover and made it large enough to mount the CNW reed valve. Matt sells the reed valve, reed cage, and top cover with the 3/8 hose connection without the piece that bolts to the 72 Commando crank case for crazy persons such as myself that want to install the reed valve off the timing cover.

Before you ask, the Comstock sump breather does not clear the cross members under the P11 frame, and I have a 2S cam that does not support a timed breather off the end of the cam toward the front of drive side crank case.

My timing case originally had a unthreaded hole at the lowest magneto mounting location. Typically the magneto gets a bolt through that hole from inside the timing chest. I threaded it for a 3/8-16 bolt I could wrench in a fastener from the cover side. Sinful I know, but I like easy, and did not want to take the timing cover off every time I come up with another idea for a breather.

The two holes into the crank case already in the timing chest were enlarged and one additional hole was added. Unfortunately, I did that around 1988 and can't find my notes yet. I think the idea was to make holes like what the 850 had in it. It is what uneducated people like myself were doing back then, before somebody decided it wasn't a good idea and plugged those holes

This is my old breather. Yikes, it did work though.

247P7562s.jpg


Old magneto hole cover.

247P7574s.jpg


Once I got the cover the right shape and could mount it, I laid out the 4 holes for the reed valve, drilled and tapped them. I also determined where the port into the timing chest would be for the reed valve. Matt provides a diagram for layout of two 3/8 port holes for the reed valve for people doing what I am doing. I changed it a little and made the port oblong and blended a taper on the port on the inside toward the center of the chest only. The side of the port closet to the tail end of the timing chest is not tapered. It's a flow theory, and probably about as useful as polishing rocker arms.

New cover and mounting plate for CNW reed valve getting hacked on.

247P7580s.jpg


Before deburring.

247P7590s.jpg


I don't have a machine shop in my garage. I did most of the work like a caveman would do it. It took me all day. I have not started the bike up yet, but will tomorrow.

The reed valve quacks like a goose kicking it over if the hose to the oil tank is off. With the oil tank connected to the reed valve outlet, it's quiet enough.

Tomorrow I'll report on my impression of how it works, and if it changed the tune at all.

Installed cover plate/CNW reed valve breather mount.

247P7596s.jpg


Installed CNW reed valve

247P7597s.jpg


Don't forget to open that shut off valve before starting the engine.

247P7602s.jpg
I like it. It's about the same as I did with a reed valve scavenged from a Triumph. I used a thinner piece of 6061 with thru bolts (safety wired) rather than tapping the plate. https://accessnorton.com/NortonCommando/it-all-started-with-a-cracked-header-pipe.32655/post-533245

Did you add any additional breather passages between the timing chest and the crankcase? There was a good post by @o0norton0o
 
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Hi Schwany,

Would there be sufficient space between crankcase and gearbox to install the breather at the rear of the crankcase as this is the recommended location? I am toying with the idea of installing this breathers on a G15, in addition to the Mk3. i will then remove the timed breather.

-Knut
There is space between the crank case and gearbox for the part and hose routing. I'm not familiar with the G15 frame though. If there is not a cross member in the way, it could be done. The breather orientation on the vertical mounted engine might be an issue. The flat section where it could be mounted is just about under the motor. I would fire off an email to Matt at CNW to find out. He is very helpful and has been quick on returning answers via email. I know less about the Mk3 than I do about what my wife is thinking at any particular time. ;)

The NYC Norton reed breather kit that screws in place of the sump drain plug would work on my P11, but my current exhaust is in the way. I thought the cross members on my frame were in the way as well, but they aren't. I would just have to be creative on hose routing to the oil tank. If I can ever find somebody in the US that can build me a set of tracker pipes with short megaphones on them, I would switch to the NYC breather. I could use stock chrome exhaust, and install the NYC breather, but I'm holding out for another custom exhaust.
 
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I like it. It's about the same as I did with a reed valve scavenged from a Triumph. I used a thinner piece of 6061 with thru bolts (safety wired) rather than tapping the plate. https://accessnorton.com/NortonCommando/it-all-started-with-a-cracked-header-pipe.32655/post-533245

Did you add any additional breather passages between the timing chest and the crankcase? There was a good post by @o0norton0o
My P11 cases are not like 72 750 Commando cases. The P11 timing side case has two holes in it already near the crank. I made them larger and added one more. I believe the P11 case also has the hole under the oil pump in it as well. Either that or I added it. Anyway, yes I did all that and more, more or less. I did it in the late 80's or early 90's when I installed the 2S cam in the P11 cases. I tried running that motor without a good breather solution back then and it hardly went over 60mph. That is when I did the PCV valve thing, and vented my valve covers. Venting the valve covers is for top end only. It does not help at all at low RPM. Matt at CNW suggested I cap those vents. I plugged them at the catch can, but will try one more time with them open to the can just to see if it spins up any quicker.

By the way, I have a light crank in the P11 and this CNW breather helped smooth out the idle, because there is now less crank case pressure at lower rpms for inertia to overcome. That's my theory anyway. I've been wrong before, or at least not nerdy techno enough to be making much sense. :)
 
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Hi Schwany,

Would there be sufficient space between crankcase and gearbox to install the breather at the rear of the crankcase as this is the recommended location? I am toying with the idea of installing this breathers on a G15, in addition to the Mk3. i will then remove the timed breather.

-Knut

Knut

I forgot to mention that the part without the '72 Commando adaptor plate is 1" thick, and the hose barb fitting is actually angled away from the cover a few degrees. On the G15, the part would be mounted further under the engine than it would on a Commando, and you would only need clearance between the crank case and gearbox to route the hose to the tank.

There is not a lot of material around the 4 mounting through holes and the hollowed out reed valve chest. If you used countersunk bolts, they would have to have a very shallow angle head. Bolts are 1/4-20.
 
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Knut

I forgot to mention that the part without the '72 Commando adaptor plate is 1" thick, and the hose barb fitting is actually angled away from the cover a few degrees. On the G15, the part would be mounted further under the engine than it would on a Commando, and you would only need clearance between the crank case and gearbox to route the hose to the tank.

There is not a lot of material around the 4 mounting through holes and the hollowed out reed valve chest. If you used countersunk bolts, they would have to have a very shallow angle head. Bolts are 1/4-20.
That is a wrong. Check your facts Schwany. :oops:

The thickness of the part is 3/4". I had 1" on the brain because that is the length the bolts would need to be for my install.
 
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I took the ole P11 out on the HWY today. Took it up to 80MPH a couple of times. Would have gone a little faster, but what is in my rear view mirror is a blur, and I don't want a ticket. During the rest of the ride I cruised with the slower traffic at 65-70MPH for a few miles. I doubt I went more than 25 miles total. On this test ride I opened up the vent hose from the valve covers to the catch can. Didn't make any negative difference anywhere in the power delivery. I plan to leave the valve covers vented for now.

The oil tank and valve cover vent catch cans had very little oil in them when I got back from the ride. This is a positive result. I'll have to do a 150+ mile round trip with some hills in it to see if that is the trend under load.

The tune is very close without touching it. I could leave it alone and just ride it, but probably won't.
 

Fast Eddie

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The best way to get the best from your cNw breather is to blank off any other breathers you have. Especially if they don’t have reed valves in them cos you’re then giving gases a way back in to the engine and thus undermining the purpose and function of the cNw breather.
 
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The best way to get the best from your cNw breather is to blank off any other breathers you have. Especially if they don’t have reed valves in them cos you’re then giving gases a way back in to the engine and thus undermining the purpose and function of the cNw breather.
True, but in my defense the valve cover venting has close to 0 pressure and 0 vacuum at the end of the hose since installing the CNW breather. So the breather is doing a better job than what I had previously. The vent hose use to pass enough pressure that I could feel it with my thumb over the end of the hose. It also passed a little oil mist as well. No more.

I told Matt I had valve cover vents when ordering the breather. Matt told me...

"I have experimented and tested the valve cover venting and it doesn't do much to help and even restricts the efficiency of a breather down low."

That to me says it does something high in the RPM range, but not enough to warrant bothering with it. That valve cover venting did help with my inefficient breather, but like I said it's not doing much of anything now.

My butt dyno can't feel the lack of efficiency down low either. ;) I have been thinking about getting new polished valve covers for years. The P11 valve cover castings are nasty looking up close, and would be a PITA to polish out. After some consideration, I'll plug the hose barbs screwed into the valve covers, and remove the long run of hose and catch can. Then order some new valve covers.

It's all a band aid fix. The NYC breather would be the right thing to do for ease of installation. With the CNW breather on the timing chest, the crank case still isn't being evacuated properly, but it's better than it was.
 

Fast Eddie

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I think you’re right, the reed valve is probably working so well that its breathing before the gasses can make it up to and out of your rocker covers.

Me thinks you can chalk this one up as a win !
 

cliffa

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I bought my Commando from the UK. While it was being shipped and knowing what a worthwhile mod it is, I bought the sump breather direct from Jim Comstock. However when I went to fit it I realized my bike had a third ISO fitted under the gearbox. As the breathers are quite large there was not enough room for it. Jim was great but I managed to sell it on.

Convinced that this was the best breather solution I was determined to make my own ( With Jim's permission), and this is what I came up with...

1627238834803.jpeg






1627238695528.jpeg
 
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I think you’re right, the reed valve is probably working so well that its breathing before the gasses can make it up to and out of your rocker covers.

Me thinks you can chalk this one up as a win !
As it turns out, plugging the valve cover vents individually was a bigger win. They were all tied together. when I went for the first test ride I only plugged the end of the hose at the catch can. This for some reason caused something odd to happen in the mid range when I'd get on the gas. Same thing happened with the hose open at the catch can. It wasn't a misfire or hesitation, just a flabby sounding exhaust note and minor lag. When I plugged each of the covers individually, I got back the linear acceleration. I don't need to do any fooling around with the needles or accel pump settings. Jobs done. I'm sure it could be better, but it runs pretty good.

Thanks for the reality check.
 
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I bought my Commando from the UK. While it was being shipped and knowing what a worthwhile mod it is, I bought the sump breather direct from Jim Comstock. However when I went to fit it I realized my bike had a third ISO fitted under the gearbox. As the breathers are quite large there was not enough room for it. Jim was great but I managed to sell it on.

Convinced that this was the best breather solution I was determined to make my own ( With Jim's permission), and this is what I came up with...
Cool. All I'd need to do is replace my exhaust. This is what is in the way. Tight like a tiger.

IMG_6105sc.jpg
 

jerrykap

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Cool. All I'd need to do is replace my exhaust. This is what is in the way. Tight like a tiger.

IMG_6105sc.jpg
That oil strainer screen isn't going to get cleaned often. I know several friends running these breathers and all speak very positively about them. Sounds well worth doing.
 
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