Serious About Porting

Discussion in 'Performance Mods' started by 210061741, Dec 3, 2009.

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  1. 210061741

    210061741 Guest

    Yes it is time for a serious porting thread.
    I have been buisy working on this PK80-J.

    Came up with a way to determine where the porting is at.
    Timing / Duration.

    Once i get the data i need i will run it through some software to find the best tweeks.

    I'll break the process down a little as i go.

    #1 Create a Port map. " a rubbing of the cylinder walls"

    We will use this to calculate the volume of each port and will also need to take note of any angles to the ports.

    #2 Buy or make a degree wheel so we can measure port timing and duration in degrees of crankshaft rotation.

    #3 Mount you engine and setup a dial indicator or piston stop to find TDC.

    #4 Adjust your degree wheel to 0 degrees at TDC.

    #5 Take your measurements.

    So far i have ground the transfer area of the crankcases nice and smoothe.
    Also skimmed the exhaust and intake ports removing only enough material to clean the ports up nice and smoothe.

    The software will tell us what to cut and where later.

    The top of the Intake port is slightly blocked by the bottom of the piston skirt.
    Maybe by about .030 of an inch.

    But the duration of degrees at that position is so short it may not effect much.

    It will be a balance between milling the piston skirt and lowering the Intake Port.

    Just remember if your ports are too big the rings could bulge out and get hung up in there.

    So cutting in the right places and shapes is very important.

    I made this degree wheel on a CNC Laser.
    The etching isn't real deep but it is there.
    I bolted a steel plate to my workbench and mounted the motor to it.
    The indicator is attached to another steel plate.

    Attached Files:

  2. 210061741

    210061741 Guest

    Completed So Far

    So far here's what i did to the PK80.
    Ground and polished the crankcase halves.
    See the before and after.
    Thinned out the transfer webbing on the cylinder side.
    Matched the crankcase to the jug transfers.
    The smoother and more step free = less resistance to flow.

    I posted a pic of the grubee crankcase halves.
    Notice how the transfer isn't ground out at the factory.


    A few other things.
    When you do this seal up the bearings.
    Mill all the gasket surfaces only enough to clean up nice on the sandpaper and glass.
    Grit in your bearings is not fun.

    Very important.

    before i assemble the bottom end i check everything for good fit and resurface all the mating surfaces. where i can.

    For this step we need only the jug and the head and crankcase halves.
    Were not putting anything in there yet.

    Assemble the empty crankcase halves.

    Tighten all the crankcase screws pretty good but not like final torquing.
    Insert the cylinder studs into the crankcase.
    Then loosen the crankcase screws a couple of turns out.
    We want all 8 screws to be very loose.

    The circular bored portion of the crankcase halves fit together.
    One half has a little counterbore and the other half has a raised step to fit into that counterbore.
    This helps locate the Mainbearings and Crankshaft but dosen't do much for the JUG.

    The reason we need the screws loose. "locate The Jug"

    Next i put the jug on and head on without the piston in place.
    Tighten the jug down pretty good.
    Now tighten up the 8 crankcase screws good and tight but remember it is coming apart again..

    I know this sequence is a PITA but it pulls the Crankcase Halves into alignment with the sealing surface of the jug.

    How else you gonna do it?

    Now remove the jug and head and head studs.
    Mill the crankcase base gasket area on sandpaper and glass.

    Remember after it's done it has to come apart again to put the internals in.
    But if you assemble it in the same sequence you should have the best match to the base gasket sealing area.

    If that base gasket leaks too bad the motor will just stop running.

    On a side note:

    I would like to encourage all the other members to get involved here and add any data or insight they may have.

    Exact specifications of the HT motors aren't easy to come across.
    So any of that stuff would fit good here.
    It will be needed to port different motors correctly.

    I also am aware there are some engine builders around here who's input would be very welcomed.

    I am not perfect and do make mistakes sometimes.

    As a Team we could create an outstanding thread here.
    Lets just stay on topic and use real factual data....." no guestimates "

    In the end we will all benifit from this work.

    Especially if the HT goes extinct and we have to machine our own.

    Attached Files:

  3. 210061741

    210061741 Guest

    Grubee Transfers.

    forgot to add the pic.
    Here they are... notice the big step.

    Attached Files:

  4. 210061741

    210061741 Guest

    The first set of data.

    Few things to note befor we get too deep here.

    This data is derrived from the PK80-J slant head and alltough the numbers may be very close to another PK80-J thay will slightly vary due to varience in stroke length.

    The only safe thing to do is make a degree wheel yourself and find your timing.
    Especially if you have a different motor.

    There is a few sites that have a printable degree wheel that you can glue to a CD and attach to the magneto magnet shaft.

    The first oops i made was putting my degree wheel on the sprocket.
    It is geared 4.1:1 so that's no good.

    I moved the wheel to the magneto.

    This may seem like alot of data and were just getting started.
    We will need to know all of this for any motor we want to port.
    There will be more added later but i need to lay out the port map in CAD and crunch the numbers i have so far.

    But for thoose who cant wait........

    A nice informative page.
    A two-stroke

    TDC= Top Dead Center
    BDC= Bottom Dead Center
    BTDC= Before top dead center
    ATDC= After Top Dead Center

    Degree wheel mounted on the magneto magnet and rotated clockwise.
    Wheel incremented 360 degrees.


    The intake port opens on the upward stroke from the bottom of the piston skirt
    and the bottom of the port.
    It then closes after the piston reaches TDC and travels back down, when the
    bottom of the piston skirt closes the port completly.

    The intake port opens at 60 degrees BTDC.

    The intake port closes at 59 degrees ATDC. "= 301 degree mark on wheel"
    360 degrees - 301 degrees = 59 degrees.

    60 degrees + 59 degrees = 119 degree intake duration.

    The exhaust port opens on the downward stroke.
    When the top of the piston opens the top of the port.
    Then travels to BDC and closes at the top of the Port
    on its way back to TDC.

    The Exhaust port opens at 253 degrees ATDC.

    The exhaust port Closes at 108 degrees BTDC.

    253 degrees - 108 degrees = 145 degree Exhaust duration.

    The transfer ports
    The transfer port opens on the downward stroke.
    When the top of the piston opens the top of the port.
    Then travels to BDC and closes at the top of the Port
    on its way back to TDC.

    The ports open at 236 degrees ATDC.

    The ports close at 125 degrees BTDC.

    236 degrees - 125 degrees = 111 degree duration.

    BLOW DOWN "The time we have to get rid of the exhaust before the transfer opens"

    Exhaust port open 253 degrees ATDC
    Transfer port open 236 degrees ATDC
    253 degrees - 236 degrees = 17 degree blow down duration.



    Bore diameter is 47mm "measured"

    Displacement = 68.8605 cc "calculated"

    Distance of piston crown above the Deck @ TDC
    .141 inches / 3.58mm "measured"
    The edge of the piston is below the deck by (estimated .100 inches / 2.54mm)

    Distance from TDC to Exhaust port open.
    1.129 inches / 28.68mm "this is the length of the power stroke"

    Distance from top of exhaust to top of barrel.
    .988 inches / 25.10mm

    Stroke Length
    1.562 inches / 39.67mm "measured"

    Con Rod Center to Center
    2 x Stroke = 3.124 inches / 79.34mm "calculated"

    Center of Crankshaft to center of con rod big end.
    stroke / 2 = .781 inches / 19.835mm "calculated"

  5. 210061741

    210061741 Guest

    Here are the approximate port areas.
    Now we have enough data to start doin something.

    Port areas.

    Port areas.

    Exhaust = .4413 / 2.8471 sq. cm. / 284.7091 sq mm

    Intake = .3463 sq. in. / 2.2342 sq. cm. / 223.4189 sq. mm.

    Transfers = .2779 sq. in. / 1.7929 sq. cm. / 179.2899 sq. mm (EACH)
    Last edited by a moderator: Dec 3, 2009
  6. 210061741

    210061741 Guest

    you guys want more or what?
    Been too darn quiet around here.
  7. michelevit

    michelevit Guest

    i'm still listening

    very interested with your porting project.
  8. give me vtec

    give me vtec Active Member

    ohhh yes... quite intrigued.

    Please keep going... I want to see how the story ends.
  9. roddy4477

    roddy4477 Member

    Yes i am extremely interested in what you are doing. Good hard data that we all can use. thanks a lot.:detective:
  10. 210061741

    210061741 Guest

  11. Old Bob

    Old Bob Member

    Blow down is critical to making power.

    To measure blow down correctly you zero degree wheel @ TDC then measure where exhaust port opens, then measure where transfer opens. The programs I have used all use port openings measured from TDC.
    From TDC the exhaust port should open @ 90°-120° the transfer will open some what later.
    For good power, blow down angle should be 25°-30°. (recommended by Jennings and Bell)
    Last edited: Jan 3, 2010
  12. 210061741

    210061741 Guest

    Timing Blow Down

    Yes you are very correct.

    Took me a wile to really get going here.

    I wrote an excell spreadsheet for timing.
    I'll give you the PK80.

    This sheet is functionable.

    yellow = input

    blue = inch input

    green is calculated 4 you.

    red don't touch.

    The thing you have to remember about the HT is you don't have gears like a motorcycle.

    We need a good range for the power band on a single speed.

    But boy theese things respond really well to slight changes.

    Download the zip and open in MS EXCELL

    The portmap is for a GT-5 highly modified that i'm working on.

    Attached Files:

  13. 210061741

    210061741 Guest

  14. give me vtec

    give me vtec Active Member

    can you post a video of the bike with the modified engine on it??
  15. 210061741

    210061741 Guest

  16. give me vtec

    give me vtec Active Member

    WOW... that seems to be a significant improvement!!! Congratulations.... that's awesome!!

    Are you planing on doing this to other peoples motors for $$$. Can I send you a barrel and have you do what ever you did to yours???
  17. 210061741

    210061741 Guest

    Currently i am working with Justin at Pirate Cycles.
    He is sponsoring alot of my research and development.
    Providing me with what i need to come up with the out
    of the box performance motor.

    Were not too far from being complete.
    Anyway i'll talk to him and see what he says.

    Like i said he sponsors me so i don't want to jump over him.

    But yes we will have jugs or a whole motor availble soon.
  18. 210061741

    210061741 Guest

  19. 210061741

    210061741 Guest

    Also if you guys are serious about porting.

    I can give you the data to do it.

    It isn't easy and you may ruin a cylinder.

    If you assume the risk i will agree to post it.

    something that is fairly safe to do anyway. " Numbers Not To The Maximum Limit "
    Still some risk involved.

    At a minimum you will need to tune your carb and run an expansion chamber.

    Let me know.


    Riding Rich
    Last edited by a moderator: Mar 2, 2010
  20. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member