reed valves on a happy times engine?

Discussion in 'Performance Mods' started by motorpsycho, Dec 6, 2010.

  1. motorpsycho

    motorpsycho Active Member

    has anyone tried putting reed valves in a h.t. engine?
    does anyone even make a reed valve kit for a h.t. engine?
    am i correct in saying that reed valves will greatly increase throttle response and give you more power?
    i'm thinking that i can modify a reed valve from a chainsaw to work.
    any ideas?
    Last edited: Dec 7, 2010

  2. HeadSmess

    HeadSmess Well-Known Member

    im currently doing it. just that i pulled my mill apart for necessary mods before finishing... so no comment. stupid grub screws :rolleyes:
  3. motorpsycho

    motorpsycho Active Member

    are you using a reed valve from a chainsaw? single valve or multiple valve?
    I'm thinking that i can make a spacer to go between the cylinder and the intake tube to house a single reed valve. the spacer would have to be just like the flange on the intake tube and it would sandwich between the cylinder and the intake tube with a gasket on each side.
    am i on the right track?
  4. HeadSmess

    HeadSmess Well-Known Member

    single flap twin hole from a chinese 50cc quad...

    ummmm...somewhere in the "wild in the streets" section...

    i removed the whole side of the cylinder and bolted on a manifold/adaptor.

    then my mill had issues... so now im kitting it up as cnc... then back to the(spare) ht to finish it :)

    the problem with the stock inlet is that its tiny... the size of valve is the issue. theres other ways to make a reed valve though. its getting the flow.

    the stock inlet also needs the piston chopped a lot to get any effect...balance... my way ive opened the port up til its almost level with the base gasket...

    using the extra extension on the crankcase lowers the overall compression in the crankcase... more volume. so the effect of reed valves is lessened again...

    the easiest and best method must be modding one of the case halves instead....which seems to be what most ppl do do... me? im doing it my way just to seeeee... but my reeds are about 2mm from the piston skirt... theyll actually open up into the space under the piston... hopefully? :lol:
  5. motorpsycho

    motorpsycho Active Member

    so there is more to this than just sticking a reed valve in the intake tube.
    this is more than i really want to do, i was hoping that it would be a lot simpler than what you are doing.

    I was thinking that i could just make a reed valve and put it in the intake and it would be good to go, but it sounds like there is more to it than that.
    Thanks for the info.
  6. HeadSmess

    HeadSmess Well-Known Member

    yep. unfortunately an engine designed with reed valves is just that...designed for them. they usually enter the crankcase with almost no clearance, keep the volume as small as possible. raising the crank compression( or "blowdown" as i think old bob puts it) its why honda back in the early days used "full-circle" cranks...unlike the cruddy ones on say, a ryobi... its crank case filler! brings the volume of cylinder and crank closer to equal.

    "re-engineering" things is only like me :) it stops me smoking so many ciggies. except when things dont work :p

    (and mills etc may seem expensive...they arent. (compered to ciggies :p )its the tools you need for them...if youre thinking of learning the joys of machining )
  7. keatonx

    keatonx Member

    Even my little weed eater has a reed!
  8. vonstringer

    vonstringer New Member

  9. 074KU

    074KU Member

    I know I am going necro on this thread but felt I could add some additonal information.

    There is to my knowledge 1 company out there that have made a reed vavle specifically for the HT engine (apparently it has been dyno tested). It is a straight bolt on conversion replacing your old intake and will accept either the standard or Dellorto carbs.

    It has a billet body and the valves are fibreglass.

    do a little searching on the google machine and you should find it with no troubles.
  10. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    Arrow Motorized Cycles makes a reed valve for the HT engines.
    I have ridden a few of their bikes and they haul butt.

    They came in 2nd at the last Grange race even though the bike
    had some problems and they are going to be racing at least 3
    bikes at the upcoming April 7th race at Grange Motor Circuit.


    Last edited: Mar 27, 2012
  11. jaguar

    jaguar Well-Known Member

    That reed valve is too far back. unless you stuff the crank then the crankcase compression ratio would be lowered too much by the extra volume between the cylinder and the reeds.
    The single petal reed valves that people often want to adapt to the Grubee engine would restrict the flow too much.
    My engine has a reed valve inside the intake port (which was slightly enlarged) AND has the crankcase stuffed. It runs really good. I wish I was in the States so I could take it to a race.
    The link you gave didn't work. Here is the right one:
    Here is something showing the empty crank space ready to be filled with JBWeld:

    Attached Files:

    Last edited: Apr 1, 2012
  12. Fabian

    Fabian Well-Known Member

    Reed valves work perfectly well on Happy Time engines so long as they are designed and manufactured correctly.

    Rock Solid Engines makes a superb reed valve system that's a virtual bolt on item.

    Send me a PM and i'll give you a web link to my photo review of the installation procedure.
  13. geebt48cc

    geebt48cc Member

    So, Fabian

    If you can, I would also like to see that.............


  14. jaguar

    jaguar Well-Known Member

    I am ordering one and will report on it but my crankcase has been stuffed for use with reed valves. So my report won't really be valid for normal users.