400/4 case split with topend in place possible?

[470four]

Hi all, I have a 400/4 with a recently fitted (1000 miles ago?) Yosh 460 kit...

Im having problems with what appears to be 4th and 5th gear slipping out into a false neutral under sustained full throttle & need to split the cases to have a look, but Im not in any hurry to disturb the top end as:

A) Its only just been rebuilt
B) this would mean using my spare & expensive Yosh head gasket set on rebuild
C) It would mean more work unbuilding & rebuilding a perfectly good top end with the resulting possibility of broken rings etc on rebuild...


Has anyone split one of these engines with the top end in one piece, still attached to the engine? I cant see why this couldnt be done? 

[matthewmosse]

Hi, done it on the 500's and 550 so given the similar desighn, no reason why not. (I'm not too sure as it has been a while but withdrawing the layshaft with staarter cluch might have been needed.
 Another thing the manual says isn't possible is a kickstart shaft replacement without splitting the cases. It's a fiddle but I have done this through the sump on a 500 with cluch case off too. Engine was on bench but I think with a bike lift that could also be done with engine in bike.

[470four]

Cool, thanks for your reply! Engine will be out anyway so if it does need the top-end off its not real bother apart from the points already mentioned? Bike had a new primary chain & clutch on the last rebuild so all good.   

[K2-K6]

I haven't worked on 400 but have done others like this and it seems low risk to at least try it and sensible to leave top end alone if it's ok and save using a additional special gasket.

I think if you build up a motor with rods already on the crank you can put it in the top case and then put the bottom on afterwards which is essentially the same thing, just you'll have to judge for yourself if there are any bits you can't locate that way up for yourself I guess.

[ttr400]

470, Yes no problem to do this to check the gearbox, if you want to remove the crank you will have to remove the cam and conrod caps.

Kevin

[exvalvesetdabbler]

Yes, I did it when I replaced the primary chain and the first gear with the bronze bush that seems to wear. I think I had  to lock the cam chain tensioner open and remove the cam chain sprocket at the top first. You can then undo the big end caps and leave the pistons and rods in place.
If I've missed something -  it was over 10 years ago.

DJW