My MX250A project.

[Nathan S]

Not that this is a super rare or special rebuild, but creating a blog-style thread seems to help me stay focussed.... If it bores you, then fair enough - just ignore this thread!

I bought a pile of MX250 and DT250 stuff from JimG in the second half of last year. After selling off some stuff, I reckon the remaining pile owes me around $600. The contents of the pile werea bit random - there was a correct MX-A rear wheel (with Mudcatcher rim), but two incorrect front wheels, for example.
The pile was ignored for several months, until I got sick of stepping over it. So rather than try to find places to put about 2.5 bikes worth of bits, I figured that the easiest way to get rid of the pile was to turn it into a bike.

The philosophy has been to make a solid, race worthy bike for as little money as possible.

The motivation is a mix of things - first is that as a kid with a DT250A, I always viewed the MX as some sort of holy grail (ha!) so buying the pile of parts was satisfying a nearly-20-year itch.
The second part of the motivation is that I'm building a 74 Montesa Cappra VR250 race bike - there's no doubt that the Cappra will be a much better race bike, but its also costing me enough (in both time and money - I want it to be 100%) that I'm not sure it will make it to the 2010 VMX Nationals. So the MX250 is a project that I know I can finish in time.
The final thing is that with the Montesa owing me so much money (by my standards anyhow), and the relative difficulty in getting hold of parts like pistons, that I'm feeling reluctant to thrash it around at every VMX club day - I suspect that I'll try to keep it nice for the big events like the Crawford River Classic and future VMX Nats.


Work so far:
I've stripped the frame back to bare metal, welded up a small crack, and paint it with (quality) aerosols:

I was 95% of the way through stripping the frame when I discovered the crack. I was literally thinknig "Jeez, this frame is awesome - dead straight, no cracks, no rust, and... oh..." when I saw it... Still, easily fixed!

I pulled apart the rear wheel, and gave the hub a clean and light polish. For such a scabby looking wheel, it came apart beautifully and had no dramas like flogged out bearing holes.
The Mudcatcher rim was replaced it with a non-catcher rim that I had. And the spokes were painted black. All of this made the rear wheel match one of the front wheels which I'd built up several years ago before selling it to Jim in another deal... 
It still needs the spokes tensioned and the wheel trued, as I greatly prefer to do this in the bike.



Lots of other bits have been bead-blasted (there's a decent sized blasting cabinet at work, and rather than sitting on my arse at smoko/lunchtimes, I make use of the workshop).  Some of these bits can be seen on the ground behind the frame in the frame pic.

Last night, the re-assembly began:


Tonight, I'll refit the swing arm, and finish building up the rear wheel.
Maybe start bogging up the fuel tank.

The tank was a freebie from Vandy, before I even bought the pile of bits... It was suitably rough, with lots of bog and a few rust holes. I attacked it with the MIG welder and is now watertight. In keeping with the low-cost philosophy, it will remain full of bog.


Costs so far:
Pile of bits $600.
Seat $50 (purchased long ago in the vain hope it would fit my RT1).
Paint $50 (all aerosols! A local hardware store is closing down and has 20% off everything).
Bars $50 (purchased long ago because a pair of quality alloy bars can always find a bike to be fitted to).
Grips $15.
Killswitch $7 (inc postage - I bought a dozen when Ballards were selling them for $6 each).
Filter foam & glue $20.
Fork seals $24 (no oil in the forks yet, so that's why its not on the list!).
Rear wheel bearings $15.
RHS side cover $20 (bought from Betric years ago, just because).
------
Engine bearings and seals $60.

Other stuff that you'd expect to pay money for (like the very good front tyre), was a freebie from a mate. There's also a lot of new nuts and bolts on the bike, because I have a very cheap supply.

I'm hoping to have it on the track for under $1500, but that will depend a lot on what I can manage for rear shocks.

[Viper79]

Hi Nathan,
What did you use to clean up the hubs, or did you blast them?

[Nathan S]

Blasted, then some 180 grit Wet & Dry to get rid of the nastier casting marks, and then 240 grit W&D, and then car "Heavy cut and polish".
The intention was never to bring the wheels to a mirror finish or anything - just to make them like new(ish).

[Viper79]

Thanks for that,  they come up well.

[Marc.com]

mine owes me about $1500, bike was $600 then I threw a good set of shocks on, swingarm of the gods etc, though recent purchase of Webco head has blown my budget.

But what you get for your money is pre 74 bike with limitless supply of spares so well worth it. I am just changing to YZ ignition and giving the barrel some love with the dremel/

[BJJ]

Nice!

[mainline]

I like your uncluttered work environment Nathan, and what's with the low fat beer? You on a diet Rick?

[Nathan S]

Having a bit of a blather about colour. I know that it should be either yellow or silver, but am failing to be inspired by the thought of either.
I'm really liking the way it looks now - everything is black, plated steel or raw aluminium. The idea of bringing any colour into the equation seems gaudy, but I know that the racing number plates will bring green and white whether I like it or not...

Current thoughts are:
Metallic grey (ie darker than silver).
or
White with a dark green stripe on the tank (like the red on the twin shock YZ works bikes).
or
Black, maybe with a yellow stripe.

All my MX plastics are pooh, so they all need to be painted regardless.

 

I like your uncluttered work environment Nathan, and what's with the low fat beer? You on a diet Rick?

  While i am trying to get my weight down, I don't compromise on my beer! Actually there aint no beer in that box - its full of Toyota Crown front springs (long story, don't ask... I have never been a Crown owner).

As far as clutter goes, this is a nice clear space by the standards of my shed.

[Freakshow]

Black tank, normal red YZ stripe ?

[Nathan S]

Slow progress - a mix of being busy with real-life and avoiding the frikken heat.

Here's how she sits now:

Yeah, basically the same as last time, but the rear wheel is finished now, and it has a throttle assembly and cable...

And here's a misleading pic that is good for my motivation:

The cases are completely empty, and its all just been 'plonked together' - obviously there's a lot of work before it will actually be this complete again.

I've also decided to fit a longer DT250A swingarm, because they're supposed to make the bikes handle better.
Here's the DT 'arm and a pair of lower fork legs drying:


Some detail pics, because stuff looked good in the shed tonight (although the camera wasn't particularly kind to me, and the photos make it all look a lot less pretty than it actually does...  ):

[mx250]

Good paint drying weather hey Nat .

[Davey Crocket]

Hey Nathan, that zerk fitting on the rear backing plate looks a little dodgy  , seriously she's looking good. Since you seem to be having a shed clean up/clear out I've got a handy tool you can build out of "junk" you'll probably have lying around. Here's the recipie ......Take 1 used wheel rim (preferably Volvo-nice Swedish steel and I'm pretty sure there's one next to your shed), add a pipe ( approax 50 mm diameter, 1.2 to 1.5 high), weld at the bottom, then weld some bit's of 10mm round bar to the top at 120 degree spacing's. These can be whatever length you choose (600 or700 mm is good) The reason for using 10mm bar is so you can bend it to any shape you need, you can also add a couple of bars down low. Now you have the perfect painting stand that you can move around without anything falling off, paint in the shed, let it flash off, take it out to the baking oven (sun), bake it, bring it back in. You'll be amazed how much easier it is to paint shit, even tanks, we've made a couple at work and there brilliant.... you can even string a frame between 2 and it wont fall over!!!....get to it son 

[BETRIC]

Nathan the MX swing arm is the same length as the DT, only diferrence between arms are the mountings for the pillon pegs on the DT

[mx250]

Nathan the MX swing arm is the same length as the DT, only diferrence between arms are the mountings for the pillon pegs on the DT

I'm glad you mentioned that, that's my understanding but I wasn't confident enough to say anything. I think the RT1/DT1 swing arm is 25mm longer and swaps.

[vandy010]

the square DT1 swingarm is real close in dimensions to the MX250/360/SC500/DT250/360 arm but it's the round RT/DT2,3 arm that is a little longer.
i think the square DT1 arm may also have a slightly smaller pivot bolt diameter.
i have all 3 swingarms here as well as the XT500c arm which again is the same dimensions as the MX250etc arm{just with heavier gusseting around the rear axle}.
cool tank