XR250, 350 top end?

[Eric SmithMember]

A mate has a question. He has been offered a new topend off an ’84-85 XR350. He currently rides a, ’84 XR250 and is trying to find out if it will go onto his 250 bottom end???

Can some confirm or deny that the XR250 and XR350 of that era had a common bottom end?

Thanks!

[Mick DMember]

Is that Jeorg by any chance?? If it is,it is certainly a small world.

[GregMember]

I had a 84, an 86 and a 88 XR250, the 88 I had converted into a 280 and never heard of anyone doing it the 350 thing that is, I dont think it can be done, I think from Memory there are some differences between the engines, could be wrong again

So I say no :laugh:

TB

[Eric SmithMember]

Thanks TB, that’s my gut feeling too, but I have heard it said that the two engines had the same bottom end – just not said by anyone with proven knowledge!

[Anonymous]

What about giving ballard’s a call ECKS?

[Mick DMember]

THe 350 and the 250 right hand crank cases are exactly the same (same part number) Although the left crank cases are different,to allow for an oil feed line on the 350. So theoretically the cylinder might just bolt on. THe gudgeon pins are different part numbers as too are the crank shaft and conrod. AS the 350 cylinder is taller I would imagine you would have to put a longer cam chain in to.
So from this I can work out that it might just bolt on,but whether you can get it to work is another matter.

Info from

http://www.mrcycles.com/fiche_section_detail.asp?section=189840&category=Motorcycles&make=Honda&year=1984&fveh=4286

[Mick DMember]

I take that back,the crank case are different,whether the bolt holes line up I couldn’t tell you from the schematic drawings.

[Anonymous]

Good work Mick!

[GregMember]

micknmeld wrote:

Quote:

THe 350 and the 250 right hand crank cases are exactly the same (same part number) Although the left crank cases are different,to allow for an oil feed line on the 350. So theoretically the cylinder might just bolt on. THe gudgeon pins are different part numbers as too are the crank shaft and conrod. AS the 350 cylinder is taller I would imagine you would have to put a longer cam chain in to.
So from this I can work out that it might just bolt on,but whether you can get it to work is another matter.

Info from

http://www.mrcycles.com/fiche_section_detail.asp?section=189840&category=Motorcycles&make=Honda&year=1984&fveh=4286

What about the shorter stroke and shorter conrod :blink:

[Mick DMember]

I mentioned that the crank and conrod are different.

[drewMember]

to add to the confusion.

dose anyone know about the XL 250’s and 350’s?

my bro has a couple of project bikes as you do.

how much taller is the 350 barrel to the 250?

i forgot to mention try getting a 350 head and bottom gasket, if the bolt holes match up it should bolt on.

but as mentioned the stroke difference, comes up blank, apart from swapping the 350 conrod and cylinder into the 250. but if it dosn’t work you have to swap it all back again. so really i’m stabbing in the dark .

[Mick DMember]

THe link I posted earlier in this thread,has all the schematics for hondas going back a fair way,maybe you could try and work it out from the diagrams and part numbers????

[drewMember]

micknmeld wrote:

Quote:

THe link I posted earlier in this thread,has all the schematics for hondas going back a fair way,maybe you could try and work it out from the diagrams and part numbers????

:blush:
yeah i was hoping to take the lazy option= pick someone else’s brain.

However thanks to your post of the Mr cycle site, i at least found out that the 85 XL and XR use the same cylinder part numbers.

AND they stock parts for the XL 70!:woohoo: !!:woohoo: !!

[Bruce CurtisMember]

I seem to recall from the dark recesses of my mind that the XR350R was a completely different motor, a mid-sized breed that showed honda was ahead in this regard, was not an upsized 250 nor a downsized 500, I had the option a few years back on an old thumpernats CR350R and the 250 motor was not compatable with the mounts etc.

BC

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