I am looking to confirm if the fork tubes (upper & lower) from a 1975 250MX will fit on a 1975 DT250B. I haven’t had the opportunity to take any basic measurements yet for comparison. But if so it would allow me to use a fork brace that I have on the shelf because the lowers have the mounting tabs/ears.

EDIT/CORRECTION
The 250MX is a 1974.
Unfortunately I cannot update the title…
Here is a photo.
imgur.com/a/MQBEx1X

What are you trying to swap?  The whole assembly?  Or just the forks themselves?

P.S.  Title fixed

Just the forks themselves. (upper chrome & lower aluminum)
Not the triple tree.
I would insert them into the DT250 triple tree.

thanks for fixing the title

I confirmed that they both use the same fork seal part number, so I assume the tube diameter is the same.
But the fork tubes themselves have different part numbers……maybe the MX has more travel.
And I confirmed that they both have the same axle part number.
But the items that slide over the axle are different most likely due to the different brake hub. So I am not sure the boss on the lower will fit the slot on my brake hub.
I am looking to fit these on a very nasty DT250B that I plan to refurbish for off-road use only. The current forks on that bike have broken lowers from a past hack job seal removal. And the tubes are rusty.

They are both 34mm tubes and 15mm axles.  

My guess is they will bolt right on.  Yamaha made a lot of parts interchangeable.  The forks are likely longer like you said, if it has a "chopper look" you can just push the tubes up through the triples a little, just pull the springs and make sure the steering brace doesn't hit the triples before the forks bottom out.

Fun fact- Yamaha used the same ball bearings and races on many models and the height of the steering stem is the same.  So the triples should bolt right on but likely won't have provisions for gauges, etc.  They are probably aluminum too.   

Shu, I have a rolling 250A, if you came over here, you could have it.

Thanks for the info Mark. I think I’m going to go for it and see how it plays out since I can get it for only $65. And I may just use that triple tree if it fits since I will be eliminating the gauges and the lights.

The link below shows the bike I am planning to refurb into an off-road version. It’s very rough but it starts right up and runs thru the gears. I had previously removed the stator and flywheel for use on my son’s DT360A, but I have another set on the shelf that I purchased for backup. This project is on deck with two others ahead of it. But now that I’m retired I should make good progress.

Sneezles,
You probably can’t view these images from Imgur, but you would see that I’m probably best to stay with this bike since it is more than a roller. But thanks for the offer!

imgur.com/a/2yKlEAt


 

A parts bike. No engine. No gas tank.

It turns out that the forks I purchased are seized up. There was no oil in them. The drain screws were loose which leaves me to believe that someone drained them years ago and never refilled them.

They looked to be in almost perfect condition, but moisture had gotten under the dust caps and there was an awful amount of aluminum corrosion under the rubber caps. They cleaned up well and I have removed the spring clips and steel washers. I have removed the socket head screws from the ends of the lowers. I removed as much of the rubber seal lip as I can with a small steel pick hoping that it would allow the penetrating oil to get in there.

I assume the chrome tubes are seized inside the bushings. I placed a bottle jack between the axle and the bottom of the triple tree using a spare triple tree and axle. I was able to get one tube to chatter its way out of the lower by a mere 1/8” or so, but the other tube is stuck solid. So I had to abandon that method due to the skewing of only one tube moving.

I am going to buy one of those plant/flower window troughs that I can lay the forks into and submerge them in oil for a few days.

Anyone ever been down this road and have any suggestions on how to free up the tubes? 

imgur.com/a/MQBEx1X

Clever tricks I must remember but I've never had one that stuck. Without looking at parts there'd have to be a circlip on top of the seal holding that and the top bush in place if it has bushes!!. If that's the case the lower bush will top out on the top bush with damper bolt out so won't come out if think it's a wire circlip on the seal or seal washer. Been 50 years so might be wrong. OK editing looked on partzilla and I'm wrong, no bushes sorry. Never had one that stuck!! But there's a first for everything I guess.