66cc engine tear down, setting it for high performance setup

Discussion in 'Performance Mods' started by DanielMaia, Feb 3, 2011.

  1. DanielMaia

    DanielMaia Member

    Received this engine yesterday, to make some "metal adjustments"

    What i thought:

    - All new gaskets!
    - New SKF 6202 roller bearings, 4x
    - Intake port patched
    - Exhaust polish and take 0.5 or 0.6mm, from the top.
    - Polish and remove edges, courves in the crankcase.
    - Remove 0.3 or 0.4mm in the cylinder head, to increase compression.

    Photos? Here you go:




    Piston in top position:

    Some damage, but i will polish all the surface:

    Piston in down position:

    Piston will be replaced:

    The major tools needed to desassembly the engine:


    Piston damaged by piston bearing:


    Exhaust port:


    Lot of work to do here :)

    And here...

    Comments or advices will be really helpfull for me, thank you :)

  2. Dave C

    Dave C Member

    Wow, it's a good thing you tore it down when you did, that piston was comeing apart :p

    How does the cylinder walls look? Is it scored, burned, or grooved? If not you might just need to have it honed at a bike shop for a new piston. If it's messed up then a new jug and piston & rings are in order. You will need the piston & rings anyway.

    Radius any air passages leading into or out of a passage. I'm not talking going hog wild with a grinder, just smooth the airflow will help a bunch.

    It's a good idea using this motor as a learner. Work steadly on it and don't get rushed at any point. I'm going to be following this due to the fact I'll be doing much the same with mine except I got the Puch Hi Compression head. For $30 it's georgeous piece of engineering. Machined combustion chamber!! First machined combustion chambers I ever saw were on Pontiacs. It's pretty hi compression, stock compression volume is just over 7cc. The volume of the Puch is just over 5cc. It would have to raise compression to somewhere over 9 to 1 compaired to stock 6 to 1. You have to drill the bolt holes slightly bigger for 8 mm studs but not for the 6 mm ones. Plus the fins surface area has to be twice as much as stock, always a good thing. If it needs less compression I can get it machined a bit larger in the sparkplug bowl area because of the centered plug location makes it easy to machine.
  3. DanielMaia

    DanielMaia Member

    Thank you lot for your post Dave, really love to read these comments :)

    Where you order that hi compression head? I may be considering one of these,

    The cylinder, it seems me its not bad, maybe i'll take some photos to show you :)
  4. Dave C

    Dave C Member


    This thread is 4-5 pages back. Post #4 has a photo of the stock, Manic Mechanic billet head, and the Puch head. Post #36 has where to get the different heads. I thought about getting the Manic Mechanic and modify to make it a water cooled head but the Puch head solves 3 things;

    1] More compression(maybe too much so) I was wrong about the CC's in the stock head, it's around 8cc so going to a 5cc combustion chamber is quite a squeeze.

    2] a MUCH better combustion chamber design being 100% machined over stock cast.

    3] cooling fins. No comparison. the Puch head wins this hands down.

    ! thing Ive noticed about the Puch head, it's asymetrical. There is more fin on one side compaired to the other in what would be top or bottom. I'm going to hang the long fins down on the exaust side for more cooling in that area and more clearance for my Boost Bottle on the intake side.

    It would be kinda funny, though, getting a Italian cylinder head from America shipped to Portugal to put on your Chinese motor. This is a great world-wide activity :D If you look hard enough you might find the same head in your country. I would not doubt there's a Puch dealer close.
  5. DanielMaia

    DanielMaia Member

    This china girl is moving countrys :D

    Yes, i think that there are here few guys with hold NOS puch parts or mobyllete, or motobecane, somethink like that :)

    Some fresh parts:

    All new gaskets

    All new SKF high quality roller bearings:

  6. skrufryder

    skrufryder Member

    You know I've been thinking about taking an old crank to work and drilling holes in it to make it light to try to achive higher rpm's do to the weight loss. any of you guys try this yet and if so what where your results
  7. Dave C

    Dave C Member

    You can do that but you have to keep it in balance or the vibration would get so bad as to tear the motor apart. Leaving holes will drop the internal compression by raising interior volume, a bad thing. Much work on race engines to reduce this volume to a minimum to the point of welding in filler and grinding the weld away for as close a fit as possible. The way I understand it the 66cc motors are not balanced for what they are and actually come out with the 49cc balancing which is why the 66's vibrate so much. There are threads in the Wild in the Streets section on balancing the crank, needless to say it takes special equeptment to do the job.

    Now, if you have access to an indexed milling table and can precicely drill evenly place holes you might attempt this.

    One way to keep the same volume is to press aluminum slugs into the holes making things lighter but retain the volume or just skip it, drill the holes and let us know :)

    Oh, if you drill you must chamfer the holes. Sharp edges in this area of high stress is called a stress riser. The sharp edges allow the start of cracks. A chamfering bit, grinding stone that comes to a point, sandpaper if you got to but the sharp edges need to be softened or it could come apart throwing bits everywhere, ruining the motor. And that's both sides of a hole, might be better just to shallow drill and not go all the way through.
    Last edited: Feb 6, 2011
  8. Dave C

    Dave C Member

    Got me to thinking some more. I haven't had one of these apart, yet, but the disks and crank parts are press fit together, right? I'm wondering if the disks themselves could be cut from a sheet of 6061 T6 aluminum plate? Have the holes bored on a milling machine, not drilled because you need what's called an interference fit. At room tempurature you can't put the pieces together but take the disks and put them in an oven as hot as it gets, like a toaster oven on 500 degrees, go to a truck stop or Wally World and get some dry ice, don't need much, and put the steel parts on the dry ice for about 30 min. The heat will expand the aluminum and cold contract the steel. The holes should be machined so there's a bit of effort to put the parts together but when the parts come to room temps they are so locked together there's no movment at all possible. It would need to be balanced from there, most likely by drilling away from the heavy side. The con rod big end pin could be drilled to lighten, too. That should be done in a lathe. I'm thinking a 3/16th wall would be enough. In that spot it's a matter of what you leave, not what you take away;)
  9. Dave C

    Dave C Member

    Daniel, that damaged piston has me worried about the barrel. The ring broke and caused the damage, right? I'm betting the jug is hashed and it's a piston, rings and jug you need. Show it to a cycle mechanic. If it's an iron cylinder it could be honed and used again but if it's chromed and scrached I wouldn't trust it anymore. Use it to practice porting :) and get a new jug. I have seen a package combo of parts for this...somewhere :p Cheap, too. under $20, here, don't know how much to ship to there.

    I'd just hate to see you do a lot of work only to have it fail because of a bad $14 part.
  10. DanielMaia

    DanielMaia Member

    Yes yes, the piston will be replaced, i have one here to put on there :)

    New parts:

    Piston roller bearing, that connects to rod, high quality made by SKF:
  11. skrufryder

    skrufryder Member

    Hey dave I was thinking the same with the aluminum crank weights. The newer motors crank weights are held on by 3 philips head screws. I think i might try taking them off and drilling some hole in the back side of the weights.If i go as far as having weits made I might as well have the crank case's milled aswell i guess.
  12. Dave C

    Dave C Member

    Be real careful messing with the counterweight. Take off weight in the wrong place and all you will have is a vibrator that shakes itself apart(worse than they do now). To lighten you need to remove the same weight from every hole 180 degrees apart. If you can't drill at 180 from eachother then don't drill at all.

    Try to search as much as you can about balancing. It's the single biggest thing you have to worry about when messing with the crank. I've talked to a few machinests. They seem to not understand why I don't want to pay $75 to balance a $11 part...
  13. DanielMaia

    DanielMaia Member

    Hey guys, more quality parts? Go for them:


    High quality oil seals, double lip (original only have one
  14. jaguar

    jaguar Well-Known Member

    Can you point me to where I can buy the SKF rod bearings?
    Unless you also replaced the lower rod bearing with a high quality one then I wouldn't go higher than 140psi combustion pressure.
    I used to think that all the high rpm vibration was from the imbalanced crank until I installed my motorcycle CDI and half the vibration went away. That means the timing is also causing some vibration.
  15. DanielMaia

    DanielMaia Member

    I bought here in Portugal, in a store dedicated to roller bearings and seals.

    Its only the roller bearings that connects piston to rod, because i cant disassembly the rod out of crankshaft.
  16. Piston notching, and a little port work is the most important part. Don't go to crazy though, or you might not have any low end power.

    Also look at the inside of the intake manifold. Mine had some casting flaws.
  17. DanielMaia

    DanielMaia Member

    Yes, its just a little improvements on the gas flow ;)
  18. DanielMaia

    DanielMaia Member

    Cylinder mods



  19. shell shock

    shell shock Member

  20. DanielMaia

    DanielMaia Member

    Moar? Here we go:

    Crankcase polished (not mirror finish because of hard work location, but its pretty smooth :) )


    The engine is already mounted. Im going to polish the head, and mount the clutch part and magneto,

    Some photos soon.

    Cant wait to put this little beast in the road