is this a good idea or no.

i got a 99 wr 400 engine in a frame that needs plastics and silencer, a tune up, lights a couple ot eher things, and im getting a wr 426 perfect codition 2001 that the top end is toast in. should i swap the top ends, or just fix the wr 426 top end. how much does it cost to totaly redo the top end, not sure yet whats wrong with it, but he says the top end is toast.

what would you guys do. ultimatly id like to fix them both

but i wana ride in the mean time of savin to fix the bikes

how about switching the entire motor, and save up to fix the 426 engine?

When you say "top end", it depends on what you are talking about...head, cams and valves or piston, cylinder and connecting rod. If it's the piston, cylinder and rod, it's a no go. The 426 has a bigger pin bushing, so the piston won't swap over. If it's the head, That's a pretty easy swap and should work fine. You will need to plug the hole in the intake tract that the hot start octopus connects to on the 400 (it's internal to the carb on the 426), but other than that, it's a straight bolt across.

I would just swap the whole motor until you can get the 426 fixed, then put the 426 back in

im not sure what yur talking about anyone ever do this before and have pictures.ive never swaped an engine before and my only fear is messing all the wires and where everything gos.but i think im going threw with thi plan starting next weekend

if you're swapping the engine, I'd be tempted to swap everything electrical and the carb etc as well - probably save you countless days of headache that way.

Or, do as Birdy suggested and just swap the head over, maybe hte 426 just needs a piston and the head from the 400.

If you put the 400 engine inthe 426 frame, don't swap the carb! The Gen II FCR is much better...has internal hot start and doesn't have the slide cracking problem that the Gen I s had. All you need to do is put a rubber cap over the vacuum nipple onthe intake tract of the 400 head (where the 400 hot start connects) and you're golden.

Good thread. I have a '99 YZ400F and an '01 WR426. I'm trying to build a bullet-proof adventure bike out of the WR and I want the the steal valves of the 400 on it. Good advice on the carbs. I'll probably also swap the jugs because the 426 has a big bore kit in it and I don't want thin cylinder walls on the adventure bike. Both bikes have the same stroke, so I'm guessing this is a straight swap as well. Anyone have advice on the jug swap?

read birdys first post above. swapping the piston and jug is not a direct swap.

read birdys first post above. swapping the piston and jug is not a direct swap.

I didn't read that one close enough. Thanks. Guess I'll keep the 426 jug.

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