yes thats right.

My chain came off my 400sf today, wrapped itself over the front sprocket, killed the engine.
I think its done internal damage to the gear box.

Had to wait for recovery, whilst listening to some old boring dude who wouldn't shut-up about his old MZ.

Pretty crap day, got it home on a trailer, then got the front sprocket cover off, and hey presto, engine casing damaged, however it hasn't penetrated the surface, so the oil can't excape, engine starts and runs.
But in neutral the fr. sprocket moves like its in 1st. And the fr. sprocket has loads of play in it now, back and forth.

OMG what can i do?
Anyone got a engine or gearbox assembly lying around?

Sorry to hear it mate.

I suppose it could have been worse: could have wrapped itself around the wheel and had you off the bike.

There were a couple of complete engine/box units on ebay last time I looked, and in fact there was a gearbox on its own all boxed up ready for shipping, but that was a couple of weeks ago now.

Hope you get it sorted.

aww man that sucks

im pretty sure most bikes in neutral with engine running still spin up the front sprocket when theres no chain attached though. not 100% sure but i distinctly remeber working on some bikes in the past where it did happen but everything was ok with the chain back on.

as the casings not holed maybe try throwing a chain on and see what happens bud??

found this on ebay too.. seems a tad dear but.. http://cgi.ebay.co.uk/HONDA-CB400-SUPER ... .m14.l1318" onclick="window.open(this.href);return false;

found this on ebay too.. seems a tad dear

That's the gearbox I saw a while back. TBH £50 sounds like a good deal to me.

I've got a spare CB1 engine if the insides are the same? It's in Portsmouth.

Other than that, odds are it wrecked the output shaft bearing, no idea what they're like to change as I never had to do it. I had a chain snap once, it exited straight out the rear.

front sprocket will turn in neutral with no load on it, just drag in the box.

Hold on before you start stripping the motor down, as above, the sprocket will turn when in neutral but should stop if there is something to hold it, there should be a bit of in and out play on the shaft too. How much does yours move