4th gear failing to engage.

[Warthog1959]

The selectors were checked before reassembly, went through the range. I can't get past 2nd when the engine is not running.

[K2-K6]

That seems quite odd.

You usually have to rotate the output sprocket (turn the rear wheel) to get all the gears but it should definitely go through all of them.

Unless something brutal has happened to the selector forks they are quite strong, hence why we are pointing towards the gear spacing on the shafts as supect i.e. the correct gear is moved the right amount by the selector but the receiving gear dogs are too far away to be connected with.

[Bryanj]

BOTH gearbox shafts need to be turning to get past 2nd easily, BEFORE i get jumped on yes it will frequently work just turning the back wheel BUT NOT ALWAYS

[hairygit]

Just remembered, the thust washers are integral with the gears on an F2 engine, so you wont have left them out, but they may have broken up

[Warthog1959]

The problem was the cracked crankcase repair. The weld was very slightly proud and prevented 4th from engaging. Unfortunate but no damage. Bike back together and running pretty good, apart from 1 of the downpipes running luke warm. The tests I did had me convinced it was the spark plug so changed all 4 with iridium's, but it is still not as hot as the other 3, The ignition is electronic so, I suppose it could be the coil or HT lead. Can one side of a coil fail? anyhow Thanks for your efforts. as a result I now have a used set of selector forks as spare. No bad thing.

[hairygit]

Try putting the lead/cap from number 4 onto number 1 and vice versa, if number 1 is still not right, it's not the lead! What condition are the H.T. caps in?

[Warthog1959]

They seem in fair condition. It is the 3rd down pipe from the left. I swapped the HT lead with 2 and the fault didn't move. I actually took the plug out and tested it for a spark in 4 and the plug failed. So I replaced all the plugs at once. BUT after a run out the down pipe is still tepid. It does not feel like it is running on 3 though.

[hairygit]

How does the offending cylinders new plug look compared to the others after a run?

[Warthog1959]

I'll check it when I next get chance to go out. Are you thinking fuelling? We did adjust the needles recently as it was running rich.

[hairygit]

Needles, fuel levels, partially blocked jet, just a case of going through it step by step and a process of elimination. I assume the valve clearances aren't too tight on the offending cylinder?