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Thread: Custom Billet 2-Stroke Cylinder Build

  1. #1

    Default Custom Billet 2-Stroke Cylinder Build

    Hello 2-stroke enthusiasts and engine builders! I'm looking for comments and critiques of a billet cylinder I am designing for my stroked Horizontal Minarelli scooter motor. I seem to have more time than money lately and since I happen to have access to CNC machines and programming software I figured I could build a functional (even fast) alternative to the cast aluminum off-the-shelf options available. The design is patterned after some big water toy motors I've seen on the Internet, but scaled down and provisioned for my application. My intent with this design is to provide a way that I can build my own water-cooled cylinder at a reduced cost compared to the high-end options available.

    The design incorporates a wet CNC ported liner, an adapter block that serves to remove the limits of exhaust width while injecting water into an otherwise air-cooled motor, a modular head with engineered squish velocity, and an exhaust stub which allows for a slip-joint exhaust pipe connection.

    Engine parameters are as follows:

    Bore: 52mm
    Stroke: 47mm
    Swept Volume: 99.8cc
    Volume Under Piston at TDC: 8.9cc
    Uncorrected Compression Ratio: 12.2:1 (93 octane pump gas)
    Corrected (Trapped) Compression Ratio: 6.5:1
    Exhaust Duration: 197, 62% of bore width
    Boost/Aux/Main Intake Duration: 126/128/130
    Blowdown: 33.5
    Target RPM at max power: 10750 (ring flutter occurs at 11250)
    Custom Intake with V-Force reeds (384A)
    28mm Keihin PWK
    Custom Tuned Exhaust, 33mm stub out
    Tuned CVT Transmission (holds RPM at a steady state regardless of acelleration or throttle position)

    Fire away!


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    Attached Thumbnails Attached Thumbnails -as2-jpg   -c5-jpg   -cylinder4-jpg  

  2. #2
    Join Date
    May 2004
    United Kingdom


    I'm no expert but I understand that you will need high silicon content in the aluminium alloy that you choose if the bore is to last any time, and it may well need 'solution hardening' - not sure if this would be before or after machining. The only high silicon I've machined was horrid stuff to get a good finish on.


    Andrew Mawson
    East Sussex, UK

  3. #3


    I appreciate your comments, but please read above where I mentioned a "wet CNC ported liner". I probably should have mentioned that the liner is cast iron and sourced from one of the premier liner makers in the US.


  4. #4


    You will want to have the bore nikasil plated for longevity. Most modern 2 strokes run a plated bore now days.

  5. #5


    The bore is a cast iron liner. I don't know if Nikasil will take to CI. Thanks, though!


  6. #6
    Registered Arich0908's Avatar
    Join Date
    Oct 2009
    BridgePort , CT


    Im going to subscribe to this thread and take a seat. I love two stroke motors.
    Good luck

  7. #7


    I would recommend an aluminum cylinder liner. it is just like the cast iron liner you talk of.
    I have had La Sleeve company make them for me . You install the sleeve, finish port it , then send it to have nicasil plated.

    Nicalsil can be put onto cast iron , usualy used to save an old vintage clinder that is on its last bore. Bu it does act as an insulator , which sometimes is not good.

    But the nicasil on the Al is very good and durable disapates heat real well.

  8. #8


    Made some progress, but man, it feels like slow motion! Anything I can get done on a given day has to be done in the hour before my shift starts. It's very frustrating to come in, turn the machine on, home it, load tools, measure tools, setup part, touch off part, trial run program, then try to make chips in the 15 minutes I have left, plus have to tear it all out and reset for the day guy.

    So the water block is 1/2 done, fixturing is done, OD turning work on sleeve is done, pipe is about 1/4 done, if that. As soon as I finish the water block I'll post up some pictures.

    Thanks for the tips on the Nikasil. I was not aware it could be used on CI. Since I've already got the liner bought I'm going to go with it for now. Next build I will keep it in mind, though.


  9. #9


    Major setback. Was told that I can't use the mills before work any more. Head-scratcher there...anyway, progress is nearly halted until I can find someone local willing to barter for some machine time.


  10. #10


    OK, I finally found a liquid cooled kit that will bolt up to my motor with the stroke and bore I require, so this project is shelved for now. It will happen eventually, though, as I'm already way too invested in the project to quit!


  11. #11


    Why not a cyliner with a variable exhaust valve?

    KIPS Valves Explained


    Last edited by Enginetuner; 04-05-2012 at 01:46 PM.

  12. #12


    Thanks for the input!

    Yes, I am familiar with some of the exhaust valves in use, but fortunately I don't need such a system. Having a CVT means I only need to tune for one optimum RPM. Having a very expensive CVT system (Malossi overrange) means I can get on the powerband immediately and hold it there at almost any HP input from the motor.

    This thing in its current iteration just screams! Only hoping I can hold it together until I can get this billet project finished.


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