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What would be involved, roughly, to fit an aprilia rs250 swingarm and rear wheel to a zxr 400?

no offence...but seriously, questions like this aren't going to get answered with the level of detail you want/require.

common sense answer is to measure your frame, go find the swingarm you want, measure that, then check all the other things, like where the rear shock mounts/mounting bolt diameters etc, how the chain will move around the arm, any issues with ride height...its an engineering challenge for YOU TO DO, not for someone else to give you blueprints, a cad file, free use of lathes and thousands of pounds in cash...

maybe exagerating slightly, but seriously, if you want to fit it:-

1. Buy it.

2. Take it to a bike/frame builder (GIA, spondon etc...) and say "Fit this swingarm, in that frame, with this shock, please".

3. Pay the man.

4. Ride away happy.

i meant would spacers be needed, cutting, filing, etc so I know whether it'd take weeks or days to do

Having owned both bikes my suggestion would be not to bother with the task.

The rs 250 swing arm is way too nice to put on a zxr 400

Also you would need to make new spacers and spindles to attach the swing arm to the zxr chassis pretty sure the rs swing arm is narrower in width.
You would need to source the rear wheel as well may be have to make up new offset sprockets to get chain line correct.
Time scale? Depends you got all the parts and machine shop a week or two.

Good luck

I would expect the rs250 swing arm, which is rated for less weight, to snap within 10miles when used on a zxr400 as there is more weight and power.....

i would go for a mille swingarm personally.

TBH big hoddie, it would take an experienced frame builder 1-2 weeks to get everything aligned, spaced, and suspended properly...not trying to be nasty, but your lack of knowledge of anything engineering-wise leads me to think that if you attempt this personally it might take you 1-2 years to finish it.

did you ever get round to sorting out your bikes suspension and brakes?

making up some spacers is as easy as learning how to use a vernier caliper, first job is to buy the swingarm, when were you wanting to buy it?

i take it you have been put off of the vfr400 single-sider?

Sorted my suspension-ish. My mate and me managed to do a fluid change, the brakes are better, but still spongey-thinking of doing the r1 rear master cylinder in a couple of weeks. Yeah, the vfr swingarm is a no go 'cause of the spacing of everything on the one side or something. My mate's studyting engineering but still hasn't got the know-how needed for something like that. Which series mille? The pre-'04 one or the newer one? Ill start looking around for a proper machining shop that can help me. What would I do with discs, calipers, shock and c + s? Mille ones or zxr with spacers? How much roughly would a shop charge me? And I was thinking after christmas

http://spondonengineering.co.uk/

best frame builders ever, and in our neck of the woods.

ring them, tell them what you want to do and they will quote you, ball park figure would be £800-£1000, its a ton of work.

if I remember correctly some of the rs 250's had the chain on the wrong side, if you really want to do it you can, me and a mate are currently putting a rgv250 banana swingarm and forks into an rd350, but his dad was an engineer who used to build safes for MI5

Thought about what you've all said and ill give spondon a ring monday, but 1st wanted to know if you think the mille suggestion, a newer zx6r or cbr400 gull arm swinger'll be best? The aim is nicer looks, strength and less weight.

Update on suspension; its going up the ramp this week to have the shock softened. Reason for the ramp-the shock is completely gummed up where I adjust it

Softened in what way, spring rate, compression, rebound?