Vintage Dirt Bike Q & A

Hi everyone,

I’ve recently acquired an MT250 and I’m in full tear down mode during the “off season” here in the great white north! I’ve got the bike stripped right down to the frame and I’m starting to clean and replace/repair parts. Although the bike is in fairly good shape, I’m noticing a few items that I could use some advice from other MT250 owners.

Condition: The bike was stored inside a shed, and although some of the parts have surface rust it’s not too bad, both cosmetically and wear/tear of components. I’m not doing a show quality type restoration here and it’s not my only set of two wheels, but I’d like a fun little bike for in town that’s reliable and clean, so here are my questions/concerns:

1) The bike has 3,000 miles on the odo. I’ve taken the top half of the engine apart, cleaned the piston and ordered new rings. The previous rings were very brittle and the lower ring snapped during removal as it was wedged in its groove. The top piston ring was capable of expanding and contracting, the bottom one was stuck. Everything in the lower half of the engine looks good (no leaks from what I can see) and the crank moves freely without making any noises or complaints during rotation. The engine is completely out of the frame (on the work bench) and I had originally planned a full rebuild but I’m not eager to crack the case if not needed. My other bikes (Ninja 1000, R1200S) are newer (age not mileage) so I’m not sure if the main seal and bearings are something that you’d typically replace due to age (passage of time) or whether the low mileage and visual inspection results can be relied upon and could save me some work here? Part of me says “do it while the bike is in pieces”, the other part says “don’t fix it if it’s not broken”. For those who’ve cracked the lower case, did you acquire a special tool, build your own or…something else?

2) The previous owner removed the battery, the kill switch and the rectifier and re-wired the headlight to provide power from the engine to the other accessories and lights. I’ve worked through the wiring diagram and managed to re-wire the bike back to the stock layout, including ordering a rectifier and NOS kill switch/headlight combo (most expensive replacement so far!). The only wiring question that I can’t resolve relates to the neutral switch. I can locate the head of the neutral switch, but what I can’t figure out from that diagram or other source (aka google) is how the wire (light green/red – hanging with the wiring harness that comes from the stator) attaches to the neutral switch? From what I can see it looks like the wire just sits (or gets pressed) between the switch and the case? In the parts diagrams it shows this wire as “free hanging” without any lead or attachment, and after looking around the switch I don’t see a connector hanging anywhere (i.e. matching stripped wire ends), and I don’t think the MT uses a rubber style cap since it’s tucked away behind the cover. Any help on this would be much appreciated!

3) With only 3,000 miles on the rear shocks and no surface rust or obvious leaks is there any reason to ditch them? Are aftermarket options, like progressive springs ($300), any better? I've read a few threads/posts on as they crack at the eyelets. I’m not expecting an Ohlins or Wilburs quality ride, but wondering if this is going to be “sub-par” regardless of the shock…which would support keeping the stockers.

New parts so far include:
-tires and tubes
- petcock valve
- kill switch / light combo
- rectifier
- battery
- engine gasket kit
- new piston rings (0.25 oversize)
- carb rebuild kit
- various hoses
- key
- rear brake switch
- lots of evapo-rust! The tank was holding gas from (19??) it poured out like brown sludge and I was convinced there was more stuck in the tank until I realized the remaining sludge was actually a thick coating of rust. Several electrolysis sessions and treatments of evapo-rust and the tank is in good shape (no leaks, just the petcock needed replacement).

Still needed:
- Turn signals (front and rear)
- Rear shocks (see question #3)
- New seat cover
- Air filter
- ??? – we’ll see in the spring!

The left seal can dry out and let air in. It can be replaced without cracking the case. I haven't cracked the case on my Mt250, but I have on my MR175's. If you already have the motor out and want to do things right, you might as well do a complete overhaul (bearings and seals). it isn't that expensive. You don't need any special tools besides an impact driver and bolt type wheel puller from harbor freight (Item #69889 on sale $12.99) to crack the case. You may want to used a slide puller for the bearings or buy the 12 or 20 ton press, but I found a large socket and hammer sufficient. Also, I built a rectangle base with a two by four I think it was 3.5 x 12 x 18 inches. It enabled me to work on the motor on its side without the crank hitting the workbench.

If the shocks aren't leaking and they a dampening the ride, keep them.

There is an mt250 air filter element on ebay, or you can contact fred <fredanddeb@actrix.co.nz>. He may have them. He is the best source for MR175 filters.

The seat covers are on ebay as well. Be very careful unbending and bending the tabs. If you do break them you may want to use a piece of perforated hanging strap where tabs can be bent out. You can rivet it to the seat pan and use the strap tabs as a substitute for the pan tabs you broke off.

Turn signals are overrated. Its grandfathered, Headlight and taillight - you are good to go.