New Breather on 1972 Combat

I just installed a reed valve breather on my 1972 Combat. It was from Don Pender, and appears to be very similar to the CNW version found here:

Niece piece of kit. It was a bit fiddly to remove the stock breather and install the new one. If you could turn the bike upside down, it would have been much easier.

The theory with this breather is it lowers internal engine pressure into the negative zone (read vacuum) minimizes oil leaks, clears excess oil in the crankcase, etc.

Years ago this bike was installed with the intake valve cover breather mod most of us are probably familiar with: a barbed spigot was installed in the intake valve cover, and a hose run to an oil collector bottle, oil tank, or atmosphere (as in my case). The engine never leaked oil, and nothing ever came out of the hose.

Now that I have the new breather which is apparently much more efficient at lowering internal engine pressure, I am wondering if I should remove the old inlet valve cover breather? Does it reduce the effectiveness of the new breather?? What do you think???

If you don't remove it, then the piston recovery stroke will pull air back into the head area and the power stroke will push it out again negating the function of the reed valve which times itself with the piston stroke to open and close when appropriate.

In my case I have the timing side reed breather modification and I also use a second Jim Schmit's camshaft reed breather on my camshaft port on the primary side. Because both breathers each have a reed valve they both synchronize with the piston travel direction and pressure flow so they can work together. If one port didn't have a reed valve then it would breath in and out negating the reed valve function of the other port...

Stephen Hill said:

I just installed a reed valve breather on my 1972 Combat. It was from Don Pender, and appears to be very similar to the CNW version found here:

1972 Engine Breather Modification

Experience an increase in engine performance Eliminate persistent leaks at gaskets, seals, tach drives, head, crank case joints and more Lower the operating temperature of the engine oil The valve can operate consistently during a far higher rpm range than the Commando engine can ever reach The...

coloradonortonworks.net

Niece piece of kit. It was a bit fiddly to remove the stock breather and install the new one. If you could turn the bike upside down, it would have been much easier.

The theory with this breather is it lowers internal engine pressure into the negative zone (read vacuum) minimizes oil leaks, clears excess oil in the crankcase, etc.

Years ago this bike was installed with the intake valve cover breather mod most of us are probably familiar with: a barbed spigot was installed in the intake valve cover, and a hose run to an oil collector bottle, oil tank, or atmosphere (as in my case). The engine never leaked oil, and nothing ever came out of the hose.

Now that I have the new breather which is apparently much more efficient at lowering internal engine pressure, I am wondering if I should remove the old inlet valve cover breather? Does it reduce the effectiveness of the new breather?? What do you think???

Click to expand...

They work fine. Removing the gearbox makes the instalation easier. On this one, the tach drive was the weak seal and after the upgrade no more sweating there.

Installing the two button head allen screws holding the breather to the crankcase was awkward, but do-able. I swapped the four button head allen screws for hex head cap screws, which allowed me to use an open end wrench to finish the job.

o0norton0o said:

If you don't remove it, then the piston recovery stroke will pull air back into the head area and the power stroke will push it out again negating the function of the reed valve which times itself with the piston stroke to open and close when appropriate.

In my case I have the timing side reed breather modification and I also use a second Jim Schmit's camshaft reed breather on my camshaft port on the primary side. Because both breathers each have a reed valve they both synchronize with the piston travel direction and pressure flow so they can work together. If one port didn't have a reed valve then it would breath in and out negating the reed valve function of the other port...

Click to expand...

Did you remove the cam breather timing disc when installing the JS reed breather on the cam breather port?

For grins I hooked up the cam timed breather port with the timing disc still inside and ran the hose to the oil tank, and installed the cNw breather on the backside of the timing chest and ran the hose to the oil tank. It worked really well for idle and low end, but cut the top end short due to inefficiency removing crank case pressure at high rpm. I plugged the timed breather port and got back my top end.

I learned the dumb way that the timing disc needs to be removed when installing a reed valve on the cam timed breather port. I did it before reading Jim's reed valve install instructions. Fortunately, I didn't buy Jim's reed valve to put on an assembled engine. Got that part right. Point is for those that don't already know it is a serious bit of work to put a reed valve on the cam timed breather port unless the cases are already split and the motor is getting rebuilt. Would be great if it was just a bolt on and go product.

The timed breather was deleted prior to '72, so definitely not an issue for Combat era cases, hence the new breather replaces the original '72 style rear crankcase breather

I did not take the timing disc out from behind the cam because I was completely assembled when I got Jim's breather.. It still works pretty well.

My '70 year model has the frame crossmember blocking the oil drain plug, so I couldn't use the Comstock breather. I did the timing chest breather modification and drilled two more 3/8" holes from the timing chest into the crankcase to aid air movement (I made sure I didn't drill into the webbing of the crankcase casting) I saw a decrease in oil leakage, with the timing chest modification and the camshaft timed disc breather, but still had a the occasional leak right at the tachometer drive port. Then I discovered and bought Jim's camshaft reed valve breather and added it to the port and all my leaks disappeared, so I have no doubt that it helped the efficiency of the camshaft port.

One of the best things about a belt drive is that you can hear the important engine noises without the racket of the triplex chain. At certain RPM's I can duck down behind the fairing and hear the reed valve clicking away at the camshaft port so I know it's working. At first I thought it was something inside my crankcase clicking, but eventually it was clear that it was the reed valve. It's funny too because it's very pronounced at certain RPM's and totally silent at other's. I'm not sure whether that means it's not keeping up at high RPM's or if it just can't be heard.

Needless to say, the only way to really know is to set up a vacuum gauge to test all the permutations, but that isn't going to happen. I thought about pumping the timing disc port full of grease and installing a threaded drill bushing into the port to drill out the timing disc from the outside. Then vacuum the grease and chips out of the port to remove the obstruction. Something keeps me from taking the chance of circulating metal chips through my engine....

Two ways of defeating the disc without taking the engine apart.

1. Block the pipe it feeds into so no air can move in or out.

2. Put a second reed valve in the disc outlet pipe so only air gets out and none can get back in.

o0norton0o said:

One of the best things about a belt drive is that you can hear the important engine noises without the racket of the triplex chain. At certain RPM's I can duck down behind the fairing and hear the reed valve clicking away at the camshaft port so I know it's working.

Click to expand...

My cNw reed valve honks when mildly kicking over the engine when cold. If I had a fairing amplifying all the racket my Norton engine makes, I'd be afraid to ride it. ha

Schwany said:

My cNw reed valve honks when mildly kicking over the engine when cold. If I had a fairing amplifying all the racket my Norton engine makes, I'd be afraid to ride it. ha

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Actually, it blocks the wind noise so you can hear the engine really well. It was the change to the belt drive that really made me notice how great the engine sounds when you duck down behind the fairing.... Um,... and needless to say, you don't duck down because you're going slow.... Add the dunstall mufflers and it sounds totally badass (without actually being anything more than a stock commando engine...

I usually ride with ear plugs. When I ride without them, initially the engine noise sounds a bit concerning.

On my combat I just put an xs650 breather into the stock breather line between the engine and oil tank in the same place I previously used a pcv valve. I am fairly confident that the pcv valve worked but the reed valve works better. On the vincent forum there have been some tests run and once the air is evacuated from the case by the reed very little air flows out of the breather as long as the engine is in good shape. Thus, you don't need a large line diameter as long as the engine is in good shape.