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T250tut · L Plate Warrior Joined: 08 Feb 2021 Karma :

HI All
Bought a new to me C250 rs cheap - or now I have found the reason its cheap :0) seems a common fault but the front lower engine bolt is seized in the mounting and previous owner has cracked the lower crankcase trying to shift it...........

Is it possible to just flip the engine and take the lower case of to swap or do you have to start at the rocker box and work downwards??

Riejufixing · World Chat Champion Joined: 24 Jun 2018 Karma :

Freddyfruitba... · World Chat Champion Joined: 20 May 2016 Karma :

bikenut · World Chat Champion Joined: 21 Nov 2011 Karma :

Go have a look on CMSNL which may help.

Some bikes it is possible to remove the engine, neccessary components then the sump, leaving head on and crank in and gearbox, but how does your engine split, vertical or horizontal.

CMSNL will show you.

Post up a link to your exact bike on CMSNL...
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bikenut · World Chat Champion Joined: 21 Nov 2011 Karma :

The power of CMSNL......

CB250rs seems to have a horizontally split crankcase, well it means less oil leaks I suppose not that I had that problem with brit bikes I fixed....

So it may well be possible to remove the lower half, but be prepared to remove all the side bits....get a manual dude, even the Haynes book of Lies will help.

The bike in question is a four stroke ? Yes ?
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Robby · Dirty Old Man Joined: 16 May 2002 Karma :

If it is a CB250RS, then I know them well. You need to start at the top and work down. Get the haynes manual, the bottom end is surprisingly busy. I avoid splitting the cases unless I absolutely have to. In this case, you have to.

Usually the problem is because someone fitted crashbars with a longer, stainless bolt. The alloy corrodes around the stainless and grips tight. Annoying it got so far as to break the cases, because you can remove the engine with that mounting plate attached, just unbolt it from the frame.

Also check the lower frame parts between the footpegs. They like to rot away down there.

jeffyjeff · World Chat Champion Joined: 02 May 2020 Karma :

That looks like a pretty old design. A quick wiki search shows the last ones were produced almost 36 years ago. Two questions. 1) can the crankcase halves be mixed and matched? I'm thinking the webs for the bearing bores might misalign. 2) Might it be possible for the OP to take the afflicted case half to a competent aluminum welder and have it welded up without too much distortion? (assuming the damaged area does not include any precision machined surfaces).
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oilrag · Derestricted Danger Joined: 07 Feb 2021 Karma :

What's the exact model and year? Can you put up a few pictures of the crack. That would be helpful. Is it leaking oil or not?

martin734 · Spanner Monkey Joined: 28 Aug 2019 Karma :

C250RS? I think that is the CBR250. I could well be wrong though, I often am Confused

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Robby · Dirty Old Man Joined: 16 May 2002 Karma :

T250tut · L Plate Warrior Joined: 08 Feb 2021 Karma :

cheers guys - yep its the CB 250 rs - a four stroke single
I have bought another bottom end and it came with kick start and selector drum in place ..... looking at it cos I havnt parted mine yet id does look like the top end could stay in place the only awkward bit will be the balancer chain........

I have 30 years on 2 T but this is my first 4 stroke so keep the advice coming please :0) and I have bought a Haynes form flea bay