Billet heads and barrels mounted on a stock 66/80 cc bottom end

Discussion in 'General Questions' started by buzbikebklyn1, Nov 21, 2010.

  1. buzbikebklyn1

    buzbikebklyn1 New Member

    I've found a machinist that has a CnC machine that's willing to make a limited run of billet barrels and modified cylinder heads for the 66/80cc motors If i help him build his own bike! (his business is a little slow of late)

    Slightly higher compression with a polished hemi combustion chamber correct squish area.
    Stronger materials, and increased cooling area for the head, the barrels have thicker walls and are iron sleeved, (to make future bore clean up easy)
    Modified port configuration and a reed block housing, im using large cut off saw reed-blocks, a straight shot intake manifold and a diaphragm carb off a small ultra light air craft engine. Increased cooling fin area. All designed for the 8mm head studs.
    As with everything i build i'm initially only having two sets made if they work well ill consider more.
    The prototypes have already been designed and a machining program created.

    I've had several pieces made by this shop in the past and I've always been impressed by there workmanship so quality is first rate.

    My question is can a well put together (good bearings, proper clearances, good gaskets and vacuum tested) stock 66/80cc 2 stroke bottom end handle the power increase?
    Can the bottom end take it?
    Am I going to have to endurance bench test the combination? it seems a shame to sacrifice a good bottom end for all this, but i need a stronger engine out of the same sized package...
    Any one tried this before?
    Oh... on another front-
    All that breww haa haa over the "50mph electric bike" has inspired me to build one to come...aah the sounds of silence!

  2. GearNut

    GearNut Active Member

    Considering that a few folks have installed moped cylinders, heads, carburetors, reed valves, custom tuned expansion chambers, ect. to these cheap Chinese engine cases and with the addition of quality bearings throughout the cases have held up; I think that you should have no problems.
    The one weak link seems to be the clutch. It cannot stand up to 5 hp or so for very long.
    Last edited: Nov 21, 2010
  3. buzbikebklyn1

    buzbikebklyn1 New Member

    THE CLUTCH! eureka, thats what i left out of the equation!
    Thanks Gearnut!
    The centrifugal replacement clutch should take 5 hp.
    Now i'm phyced!!
  4. Fabian

    Fabian Well-Known Member

    Has the billet 80cc cylinder project gone ahead, because if it has, i want one to test?
  5. jaguar

    jaguar Well-Known Member

    all important is port timing. what did you design it to be? (hopefully more exhaust duration for higher RPM)
    too bad there is no mention of a good quality motorcycle piston/rings to be used with this new cylinder.
    keep the cranking psi less than 140.
  6. HeadSmess

    HeadSmess Well-Known Member

    make the head and cylinder spigotted so theres no need for a gasket, make sure the squish band is perfect or forget about it, um....

    use a reed cage from a commercial race engine like the aprillia 50.

    give it a manifold for a mikuni vm18 or 20... or a fat walbro like used on old mcculloch chainsaws... at least a 22mm bore!

    on that note, a tapping point for pulse feed if a walbro or fuel pump is used.
    (some of us like having the tank BELOW the carb ;))

    jag raises a very good point...make it suit a decent race type piston with narrow rings.

    a centrifugal clutch shouldnt really be a problem with 5hp...they do grip harder as they spin faster, remember. the standard clutch though...its controlled by a combination of contact area and spring pressure alone. you cant really make the spring stronger... removing a few pads does increase pressure per pad though... less area but more pressure... seemed to work ok for me.

    why centrifugal clutch? then you need a pullstart. then you might as well stick with a fourstroke engine...