CB250RS Drive Sprocket Seal

[andy_c101]

I really can't believe it!
(Apparently) It seems that back in the 80's Honda designed an engine (the CB250RS) where you have to split the crankcase in order to replace and fit the final drive sprocket shaft seal!
Crazy!
- unless anyone out there knows a way of fitting a new seal without a complete strip-down of the engine bottom end & gearbox.

Andy
 

[Bryanj]

i can't remember, is it a vertical or horizontal split crankcase mate

[ka-ja]

hi,
     Not so rare, the 400/4 final drive oil seal and a gear shaft blanking plug are trapped in by the crankcase halves, not such a bad idea if you think of how much oil you could loose if the seal "popped out" while running at speed.

[Bitsa (Ralph Wright - RIP)]

Hi Andy
Yeah bit of a bummer but you can dig it out carefully and replace using a damn good fixing sealant like previous if it pops out big sh t.Have done it with other models only because customers did not want to pay for full strip.Engine was horizontal split cases.
Cheers
Bitsa

[andy_c101]

Yes, it has horizontal split cases.
I did try installing a new seal without splitting the cases.
I thought it was worth trying, (& yes with some Honda engine gasket sealant in the casing groove too), but the seal just got all chewed up!

Now reading up on the procedure for the engine strip n rebuild.
I hope I don't find any new 'horrors' inside, when I open it up!

All good experience I suppose!

Cheers

Andy

[andy_c101]

Managed to spilt the crankcase today.

Once the top-end, cylinder etc. was off, I was able to split the cases WITHOUT having to strip/remove all the side-case parts such as generator; clutch, oil pump and balancer shaft & its chain.
So that speeded things up quite considerably.
With the balancer shaft chain still on, the upper case doesn't completely lift away, but enough clearance to allow access to change the final drive seal.
While doing this I have also swapped the final drive assembly shaft, as the old drive splines (for the chain sprocket) had worn badly leaving much backlash (not uncommon on these old single 'thumpers').
 

Just need to button it all back together, top-end 'n all later in the week.
[I don't know why I was so hesitant in the first place; the moral is 'just do it!]
Andy