Results 1 to 13 of 13
  1. #1
    CB750 Enthusiast CB750-Bobber's Avatar
    Join Date
    May 2012
    Location
    Wyalusing, PA
    Posts
    74

    Oil always drips from my case breather...normal?

    As the title states, the issue i'm having is that everytime I ride my 78 CB750K it drips while running, not a ton maybe 3 drips per minute..Im running an 3 qt. oil bag with 1/4" ID supply and return lines. Is it possible that the ID is too small and not allowint the pump to return the oil to the bag fast enouth therefore the "excess" oil is forced out of the breather?..... The obvious issue is its annoying and leaves oil spots where ever its parked, the other more pressing issue is it spatters on my rear tire while Im riding creating a safety hazard.. Any input would be appreciated..Thanks in advance
    "Yeah, you and 40million other 'bikers" are riding those over priced Harley's that are made in Japan too."

  2. #2
    Moderator dirtdigger's Avatar
    Join Date
    Feb 2012
    Location
    Black Hawk SD
    Posts
    2,813
    1/4" really is pretty small for the 750. FYI Cycle Exchange recommends running 1/2" oil lines to ensure adequate oil supply to the motor. I also run only 1/2" oil lines on my builds. To keep the motor happy you really should use a bigger line. Is it the breather line on the head or on the back of the case that drips? Has it always done this with the 3qt oil bag? Reason I ask, stock 750 oil capacity is 3.7qts, I have run a 3qt system for a short bit on one of my bikes. It was a big bore motor and the oil was getting too hot and the oil would expand enough and bleed out the oil tank vent. Never had oil come out of a breather line though. I run oil coolers and at least 4 qt oil tanks on any 750 I build. Just something to think about. Another thought....check to make sure the the breather on the valve cover is open and not causing crankcase pressure to build up and force oil out.

  3. #3
    CB750 Enthusiast CB750-Bobber's Avatar
    Join Date
    May 2012
    Location
    Wyalusing, PA
    Posts
    74
    Thanks for the response DirtD' I agree with the 1/4" being small It was a mistake at the time, one of those.."o'crap, this hose is smaller than stock lines, NAPA is closed and I really want to fire this puppy up" situations..I'll definatly replace it as you have reaffirmed my bandaid was stupid..lol As for breather vs. valve cover vent..Its deff the case breather as the nipple is on the back of the case by my battery. Also the valve cover breather..Im not 100% sure its not blocked in the hose I put on there a while back so I'll recheck tomm.. Lastly, the 3qt bag..it has always been..bought it as a roller...a frame with wheels and a halfway bolted in engine with no carbs..with painted tins, drag bars and bar-end signals??? Soooo, there was no plumbing or wiring either.. I simply removed the stock lines from the adapter ends that mate to the case, tapped them with NPT threads and installed 1/4" barbed male ends.....SO the fix sounds easy enough...just have to looks at the oil tank/bag orifices..It a cycleX tank so one would think they thought about this as well...but...Im pretty sure they are 1/4" or so female bungs..gonna have to confirm and drain/drill and tap if they arent atleast 3/8" IMO..
    "Yeah, you and 40million other 'bikers" are riding those over priced Harley's that are made in Japan too."

  4. #4
    CB750 Enthusiast CB750-Bobber's Avatar
    Join Date
    May 2012
    Location
    Wyalusing, PA
    Posts
    74
    Just wanted put this info out.. If one recommends 1/2" id oil line yet runs 1/4 npt bungs in there custom oil tank isnt that theoretically the same as running 1/4" lines?...The system is only as free as the smallest diameter..true?

  5. #5
    Quote Originally Posted by CB750-Bobber View Post
    Just wanted put this info out.. If one recommends 1/2" id oil line yet runs 1/4 npt bungs in there custom oil tank isnt that theoretically the same as running 1/4" lines?...The system is only as free as the smallest diameter..true?
    I would think so. I'm pretty sure with air lines that a restriction at the start of line will affect everything after it and a restriction at the end isn't as bad. Maybe fluids work the same way? I wish I knew more about fluid dynamics.

  6. #6
    CB750 Enthusiast CB750-Bobber's Avatar
    Join Date
    May 2012
    Location
    Wyalusing, PA
    Posts
    74
    I looked closer today and my lines are actually 3/8".. OOPS my bad, either way the bungs are 1/4"//kinda odd.
    "Yeah, you and 40million other 'bikers" are riding those over priced Harley's that are made in Japan too."

  7. #7
    CB750 Enthusiast Sprocket's Avatar
    Join Date
    May 2012
    Location
    Brighton, MI, USA
    Posts
    72
    My chop leaves a mist and accumulates to drips off my frame. The motor isn't dripping, it's a mist that is captured by the accumulator on a stocker and fed through the airbox like PCV valve in a car. I've just been too busy (lazy) to do what needs to be done. Build a small breather/reservoir. Cap the ends of a small piece of tubing, say 1 1/2". On the top, mount a small bung with a barb to fit a small breather filter from Autozone (or any of those cheap auto stores) On the bottom install a petcock to drain the oil when it get's too full. On the side, near the top, weld on a bung with a barb the size of the hose from the motor.
    I like to build them with aluminum and polish the shit out of it, stainless can polish up pretty nice too, or the cheap way out is obviously cheap exhaust pipe and paint.

    On big inch drag race motors with dry sump oiling, like our bikes have, We use vacuum pumps to evacuate the crankcase pressure and vent it into a can just like I described above. Just check it once a week and put the oil back into your oilbag.
    Dan "Sprocket" Harris
    Sprocketwerx Motorsports
    Custom chopper parts, drag race support, machining and fabrication.
    My rides/projects: 2-CB750, 1-CB650, 1-CB450twin, 2-XS400, a bunch of XS650, 2 XS1100

  8. #8
    CB750 Enthusiast CB750-Bobber's Avatar
    Join Date
    May 2012
    Location
    Wyalusing, PA
    Posts
    74
    Quote Originally Posted by Sprocket View Post
    My chop leaves a mist and accumulates to drips off my frame. The motor isn't dripping, it's a mist that is captured by the accumulator on a stocker and fed through the airbox like PCV valve in a car. I've just been too busy (lazy) to do what needs to be done. Build a small breather/reservoir. Cap the ends of a small piece of tubing, say 1 1/2". On the top, mount a small bung with a barb to fit a small breather filter from Autozone (or any of those cheap auto stores) On the bottom install a petcock to drain the oil when it get's too full. On the side, near the top, weld on a bung with a barb the size of the hose from the motor.
    I like to build them with aluminum and polish the shit out of it, stainless can polish up pretty nice too, or the cheap way out is obviously cheap exhaust pipe and paint.

    On big inch drag race motors with dry sump oiling, like our bikes have, We use vacuum pumps to evacuate the crankcase pressure and vent it into a can just like I described above. Just check it once a week and put the oil back into your oilbag.
    Dan, thanks a bunch..makes sense..ill be looking to either fab up something or just install a breather to help disperse oil explusion..thanks again

  9. #9
    CB750 Member mycb750's Avatar
    Join Date
    Jun 2012
    Location
    United States
    Posts
    5
    Also might suggest ring blow-by. Have you done a compression test lately or done a top end rebuild? Sometimes upside down rings cause lots of breather oil mist/smoke from the blow by.

  10. #10
    Quote Originally Posted by Sprocket View Post
    My chop leaves a mist and accumulates to drips off my frame. The motor isn't dripping, it's a mist that is captured by the accumulator on a stocker and fed through the airbox like PCV valve in a car. I've just been too busy (lazy) to do what needs to be done. Build a small breather/reservoir. Cap the ends of a small piece of tubing, say 1 1/2". On the top, mount a small bung with a barb to fit a small breather filter from Autozone (or any of those cheap auto stores) On the bottom install a petcock to drain the oil when it get's too full. On the side, near the top, weld on a bung with a barb the size of the hose from the motor.
    I like to build them with aluminum and polish the shit out of it, stainless can polish up pretty nice too, or the cheap way out is obviously cheap exhaust pipe and paint.

    On big inch drag race motors with dry sump oiling, like our bikes have, We use vacuum pumps to evacuate the crankcase pressure and vent it into a can just like I described above. Just check it once a week and put the oil back into your oilbag.
    Now this shit right here is why I love this site. Knowledge and ideas you wouldn't come up with yourself. Great stuffs..
    Everybody has a plan. Until they get a bee in their helmet.

    www.barndrunks.com

  11. #11
    CB750 Enthusiast Sprocket's Avatar
    Join Date
    May 2012
    Location
    Brighton, MI, USA
    Posts
    72
    CB750-Bobber... when someone comments on your bike dripping oil, tell them it's practicing to be a Harley...lmao
    Dan "Sprocket" Harris
    Sprocketwerx Motorsports
    Custom chopper parts, drag race support, machining and fabrication.
    My rides/projects: 2-CB750, 1-CB650, 1-CB450twin, 2-XS400, a bunch of XS650, 2 XS1100

  12. #12
    K2750tracy K2750tracy's Avatar
    Join Date
    Feb 2012
    Location
    Hanover Pa
    Posts
    466
    I say it doesnt want to make the harleys feel inferior

  13. #13
    CB750 Enthusiast CB750-Bobber's Avatar
    Join Date
    May 2012
    Location
    Wyalusing, PA
    Posts
    74
    Lol...ok in order as I missed "mycb750's" comment.. No rebuild done, I havent done compression test yet because im lazy...I will now because it makes sense .. Regarding the Harley comments...yeah, I too am marking my spot like a dog/harley every where I park!

Similar Threads

  1. Cracks on lower case
    By Andy in forum General Motorcycle Discussion
    Replies: 6
    Last Post: 03-03-2012, 04:24 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •