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    #1

    crankcase ventilation question....

    on a stock hawk, only the rear head vents the crankcase.....

    i popped the front cover off, and while drilling the cover would be no problem, the head lacked the crankcase breather connection hole..

    obviously i cannot do this unless i pull the head off and dril it out.. but is there any real benifit to that?

    looking at hawks, and from what ive read and what i carefully looked at on some faster race bikes... i think there is... if nothing else, two holes are better crankcase vents then one..


    im thinking about putting a hose on both, and having them go into a air/oil seperator can.. allowing them to breath easily, and not spew oil.

    anyone else done something similar?
    Tags: None
    #2
    this looks somewhat like an excellent solution to a problem that does not exist ...........

    i'm sure the entire crankcase vents adequately through there unless you have abnormal blow-by.
    "It's only getting worse."


    MY rides: '97 VFR750, '90 Red Hawk, '88 Blue/Black Hawk, '86 RWB VFR700 (3), '86 Yamaha Radian, '90 VTR250, '89 VTR250 (2), '73 CB125, '66 Yamaha YL-1

    Sold: '86 FJ1200, '92 ZX-7, '90 Radian, '73 CB750, '89 all-white Hawk, '88 blue Hawk, '86 FZ600, '86 Yam Fazer 700 , '89 VTR250, '87 VFR700F2, '86 VFR700F.

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      #3
      A better mod - the AT heads have screw-on valve inspection covers so you can set the valves w/o taking the main covers off (or tie yourself up in even more knots trying ...)
      '95 ShaftHawk 650P>
      Front: Bros Mk2 front wheel; Mk1 forks; MetalGear disc; NC30 caliper; cb1 yoke.
      Breathing: Hacked up and shortened ART tri-can on collector and link pipe from DemonTweeks.
      Other: RGV bars; DefT dash; modded subframe; modded rearsets; relocated ignition.

      '91 Bros 650 Mk1>
      Currently off the road.

      Comment

        #4
        Originally Posted by squirrelman
        this looks somewhat like an excellent solution to a problem that does not exist ...........

        i'm sure the entire crankcase vents adequately through there unless you have abnormal blow-by.
        well, i DO have abnormal blow-by... but that wasnt the reason i was thinking about doing this.

        looking at the crankcase vent, i realised that while its ADEQUATE, it doesnt appear to be ideal for getting that last big of power out of a modified performance motor.

        Comment

          #5
          I dont know if another vent would help! but I know that heavily built race engines (not bikes) have vacume pumps to reduce the amount of crank case pressure behind the piston. but that would definatly not be applicable on this motor. Im sure the existing breather is enough to expel any case pressure that would hinder the perfomance. if you did I think you are talking maybe gaining 1/16 HP.

          Just my 2 Pennies, But what do I Know???!!!

          Comment

            #6
            You might be surprised.

            The thing about a Hawk and some other twins, the pistons relative movement to each other isn't offset, say like it is in a traditional an inline 4. So there is more than just blowby being vented, the engine actually "breathes" air in and out. If you open up the breathers (or use the starter hole on a pure race engine) and use a Ducati Corse type system with a reed valve to pump down the cases, I have seen power gains...
            J.D. Hord
            Keeper of Engine Nomenclature, 9th Order

            Comment

              #7
              Can you put a spare rear valve cover on the front pot?
              '95 ShaftHawk 650P>
              Front: Bros Mk2 front wheel; Mk1 forks; MetalGear disc; NC30 caliper; cb1 yoke.
              Breathing: Hacked up and shortened ART tri-can on collector and link pipe from DemonTweeks.
              Other: RGV bars; DefT dash; modded subframe; modded rearsets; relocated ignition.

              '91 Bros 650 Mk1>
              Currently off the road.

              Comment

                #8
                Yeah, you can, but it still might not vent. Some of the front heads have a bit of casting that blocks the venting thru the head. Others are open... I have seen it both ways.
                J.D. Hord
                Keeper of Engine Nomenclature, 9th Order

                Comment

                  #9
                  yea, mines closed off on the front head. it looks like just casting flash.. a drill or dremel should be able to take care of it easily.

                  my idea is to use a PCV valve right before the breather.
                  its not as effective as a reed valve or anything like that, it wont hold a vacuum, but it should lower the pressure.

                  ive actually thought of running a vacuum pump.. some of my race motors (automotive, not motorcycle) have run them, and ive seen some large gains.. my LS1 alone gained 25hp on the dyno, and its just a street motor...

                  the problem with it on a motorcycle, is space, fitment, and power gain per pumping loss... if i had the ability to say, build a custom pump that fit where the starter goes, it may be an option... but i dont have the machinery, dyno or time to figure out anything like that.. lol.




                  JD, this was one of the things i wanted to ask you about, but i had forgotten when i was on the phone. lol.

                  Comment

                    #10
                    Last year at Mid-Ohio I was snooping and the Rockwall Honda Formula Extreme CBR600's had electric vacuum pumps mounted in the rear of the subframe. The bikes were former Erion or AmHon from what I heard so I don't know who put the pumps on but... they were there.
                    J.D. Hord
                    Keeper of Engine Nomenclature, 9th Order

                    Comment

                      #11
                      Wow great info! I did not Know that a vacume pump on a street motor (LS1) wound make that much power !!!

                      I would think now it might be a good thing to look at on a twin!

                      Comment

                        #12
                        Originally Posted by Rydtheslyd
                        Wow great info! I did not Know that a vacume pump on a street motor (LS1) wound make that much power !!!

                        I would think now it might be a good thing to look at on a twin!
                        stock shortblock, stock heads, only internal mod was a big cam... redline was bumped up to 6800... saw a NICE increase.. i was quite happy.

                        best part is, the AC compressor was run off a separate belt and bolted to the block by itself... makes for a perfect location for the pump.

                        it also got rid of the occasional detonation due to oil consumption.

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