Timed crank case breather

Discussion in 'Norton Commando Classic Motorcycles' started by Gilesy, May 12, 2018.

  1. Gilesy

    Gilesy

    Joined:
    Aug 27, 2017
    Does this arrangement give any vacuum in the crankcase? I'm fitting a Yamaha reed valve and in the fitting instructions it says to remove timed breather disc for it to work properly, easier said than done. Is there any benefit then of fitting the reed valve?
    Thanks
    Giles
     
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  2. gtiller

    gtiller VIP MEMBER

    Joined:
    Nov 5, 2012
    If you still have the breather plate and rotary disc still in place on the end of the camshaft, it will massively reduce the effectiveness of any valve you add.

    Breathing through this port is also somewhat of a bottleneck too, plus blowby is cold, sticky and mayonnaise-y by the time it hits your new valve assuming that you are positioning it up by the oil tank.

    Personally, I’d block it off and fit one of @comnoz’s sump plug breathers, then remove the discs and spring if you ever split your cases.
     
  3. nortonspeed

    nortonspeed

    Joined:
    Jun 29, 2008
  4. o0norton0o

    o0norton0o

    Joined:
    Apr 27, 2015
    I have a mike's xs reed valve modification on the timing chest blanking plate of my '70 commando. I also left the timing disc breather in place because I didn't want to take apart my engine to remove it. It may make my crankcase vacuum pressure higher, but it also provides a second route for pressure to escape out of the crankcase. Adding the timing side breather really helped with annoying engine leaks, which is the main reason I did the modification. I don't think the vacuum adds any significant HP to your engine, so I don't care if I don't have the lowest possible vacuum pressure in my crankcase.

    The thing to do to the timed port in order to improve it's sealing capabilities would be to use Jim Schmit's breather in that breather port after the timed breather discs. The timing discs would restrict the outward flow initially, but you would still get the benefit of Jim's reed breather sealing out the return pressure. (which the timing disc alone doesn't do nearly as well as a reed valve) I've often thought of adding his reed valve to my bike and having 2 reed valves operating together...

    But right now I have the stock timing discs and the mike's reed valve working together with no ill effects.
     
    Last edited: May 12, 2018
  5. baz

    baz VIP MEMBER

    Joined:
    May 26, 2010
    I still have the timed breather on my commando, also I have an acetylene torch reed valve on the back of the timing cover
    This is joined with a teepice to the timed breather pipe,then to the oil tank
    It's been that way for over 20 years with no oil leaks or problems
     
  6. MFB

    MFB VIP MEMBER

    Joined:
    Mar 29, 2012
    I left the disc in my 1970 Commando, and blanked it off like this.
    You may note the strange metal box the reed valve is attached to. That's my home made catch tank. The engine doesn't breathe to the oil tank any more.
    That enabled me to let the oil tank breathe to atmosphere via the former engine breather port, and blank off the pipe in the oil tank that dripped condensed oil vapour into the air filter. View attachment 5041
     

    Attached Files:

  7. Gilesy

    Gilesy

    Joined:
    Aug 27, 2017
    Thank you all very much. The engine is pretty oil tight so I think I'll leave my current arrangement for the time being. My timing chest has a plate on the back so I'll get another one and mount the Yamaha valve on that, then if I have to take engine down again I can remove disc and drill holes in timing side crank case as per Mick Hemmings video.
    Cheers
    Giles
     
  8. MFB

    MFB VIP MEMBER

    Joined:
    Mar 29, 2012
    Sounds like a wise decision. I had mine stripped down anyway so I did the breather mod. as one of several upgrades. My engine didn't leak oil either so I can't tell whether it improved things or not.
     
  9. jseng1

    jseng1

    Joined:
    Nov 26, 2009
    An easy way to tell if the one way breather is working and helping is to loosen the oil tank cap while the breather hose is still connected to the oil tank (engine idling). Without the one way breather the crank case pressure will cause the oil cap to bounce up and down. With the one way breather the crank pressure is reduced and the oil cap should pretty much just sit on the oil tank. Less pressure in the crank case means fewer oil leaks.
     
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  10. texasSlick

    texasSlick VIP MEMBER

    Joined:
    Jan 2, 2013
    With the timed breather, I measured the pressure in the rocker box on my Atlas, and found it to be negative 18 inches of water from 2000 rpm up. I then fitted Mikes XS reed valve to the timed breather port, with the rotary disc still in place. I then measured the pressure again and found no difference.

    Thus it would seem to be no benefit to fitting a reed valve on the timed breather port unless you split the cases and remove the disc.

    I have since blocked the timed breather port, fitted Comnoz's sump plug breather, but as yet made no further pressure measurements as I have not yet cranked up after rebuilding the head.

    You might read again reply #4, concerning fitting the reed valve to the timing case, while leaving the rotary disc in place.

    Slick
     
    Last edited: May 13, 2018
  11. robs ss

    robs ss VIP MEMBER

    Joined:
    Aug 16, 2016
    Slick
    Wouldn't blocking the hose from the timed breather be better than removing the disc(s)?
    If you simply remove the discs (pun intended) then there is an open path from crankcase to atmosphere via the hollow cam.
    If you block the hose, with a ball bearing or similar, there is no path to atmosphere and you can remove the discs at your leisure - next time you split the cases.
    Cheers
    Rob
     
  12. texasSlick

    texasSlick VIP MEMBER

    Joined:
    Jan 2, 2013
    Rob:

    I blocked the timed breather port by installing a 1/2-20 plug. With the plug, there is no path to atmosphere thru the timed breather port. The breather hose is now connected to the Comnoz sump plug breather.

    In a previous thread, Comnoz posted an oscillogram of crankcase pressure waveforms. I converted his data to an estimated average negative 35 inches of water, or about twice that obtained from the rotary valve (with or without the XS valve in series). I hope to verify that estimate after I crank up, and will post results.

    Slick

    PS: more info here - https://www.accessnorton.com/Norton...tyle-one-way-case-breather.22001/#post-328574
     
  13. robs ss

    robs ss VIP MEMBER

    Joined:
    Aug 16, 2016
    Thanks Slick
    So, if you blocked the timed breather port it would appear there is no rush to remove the spring/discs - unless you are already splitting the cases for another reason?
    One'll just be rotating against the other with zero effect.

    Rob
     
  14. o0norton0o

    o0norton0o

    Joined:
    Apr 27, 2015
    Regarding Jim Comstocks's sump breather; The '70 commando has a frame cross member that later commando frames don't have which interferes with mounting Jim's sump breather.
     
  15. texasSlick

    texasSlick VIP MEMBER

    Joined:
    Jan 2, 2013
    That is correct, Rob. The only benefit to removing the disc and spring with a plugged port, would be to save a modicum of weight and reduce friction by some near-to-zero amount.

    OTOH, if one fits a reed valve to the timed port, the disc and spring should be removed, otherwise, as my measurements show, no additional benefit results. Someone needs to make a pressure measurement for reed valve on timed breather port, sans disc, to determine if any benefit is obtained over the rotary valve alone.


    Slick
     
    Last edited: May 14, 2018
  16. Blue750

    Blue750

    Joined:
    Mar 17, 2018
    To the guys above with the timed breather and reed valve on the timing case, have you also drilled the cases? I also have the timed breather and have been contemplating on using a reed valve on the timing case. But having to drill the crank case has been holding me back.
     
  17. baz

    baz VIP MEMBER

    Joined:
    May 26, 2010
    no my crankcase isn't drilled , i didn't have a clue back then if it would work or not
    but on my bike it works fine,but keep in mind the reed valve i use is from an acetylene torch and probably dosent have the capacity that others have??
     
  18. MFB

    MFB VIP MEMBER

    Joined:
    Mar 29, 2012
    Yes I drilled the crankcase. You have to if you want it to work. The reed needs strong pulses to operate it. Comnoz's principle of mounting directly to the crankcase works best. The more remote the reed is from the crankcase, the less effective it will be. Despite this, people have found that a timing case mounted reed valve has cured oil leaks.
     
  19. o0norton0o

    o0norton0o

    Joined:
    Apr 27, 2015
    I drilled my timing side case in 2 places. One 3/8" size hole that I carefully located at the proper angle behind the timing chain gear, so it would be between the "webbing" of the crankcase casting. (so the hole weakens the crankcase as little as possible) The other hole I drilled was a 3/16" hole just behind the oil pump (yellow arrow, you can't see the hole) to allow oil to drain back to the crankcase to be scavenged rather than have a potentially higher level of oil in the timing chest... (in retrospect, I don't think I needed to drill that hole...)

    the other red arrow you see in the picture points to an existing stock hole. And lastly, you see the back side of my reed valve on the blanking plate... Here's a pic.

    [​IMG]

    I did mine on the bike with a shop vac adaptor sucking the chips as I drilled. I followed that up with back to back oil changes after the next 2 rides with no complications from doing it since. I love that it's not an oily pig anymore... I really hated that most about my commando. It was always covered in a film of grimey oil. I couldn't touch anything without coming up with greasy black fingers. It's much better now, but not perfectly oil tight...but I was never one for perfect tidyness. I much prefer to persue mechanical perfection
     
    texasSlick likes this.
  20. Blue750

    Blue750

    Joined:
    Mar 17, 2018
    Thank you all for explanations and tips. Highly appreciated!
     

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