Eli Lawson
Forum Apprentice
I was tightening my upper shock mount bolt to factory specs and broke it off! What do I do please help
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Upper shock bolt broke!!
- Thread starter Eli Lawson
- Start date
Dogma
Forum Sage
If the threads broke off and the post is still there, you can clean up the end of the post and tap it. An M5 stud, thread-locked into the post on the frame, and a nylon locknut works well. Use a stud, because it gives you a replaceable thread. Mine didn't break, but I did strip the threads off. I didn't have enough washers to keep the acorn nut from running out of internal threads, and that's how the damage started. Once it started, it was a matter of time.
Don't tap drill any deeper than you need to. The highest stress in the post is where it meets the frame, but the hole will be on the "neutral axis of the beam" if you keep the hole straight and centered. It might be strong enough even if you drill through, but why try to find out?
If the post has to be replaced, I've heard stories of drilling it out and replacing it with a shoulder screw. I seem to remember something about cutting the head of and welding the screw into the frame for the strongest fix. Hopefully if it comes to that, somebody who's done it will chime in with better instructions.
Don't tap drill any deeper than you need to. The highest stress in the post is where it meets the frame, but the hole will be on the "neutral axis of the beam" if you keep the hole straight and centered. It might be strong enough even if you drill through, but why try to find out?
If the post has to be replaced, I've heard stories of drilling it out and replacing it with a shoulder screw. I seem to remember something about cutting the head of and welding the screw into the frame for the strongest fix. Hopefully if it comes to that, somebody who's done it will chime in with better instructions.
I would not use a stud in that situation. The shear force is reduced because of the cut threads. You want a bolt with a long shank, and just enough thread to tighten it together. You would be better off drilling all the way through and using a bolt with a long shank. You only need to tighten it enough to keep it in place. Some Blue Loctite will assure that.
The best way would be drilling it, sliding a bushing through, welding the ends and then sliding the bolt through, which will still be a long shoulder bolt.
The best way would be drilling it, sliding a bushing through, welding the ends and then sliding the bolt through, which will still be a long shoulder bolt.
Number 35 here. cut broke stud off flush with frame. drill down the center the right size, insert new stud and cut to length. Cap weld it on the inside of the frame. Been using them for years. Same thread as the acorn nut
https://www.kawasaki.com/en-us/owner-center/parts/143389/1979/KZ750-B4?cm_re=PARTSLISTING:1979KZ750-B4-_-FINDDIAGRAM-_-PARTBUCKET
https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2499334.m570.l1313&_nkw=92004-048&_sacat=6000
https://www.kawasaki.com/en-us/owner-center/parts/143389/1979/KZ750-B4?cm_re=PARTSLISTING:1979KZ750-B4-_-FINDDIAGRAM-_-PARTBUCKET
https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2499334.m570.l1313&_nkw=92004-048&_sacat=6000
Easy fix the shoulder for the eyelet already there.
Eli Lawson
Forum Apprentice
Thanks a bunch for the advice
I snapped one off of my 650G and had a shoulder bolt (or screw which ever is the correct term) with the head cut off it welded on. It had the same threads as the original. Worked like a charm.
I've installed the shoulder bolt fix. Works fine!
I have no memory of what the length measurements were, but it'll be somewhere in this page, if the link works:
https://www.mcmaster.com/products/s...e~m10/shoulder-diameter~12-mm/material~steel/
These are very hard, strong grade 12.9 steel.
The stud diameter is 12mm, and the thread is 10mm. Make sure you scare up a new nut with the correct thread pitch; stock is 1.25x10mm, but the shoulder bolts are only available in 1.5x10mm pitch.
You drill out in increments using lots of lube, and stop at the point where it's a press fit (15/32" is 11.9mm, and I think that's what we used). Drive the shoulder bolt in and it'll be quite secure. You could also figure out an arrangement with spacers, washers and nuts to draw it in.
There's little or no sideward force, so tapping the remnant of the stud in the frame can work perfectly fine as well. You basically just need to retain the upper end of the shock; there aren't any forces yanking these off.
If you can weld the other end, great. But with a good tight press fit it'll work fine with or without welding.
I would NOT weld the outer area; that would tend to weaken the bolt right at the point where it needs the most strength.
I have no memory of what the length measurements were, but it'll be somewhere in this page, if the link works:
https://www.mcmaster.com/products/s...e~m10/shoulder-diameter~12-mm/material~steel/
These are very hard, strong grade 12.9 steel.
The stud diameter is 12mm, and the thread is 10mm. Make sure you scare up a new nut with the correct thread pitch; stock is 1.25x10mm, but the shoulder bolts are only available in 1.5x10mm pitch.
You drill out in increments using lots of lube, and stop at the point where it's a press fit (15/32" is 11.9mm, and I think that's what we used). Drive the shoulder bolt in and it'll be quite secure. You could also figure out an arrangement with spacers, washers and nuts to draw it in.
There's little or no sideward force, so tapping the remnant of the stud in the frame can work perfectly fine as well. You basically just need to retain the upper end of the shock; there aren't any forces yanking these off.
If you can weld the other end, great. But with a good tight press fit it'll work fine with or without welding.
I would NOT weld the outer area; that would tend to weaken the bolt right at the point where it needs the most strength.
Dogma
Forum Sage
I would not use a stud in that situation. The shear force is reduced because of the cut threads. You want a bolt with a long shank, and just enough thread to tighten it together. You would be better off drilling all the way through and using a bolt with a long shank. You only need to tighten it enough to keep it in place. Some Blue Loctite will assure that.
The best way would be drilling it, sliding a bushing through, welding the ends and then sliding the bolt through, which will still be a long shoulder bolt.
The purpose of the stud is to provide a replaceable threaded element. It's especially necessary on this kind of fix because of the smaller threads. The stud only replaces the broken off threads, not the post that carries the suspension loads.
You don't really need to weld the bolt head on, or cut it off. If it fits, it a shear force your dealing with. Tightened up, with no slop, and it will be fine.
It might be fine, but the weld is better if you can arrange it. Much closer to original condition. A tightened bolt can't transfer loads to the frame as well as a welded post.
Beside all that, Chuck Hahn has worked on more of these than almost anyone else, so just take his advice when in doubt. If he's not sure, you can trust him to say so. You can also trust him to know when he doesn't know.
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I read this thread wrong. I thought he ruined the part on the bike. If the broken bolt is still in there, punch a hole in the center, and work you way up with drills till you see the threads. Hold the thread up to the light, your drill should be no bigger that the diameter of the bottom of the threads. If you do it right on center, with a very small punch, you will be able to knock the thread in and pull it out with a set of strong needle nose pliers. In a worse case scenario, Heli-Coil (double up on the Heli-Coil) it and be done with it. I thought for some reason that the frame part was buggered. Thanks for your post Dogma. It cleared some things up for me.
I have a small machine shock, Mig/Tig welders, etc., and doing this stuff when it;'s in front of me is obvious. I don't know why I read this all wrong. It's just a bolt broken into a threaded hole. I had to drill out all 8 studs on my '84 GS750ES to get the studs out, which all broke. Heli-coiled all eight, and replaced the studs with # 8 bolts. Very easy to take off and put on now. I centered so well on the studs, I was able to pull out every thread. I Heli-Coiled it as aluminum and steel don't really like each other, especially up front subjected to rain and other catalysts (electrolysis) which causes corrosion.
I have a small machine shock, Mig/Tig welders, etc., and doing this stuff when it;'s in front of me is obvious. I don't know why I read this all wrong. It's just a bolt broken into a threaded hole. I had to drill out all 8 studs on my '84 GS750ES to get the studs out, which all broke. Heli-coiled all eight, and replaced the studs with # 8 bolts. Very easy to take off and put on now. I centered so well on the studs, I was able to pull out every thread. I Heli-Coiled it as aluminum and steel don't really like each other, especially up front subjected to rain and other catalysts (electrolysis) which causes corrosion.
