GT5 66cc Head Nut Size!

Discussion in 'General Questions' started by SEGACDX, Oct 11, 2014.


    SEGACDX Member

    Well one of my Head Nuts on my old motor stripped away so I need to replace all four of them to be safe.

    I need to know the Size of the Nut and thread seize of the Nut I can replace them and where I may find replacements.

    If anyone knows I would like to hear it I plan on going out to look for a replacement with the Nut and one of the connecting rods to make sure it fits right.

    Hope to hear from you guys soon!

  2. Zen builder

    Zen builder Member

    Should be 8MM . The 4 cylinder studs in my engine are 4.5" long,Probably the same with yours, if you have the standard HT engine.
  3. crassius

    crassius Well-Known Member

    in 8mm studs, I have seen 1.0 thread on both ends, 1.0 thread on bottom with 1.25 thread on top, and 1.25 thread on both ends - in some cases, the top thread has also been an interference thread to prevent loosening

    safest would be to take a good one out & check both ends

    SEGACDX Member

    So I got the Head Nuts. They where not 8MM but they where 5/16" Nuts Fine Thread. How Strange.
  5. Bzura

    Bzura Member

    I would be very careful and recheck the fit with those 5/16" nuts. China doesn't use anything but metric hardware, and although those SAE nuts feel like they threaded onto the studs they're probably just barely hugging the threads enough to stay on. You're going to blow them (and the head) right off as soon as you fire it up.

    Most GT5's have fine threaded head studs, but as mentioned above it can vary.

    SEGACDX Member

    Yea I tried 8MM nuts and they would not fit at all so I got a bolt and used it to test the Nuts I was replacing, they would not fit at all on a 8MM bolt but they did fit on a 5/16" Bolt.

    I think I may have just got a unusual engine.

    They seem to fit on very snug, I have ran and ridden it a bit and it seems to be holding better than the older Nuts.

    I also checked the threads on the 8MM and 5/16" Fine thread, the 5/16 was almost identical so that's why I went with those.

    If the head does blow off well then I guess you told me so.

    I'll update you on how they hold up.