Mercane Widewheel steering stem issue

well after expecting something like this for a while its finally manifested

Now this is something which I became aware of as a possibility something like a year back with the first reports appearing on reddit. Having some basic engineering skills and understanding a bit of how metals bond (or don't) with each other I expected to see this on my scooter one day or another. So I kept an eye out for it.

Below is the first example of this that I saw.. but his had been progressively ignored (because people are stupid) for some time.

Fig 1

the problem stems from what I believe to be a manufacturing design defect in the Mercane and that is based in the problem of "how do you marry a steel steering stem into a cast aluminium suspension / wheel holding system?".

As I see it (I've not yet done a full destructive analysis) the tube that is the steel steering stem is attached into this cast aluminium system.

The steel tube (in my above video) holds the steering bearings and looks like this when pulled out:

 Fig 2

note that the bottom bearing is still attached (as is visible in my video).

Note also that the tube (steering stem) being held appears to be plugged but also bears marks consistent with the broken section in Fig 1 above.

These images are all from the same failed stem. A second failed system was presented to my by some narcissistic fucktard in Melbourne who was trying to get me to help him with a warranty claim (although he'd been smasing into bumps and gutters with reckless abandon.

Fig3

His shows quite well how the steering stem had been deeply embedded into the top bracket (if I may call it that) and shows a steel base remaining. There are marks on that consistent with the shaft (which I'd like to have seen but said moron was unable to bother photographing as I requested).

My current working theory is that the steering stem is plugged at the bottom and has a plate welded onto it that allow the steel tube of the steering stem to be held onto by being welded to the plate. This weld has broken and leaves us with a tube that comes away from the plate as per Fig 3, but the base plate is still embedded in the base of wheel assembly.

So if I'm right then the issue is the failure of the weld and then the eventual (and inevitable) failure of the joint that the tube seats into. Something like this

Fig 4

If this is correct then I can basically repair this by:

• drilling a hole through the steel from below penetrating the plate and the plug at the base of the tube
• if the tube comes out (which I anticipate it will) putting some epoxy in there to help hold it
• putting a bolt through the hole to hold it together

I believe that this may even be a good idea (the bolt) to do preemptively on any Widewheel of this vintage that may as yet not suffered this failure

Today I pulled it down further for a good look, this video covers some of the points covered in the earlier video, but goes further.

While here, steering head bearing dimensions:

• outer race external diameter 37.91mm (don't forget it has a taper)
• stem is inner 27.12mm so inner race must fit that

Now in case anyone thinks this level of war is "BAD" let me say this is an exemplar of what I've done with my scoot for the last year of its life

Now as I said, I regularly inspect because I value my skin and bones, but as you can see I've enjoyed it, and I believe its eminently repairable (and actually still functional right now).

So lets see where this goes, as I'd like to avoid the front falling off

---

PS: I've now done the following

1. drilled in from the bottom of the assembly
2. tapped a thread into that hole 
3. fitted a bolt so that it goes through the thread
4. fitted a nyloc nut onto the top of that bolt so that it can't loosen

Video

Images

and

and looking down the stem...

so that's not coming off any time soon, and so if it gets loose again it will mean that both the weld has broken and the bolt has sheared ... I expect I'll notice before then.

HTH