Cylinder head pressure venting...(2012)

[Bob Z.]

Has any one else tried this method of venting pressure from a cylinder head?

From a Norton Owners Club thread:
Quote: Another very simple solution
I have a 1969 Commando and was always having a problem with oil leaks for no apparent reason, especially out of the tacho drive. Previous to my ownership, the crankcase breather had been moved from the end of the camshaft, this hole being blocked up with a bolt, and put down the bottom at the rear of the crankcases as on the later Combats. I tried all the ideas on the tacho drive; most of them worked for a while, but then the dreaded leak was back.
I drilled and tapped the rear rocker (inlet) cover, screwed in an air hose fitting and clamped a piece of clear plastic tubing to it. I then teed this into the breather hose between the bottom of the cases and the oil tank. I used the clear tubing because I thought it would be interesting to observe oil flow if any.
My theory is that the top end of the motor becomes pressurised and retains that pressure which encourages the oil leaks. Another pipe hooked onto the engine like this simply means another breather or more breathers or better breathing, whichever way you want to look at it. The more breathing the better!! Now I don't have oil leaks from the top end or the tacho drive or anywhere else for that matter. I like to trundle along at a good 70 m.p.h. when I can, keeping her well up on the top side of 4000 r.p.m. There is some oil flow visible through the tube, but there seem to be no problems associated with this.
I run the final tank breather to the ground and get no puddles under the bike or oil spray over the rear as I ride. Drilling the rocker cover means no major modifications to anywhere on the engine, only the rocker cover. I fitted the biggest fitting I could into it which meant the hose size is similar to that which comes off the regular breather. If you still have the breather on the end of the camshaft, it would mean simply teeing into that line. I did no other modification to the breathing system at all and it has meant no more leaks. If you were to do it and it didn't work or you were not happy with it, the worst you have done is wrecked a rocker cover.
Bob Davis (bobmel@bigpond.com.au) on NOC-L 17th. Jun 1999 End Quote


I drilled and tapped a 1/8" NPT X 3/8" barb fitting onto an inlet rocker cover and will run a line into the line coming off of the oil tank breather.
I will let you know how it turns out.

 

[Onder]

Used to do rocker vents on Triumphs. But if you read up on the threads on
breathers or reed valve you will see that currently accepted thought is that
straight venting isnt effective and actually uses power to pump air in and out.
Reed valve evacuates case and maintains a lower than atmospheric pressure.
But take a look at the threads.

 

[acotrel]

A breather without a PCV valve will do nothing. See my comments on the other post on this s ubject.

 

[MikeG]

FWIW-My BSA A10 has spewed oil from the rocker box area for 14 years. I've tried every trick known to man and the BSA gods to stop it, including putting a PCV valve into the intake side rocker cover. All to no avail. It still weeps/seeps/leaks depending on how hard I ride it. My newly aquired 71 Commando had one persistant leak at the tach drive that I was getting ready to do the seal mod to. Before I got to that I installed one of Jim Comstocks reed valve breathers that threaded in in place of the sump plug. I now have NO leaks anywhere and whatever wetsumping it does is pumped back into the tank much quicker. If the BSA did'nt vent from two different spots this would be a killer modification to make to it, perhaps someone smarter than me could figure it out? Anyway, without a reed valve of some type extra holes are pretty much wasted effort IMHO.

 

[ML]

Yes, I run one on my 850, but the attachment is above the rocker cap mounting nut and is a 90 degree bend. The 1st time I did this, it immediately cured a persistent leak and I have continued to use it for 7 years without any detriment. The outlet hose vents to a seperate catch bottle and the motor vents to the oil tank as per normal. I also have a brand new XS650 reed valve gadget sitting in spare parts as I really have no need for it. The bike is entirely dry and runs very well.

 

[Snorton74]

The Comstock breather from CNW bolts right on to commando motors built before 73. Later models need the cases broken down. If you have the later model commando and are leaking oil, you should get it.

 

[comnoz]

The Comstock breather from CNW bolts right on to commando motors built before 73. Later models need the cases broken down. If you have the later model commando and are leaking oil, you should get it.

My breather available through CNW bolts on to the 72 style combat case. That is the one with the original breather bolted to the back of the case and no sump plug. All other engines need machine work to the cases to mount it.
It uses the same reed assembly as the sump plug breather that screws into any Norton without a crosstube under the sump plug hole. I will have a sump plug breather available for the cross tube models in the future. Jim

 

[concours]

Venting the rocker arm area is a band-aid for poor crankcase venting. ALL the pumping action is from the pistons rise and fall, all happening downstairs. If the crankcase is vented properly, the top end takes care of itself (oil drain passages).

 

[Bob Z.]

Venting the rocker arm area is a band-aid for poor crankcase venting. ALL the pumping action is from the pistons rise and fall, all happening downstairs. If the crankcase is vented properly, the top end takes care of itself (oil drain passages).

Thank you , understood.
When I read the original quoted message, I was thinking that all the engine pressure controls such as the reed valve are located on the crankcases.
I did not know how easily the cylinder head air volume flowed to the pumping crankcase air volume.

My 1972 with the breather on the rear of the crankcases has a plastic brake booster valve in the line to the oil tank and the engine is oil tight.

I wanted to see what would come from the inlet rocker cover vent in an oil tight, crankcase air vented engine. Suction, discharge or neutral air pressure?

I'll hook it up this weekend and give a quick report.

 

[DogT]

I will have a sump plug breather available for the cross tube models in the future. Jim

I'll be on that list. Did you find that most 68-70 models wouldn't work? I thought you said some did?

Dave
69S

 

[comnoz]

I will have a sump plug breather available for the cross tube models in the future. Jim

I'll be on that list. Did you find that most 68-70 models wouldn't work? I thought you said some did?

Dave
69S

I have found it depends on the location of the crosstube. Some are closer to the sump plug than others. I haven't found a definite way to tell if it will fit without looking. Jim

 

[Mark]

I have seen Power Brake Vacuum Booster Check Valves used in place of PCV Valves.
(they perform very well).

 

[VintAge]

Can't resist an unsolicited testimonial: since I installed the reed valve breather in place of the sump plug on my '74 850, my niggling, always there oil spots have disappeared. Since the old horse is, however, a world class wet sumper, it will mark its territory if I let it sit unused too long and the level gets high enough. That's just a good excuse to ride it more often.

Also, I've stopped worrying about draining and filling if I do let it sit for too long. Start it, hold a middling high idle til it will idle on its own and drive off. Cleans out the sump quickly, no smoke, nothing from the vent hose, runs great. Thanks Jim!

 

[comnoz]

Can't resist an unsolicited testimonial: since I installed the reed valve breather in place of the sump plug on my '74 850, my niggling, always there oil spots have disappeared. Since the old horse is, however, a world class wet sumper, it will mark its territory if I let it sit unused too long and the level gets high enough. That's just a good excuse to ride it more often.

Also, I've stopped worrying about draining and filling if I do let it sit for too long. Start it, hold a middling high idle til it will idle on its own and drive off. Cleans out the sump quickly, no smoke, nothing from the vent hose, runs great. Thanks Jim!

I appreciate the feedback. Jim

 

[MikeG]

Can't resist an unsolicited testimonial: since I installed the reed valve breather in place of the sump plug on my '74 850, my niggling, always there oil spots have disappeared. Since the old horse is, however, a world class wet sumper, it will mark its territory if I let it sit unused too long and the level gets high enough. That's just a good excuse to ride it more often.

Also, I've stopped worrying about draining and filling if I do let it sit for too long. Start it, hold a middling high idle til it will idle on its own and drive off. Cleans out the sump quickly, no smoke, nothing from the vent hose, runs great. Thanks Jim!

Ditto : #1 best improvement I've made.

 

[beng]

Norton put a breather tube on the rear rocker cover of the 650 engines produced at Bracebridge Street from late 1960 through the time the plant was closed up at the end of 1962.

They drilled the rear rocker cover hole out larger and had a long stud which would let a banjo fitting and supporting parts fit there. About half-way through Norton's last year of production, 1962, they added a froth tower with a fitting to connect oil breathers to.

Of course the breather had a lot of little parts and took time on the assembly line to put together, so it was one more thing that AMC axed along with the employees, factory and many other little refinements the original Norton motorcycles had......

 

[Brooking 850]

Mine as well, thanks Jim, have a second one for Bike #2 project.
Regards Mike

 

[rpatton]

Kenny Dreer ran a breather tube out the intake valve cover, and an external line to replace the stock internal drain circuit under the intake valve gear. As long as the breather tube from the head connects to case and the case has the usual reed valve it seems like it would work ok.

the-kenny-dreer-vr880-undressed-t1314.html#p9104

 

[ILLF8ED]

Bringing back this string rather than start my own new one. I have the XS reed valve inline with my crankcase breather and have been getting some oil spray on the front of the primary after running the engine hard. I noticed oil bubbles at the cap nut on the intake valve cover and see oil is getting sucked forward to the front of the engine then blowing onto the primary. From this string my conclusion is seal the cap nut better as the reed valve already in place has the best chance of preventing oil leaks. All agree?

Thanks

 

[concours]

Bringing back this string rather than start my own new one. I have the XS reed valve inline with my crankcase breather and have been getting some oil spray on the front of the primary after running the engine hard. I noticed oil bubbles at the cap nut on the intake valve cover and see oil is getting sucked forward to the front of the engine then blowing onto the primary. From this string my conclusion is seal the cap nut better as the reed valve already in place has the best chance of preventing oil leaks. All agree?

Thanks

That's a long ride for the oil to come out of the intake rocker cover and end up on the front of the primary. I anoint the aluminum seal with Loctite 518 and it's never leaked a drop. XS breather plumbes like yours.