CNW Crankcase Breather Gasket

I posted in several threads my experience with the CNW breather but it may be a topic worthy of its own thread. I followed the instructions (or so i thought) and when i ran the bike for the first time, i got this





At idle, the leak was about 1 drop/sec but at higher RPMs the leak was much more severe (left a nice trail down my driveway). I tried tightening the bolts, but that seemed to make it worse. I attribute the leak to the gaskets. They are thin and narrow at the corners (2 worse than others)



The holes are also slightly smaller than the bolts. Both of these conditions lead to possible tears and bunching.

Has anyone else experienced this problem or is it user error on my part? The breather itself is awesome (like all of CNW's products), it's just this gasket.

Try making your own gasket from 1/16" synthetic cork.
I know this does not answer your question, but it may solve your problem.

Slick

That's essentially what i'm doing, just curious if others had similar issues or if it's user error

I definitely had the same problem with my original gaskets. I used Hylomar which made the gaskets squeeze out over time.
To fix it, I made my own gaskets out of some good 1/32 gasket material (Fel-Pro supplied by NAPA.) I used Permatex #2 which firms up after tightening. It also puts a time limit on how long you can take for assembly. I managed to install the unit both times without taking anything else apart. I did that by cutting the bolts to a custom length.
So far so good.

I got mine straight from JimC, though there's no additional plate as appears to be the case with yours, mine just mounts directly to the crankcase, though I do recall the gasket area around the bolts is minimal. I smeared the gaskets lightly with RTV and it has never leaked.

Be sure to top up your oil level before you take the bike out

Repeating myself, since I already mentioned this in your restoration thread.

My cNw breather is on the back of the timing chest. It does not get bathed in sump oil.

I believe I ran the bolts through the part and cNw gaskets before I installed the part the first time. A thread past the back most likely, so I could get the bolts started and everything stayed in place. I did not end up using Matt's bolts though. I used SS button head hex bolts. I got two R&R's out of the cNw gaskets before one of the two gaskets wanted to stay on the part and tore during disassembly. They are coated gaskets and in my case once the motor fully heated up a few times one of them stuck. So I made a new one. The gaskets did not tear during assembly, but they are fragile.

For me it's easier to make thicker than paper gaskets like those cNw gaskets out of card stock. I used a 1/4" hole punch for the bolt holes. No sealer on the gaskets. A little on the first 3 threads of each bolt.

TomU said:

I posted in several threads my experience with the CNW breather but it may be a topic worthy of its own thread. I followed the instructions (or so i thought) and when i ran the bike for the first time, i got this

View attachment 101682

View attachment 101683

At idle, the leak was about 1 drop/sec but at higher RPMs the leak was much more severe (left a nice trail down my driveway). I tried tightening the bolts, but that seemed to make it worse. I attribute the leak to the gaskets. They are thin and narrow at the corners (2 worse than others)

View attachment 101684

The holes are also slightly smaller than the bolts. Both of these conditions lead to possible tears and bunching.

Has anyone else experienced this problem or is it user error on my part? The breather itself is awesome (like all of CNW's products), it's just this gasket.

Click to expand...

I didn't have the problem with mine, supplied direct from Jim Comstock who made them for CNW anyway. It is a good product.

After a while I got a minor seepage (really the odd drip) because the bolts came loose, I loctited them, fine. (yes, I should have done it anyway!)

After more time and several strip downs (it's a race bike), I found the gaskets becoming compressed and generally worse for wear, again leading to minor seepage, so I made a new paper set out of slightly thicker gasket material. Again fine.

My opinion, we can't rule out mishandling (sorry), but it's unlikely, and I suspect you were unlucky and got a gasket that should not have passed QC.

I'm not sure if I would be 100% satisfied with the reed stopper plate either. On the petal marked X Y, there is a bit of extra metal hanging down.....file it off.....

I bought a cheap eBay reed block just to carry a spare, and it's better than that!

Hi guys,

Between Jim Comstock, that developed this great breather and myself, that makes the breather bodies and adaptors, we have a few hundred of these installed over the years and while we have not been completely satisfied with the gasket quality, there has been no reason, due to feedback from customers, to do anything different.

That said, since TomU made some posts yesterday, today I have contacted a die cut gasket company in California that I will send a valve assembly to so they can create a drawing, make a tool/die and make me 500 or so gaskets. It will be a better fit, better material and a little thicker. This should at least rule out the possibility that a gasket may be failing.

I do have to say that I find it a very backwards approach to first post on a forum (in 'several threads' no less') about something going on with a product before contacting the company that you bought it from to see what response you may get.

I am always striving to improve on the products that I offer and feedback is of course appreciated and helpful, both good and bad. With all that I have on my plate these days, its a bit overwhelming and I have to put things in order on when I can address them but I just took a couple of hours to work through this gasket and hopefully we can have a better product shortly.

If someone that has the cNw breather wants some of the new gaskets when they are done (most likely January), then just get a hold of me at the shop, nortonworks@fone.net

Matt

I'd say the ^^^^ is a glowing reference and endorsement for CNW I doubt many others would respond in such a positive and measured manner, good on ya Matt !!

1973x75 said:

Thank you for the offer for the improved gaskets. Is there a way to swap them out without too much dismantling of the primary/gearbox/engine? I’m thinking maybe using a smear of sealant around the breather.

Click to expand...

Both the surface mounted (machined cases) and the 1972 style can be replaced without having to remove much, if anything at all. Its definitely a tight fit between the engine and gear box but I have done many in the shop where nothing was removed in order to get to the breather

You should definitely use some type of sealer on all gaskets surfaces before installation. This also with the new gaskets I will be making

If you are talking about trying to stop a leak by applying a sealer on the outside of the breather, I personally do not think that will solve anything in the long run. A temporary band aid at best.

Matt

The way I would make a gasket for this...and many other parts. Ideally wait for the new gaskets but if you want to get things up and running later in the day here's how I would do it.

1) cut a square of gasket material bigger than you need. Cut to similar size 2 pieces of plywood or flat wood of some sort.
2) clean offf the part with carb cleaner or similar. Apply Yamabond or what ever. Let it get tacky then push the part onto the gasket material.
3) sandwich the part between the two pieces of plywood and lightly hold it in a vice. Let it sit until cured.
4) Then discard the plywood and trim out with an Xacto knife, fresh blade. It goes quick and easy and comes out perfect.

Schwany said:

I used SS button head hex bolts.

Click to expand...

Not only looking better, button head bolts are slightly thinner than hex head bolts and may alow enough clearance to remove without having to remove the clutch. Only issue might be getting them out again, especially if they are loctighted

And happens to be the case that I seemed to have misplaced one of the bolts, but have 1/4"-20 x 1" button head bolts

cNw said:

I have contacted a die cut gasket company in California that I will send a valve assembly to so they can create a drawing, make a tool/die and make me 500 or so gaskets. It will be a better fit, better material and a little thicker.

Click to expand...

That's awesome. Was not expecting that.

Slightly longer bolts may be required with thicker gaskets.

1973x75 said:

Is there a way to swap them out without too much dismantling of the primary/gearbox/engine? I’m thinking maybe using a smear of sealant around the breather.

Click to expand...

The bolts are 1". You can get one bolt out easy. The others require more clearance from the gearbox. This means loosening the GB and moving it back. For me, this meant removing the lower GB bolt (had to remove the right side exhaust to get that out), loosening the upper mount, and the icing on the cake - removing the clutch basket to allow it to move back enough to get the bolts out.

Sealant on the outside won't do any good

EDIT: I retract my statement that you need to remove the bolts. You only need to remove the bolts enough so they are not engaged with the mounting plate (the piece that's connected to the crankcase). Then the entire housing (with the bolts) can drop down. There should be enough clearance without having to mess with the gearbox (a quarter inch or so)

SteveA said:

My opinion, we can't rule out mishandling (sorry), but it's unlikely, and I suspect you were unlucky and got a gasket that should not have passed QC.

Click to expand...

Possibly

TomU said:

Not only looking better, button head bolts are slightly thinner than hex head bolts and may alow enough clearance to remove without having to remove the clutch. Only issue might be getting them out again, especially if they are loctighted

And happens to be the case that I seemed to have misplaced one of the bolts, but have 1/4"-20 x 1" button head bolts

Click to expand...

You would probably need to cut or grind down the short leg on an Allen wrench to R&R the button head bolts for your install.

I use button heads on my case mounted breather. Not because they are nicer looking (and they are) but it prevents over tightening since the Allen key can only do so much. Stripping the relatively shallow threads in the case would be a big issue of course

On the 72 breather that uses an adaptor (like what Tom has), I use a hex head because its a tighter fit and you may not have room to get an Allen key in on the top of the bolt head but can always get a hex wrench in from the side when using a hex head bolt.

Matt

I used the one good surviving gasket as a template for the one I made. That was the advantage of not using a gasket sealer with those cNw gaskets. They are kind of crumbly and fragile. Granted where my breather is located I don't have the same issues with oil like a breather mounted on the back of the crack cases.

Fiberglass reinforced silicon would be the way to go with the gaskets. The gaskets would be thinner, seal better, and be reusable. Breather cost would go up, but Matt could blame it on covid and the world wide shipping crisis or whatever the popular crisis of the day is.

TomU said:

The bolts are 1". You can get one bolt out easy. The others require more clearance from the gearbox. This means loosening the GB and moving it back. For me, this meant removing the lower GB bolt (had to remove the right side exhaust to get that out), loosening the upper mount, and the icing on the cake - removing the clutch basket to allow it to move back enough to get the bolts out.

Sealant on the outside won't do any good

Click to expand...

The clearance between the engine case and the gear box will vary between bikes depending on primary drive set up.

To have the move the gear box back with the upper adjuster typically takes care of it.

To have to remove hardware and clutch basket is very unusual and something I have never heard of before. You do not have the ‘get the bolts out’ to remove the breather body.

Fact is that the screw threads only extend a small amount from the breather body so if you have that assembly already together (breather body, valves and 4 screws), then you just slide in place and tighten up. In other words, if you have a little more than 1/4’’ of space between the hex head and gear box, you have enough room to remove and install it.

Matt