Can the cylinder head be rotated to make clearance from spark plug to frame? Bending intake?

Discussion in '2-Stroke Engines' started by mikedabomb, Feb 1, 2016.

  1. mikedabomb

    mikedabomb Member

    I'm trying to fit a HT 66cc in a really big aluminum frame. Thought it would fit, but I'm having serious trouble because the frame is really fat aluminum tubing, so a lot of space I thought that I had really aint there. The title explains my question. Can the cylinder head be rotated? Also, do I have to buy the offset intake, or can I heat it with a torch and bend it myself? Any heat necessary? I got one of those engines with the really long, bent clutch arm...supposed to be better than the regular one? Well it's so long that it hits my freakin' seat tube :(

    Also, any random tips to help this thing fit are greatly appreciated.

    Thanks for reading
    Last edited: Feb 1, 2016

  2. Purple Haze

    Purple Haze Active Member

    Yes, the head can be rotated, but performance may suffer a little due to flame travel. An offset intake can cure a lot of clearance issues, just make sure your throttle cable is long enough. The clutch arm can be removed from the shaft (it's splined) and rotated to a different position. Please don't try bending the stock intake! Some members on here have fabbed an intake extension from auto heater hose and clamps, someone even fabbed one out of PVC pipe and fittings.
  3. sbest

    sbest Active Member

    Purple Haze is steering you right.
    You can rotate the head ANY direction you want, but plug to the rear seems to be best for performance and cooling.
    I tried plug to the front but had detonation and overheating. Perhaps a cooler plug would solve that?
    The plug can be mounted to either side also but cooling will suffer unless you gear up some ducting. I gotta try it...

    My bike is fat tubing.
    I filed out the front mount cradle to the same diameter as the studs, then dented the bike frame with a rod for stud clearance.
    Had to put extensions on the tank studs. Just steel tubing threaded inside.
    I am using a "Z" offset intake to clear the carb from the frame. The stock cast aluminum one will not bend at all.

    In the back I cut the tube cradle block as short as I could, about 1/4" or 6mm and filed it to fit the seat stem tube.
    These two things got the motor as low as practical and gave more room for the cylinder head.
    I have the long bent clutch arm, it barely clears. Totally unmodified.

    I also had to bend the exhaust pipe to clear the big diameter frame tube.
    I used a bench mounted vice and long bar for leverage.
    The fat framed bike is solid riding, even on rough roads. Worth the trouble.

  4. danlandberg

    danlandberg Member

    I HAD an old Royce Union with large tube frame. (Pic in stoldebikes). I used flat plat and mufler U clamps to mount the engine. Adding a second rear mount block put the engine further forward but also higher in the frame. I don't know about performance differences but I run the slant head with spark plug forward. If throttle cable is an issue running into the top tube, a billet aluminum intake dropped the carb down and forward. ( the intake is short and straight ) + ported for better performance. But then you will have clutch cable issues. Al Fisherman used to sell a clutch cable roller set up that cure's the problem. (It's a must have item, even without any other modifications). I prefer not to heat, weld, pound, file or drill on any frame. (Integrity issues) Unless your an expert blacksmith. LoL. Some of us ride faster than 30 mph, and frame integrity is of great importance. Remember, bicycles were not made for motors, the Chinese made motors to fit bicycles. Your bike does look good! Be safe, and obey the laws. Sidewalk riders give all of us a BAD name.
    Last edited: Feb 17, 2016
  5. KCvale

    KCvale Motorized Bicycle Vendor

    I rotate the head 180 on about 75% of every 2-stroke slant slant I have ever built so the plug faces forward.
    Depends on the bike frame and where I want the CDI.

    So yes you can but best be equipped with a torque wrench first if you don't want to be blowing head gaskets or warping your head.
    No mater how good you think your 'feel' is, this not something you want to bet your life on when a simple tool will help you do it right.

    What I do on a 66cc slant head is go in a X pattern 5 FT# at a time until all are at 20#.
    This is more than the 'book' says, but I have NEVER had a bike come back for repair because of a head problem.

    For 48cc engines with it's lower power and less hefty studs ~12 FP, but regardless you have to use the X pattern in small steps to get equal balanced Torque on each bolt as you seat the head to the cylinder.

    As menti0ned we do it all the time here with no issue, just follow the procedure an you will be fine.