I'm trying to rebuild the upper arm at the moment. I've got it out of the subframe, got the shaft out but can't work out how to get the old bearings out. Can anyone tell me please?

The correct way to remove it is with service tool 18g 581. It's probably unobtainable, so I guess a punch of the correct length could knock it out.
Another way, though more risky, would be to remove the needles, and fold the bearing casing over inside the arm, then remove with pliers.

i have done this recently. if the are rusted in really bad you can also use a die grinder and a bur to grind the bearing in 2 places and use a chisel to split it.

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FOR SALE MInidlx, 1293, GR head, RE-13, GR worked Redline Manifold, 45 mm DCOE,pulsar dizzy , "S" Disc's, Mk II "S" box, 3.65 diff. Minator 10X6's On the loose

Doesn't sound like this is going to be easy!!
The shaft feels OK in place - no side to side movement so I think the bearings are OK. The only reason that I was going to replace them was because I am going to get the suspension arms powder coated and I thought just to be safe I'd put new bearings in after wards, but since it appears to be a major to remove the bearings I might just stuff a rag down inside the shaft to keep the powder coat out and re-use the existing bearings, shaft etc.

I get them out the same way I get idler bearings out of the flywheel housing...
I put a big bolt in there and carefully MIG tack weld its head to the bearing casing in 6 or 8 places.
Then I put a bit of tube and flat washer over it, screw a nut on and wind the sucker out.
For the 2nd one, shove a bit of pipe or steel bar inside the arm and hit with BFH.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Or you could get a hacksaw and remove the blade. Thread the blade through the arm and put it back on the frame. Hold the arm in a vice and saw through the bearing cases. Same result as Stuartminidlx just different method. Either way take it slow and watch the housing.

Really shouldnt be too hard so give it a go. Not exactly sure how powder coating is done but it involves an oven so they may remove the rag before they put it in. Also anything over about 150deg will damage the bearing needles.

No way you will hacksaw these needle bearing cases, they are about Rc63 hardness.
Even a good `HSS' hacksaw blade will curl up with no teeth...
Hacksawing does work on bronze bushes, but not these puppies.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.