Tapping threads in engine to u.s standard

Discussion in '2-Stroke Engines' started by alec, May 8, 2012.

  1. alec

    alec Member

    I couldn't find any metric bolts and nuts near me that were the right length and size so I re tapped mounting stud holes to 1/4 20 and one of the crank case bolts for mounting. I was considering re tapping all of the holes to u.s standard because of bolt availability. Of course the cylinder studs would be the same but everything else.
    any input on this?
     

  2. The_Aleman

    The_Aleman Active Member

    I've found all my metric at Ace, Lowe's, and Home Depot in Cali. Should be plenty of those in Glendale!

    Of course, replacing those metric mounting studs is a good move, IMO. They are very prone to breakage. I just replace the intake/exhaust with metric bolts.
     
  3. Cavi Mike

    Cavi Mike Member

    You're not re-tapping anything, you're cross-threading. There may be some full threads in there but you've completely cut away threads in other parts. These castings are already extremely weak and brittle as it is. I'd strongly advise not to mess with this any further.

    I actually strongly advise this thread be deleted to make sure someone doesn't get this idea in their head and then make the same mistake you did.

    Be ready for those threads to strip out because they will.
     
  4. alec

    alec Member

    I didn't cross thread I drilled out and re tapped
     
  5. The_Aleman

    The_Aleman Active Member

    Actually Cavi Mike, since most the studs are 6MM, and prone to getting stripped out anyway, running a 1/4-20 tap is a very good option. It's a simple swap. I've done it on 3 of my engines since '06 with zero issues. 2 HTs and my current HS.

    The factory studs are notorious junk and there are nice options in SAE studs. My favorite is the 1/4-20 / 1/4-28 double-end stud. The 1/4-20 goes in the case (with red loctite) and the 1/4-28 makes for fine tightening.
     
  6. alec

    alec Member

    @ The_Aleman, yes there are alot of those stores but none of them are local so I am stuck with osh and do it center which are die hard on having 90% of their fastener inventory being SAE haha.
     
  7. DeathProof

    DeathProof Member

    ive also retapped my exhaust mounts on engine and works great
     
  8. Fabian

    Fabian Well-Known Member

    Completely agree with Cavi_Mike:

    You're not re-tapping anything, you're cross-threading and even if drilling out, you most likely won't have a full thread cut into the bore hole, as there isn't a lot of casting material to play with.

    It surprises me why people do such things when hardened metric studs are readily available through SickBikeParts at the click of a computer mouse and credit card.
     
  9. alec

    alec Member

    I did it because the oem studs were stripped when they were put in inches factory. After I unscrewed them to get some new studs I examined the holes and the whole front half of the threads were destroyed. I re tapped and I looked down in the hole and found full perfect threads and the bolts thread in as smooth as ever.
     
  10. Al.Fisherman

    Al.Fisherman Active Member

    This is why I took the time and wrote up his document, for that very reason. There shouldn't be a problem stripping threads or breaking bolts. I've only dealt with 6 HT's (not many by some standards), but have never stripped a thread in the case or stud. Although I have never heard of stripped threads from the factory (although it could happen, faulty casting) as the threads are most likely cut by a machine. All stripped threads or studs are caused from a few factors. Cheap soft studs, over torque, under torque, and or incorrect instillation

    https://docs.google.com/document/d/1GcesQihc7-mm3hJGf7UPiqOaRXZ8ekUT99QUZq2qXXE/edit
     
    Last edited: May 9, 2012
  11. Cavi Mike

    Cavi Mike Member

    For starters, 1/4" is only .014" larger than 6mm, I don't know what any of you heard.
    1/4in = .250"
    6mm = .236"

    You're not going anywhere with .014". You've ruined your threads, that's all there is to it. You'd need to go to 5/16" or run a 1/4" Heli-Coil insert.
     
  12. Cavi Mike

    Cavi Mike Member

    The tap on the left is an M6x1, this is what the holes originally were. On the right is a 1/4-20, what you've just cross-threaded into your motor.

    The green lines indicate where the threads will line up and you'll have something for the screw to hold onto. Orange will be partial threads and red are completely missing threads from where the 1/4" tap simply cut away the M6 threads and left you with nothing.

    [​IMG]
     
    MotorBicycleRacing likes this.
  13. alec

    alec Member

    Well from the looks of the threads they are complete and pretty good. You can dump over the idea all you want but in the long run it worked and that's all that matters
     
  14. Al.Fisherman

    Al.Fisherman Active Member

    Hey, no argument here, I'm all behind you 100% on this. It's a no brainier.
     
  15. Cavi Mike

    Cavi Mike Member

    From the looks of what? You can't see inside that hole. And I will dump all over this because it's a really stupid idea and it won't work for long - I guarantee it - and THAT is all that matters.

    *edit* And since this picture I took of the taps wasn't enough to convince you, I'll make a block at work tomorrow and cut it in half so you can see just how terrible your threads are.
     
  16. Al.Fisherman

    Al.Fisherman Active Member

    Isn't it funny, how people ask for your input, then wants to argue with you? Wonder where he got all of his experience from? Sure wasn't from anyone that knows their s^^t.
     
  17. alec

    alec Member

    Actually I got my info from my grandfather who is a grand craftsman. He can cast and machine engines from scratch and make every part on a motorcycle. He's even created replica .50 Hawkins rifles by hand. I didn't argue all I said is that it worked for me and the threads are strong.
     
  18. alec

    alec Member

    For example when I first showed him the engine, my grandfather had the coolest ideas to fabricate special mounts which he explained the design and other stuff to align the chain and other stuff like that. He knows his stuff. Once again I'm not trying to be argumentative.
     
  19. alec

    alec Member

    Also do you really think the OEM threads are any better? All of mine were almost nonexistent because its s#@% China quality.
     
  20. tooljunkie

    tooljunkie Member

    this looks like one o them agree to disagree scenarios.
    i have ran a metric die down a standard bolt,curious what the threads would look like.
    similar result would be when tapping a metric hole to standard.threads are fugly.
    i wouldnt expect to ever get it apart,as galling is almost a sure thing.
    as a last resort,yes i would do it,but i prefer to go up to the next bolt size.

    heli-coils are the strongest repair in crappy cast aluminum.
     
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