CB250rs

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CB250rs

A while ago i remember someone saying there was a 500cc engine that fits on the CB250rs frame...can anyone remember what it was?...ta muchly xxxx

I think it might be an XR or XL single. Some bike mag did it many many years ago. I only remember 'cos I thought it was interesting and something I wold like to do aswell.

Cool ta....the engine in the CB at the mo wont start...solenoid probs and discontinued parts....so if i ve to buy a new engine might as well go bug summat meaty in lol

I think the XL500 engine fits but you may need to have some custom bracketry made.Might be better off finding a reasonable XBR500 though.

Find an XL500 lump that ISN'T totally knackered by now, I'll be well impressed.TU250's are the future.

fifitrxibelle wrote

A while ago i remember someone saying there was a 500cc engine that fits on the CB250rs frame...can anyone remember what it was?...ta muchly xxxx

Thought it was the FT500 engine?

fluteplayer wrote

Thought it was the FT500 engine?

Are there any left with working starter motors?

used to be the ft500 coz the cb250rs chassis used to handle quite nicely and they made a good single cylinder race bike.

Fifi,It's the XL500 (S or early R model) or FT500 motor that fits. The FT is the same as the XL but has a starter motor. I did the conversion a few years back and it's not that difficult but not exactly a straight swap. Basically you need to :modify the top engine mount - either move it or leave it offshave about 1mm off the cases at the bottom rear mountmake up a new set of exhaustsspace the carbdo something with the airbox or use an open filtermodify the throttle cable mount.Mine was done on a real budget and didn't last long as the motor was tired when I got it. To be honest unless you really want a CB500RS then you're better off buying a 250 for spares or repair and just swapping the motor over.Hope this helpsTony

The starter motor problems on the FT500 are easily cured with a phosphor bronze bush.I despatched one for over a year and put 50+k miles on it.TBH the FT engine is not that much faster than an RS250 (despatched one of those as well) and certainly not worth the fairly extensive mods required to graft into a 250 frame.You'd be better off fitting an XR250 engine, they are still a current model engine, so spares are not a problem. There is an abundance of tuning bits for them, cams, big bore kits etc,.OK, so most o them are kickstart but thats not a major problem, fitting an RS250 starter shouldn't be a problem.The XR engine should fit with minimal mods and you'd be able to use the RS exhaust, ignition etc. Crust

I did this conversion in the 1980s with an XL500 engine (6v generator). The engine bolts are bigger but the spacing is the same so the holes in brackets had to be drilled out. I moved the voltage regulator from under the tank to the front down tube and made a shorter head steady bracket. I swapped the generators over and adapted the carb and cables to fit. I had to dent (by hammer) the tank to clear the rocker cover and I had to mis-out the decompressor cable. I geared it up using chain and sprockets off a 400 Superdream. It ran very well with plenty of grunt but was a bit wallowy until I changed rear shocks to Marzocchis and then it was really good. I ran it for a couple of years like this before selling it. I've checked with DVLA and it still exists but is Sorned. Hope this helps. JB

This is some great stuff herre!

tevie54 (not verified)

I've still got mine and its great, track days, commuting, touring it does them all, a well recommended conversion

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