Fine m8x1.0 bottem end studs, Socket head cap solution

mrfubs · Jun 13, 2013

Okay so i know there are others out there that have wanted to replace the head studs with allen head bolts for different heads and what not. A lot of us have the 8mm head studs with fine(1.0) threads, the newer engines have coarse(1.25). We all know you cannot find bolts 101mm or 4" long with a 1.0 thread pitch with a socket head cap.
I found out 5/16-24 which is the fine thread almost has the exact same pitch.
I bought 4 5/16-24x4" socket head cap bolts at the local hardware store, i had a 5/16-24 tap and tapped the holes in the case with ease. 10 minutes later it worked like a champ.

So those out there that are stumped on what to do i hope i helped! if u need pics let me know!

2door · Jun 13, 2013

Good luck. I'm concerned that you have effectively compromised the case threads by re-tapping them. Keep a close eye on the torque value.

The irony is that you can buy an 8mm X1 die but 8mm X 1 fasteners are almost non-existant. At least in the length we need for cylinder/head attachment.

Good luck and let us know how that re-threading works for you.
Just curious, did you consider installing heli-coils instead of re-tapping the case?

Tom

crassius · Jun 13, 2013

torque value is often rated as friction of the threads of steel nut on the threads of the steel shaft - not sure what diff there will be with steel shaft into aluminum case

2door · Jun 13, 2013

crassius said:
torque value is often rated as friction of the threads of steel nut on the threads of the steel shaft - not sure what diff there will be with steel shaft into aluminum case

It is different but there are published torque values for dissimilar metals. I had one but lost it on a computer that crashed. I'll look for it again and post it here if I can find it.

It specifically addressed steel fasteners into aluminum castings. There wasn't a big difference but they obviously are lower than steel into steel or cast iron.

Tom

mrfubs · Jun 13, 2013

I would have to agree with you that the torque values are different, I didn't go through the hassle of heli-coils because I figured it was just a small engine and didn't require a tremendous amount of torque 12lbs or so?

2door · Jun 13, 2013

mrfubs said:
I would have to agree with you that the torque values are different, I didn't go through the hassle of heli-coils because I figured it was just a small engine and didn't require a tremendous amount of torque 12lbs or so?

We typically recommend 120 to 140 inch pounds for 8mm studs. That applies to the stud into the case as well as the nuts on the cylinder head. Your 12 ft. pounds should be in the ball park.
Let us know how your threads hold up. Personally I've always preferred to use bolts as opposed to studs and nuts for applications like these. You only have one set of threads to worry about instead of two. My concern with rethreading the case as you did would be failure of the threads by over tightening or repeated removal. Good luck.

Tom

mrfubs · Jun 13, 2013

ill let you know! as of right now i will not be riding for a while i have a broken back, at the most i can only run the engine on a stand which i haven't done yet. I also did not specify that im using 4" bolts with a puch 74cc 47mm bore head. so there will be some minor differences in bolt length needed, may have to trim the bolt down a fuzz.

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Fine m8x1.0 bottem end studs, Socket head cap solution

mrfubs

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crassius

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mrfubs

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