Vintage Dirt Bike Q & A

Hello from Kansas.Nice site on old bikes! Got a low mileage barn find 76 mr250 from original owner that I play with from time to time. Had a points issue which finally got fixed. The other night I took it out for a blast(and boy does it blast)and it started crappin out. I found out it sheared the crankshaft around the woodruff key. Anybody had any similar experience. Flywheel was tight and nothing hindered its rotation. I have the piece that broke out of it and am contemplating welding and grinding back together but just wanted to see if a replacement crank might be laying in somebodies barn or shop. Got a lot of old parts bikes out here. Maybe get a swap goin on some stuff.Thanks for looking-Jeff

You wouldnt happen to have a speeodometer and headlight setup from an mr250 would you I could really use one.

Whoa! The shaft itself broke??!! Normall, the woodruff key just shears off. If the key is sheared, just knock it out and replace it. If the crank is broke, I wouldn't even attempt to weld it. Look on ebay for a replacement. They come up pretty regularly.

Thamks for the replies.Woosh all I have are the original(not working) speedo from mine and the little OEM headlite still in use when bike is running. Yeah Mitchie the back side of the tapered part of crank next to the key slot broke out. I could see where it had been cracked and finally gave out. Contemplated cutting a new slot in flywheel 180 degrees around and matching keyhole in crank. What have i got to lose.Crank bad anyway. I looked at some old posts and see that the general thought is that a CR crank will interchange. Any others? I saw one for an MT on the BAY but don't know if that will work or not. I will list some of my parts bikes in a later post.Thanks Jeff

If its just a sliver on the side of the shaft that broke, I might try to weld it and machine it back. I thought you meant the shaft was completely broken off. Your idea is very good too, although I guess it would be critical to make sure your alignment was perfect. I have been told an MT and CR crank would work, but I just looked them up and the middle parts numbers are different. MR is 395, CR is 381 and MT is 358. So I don't know if either will actually work correctly.

The 73-74 cr250 crank is different than the mt250 crank it is 8mm narrower at the weights sorry I didnt measure the total width of either one. You may want to ask someone on ebay to measure there mt250 crank to see if it works there are a lot of them.

Allright, thanks fellas. I guess I'll fire up the old LINCOLN wire feed. HAHA I called Honda dealer today and the left half crank is available NOS for 188.00 dolla bucks. Right half is NLA. Keep that in mind as a last resort I guess. Maybe the Elsinore gods will smile down on me. -Jeff

If you haven't already purchased a new crank half, don't. The key is for alignment purposes only. What holds the flywheel in place is the tapered fit. Use locktite to glue the chip in place, but make sure the chip is seated all the way. You don't want any high spots. Then use valve lapping compound to seat the taper on the crank to the taper in the flywheel. Once this is done, wipe off the excess compound, but do not clean it with solvent. Put the key in, install the flywheel, and tighten the nut to the specified torque. I've done this many times. I don't even use keys on the go-kart engines I build.

Good Luck

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Current or previous bikes

1970 Yamaha CT1 175cc
1981 Honda XL250s
1984 Honda CM450c
1976 Honda MR250
1986 Honday CR250
1989 Yamaha FJ1200
1988 Harley FXR Superglide
1985 Honda Rebel 250
1999 Honda Nighthawk 750

All gone except my MR250.

I may have a MR250 crank if you need one. You may need to use your rod since a couple I have have wasted rods. Also I have gasket sets for the MR250. Jerry at mailto:elsinorestuff@qwest.net