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Author Topic: RM250 Rebuild  (Read 16816 times)

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Offline TMKIWI

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RM250 Rebuild
« on: February 23, 2013, 07:16:38 AM »
Just picked up a basket case 85' RM250.
I bought this off a guy I race with and he used this bike and another to build 1.
All the important bits are there and I got it for sfa.
Plan on doing a full nut and bolt rebuild to match my 125.
I may shoehorn the motor into my spare 125 frame which is already rebuilt.
I need to do some measurements to see if it will work or not. If not, this frame will get rebuilt instead.
I will put an order in tommorrow for , new plastics,piston,rod,stator,exhaust etc.
Have pulled the barrell and will need a new os piston and rebore. The rod feels fine but will spilt the cases and see what is needed in the tranny and replace what ever is needed.



« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline TMKIWI

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RM250 Rebuild
« Reply #1 on: February 25, 2013, 07:38:42 AM »
Pulled the motor from the frame and did a bit of measureing.
The 250 frame has different pivot points for the full floater compared to the 125.
The swingarm pivots are 7mm wider compared to the 125.
The cases are the same width between the 2 motors but the 250 frame is wider to compensate for the wider swing arm pivots.
I could make the 250 fit the smaller frame but I would have to use all the 125 suspension and swingarm. I need those to build the other 125. It is not worth the trouble.
So looks like I need to repair the 250 frame which is a bit beat up but nothing a bit of time with a welder won't fix.

1 bit of good news, I found out that the 125 stator will fit ( I have 2 spare ) so that saves me 300 bucks.

I went to split the cases tonight to find out what it needs inside and as usual half the case screws were seized.
Looked and looked for my impact driver and couldn't find it.
I drove back to work, couldn't find it in my workbench. This is a new driver I bought last year after I lost my other one. :-[
Now I can't find my new one.  ><img src=" title="Angry" class="smiley">
Will borrow 1 tommorrow and get the motor apart.

Another thing I found when I striped the frame yesterday was the fork clamps were majorly over tightened.
I loosened the clamps and they opened up alot. I measured the forks and they are 41mm. In 43mm clamps. ><img src=" title="Angry" class="smiley"> F****n idiots. >:-D
Looks like the disc front end will have to come out of the 125 and the drum setup put back in.
Luckily I have 4 bikes to make 2. The joys of old bikes.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline evo550

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RM250 Rebuild
« Reply #2 on: February 25, 2013, 09:08:50 AM »
Those forks "look" right, wonder what their from at 41mm.
Shock looks a bit short at one end also.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline SachsGS

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RM250 Rebuild
« Reply #3 on: February 25, 2013, 03:14:28 PM »
"Farmerized" bikes in NZ? :-X

« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline TMKIWI

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RM250 Rebuild
« Reply #4 on: February 26, 2013, 07:24:19 AM »
Quote from: evo550 on February 25, 2013, 05:08:50 PM
Those forks "look" right, wonder what their from at 41mm.
Shock looks a bit short at one end also.

Yeh I thought the forks were the same as on my 125 ( which I have found out are off a DR250, which are the same as a 86" CR ) but who knows.
The rear shock is just holding the bike up. I am waiting on the custom shocks to get finalised and will fit them to both bikes.

Quote from: SachsGS on February 25, 2013, 11:14:28 PM
"Farmerized" bikes in NZ? :-X



Stupid **** happens everywhere. :-[

Found my impact driver and got most of the engine split tonight. Now need to find my flywheel puller.
Most parts have been ordered.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline evo550

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RM250 Rebuild
« Reply #5 on: February 26, 2013, 08:45:04 AM »
Forks might be off a TS 250, did you get them in NZ ?
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline _X_

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RM250 Rebuild
« Reply #6 on: February 26, 2013, 01:31:37 PM »
no worries, uniflow can't remember where he puts his trophy's.HA!
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline TMKIWI

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RM250 Rebuild
« Reply #7 on: March 01, 2013, 03:55:15 AM »
Split the cases yesterday.
The gearset is in good shape dispite the gunge sitting in the bottom. :-X





The crank is getting a full rebuild which is just as well.



Bead blasted the frame today and also the barrell and mag cover.
Will drop the case bearings out tommorrow and bead blast the rest of the engine.
Hopefully weld up the frame on monday after work and get it painted.


« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline evo550

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RM250 Rebuild
« Reply #8 on: March 01, 2013, 04:28:15 AM »
86 cr's would have been all 43mm's.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline TMKIWI

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RM250 Rebuild
« Reply #9 on: March 01, 2013, 06:31:16 AM »
Quote from: evo550 on March 01, 2013, 12:28:15 PM
86 cr's would have been all 43mm's.

Yes they were, that is what is on my 125.
What I was saying was, I am going to put that front end on the 250 and the original 43mm drum brake front end back on the 125.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline TMKIWI

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RM250 Rebuild
« Reply #10 on: March 02, 2013, 03:50:17 AM »
Couple of bits I have bead blasted.



Cylinder will be bored once the piston arrives and head modified to 82' specs.
Conrod will be here in a couple of days so the crank can be rebuilt.

Old school exhaust port. Power valves are for girls. ;)







Question for any engine experts.
In the 2 photos above you can see a pronounced ramp on the roof of the intake.
I am quessing it is there to create turbulance.? Is that correct.
Only ask as I am going to clean up the ports a little and want to know if I should leave it as it is.
Cheers
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline TMKIWI

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RM250 Rebuild
« Reply #11 on: March 08, 2013, 01:13:31 AM »
Got some presents Yesterday.



Renthal bars,grips & chain. Zeta forged pivot lever, Wiesco forged piston & VForce reed cage.



New plastic kit , seat cover & clutch & throttle cables.



Bead blasted engine cases.





CCing the head.



The crank is having a new rod fitted at the moment and will drop the cylinder and piston off to him on monday
Engine parts from Mrcycles should be here next friday as well as my exhaust and racetech suspension parts.

« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline _X_

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RM250 Rebuild
« Reply #12 on: March 08, 2013, 01:21:25 AM »
moto tassinari = new england. got that right kiwi.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline evo550

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RM250 Rebuild
« Reply #13 on: March 08, 2013, 07:22:26 AM »
What's your DC plastics like?
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline opfermanmotors

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RM250 Rebuild
« Reply #14 on: March 08, 2013, 02:42:02 PM »
2 Stroke ports are "chamfered", i.e. rounding off the ports so they aren't sharp edges.  This prevents wear and tear on the piston and rings as they pass over the ports (i.e., like going past a gillotine every stroke!).  4 Strokes have valves at the top so they don't have to worry about that :)

« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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