Tapping threads in engine to u.s standard

[alec]

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?

 

[The_Aleman]

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.

 

[Cavi Mike]

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.

 

[alec]

I didn't cross thread I drilled out and re tapped

 

[The_Aleman]

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.

 

[alec]

@ 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.

 

[DeathProof]

ive also retapped my exhaust mounts on engine and works great

 

[Fabian]

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.

 

[alec]

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.

 

[Al.Fisherman]

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