Does anyone know of a specialist engineer, ideally in the Birmingham area, that is capable of carrying out some undercutting of my motorbike gears (to stop it jumping out of second). The ZX10 engine is fitted in my race car and occasionally jumps out of second when under hard acceleration.

I didn't think the second gear issue could be resolved by undercutting? It's normally the gear dogs worn due to old age and/or unsympathetic shifting.

You may well be right. Can you only machine them back to right angles, as supplied when new? Or are new gears the only option? I presume it's 2nd and 6th that are not staying locked together.

I had the same issue in my MK Indy R1 engine car jumping out of second gear
The quickest and cheapest way I found was to buy a complete engine and box and split the two
I put the good box onto my engine which I knew was good
I then had a complete spare engine as a back up. This turned out to be a good move as the engine threw a rod through the block at oulton park!

Latest info.
First gear machinist I approached said it was possible to undercut the gears but it was too much of a faff for him to take on. It was also going to be very expensive.
Second machine shop has agreed to recut the gears by spark erosion(?) because they are fully hardened, but can only do them at 90 degrees by this method. Cost is not cheap but new gears were not cheap either (if they were not obsolete!).

I think you ought to balance the cost against their expected lifetime, not just each other. But also consider good second hand parts as a middle ground?

Try Nova racing. It won't be cheap though.

http://www.novaracing.co.uk