Hitchcocks Forum

Is it just me?

It's the electra X type forks. Just broke my second fork lower, snapped through the casting where it pinches the wheel spindle on the right hand side.

This one went as I was doing it up, wasn't even at the point where I was properly tightening it, I was twiddling the bolt down with the long end of an allen key and was just past "finger tight". I'm beginning to wonder if they anneal these castings after machining them.

To snap one leg seems very unfortunate, to snap two suggests something is amiss. There shouldn't be that much movement. Are you sure the spindle isn't undersized?

The early (pre 2012) C5 forks with the leading axles seem to be a bit meatier (if that's an appropriate term for cast alloy) around the spindle, and they would fit place of the Electra type as the stanchions still have external screw threads at the top. You'd need the longer front wheel spindle to suit, and the mudguard brackets are different.

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PeteF wrote: ↑

Thu Jul 23, 2020 1:54 pm

To snap one leg seems very unfortunate, to snap two suggests something is amiss. There shouldn't be that much movement. Are you sure the spindle isn't undersized?

Have to tap the spindle in with a rubber mallet. Maybe it's oversized? Don't know what size it's supposed to be. It's a proper electra X one from our hosts.

I think I'll fit a shim in the "slot" on the next one to reduce the amount of possible movement before it's under compression from the pich bolt.

Got the new fork end in and had a measure both at this one and the broken one.

The spindle is 20mm dead on OD. Fine, that's what I expect it to be given the bearing size and it's one of two I have.

The hole in the new fork leg -and as far as I can measure the broken one- is 19.5mm totally relaxed (no bolt doing up the pinch) so it would have to be forced open for the spindle to go through. Pinching it down would reduce the ID further placing a significant stress on the cast aluminium, forcing it to bend around the solid metal spindle. It also means the metal of the clamp is not making even contact all the way round the spindle causing further stress risers.

From asking a couple of engineering friends, they would normally machine a clamp of that type to either the exact diameter of the pin or a couple of thou larger to allow for galling/corrosion.

Current plan is to (again, on engineer friends advice) make a tool out of some steel tube with a slot in the end and insert a "flap" of emery paper. Using that as a reaming tool in a pillar drill will evenly remove small amounts of material resulting in a rounder hole than trying to run a 20mm drill through it. Once I have it to 20mm dead, I'll give it a try. If it doesn't grip proplerly, I can then use a bit of emery cloth and take a little out of the slot.

When I think about it properly. In this application, the right hand fork leg isn't actually helping to compress the bearing anyway (the step in the spindle butts against the bearing spacer). Doing the spindle up compresses the bearings against the left fork leg and aligns the disc with the calliper. All the clamp on the right hand fork needs to do is prevent the spindle moving sideways in the leg or rotating once that's done. It's probably best that it's "floating" right up until the pinch is done up to keep the fork legs totally paralell.

With a hole this size, I've found a Dremel with a flap wheel to be a real friend

Or even a half-round engineer's scraper, assuming you can find a half-round engineer...

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Adrian wrote: ↑

Sat Aug 15, 2020 12:56 pm

Or even a half-round engineer's scraper, assuming you can find a half-round engineer...

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I know a few half-cut ones.

The pinch needs to be a perfect round in order to --pinch.

I f I was you I would turn the wheel spindle half a mil. I understand the machining of the RE was a hit and mis fare with Monday morning and Friday afternoon motivating accuracy.

And. That's another one gone. I'm not trying a 4th. To say the air was blue would be an understatement, sodding thing even waited until I'd filled them with fork oil.

I even briefly considered going back to drum, then remembered this bike will hit 90mph. I think it's now a toss-up between finding a complete set of later fork legs with top threads and traditional stays or making up a plate to mount the calliper on a set of drum brake fork legs.