Tapping threads in engine to u.s standard

[The_Aleman]

I've never had a problem with mine lasting. The threads outlasted the motor in every case on my 2-strokes. Going on a year now with my HS.

Never had a problem screwing an SAE thread in and out in such a scenario. Once I knew it screwed in and out, I loctited it in there.

 

[Fabian]

Quote "Cavi_Mike"
*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.

I'm particularly keen to see photos of the block cut in half detailing the dimensional differences between 6mm and 1/4 taps, for i have tried using the exact same procedure of the OP running a 1/4 tap down a stripped 6mm bore hole. It failed miserably; not even leaving the option to use a 6mm helicoil.
I had to junk the China Girl case half, as i wanted to stay metric.

Using loctite as a method to increase the fastening strength of compromised threads isn't ideal as loctite has a specific temperature range for optimal integrity. Once outside of this window it will fail to provide adequate fastening strength.

At the tail end of this debate you can't argue with the maths.

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.

 

[alec]

The Chinese 6mm are a bit smaller but you cannot speak for my threads because you have not seen them. I can see down the hole with a special light and they are pretty good threads.yes the math says I ruined it but the old threads are not there. Only the 1/4 20 threads are there. Call me a liar but it works for . I say the threads are smaller because before I re tapped every metric 6mm bolt I put in was an extremely right fit and no I wasn't cross threading.

 

[Fabian]

No one here is calling you a liar alec, and i have attempted exactly the same repair as yourself.
In my case, the repair was a miserable failure - maybe i am simply no good at doing such repairs

 

[Al.Fisherman]

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.

Really????????????? Grand Craftsman (what is a "Grand Craftsman"?) You are like my son (when he was 16), you don't want any input, all you want is for us to agree with your repair, and on this end of the keyboard, (as my wife would say) it ain't gonna happen. It's hard to dispute math.

 

[Fabian]

Gosh Al, your response is far more straight to the point than mine, using the immovable laws of mathematics as some kind of method to support your assertion.
At least i tried to empathise with the OP on my (dodgy brothers) repair attempt; trying to make it work; hoping for a miracle but being the receiver of miserable failure.

Sometimes i hate the laws of maths and physics, because it always leaves room for tragic error; something my father mentioned many times as i naively tried to reinvent science with a hammer instead of algebra. Actually my father called me by many names; mainly related to my actions but i've always kept hidden the time when i tried to run a 1/4 inch tap through stripped 6mm threads - i can't bring myself to think of the names he would have called me for that!

 

[Lunardog]

I do love to play the devil's advocate. First I'll say that I agree completely with Cavi, Fabian and Ron. The repair you preformed may work but probably will not last in the long run as you may have working threads in the hole but you have removed some also in the process. One factor in your favor is the engine its on doesn't require high torque specs and it may hold. The other side of the coin is the heat and vibration from these things is high and is going to work against you in a big way. That being said I have driven through the city for 5 miles before I remembered my coffee cup on the roof of the car and thought no way it could still be there yet opened the door and found it sitting right where I left it. I.E. Sometimes luck is a factor. In closing I'd say, it may work now and may hold out till the motor blows.Odds are it wont. Point is you have some great information from experienced members here and if it doesnt hold you are armed with the info to make the CORRECT repairs. Great pics to explain the point from Cavi by the way. Good luck and be careful.

 

[Cavi Mike]

This is what it looks like when you cross a 1/4-20 into an M6x1 hole. Pretty, eh? And this is 6061 billet, I can't imagine how terrible a mystery aluminum cast looks. But hey, alec's granpappy was a "grand" craftsman, I must not have any idea what I'm talking about.

 

[alec]

Well I tested my "crappy threads" and torqued down a bolt until it literally pulled apart. No damage to the threads..

 

[tooljunkie]

better use stud and bearing mount,it will fill a .020 gap.
its fugly as i mentioned earlier,but looking at the edge cut it would seem there is 60% or marginally better of the threads.now depending on the tap-(taper,plug or bottom)
how many of the "good" threads are there to grab? in a 12-20 mm deep hole it can be anywhere from 6-12 full threads left to grab.
peaks 60% valleys 100% threads would pull easily with a quality bolt.

by the way,cavi mike-nice pic detailing the threads.

lmao,a bolt that is weaker than aluminum.SAE china bolts? or all thread?
show me a pic of the bolt head,that you pulled apart.

all these guys are trying to say,Alec,is dont waste your time rethreading good threads,and then using sub-quality sae hardware.
custom built failure.

my son was 16 too.