Clutch Modifications

Discussion in 'Whizzer Motorized Bicycles' started by Quenton Guenther, Mar 5, 2009.

  1. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Just a few comments concerning the Whizzer automatic clutch.

    Due to a special request, I will pass on a few changes I made to one version of the automatic clutch.

    It is important to note the latest version of the automatic clutch from Whizzer can not be upgraded with my modifications. Due to current design, I can only exchange the hub with a previous version that has been modified. The reason the current version can't be upraded is because replacing the sleeve with the Rockwell 58 hardened sleeve weakens the area where the shaft is affixed to the hub. This problem centers around the use of additional
    bearings and the removal of too much metal to support the shaft.

    On my 1950 Sportsman it is possible to lift the front wheel off the ground [wheelie], and I have been asked to share the methods used to make the clutch work this well.

    It is important to explain how the clutch operates in order to make the changes have merit. Because of bogus information, many think the clutch works better on a stock motor, however the opposite is actually true. The quicker the shoes can be "thrown" against the drum the quicker it "locks", and the better it works. The flaw in the design is centered around the clutch operating at idle, it is at this time the bearings are riding on the soft bearing race. Only when the shoes are engaged does the clutch work as one piece, and shifts the assembly to use the smaller bearings that hold the assembly to the arm.

    During testing and high mileage runs it soon became apparent the quicker the clutch was engaged the more reliable it became. The factory was in fact at odds with the known tests and cancelled warranties over these proven theories. The more the clutch was used at low speeds the quicker it failed.

    Here are the changes I made to make it work best and last the longest. The soft bearing race was changed to a Rockwell 58 rated bearing sleeve, removing the problem of the bearings "eating" the sleeve. During the replacement of the bearing sleeve I also noticed the hub wasn't always parallel to the bearing surface causing a mis-alignment of the shoes. During the sleeve replacement process I found it necessary to cut the inner hub to match the shoe angle. During the rebuilding process it also became clear the inner surface wasn't always level, but machining the inner surface corrected that. Another change that helped the clutch engage better was to "rough" the inner surface to help make the shoes grab better [sand blasting the inner hub was suggested in a post on this site], and aided in a quicker engagement. Drilling holes in the hub was another change that helped remove any "dust" and also created a better mating surface for the shoes.

    I tried many different shoe combinations and springs, but the original springs worked best, but I "stretched" them slightly to reduce the opposition to the centrifugal force to allow quicker movement.

    Lots of quick power, better bearing surface, weaker springs, and 20" wheels are the reasons my bike will pull wheelies using the automatic clutch.

    Have fun,

  2. ren

    ren Guest

    Hi Quenton, how did you stretch the springs, and how were you able to stretch all three the same amount?


  3. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi Randy,

    With the shoes installed I simply pulled the shoes way past thier normal position. In the same direction as they would normally move but without the hub to stop them. After a few times [4 or 5] the springs will stretch.
    If stronger springs are used the stall speed is a lot higher, but the clutch engages more suddently. If springs too strong are used they won't have enough pressure against the hub. If springs that are too weak are used the shoes can dis-engage and engage [bounce] causing intermitten clutch lock up.

    Most automatic clutches are usually changed via different spring rates to change their use. Competition clutches are a good example of spring options.

    Have fun,
  4. Springs

    I noticed that the stock springs are a lot smaller in diameter than all of my other centrifical clutches from other bikes. I have also noticed that when the Whizzer clutch gets hot, after say climbing a hill, that its performance drops significantly. So I thought maybe using stiffer springs would keep the shoes from engaging at all when the bike is idleing therefore reducing the amount of heat. I know that the holeshot mini moto clutch springs are a lot stiffer than the stock Honda springs. Your explanation of the wheelie bikes lighter clutch springs goes against my tighter spring theary. But I have not tried stiffer ones yet.

    So Q. my question to you is have you ever tried tighter springs? If I knew where to get some I would try it.

    I also tryed using the manual clutch lever to keep the auto disengaged while idleing. It seemed a big improvement, but it will not stay tight like the manual pulley will. It works for a while then it gets loose & obviously this could be dissasterous. I have not abandoned that set up completely, just trying to come up with a better idea. By the way sandblasting the inside of the drum was definately worthwhile.

    After all the tinkering I have to say that the clutch works pretty well now. Just doesn't perform as well as I think it could. Heat is the enemy.... I want it to lock up solid and move when I gas it. All other centrifical clutches that I have owned work best when they are new. Why can't this one be like those??
    Last edited by a moderator: Mar 8, 2009
  5. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi Zomby,

    I tried heavier springs when the clutch was first sent to me for testing. I think the springs were from the extra large clutch offered on the 2001 Pacemaker II. When the heavy springs were installed the motor wouldn't activate the clutch until it exceeded 3800 RPMs. The problem is related to the motor to clutch ratio. The motor has a 2.5" drive pulley and the clutch pulley is 5" yeilding a 2 X 1 ratio [actually 2.06 X 1] . When 3rd Mel. made a clutch for the Whizzer it had a 4.1" [approx. 1.68 X 1] clutch pulley and spun much faster than the Whizzer version.

    If you find & try stronger springs let us know the results.

    Have fun,