Crank case breather

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I experience the same thing here in Canada. A $30.00 part costs $70.00 by the time you get it here. It's just not worth it time after time. UPS ground shipping is the worst, they add a hefty brokerage fee for filling out 1 or 2 minutes of paper work. They must make a small fortune on brokerage fees. In contrast the post office has a flat $5.00 brokerage fee.
 
I was turned on to a great idea recently; in a discussion on crankcse breathers, George Baker suggested a reed valve from the Air Injection unit off a new Triumph, installed as a one-way breather.

So, the AI unit from my wyfe's '02 Bonneville-

Crank case breather


I simply took a recipro saw and cut off the two reed modules-

Crank case breather


Here's a close-up of one of the reed units-

Crank case breather


The opening on the unit is centered, while the reed valve's "active" zone is on one end, so I figured I'd trim the opening for better alignment-

Crank case breather
 
Trimmed out the aperature in the body to the same size as the reed valve's opening-

Crank case breather


(2) 1/4" holes for the mounting hardware, and a 3/8" hole for the breather opening-

Crank case breather


Hand-cut gasket from a bit of piston box-

Crank case breather


A little RTV silicone sealer and all nipped up-

Crank case breather


(Plugged the existing breather pipe with a 3/8" bolt & some RTV)

I can't test ride the bike for another day or two, but I'm fairly certain this will beat the generic valves for performance and durability.

I'll be making a batch of these for sale, the included gasket will be the pattern for drilling.
 
I don't think that's going to do much. Not enough pressure out the timing side with those little holes. Good luck.
 
What's your missus going to say when she finds her bonny's been robbed for parts ?
 
It's got a 3/8" clear port, the OEM tube is slightly smaller.

The wyfe won't mind, I already traded her Bonnie for a '53 Thunderbird chopper I built for a guy that's in too ill health to kickstart any more...
 
IMHO the CNW mod is the only way to seriously improve the breathing. It also provides the benefit of improving drainback from the intake rocker box because the mod reduces presurizing the timing case (where the drain dumps). Just wish there was a way to do it without engine disassembly. Frankly, a fair sized hole/tube in the crankcase to atmosphere would probably work almost as well but you can't really drill holes with the engine assembled because of dumping the swarf into the moving parts.

To me, running the crankcase pressure into the timing section is silly and I can't figure out why that was done in the first place. And that TINY oil passage from the int rocker box...what's up with THAT? On my engine you can barely fit a medium sized wooden matchstick - not a full sized kitchen match - into the passage when the heat insulator and valve spring washer are in place.
 
I was able to drill the three holes with the engine on the bike, simply by masking off the timing chest and leaving the "operating field" unmasked. Piece of cake.

From what I've seen of several other breathers that utilize the path through the timing cavity, this one will be equal to them in operation, and POSSIBLY more durable than check-valve type units.

Oil return flow on a Commando needs it's own thread; there are several good ideas, several bad ideas, and several Rube Goldberg ideas to address THAT issue. The factory return system is adequate unless you are sustaining high revs or going racing.
 
GP, I agree that drilling in the timing case would not be an issue. But I believe that the crankcase breathing should not involve the timing case at all. I think the breather opening should be directly from the crankcase and that the two little holes from crankcase to timing case should be blocked. THis is essentially what CNW does. Again, I don't see any good reason why the original setup includes the timing case but I would like to understand why Norton set it up that way. Since it would have been easy to put a hole/fitting in the crankcase, they must have had a reason to think it was better through the timing case. I'd like to understand their reasoning but I can't at the moment. ;)
 
I run the original elbow breather on my '72 Combat plus an 850-style breather with a 5/8" hose that loops over the air-filter backplate and terminates in a mini K&N-style pod located just at the frame rail behind the gearbox. This permanently eliminated all pressurization problems when I installed it ten years ago. It's amazing how much air moves through both breathers at idle. The exaggerated loop must keep the oil out of the external breather--the bike rarely needs oil between changes.


Tim Kraakevik
kraakevik@voyager.net
 
"Again, I don't see any good reason why the original setup includes the timing case"

The original didn't include the timing case, it was designed by Bert Hopwood to breathe through a timed breather on the drive side of the camshaft!!
 
I'm not sure that all of the one way valve devices are the total solution. What's the purpose? To evacuate crankcase / blow by pressure and eliminate joint leakage. I have a stock Mk2 850. In addition to the timing side breather, I simply use a 6mm breather tube on top of the inlet rocker cover . It is piped to a catch bottle and then vents to atmosphere. The timing side hose goes to the oil tank as per normal. There are no oil leaks, no mist, no smoke and I couldn't care less if .005 of a HP was not gained in the process!

Mick
 
I'm not sure that all of the one way valve devices are the total solution. What's the purpose?
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To keep the engine from sucking air into the crankcase on the compression and exhaust strokes.

With the crankshaft seal being the usual culprit, you probably won't know if it is passing oil unless you are running a dry primary.
 
ML said:
... In addition to the timing side breather, I simply use a 6mm breather tube on top of the inlet rocker cover . It is piped to a catch bottle and then vents to atmosphere.
Click to expand...

I have heard that this impedes the oil drain-down fom the head, possibly affecting cam oiling.

I DON'T KNOW HOW TRUE THIS IS, it's just something I heard.
 
Mick...do you have a "substantial" flow of air out of that rocker cover-mounted hose? If you plug it does the airflow increase from the oem hose?

Frankly, IMHO, it is physically impossible for there to be enough breathing capacity with the small size of the passages involved in the oem setup, especially if you then factor the adapter that reduces the hose size that goes to the oil tank.

One of the things i've been contemplating is removing the oem breather tube from the 850 and substituting a piece of copper tubing with the same OD. This would end up being a tube with considerably more ID since the oem tube has a very thick wall...
 
I'm going to install a small K&N style filter on the end of my breather hose and just plug up the oil tank neck fitting.

Actually, it's just the first few strokes that will produce any significant expulsion from the crankcases with a one-way valve. After that, it's doing it's job and keeping a fresh charge out of the crankcases.
 
Again, I don't see any good reason why the original setup includes the timing case but I would like to understand why Norton set it up that way.
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Perhaps to use the timing chest as an oil separator since the '72-'73 750 version pushed a considerable anount of oil up through the breather tube when the engine wet sumped?
 
Perhaps to use the timing chest as an oil separator since the '72-'73 750 version pushed a considerable anount of oil up through the breather tube when the engine wet sumped?
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That is interesting because when my original Combat (with an 850 style breather, original blocked, holes in timing case and original front pickup) wetsumped at speed, oil blew out of the case barrel joint. Now, this was with most of the oil in the cases and little in the tank but despite huge pressures in the main cases oil did not find it's way thru to the timing gear area and up the '850' breather. You'd think that with a 1/2" to 3/8" pipe going to the tank it would be least path of resistance but no it wanted to exit the joints. I never and don't understand that. The tank breather in those days went to the aircleaner so it wasn't sealed.
 
Keith1069 said:
Perhaps to use the timing chest as an oil separator since the '72-'73 750 version pushed a considerable anount of oil up through the breather tube when the engine wet sumped?
Click to expand...
That is interesting because when my original Combat (with an 850 style breather, original blocked, holes in timing case and original front pickup) wetsumped at speed, oil blew out of the case barrel joint. Now, this was with most of the oil in the cases and little in the tank but despite huge pressures in the main cases oil did not find it's way thru to the timing gear area and up the '850' breather. You'd think that with a 1/2" to 3/8" pipe going to the tank it would be least path of resistance but no it wanted to exit the joints. I never and don't understand that. The tank breather in those days went to the aircleaner so it wasn't sealed.
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Those tiny holes into the timing chest are not that efficient. And when the crankcase filled with oil the viscosity basically "blocked" the holes and it came out elsewhere. No matter how big the pipe coming out the timing chest was, the oil never made it that far.
 
mike996 said:
Mick...do you have a "substantial" flow of air out of that rocker cover-mounted hose? If you plug it does the airflow increase from the oem hose?

Frankly, IMHO, it is physically impossible for there to be enough breathing capacity with the small size of the passages involved in the oem setup, especially if you then factor the adapter that reduces the hose size that goes to the oil tank.

One of the things i've been contemplating is removing the oem breather tube from the 850 and substituting a piece of copper tubing with the same OD. This would end up being a tube with considerably more ID since the oem tube has a very thick wall...
Click to expand...

Couple of observations: Certainly the inlet rocker breather does flow. After 500kms I get about 250cc of oily fluid in the catch bottle. This in not a new motor, its done some miles. GP commented that there is some thought that breathing in the top end prevent oil flow down from the head. I can't see this happening. If you only have the stock timing side breather, there is more pressure in the cases expanding. With the additional upper breather there is less pressure. I have never found an excess of oil in the rocker chamber. I guess the simple answer is with more outlets, there is less internal pressure thus less propensity for leaks.

Mick
 
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