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Thread: Alright this is a two question deal

  1. #1
    Join Date
    Jul 2005
    Location
    Bloomington, IN
    Posts
    4,644

    Smile Alright this is a two question deal

    One) This is probably a ridicoulously stupid question, but how exactly are those step blocks/hold down kits used? I keep seeing them advertised but dont know how you use them/set up a piece with them.

    Two) Completely unrelated, anyone have ideas to simply modify a plastic cam shaft. Specifically i'm looking to gain some more valve travel hill-bily style by cutting a small amount off of the section where the tappet rides in the closed position while keeping the lobe itself intact. By replacing stock tappets with loner, the difference in thier resting position to open will be greater thus lifting valves higher. (this is for a lawnmower engine with plastic cam) i should also add i dont have a rotary table and dont plan to buy one, or indeed very much tooling at all, for this project since it is just a jerry-rigged type set up.

  2. #2
    Join Date
    Oct 2004
    Posts
    767

    Post

    One: Are you talking traditional hold downs with the triangle serrated blocks? If so the end of the hold down is also serrated and grips the serrated slope of the triangle.

    Two: What you are talking about is reducing the base circle of the cam. This is a very common mod when regrinding camshafts. As long as you maintain proper geometry near the base circle so the valves don't slam shut it should work. Now that will give more lift with longer tappets but will the heads of the lawnmower actually flow more air, I don't know. Second more lift can reduce velocity and therefore reduce torque. With a plastic cam I doubt this thing revs very high and therefore doubt added lift will be of much benefit. Besides with enough lift and overlap it might not be streetable anymore and will have to ride around on a trailer with the other trailer queens.

    In all seriousness though check out what the junior dragster folks are doing with 5hp briggs engines, they are making huge power and running really quick 1/8 mile times.

    ------------------
    -Christian D. Sokolowski

  3. #3
    Join Date
    Oct 2003
    Location
    mesa, az
    Posts
    2,242

    Post

    <font face="Verdana, Arial" size="2">Originally posted by Fasttrack:
    One) This is probably a ridicoulously stupid question, but how exactly are those step blocks/hold down kits used? I keep seeing them advertised but dont know how you use them/set up a piece with them.

    </font>
    http://www.jjjtrain.com/vms/Media/mill_table_clamping/mill_clamping_tslot_and_step_blocks.WMV
    The above link is a nice little short vid, and the below link is where I got it from.
    http://www.jjjtrain.com/vms/mill_table_clamping.html#2


    Sorry someone else here will probably be better able to help you with the cam.

    FuQ

  4. #4

    Post

    Fasttrack, you may want to enquire about opening and closing ramp configurations, valve assembly acceleration rates along with coil spring shut height, seat pressure, coil bind. If this is a flat head, you can replace the side cover with a plastic 'window' and observe the action with a strobe light with advance and retard triggering activated by the flywheel. Last Old Dog
    Added: rsr911 beat me to the punch, good thoughts, nicely done Christian

    [This message has been edited by Last Old Dog (edited 01-30-2006).]

  5. #5

    Post

    Fasttrack,

    Re: Two) The woodshed cam grinder is one of those mini sanding belts turned inside out, looped over the heel of the cam and spun by a rubber pulley on whatever motor or drive you can jury rig. No dials on this machine so you'll have to just sand it and mike it till you've taken off what you want.

    Jan
    .
    "Opportunity is missed by most people because it is dressed in overalls and looks like work." Thomas Edison

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