RS125 rolling chassis for Moto 3 conversion

[steveyb]

If anyone is interested in a complete Honda NX4 (post '95) RS125 rolling chassis for making their own Moto 3 conversion please contact me.

[Shaun]

What would ya put in it and why? NZ realistic of course

[gixerracer]

What would ya put in it and why? NZ realistic of course

If you was at the south island nationals you wooda cen Scott Moir on his thing he was making the F3 boys look silly( Til it shat its self)

[steveyb]

The starting proposition is the CRF250 engine, specifically the CRF250X engine with the CRF250R top end on it.
X has the taller gearbox, R has the high power head, but one does need to more engine work as the standard rods etc are not really up to it. As Fatty Gixxer says, Scottys (built by Brent Symes in Napier) bike is a real weapon and goes really well with the 450 engine in it), But when the engine shat itself big time it really made a mess. Scotty has done heaps of work on it.

I have looked into it, not in too much detail though, and I reckon of the engines that are readily available, the KTM 250 MX engine is the way to go. Higher rev ceiling, more power and a bit more compact than the Honda. But the other european engines are probably better. One of the SuperMoto engines from TM, Sherco or GasGas (do they have a 4T??) etc etc??
Only slight mods to the chassis are needed, maybe some swingarm bracing, cutting frame to fit the engine, modifying gas tank, oil hoses and fitting exhaust system etc.
Scottys is a template as the 250 and 450 bottom ends are the same size. Can't recall if Brent put extra bracing on the swingarm or not.
Building one of these GPMono/Moto3 bikes is a real engineering treat I reckon. You need to fit the engine properly then do work on the engine to make it work and last at the high RPMs.
Maybe the new CBR250 motor will be a good starting place? Not sure.

[Ivan]

I looked at it myself theres abit involved like all things but can be done and would be a real treat the 250 motors are abit smaller to than the 450 so fitting them should be abit easier, Id be keen on doing something like this to much money tied up else were

[Ivan]

good option of motors out there to you can pick up and tune for this, Yamaha YZ250F that would be my option, but theres the CRF250 RMZ250 KXF250, bikes like The WR250 and CRF250X then your Europeon ones havent had much to do with them, I have rode most of the above mentioned ones and find the Yamaha the best motor but that is probably personal preferance I really wanna see these in New Zealand take off tracks like Taupo would be awsome on one of these

[crazy man]

l dont think 24hp 250cc mx engines would cut it some how

[quallman1234]

l dont think 24hp 250cc mx engines would cut it some how

Interesting pipe dyno charts of a CRF250R. 35HP Is probably a resonable realible expectation. Which isn't too far off a standard RS125R. There is potential for it but there is a-lot of money in changing those valve thingies.

Best you start learning to alloy weld Mr Bagshaw .

http://www.dirtrider.com/141_0406_retraction/index.html

[Ivan]

Interesting pipe dyno charts of a CRF250R. 35HP Is probably a resonable realible expectation. Which isn't too far off a standard RS125R. There is potential for it but there is a-lot of money in changing those valve thingies.

Best you start learning to alloy weld Mr Bagshaw .

http://www.dirtrider.com/141_0406_retraction/index.html

If you keep the maintenace up these motors are very reliable, I know a lot of guys been racing 4 strokes in MX for years they never had blow ups, and motox bikes are thrashed hard out rev limiter launches rev limiter warm ups etc the basic maintenace and they will last for a long time,

my 07 yzf450 had 122 hours on it when i traded in never been rebuilt never had any trouble

[lostinflyz]

MX motors left alone are pretty darn reliable, start fiddling to make power and they start going munchy munchy. I think for 450's it is either 55 or 60 and thats the absolute limit when it switches like a light bulb from ok motor to continuous grenade (ask Mr. Moir what his was throwing and for how long at nats). Unless you go spend enough to make it a road race motor (i.e. throw the entire internals in the bin).......

anyway someone should buy this and give it a shot. It'd be a great little bike

Oh and bolt one of them IODA racing moto3 engines in it!!!

[CHOPPA]

The moriwaki MD250 is just a crf250x engine in a rs125 chassis and when I saw mike jones racing one in oz he was giving the ex factory aprilia rsr125s a good go

[crazy man]

Interesting pipe dyno charts of a CRF250R. 35HP Is probably a resonable realible expectation. Which isn't too far off a standard RS125R. There is potential for it but there is a-lot of money in changing those valve thingies.

Best you start learning to alloy weld Mr Bagshaw .

http://www.dirtrider.com/141_0406_retraction/index.html

l used to dyno l lot of these bikes. not one in stock put out over 24hp the best pipe we tryed gained 2.5 hp. 90% of engines lost power with cams, high comp piston, ignition system. ported head. l must of dynoed over 20 of them . l dont beleave anyone else till l see it been done. even l was told never to tell anyone on what they went like. l think the 120k gearing they have make them fell not to bad. l would say its posable to get some good hp from one but takes someone that realy knows what there doing

[steveyb]

All of the above may well be true, but correct me if I am wrong, with the light weight of the bike overall, and the vastly improved torque curve of the 250 over the 125 is it not so that the gearing on the 250 can be a lot taller and hence the speeds of the bikes will be similar at the end of the day?
But yes, ultimately if the 250 is to be truely truely competitive with good 125 bikes I would think that various hop-up stuff would need to be done. Maybe not a huge amount of work, but as an example as mentioned above, one needs to put the CRF250R top end on the CRF250X bottom to get the basis of the motor needed for this sort of thing.

Just buy the thing and get on with it will ya?

I would do it myself with Qualman making a mess of the welding, but I need the money and would like to keep the engine and stuff out of the bike. :-(

[oyster]

Make sure it doesn't end up a bucket. It's all legal and it's a free world, but in my opinion a technical moral crime. Too many of those beautiful handbuilt GP chassis are ending up there lately. Like turning a Manx Norton engine into a workshop compressor

[speedpro]

Make sure it doesn't end up a bucket. It's all legal and it's a free world, but in my opinion a technical moral crime. Too many of those beautiful handbuilt GP chassis are ending up there lately. Like turning a Manx Norton engine into a workshop compressor

What an arse. Check Nigel Duff's bucket before commenting on RS buckets. There's others that would put "real" bikes to shame.