Chinese engine's head bolt sizes

Discussion in '2-Stroke Engines' started by alhickabee, Apr 29, 2009.

  1. alhickabee

    alhickabee New Member

    Hello everyone,

    My 67cc engine kit from is supposed to get in tomorrow and I've been reading up on all of the little stuff that needs to be done before running these motors. Just wondering what size the head bolts are so I can get the right sizes from Sick Bike Parts (I'm thinking they're 6mm). I'm planning on ordering the following from them:
    Engine hardware kit
    Head stud kit
    Head gasket
    NGK BPM7A Spark Plug
    Spark wire
    Fuel valve
    Fuel filter
    Carb o-ring
    gas cap o-ring

    And doing most everything advised in these two threads:

    I plan on using loctite on everything, torque specs, exhaust mount, using higher grade bolts on the rear sprocket, remove petcock screen after removing as much rust as possible, clutch alignment, heat-shrink/solder all the connections and anything else I can think of.

    I also plan on doing a lil port matching while I have the engine apart, any reason not to do this? Also any more tips or links would be appreciated.


  2. Shadeslay

    Shadeslay Member

    Unless you plan on pulling the head to do some mods to it, I would just avoid it unless you run into problems. I've ran mine fine for over 400 miles without doing anything to the head bolts. I did have to snug them up once about 2 weeks in, but haven't needed to touch them since.

    If you do need them later on, you can just run down to the hardware store and pick up some all thread. I haven't even done half that stuff myself and considered myself cautious. The way you break these in, you'll likely find your problem areas "places you need lock tight etc.." just by breaking in the motor. The first few rides just go over your bike each time checking everything. I really never encountered engine stuff working loose, it was always the bike parts.
  3. Junster

    Junster Member

    I finished my build today. I used the SBP engine hardware kit. It was a great upgrade. One thing I noticed was the gasket mating surfaces on both the intake and exhaust were anything but flat. I turned to motor till the piston was blocking the ports then packed the inside (edit: of the port) with t paper. I took the studs out to do the upgrade but before I put the new ones in I used a wide flat file and slowly worked the gasket faces till they were flat. Did the same to both ends of the intake tube, and with a piece of sandpaper on a mirror did the mag cover till it was flat on the gasket side. Then I siliconed the intake tube (edit: just the intake tube not the motor) where it meets the motor put the gasket on and lightly bolted it to the jug. The next morning I took it back off and used a round file to cleanup the inside edge and the gasket at the same time. now the gasket is glued to the intake. Just a lil grease on the gasket surface before you put it back on the motor and it won't stick or shrink. No leaks. Did the same to the mag cover (except the gasket trimming). It seemed to fit alot better. Also check the engine mounts, Mine had an 1/8" of flash, easily trimed with a half round. Oh and I cut inner tube pads for everything that touched the bike frame. I cut them to size and used weatherstrip glue to bond them to the engine mounts etc so I didn't have to fight keeping them in place while I was installing everything. It worked great. This is my first build but it went really well. Rode it 4 times today. Longer trips each time after it cooled. You could feel the ring seating about halfway thru the 4th one. Hope I didn't get carried away here. This is way fun.
    Last edited: Apr 29, 2009
  4. Junster

    Junster Member

    I bought their tank petcock also, very nice.
  5. alhickabee

    alhickabee New Member

    Thanks for the help guys. This engine has to reliably get me to and from school and my internship, so the engine's gotta be built-proof. I'd rather spend the money now:D!! I'll have the engine tomorrow so I'll just wait till then to order the stuff from SBP.

    Junster I'm jealous. If I can get mine running by weekend after next, I'll be quite happy.
  6. Pablo

    Pablo Motored Bikes Sponsor

    I would guess on the 67CC Bikeberry uses 8mm. I have asked them and they did not respond to my email. The problem is, do they use 8mmx1 or 8mmX1.25? You will have to wait until your engine arrives to check yourself. Sure you can buy allthread if it's 1.25, but then you'll need to cut it, and get the hardware, and of course it will be whatever grade the store has and the price will be a wash if you count your time. If it's 8mmx1, I doubt your local store has it.
  7. Mountainman

    Mountainman Active Member

    just the facts -- fun little THINGS -- when good

    just the facts -- fun little THINGS -- when they are running good

    these little Happy Time engins fall just a ((slight bit short)) of being called reliable

    just a rough figure to throw out here
    thinking that a RELIABLE engine should start right up and get me there and back
    at least 24 out of 25 trips ((rides)) out
    from what I have seen regarding the HTs
    this will not be happening -- not for very long anyway

    just don't want you to get your hopes set too high

    must remember also -- what one paid for the little THING -- not much

    ride that MB thing
  8. Pablo

    Pablo Motored Bikes Sponsor

    Maybe the statement - should be: They can be made to be MORE reliable. I've actually never been stranded or anything nasty. There are are a couple things at play: a) preparation on the part of the owner - there ARE things you can do. We all know this. b) luck of the draw. If you get a winner from the factory or you get a loser from the factory. There is no polite way to say this: Some of the engines are **** from T=0. Some go the full expected life. 50 miles into an engine usually will tell you if you have a winner.
  9. Mountainman

    Mountainman Active Member

    that's the difference

    that's the difference -- between true quality and a so so so

    preparation -- with the quality engines -- needing almost none
    I just jump on mine and ride and ride -- nothing ever goes wrong

    plus with the quality engines -- just a guess here
    99 out of a 100 are a winner

    I like those odds as I ride that THING
  10. Skyliner70cc

    Skyliner70cc Active Member

    I've got years and many miles on my HT bikes. the only one that I've had fail me was one that i abused and overrevved by going full throttle downhill on a single speed. All others have been very reliable provided I upgraded some parts/hardware during my install.

    One reason I replace the headstuds is because many times the tops have damaged threads by the acorn nuts. I also JB weld my studs now into the block and use a quality replacement so i never have to worry about them snapping if I overtorque them. I've also had too many studs vibrate loose and pull out of the frail bock threads. JB weld with new quality studs fixes the problem.

    One of the best reliability improvements you can make is get a SBP shifter kit. Sure, I rev the heck out of my engine while accelerating, but once up to speed, lower rpms should increase engine longeivity.
    Last edited: Apr 30, 2009
  11. Pablo

    Pablo Motored Bikes Sponsor

    Indeed - just throw those stupid acorn nuts in the trash!
  12. alhickabee

    alhickabee New Member

    I should have been a little more specific when I said reliable, as reliable as possible is what I'm shooting for. I know there's gonna be quite a bit of tinkering, that's the fun part:D right. I just mean I don't want the thing coming apart on me or catastrophically failing while riding... The engine will be here today so look for the start of a build thread this weekend. Thanks for the help guys!
    Off to school peace

    Oh and I plan on adding the SBP shift kit in a couple of months
    Last edited: Apr 30, 2009
  13. Pablo

    Pablo Motored Bikes Sponsor

    Much wisdom for four posts!! Peace be with you.
  14. alhickabee

    alhickabee New Member

    I just wanna make sure I got this right before I order. The head studs are the same size and pitch as the intake and mounting studs sooo that's M6-1.0 right? It's a 10mm nut on everything too..
  15. Pablo

    Pablo Motored Bikes Sponsor

    Yep those be 6mm.
  16. alhickabee

    alhickabee New Member

    Thank you sir!
  17. Ed Johnson

    Ed Johnson New Member

    hmmm....seems ive been pedaling mine since i ready to take the dacs motor and use it to for a planter.
  18. Flapdoodle

    Flapdoodle Member

    Let me just throw in my two dong or whatever they use in China... Build it like you were going to race it, but baby it if you are seeking reliability.