Repairing a broken shock mounting

[Can'tWeld]

Hi all,

I have a slight problem with my bike. The shock absorbers go in between the rear swingarm and the frame, and have four mounting studs. Unfortunately, being typical Suzuki, they are made out of cheese and when I got the bike part of the stud was snapped off - the remaining thread is in a bad way and it's impossible to get the dome nut back on...

They are mounted on a sort of plate which seems to be welded to the swingarm and frame.

Now I was just wondering the best way to fix this. Someone has kindly offered to drill and tap a hole down the center of the stud so I can put a bolt in - would this be the best way or would it be possible to cut the entire plate out and weld another one in?

Let me know what you think.

Cheers.

 

[pedrobedro]

If you can drill and tap it and put a bolt in with a washer to hold the damper that would be the easiest solution and perfectly adequate.

 

[mike os]

If you can drill and tap it and put a bolt in with a washer to hold the damper that would be the easiest solution and perfectly adequate.

Agree, replacing the stud is overkill unless you are doing a concourse restore

 

[the snooper]

personally i would cut back old thread grind to a point and weld in some new thread as picture below i wouldnt drill out and tap original as it would make the stud weaker

 

[Pete.]

It wouldn't need a very large bolt or to be tapped very deep. You could easily tap a thread only 15mm deep into the mounting and it wouldn't affect to point of greatest stress (the base of the stud). I would have no problems with doing that, though I'd prefer to re-manufacture the whole stud, cut it off flush, drill it out of the plate and fit a new stud in & weld it.

 

[Robotstar5]

Drill and tap then use a socket set screw threadlocked in, would allow you to use the dome nut.

 

[Can'tWeld]

For an easy, quick fix - what about drilling a hole through the threaded bit and putting a splitpin through? I know they did it this way on old range rovers - is there any reason not to do it (will it pass an MOT, etc?)

Need to get the bike on the road ASAP.

 

[michael1703]

could you run a die on the thread and cut a thread a mm or two under and fit a nut with a smaller thread ?

 

[Can'tWeld]

Possibly but I've never used a tap or die before in my life which is why I'm a bit hesitant, plus don't you need a drill press to do a good job?

 

[MrFluffy]

No, people have been tapping and cutting threads on with a die freehand for time immortal. In fact I think I had to do that for some exam at school in metalworking which is starting to become distant past (which you can tell, as they still taught engineering and had a workshop )

Just buy a die a bit smaller and smear the old bolt with tapping fluid. 3/4 turn then back to break off the swarf, repeat until cut. You can practice on a bolt in the vice or something and its a skill worth having. Just tap on enough thread to take a nut and snug up the inner bush on the shock eye. If its not possible Id go with drill and tap a setscrew, certainly wouldnt be welding a threaded section on as the heat treatment on the bolt might get upset.

Another option is cut it flush like pete says, drill it out and put a bolt the diameter of the original stud right through from the inside of the frame, then weld it into position. Its the same thing as making a proper stud but a lot quicker

 

[Country Joe]

No, people have been tapping and cutting threads on with a die freehand for time immortal. In fact I think I had to do that for some exam at school in metalworking which is starting to become distant past (which you can tell, as they still taught engineering and had a workshop )

Only way I've ever done it, can't even imagine doing it on a lathe, don't imagine it would be able to reverse for a mo, to clear the swarf!
I too, only just remember metalwork!
All the Best,
CJ

 

[Angusdog]

TimmyTen's Youtube clip on making threaded bosses is probably all you need to know about using a drill press to cut a thread using a tap. You don't use the motor to drive it, you just use it for the alignment. It's little jobs like this that made me buy one of the much maligned but actually quite useful 7x12 mini lathes.

I would use a die to clean up the remaining thread as suggested earlier, mount the shock and then see how many threads remain to grip the nut. You only need six and in this case the nut is just there to keep the shock from moving sideways off the stud, so there's little loading on it. Using a die to clean up a thread is pretty easy; just keep it square to the stud and take it slowly.

 

[Can'tWeld]

Cheers everyone; I'll pick up a set of taps and dies today and have a go this weekend!

 

[MrFluffy]

Only way I've ever done it, can't even imagine doing it on a lathe, don't imagine it would be able to reverse for a mo, to clear the swarf!
I too, only just remember metalwork!
All the Best,
CJ

I use my lathe to run a die down studs because its easier to get it square and Im naturally lazy
I made up a tailstock die holder a while back, now I put the gearbox in neutral and wind the chuck containing the workpiece round by hand. That way its just really using it as a big jig to hold things true while it starts and if the tap or die wants to come forward faster, it just pulls the die/tap holder out the tailstock taper rather than worrying about feeding accurately once its started. For tapping central into a shaft, a jacobs chuck in the tailstock gripping the tap shank. That's pretty also how you go about it in a DP too, and it pulls the quill down against the return spring to auto feed it the same.
I've power tapped on the mill with big machine taps and no tapping head, but that scares me as its a whole different ball game, when it goes wrong it goes wrong properly with bits of exploded tap or workpiece making their exit from the table area

CantWeld, I reckon the worst that will happen with hand cutting it is a "drunken" thread (its not quite square). Which although not "right" will still work for your purposes anyway just be a bit stiff to get the nut on after a couple of threads, like everyone's said the final nut fastener's job isn't under any real loading, its job is just to keep the shock eye inner steel bush nipped up and stop it rotating or sliding off. The trick/skill is to keep it as square as you can as it starts. Sometimes I find it easier if I file a small even chamfer on the bolt end to get it started.

I own a sp400 suzuki, which I've had to sort this out on in the past too, too many years of hamfisted people changing shocks on a regular basis

 

[Robotstar5]

The trick/skill is to keep it as square as you can as it starts. Sometimes I find it easier if I file a small even chamfer on the bolt end to get it started.

A trick I use when threading conduit is to put in a small nick with a sharp file, gives the die somewhere to start.

 

[Can'tWeld]

Ok, I bought a 20 piece tap and die set from Fleabay.

So basically, to start with I try taking a die of the same size as the existing thread and then recut it? Simple as that?

Should I grind the end of the stud off where it's snapped so it's flat?

Cheers everyone.

 

[pedrobedro]

Yes try the same size if there is enough to clean up. Grind or file it flattish, file would be less violent and just chamfer the sharp edge off to help start the die nut.

 

[Can'tWeld]

Sorry for the idiotic questions...

I've decided to cut the threaded bit off and just put a bolt in, as I don't really want the nut falling off and I did manage to cut a thread using the die but I don't trust it.

So I've decided to use an M8 hole - the tap and die set I have only has one of each tap though, they look like plug taps. Do I need a taper tap and a bottoming tap as well or will I be OK just using the plug tap (as the bolt is going to tighten up on a washer and not actually reach the bottom of the hole?)

Just to clarify, have I got the following sequence right...:

- Create a pilot dint with a pin punch
- Drill an 8mm hole of about 1.5cm-ish deep using an HSS bit
- Use the M8 tap to tap it, winding it in a few threads at a time and then backing it out
- Put a bolt and washer in

?

Sorry for the silly questions but I'm clueless with this sort of stuff!

 

[JayRS4]

I wouldn`t go drilling an 8mm hole, where`s the thread going to go? I can`t remember tap drill sizes off the top of my head, but for an M8 thread, it`ll be roughly a 6.5mm hole.

Tap, half a turn in, 1/4 back, thats how I was taught anyway, oil if needed.

 

[BillJ]

I wouldn`t go drilling an 8mm hole, where`s the thread going to go? I can`t remember tap drill sizes off the top of my head, but for an M8 thread, it`ll be roughly a 6.5mm hole.

7mm for a fine thread, I believe, or 6.8mm for a coarse thread. 7mm would probably do fine for both since there is no real load on the screw.