Bushing rocker spindles

t ingermanson · Feb 10, 2026

Why not do a bit of everything? Enough of an interference fit to make you comfortable with localized heat, retaining compound, a bit of peening around the outside, and a grub screw through the exposed front of the boss into a little hole in the bush, and don't forget that there are better spindle cover plates these days to help eliminate spindle rotation, the whole reason why we're here, and your only mode of failure once in play.

There's very little required of this hole. It's easy to get wound up, but go slow, take it easy with little bites with the boring bar, and you should be fine. This material loves to be machined. Tidying up a bit of eccentricity once in position should not be a problem if you give yourself enough material. Practice a couple times and then you'll be answering our questions! You've got this!

t ingermanson · Feb 10, 2026

Fast Eddie said:
why not fit super thick bushes, ie with only a pilot hole, loctite the suckers in, then bore them in situ ?

I think you're onto something, but super thick bushes would require the ID of the bore in the head to be large (duh...), which may weaken the boss, and would definitely change how it expands and contracts with the heat used to set the bush (worst case, the boss could crack as it cools unevenly), or the bush would have a thick wall, which would change how it expands and contracts with the heat, as well as the ultimate interference of the fit. If you went with too thick of a wall in the bush, when you went to bore it out, you could change how tightly the bush fits into the bore in the head and it could potentially come loose. There's a needle to thread here. How big the eye of this needle is, I don't know, but a couple/few tests would say a lot.

As usual, it's all about the prep and plan, for what seems to be an easy task.

Fast Eddie · Feb 10, 2026

t ingermanson said:
I think you're onto something, but super thick bushes would require the ID of the bore in the head to be large (duh...), which may weaken the boss, and would definitely change how it expands and contracts with the heat used to set the bush (worst case, the boss could crack as it cools unevenly), or the bush would have a thick wall, which would change how it expands and contracts with the heat, as well as the ultimate interference of the fit. If you went with too thick of a wall in the bush, when you went to bore it out, you could change how tightly the bush fits into the bore in the head and it could potentially come loose. There's a needle to thread here. How big the eye of this needle is, I don't know, but a couple/few tests would say a lot.

As usual, it's all about the prep and plan, for what seems to be an easy task.

I only meant to make the bush thicker initially, by not machining out the ID. Once firmly loctited in place, machine the ID.

Peteyoung75 · Feb 10, 2026

Thanks folks that all makes sense. I’ll be back on it at the weekend (hopefully) so we’ll see what happens. I’m quite happy to just peen or pin so will do a couple more tests.
Cheers

t ingermanson · Feb 10, 2026

Fast Eddie said:
I only meant to make the bush thicker initially, by not machining out the ID. Once firmly loctited in place, machine the ID.

Yes. That's the later half of my reply. Reducing the wall thickness once fitted can change how it handles the interference with the ID of the bore with a light interference like this. At the extreme, it can also make things go sideways if the boss cools irregularly. Half of that boss is hanging out in the breeze and anything dramatic done (heating and fitting an interference fit bush can certainly qualify as dramatic) to this side can affect the other side of the boss for the other spindle.

Could be a lot of handwringing over nothing. Not going too extreme one way or another should work out fine. The hardest part is almost always the piece holding, and that's all done.

Peteyoung75 · 2026-03-03T09:21:27-0700

Bit of an update. I’ve made a drilling jig to hold a 2,5mm drill on the interface between the head and outer edge of the bush. Tapped it m3, made a screw, wound it in and cleaned it up. Ran the reamer back through and gave it a tickle with a 1/2” flex hone. Heated the head up in the oven and the spindle slid in nicely, locking in place when the temperatures equalised. I’ll make a small thumb nut style tap wrench so I can tap the hole next to the inner bush also. If that’s a pain I might use a short roll pin there. Getting somewhere.

Bushing rocker spindles

t ingermanson

t ingermanson

Fast Eddie

Peteyoung75

t ingermanson

Peteyoung75

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