SBP Headstud Misfit

Discussion in '2-Stroke Engines' started by Dave C, Feb 19, 2011.

  1. Dave C

    Dave C Member

    Ok, well, this is a bunch of :poop:. I got to install the SBP upgrade head studs and they don't fit. They are too large. By a tiny amount. I can get the studs in a turn or so and that's it. I checked the nut from the kit on a stock stud, it is a bit loose.

    I have two options, neither I like. 1 is to tap the block out bigger, 2 is to use regular nuts on the stock studs :(

    Engine is from BGF and is one of their Z80 motors.

  2. spad4me

    spad4me Member

    It sounds like you have six mm stock studs and you purchased an eight mm sick bike parts stud kit. They have m6 m8 and m125 stud kits
  3. Dave C

    Dave C Member

    Nope, not 6mm. Will not fit through the 6mm holes in my Puch cylinder head. I bought the head knowing I'd have to drill the holes out and I haven't done that yet. Plus the nut for the SBP stud is close to fitting but it's like the stock stud is 7.5mm and not 8mm.

    I think it's the Z80. I got a CNS carb intake from Pirate Cycles and the bolts will not go in all the way, they are about a quarter inch too long.

    I think about the first of the month I'll be off to Harbor Freight for a metric tap set :p
  4. BiMoPed

    BiMoPed Banned

    There are two 8mm thread pitches
    Head Stud Kit M8-1.25 and
    Head Stud Kit M8-1.0
  5. Dave C

    Dave C Member

    The stock stud has both fine threads and coarse. Fine thread in the block and coarse thread up top. To top it off the threads arn't rolled or machined, they're pressed!! I can feel a parting line in the threads. The might have left them to aid in cutting the threads in the block, I don't know.
  6. Pablo

    Pablo Motored Bikes Sponsor

    Did you email tech support at SBP?

    This is the first time I heard of such a thing. That just sounds odd.

    Maybe I'm missing something - why not just go with the thread size in the block?
  7. Dave C

    Dave C Member

    No, I haven't. I was working on the motor last night. I was changing out the studs when I discovered the new ones don't fit. When I hold them up together I can see that your stud is slightly bigger and I don't mean the difference between 6mm and 8mm, we're talking thousandths.

    Came here to see if anybody else had run into this. It's a BGF Z80 of the 2xxx serial numbers. Manufactured 2010, I think.

    I could mail you a stud if you like, the stock ones are not going back in.
    Last edited: Feb 19, 2011
  8. Pablo

    Pablo Motored Bikes Sponsor

    So you have M8X1.00 in the block, and the top threads wre M8X1.25?
  9. Dave C

    Dave C Member

    If 1.00 is fine thread and 1.25 is coarse then yes. But like I said, the stock threads in the block are slightly smaller not allowing the SBP stud to screw in more than a turn or so. Your nut with the kit rattles on the stock stud. I'm sure I got some bastich thing they did when they run out of the right thing or just use :poop: that barely meets spec. It's no big deal to have different sized taps for slightly off studs. The Chinese couldn't care less that SBP makes parts that are supposed to fit their motors. Whatever they put out will eventually be sold.:rolleyes7: