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Yamaha dt250mx gearbox problem


G Digger
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070A69F5-45FD-4349-9528-F2EF476F9620.jpeg1124B828-6F8F-4C83-BF90-E1262B62BECF.jpegHi

I’m having problems with my gearbox after strip down.

I believe the problem was already there before as it was a non runner and when stripping I noticed the gear change shaft was bent about 2mm.

I have straightened it now to about .5mm.

When I try to change gear when gear selector is built up I get nothing but if I use a flattened file as a selector it changes ok.

see photos 

Any advice would be great cheers Graham 

 

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Hi Dig...I've had a look around the net, found a DT400 Manual which has a picture of the same part...we're not allowed to post links to manuals.

 

Unfortunately it doesn't explain why the cogs are lined up like that, as in, for example put the gear in neutral then attach the cog to be similar.

Have you got a haynes manual? might be worth it.

I'd imagine its probably something simple which is causing the issue.

 

Edited by NE0
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Hi thanks Neo.

I’ve had a look. It appears to link one tooth different to how I have it. I think I have tried it all ways but I will have a go in the morning.

I have changed the internal selector drum, selector forks plus shafts.

they looked ok but I thought there must be a reason why the shaft was bent!

they are used but I thought I’d try them.

internally I think it’s all good because when I use the file to rotate the selector it works through all the gears.

Thanks again Graham 

will let you know tomorrow 👍

Yes got a Haynes manual but very vague description. Does look similar to how I’ve done it. Also I downloaded a manual off emanual but again a bit vague👍

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Hi Neo

have tried on every tooth tonight and it doesn’t move the drum. I think the movement when using the file is because it is radial so it’s moving it using 2 pins (top and bottom)but when using the selector it’s a push or pull movement on one of the pins.

I think the selector drum has to be addressed so the change is lighter and smoother so I think it’s cases split and further internal investigation.

will keep you informed.

cheers mate and thanks again 👍

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Could I have a picture of the shaft end WITHOUT the file in it and a picture of the back of the shifter please?
It's probably nothing (I'm no mechanic), but I had a thought I wanna check with the pictures...

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On one of our sister sites, someone is describing the same part, although I've not joined to see the photos etc...

https://yamaha-enduros.com/index.php/forum/general-discussion/6495-74-dt250-shifting-issues

They are describing the pawl and Blackhat250 was involved. is that the same Blackhat250 member who was a regular here? Maybe he can help if he sees this post?

Trouble is, according to his profile, he last visited back in August 2022. Hope he's ok?

Edited by NE0
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20 hours ago, G Digger said:

5A2DC811-34DD-428E-867F-8A0F80E564B2.jpeg892F3CC8-C7A3-4C93-930D-4C707C101F0F.jpeg4D6EF107-0639-403B-B088-5E9F92018224.jpeg804D7A30-FFC8-4B85-9352-5C06F16CA633.jpeg

Top picture: The legs on that 'spider' bit look worn.
Bottom picture: There appears to be a worn nick out of the leaver.
Not a clue whether these would be a problem, but, it might be worth looking into...

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Hi

The top picture where you can see the worn bits on the spider, I'm not sure if that's just some bits of the file I used.

I think the selector actually connects with the dowels behind that plate. see 2nd picture.

The spider like thing I think that is just a way of securing the dowels in situe, i.e bent over them to secure in place.

As for the nick on the lever I will have a look at that, I have just bought a second hand replacement for that.

Anyway thanks for your help. Will let you know what I find

 

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Hi Snakebite

I've had a look. You are quite observant there is a nick in the change shaft but I think it’s how it’s made for clearance to stop it fouling on the drum. Have cleaned the drum now. Have put it together again tonight and it went through all the gears ok (WHAT !!!). Didn’t do anything different. Had to disassemble it to fit new shaft when it arrives so hopefully it will work 🤞.B7BB7B8F-F002-4326-9B50-C3450F740835.jpeg7D727802-9210-48E2-978A-1046D1674DE8.jpeg96B277EC-BDCA-467E-8D6B-53322DBCFA00.jpeg

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Aaah! New pictures, excellent! lol

On closer inspection, the 'spider' appears to do nothing other than hold in those (now obviously) removable pins... So no fault there.

Yes, the nick appears to be machined, it's way too square cut to be wear...


The fact that it works now when rebuilt in the same way, suggests that something was binding.

Check to make sure there is absolutely no grit or foreign objects in the bottom of any of the locating shafts.

Check there's no tiny nicks or foreign debris in the teeth of the two parts (polish with some 800+ wet&dry (wet) if required).

Check there's no play in the two shafts in the casing.

Am I right in thinking one of those dooberies (the one on the left in the original picture) has been re-welded?
Check that the fit between the teeth isn't too tight (it looks tight). I think there's some old trick about being able to check interlocking teeth by operating them with a piece of paper in between... Maybe someone can explain the idea properly.

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Hi

I looked into the welded part and apparently the later models came with this part welded. Must have been a mod due to problems before. 
the teeth aren’t tight so that’s 2 things off the tick list although I am changing the shaft for the one I’ve bought as this one is slightly bent (about.5mm)

Thanks for all your help will let you know how it is when it’s running 👍

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Well, as I say, I'm no mechanic, but that's how I'd go about finding the problem.

Good luck! :D

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Hi Dig, Looks like you're making some progress, I note there is an index mark (raised dimple) on the middle tooth of the selector cog in the recent top photo.

Yamaha uses several of these dimples and indents on parts inside the gearbox, my 175 has several parts with them, when you put it back together, you align the marks etc or they are aligned when the box is in Neutral.

Is there a corresponding mark on the other cog it interfaces with? or does it relate to the roller shifter head( the bit with the spider)i.e that bent over tab for example on the exposed spider.

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  • 3 weeks later...

Hi

sorry for late responce.

bike back together all gears shifting nicely, neutral abit hard to find but manageable. read somewhere if chain a bit tight can cause this issue so i will loosen chain to see if improves.

Thanks for everybody's help so far, cheers Graham1C6C9D37-4973-4A8A-B123-31242E2B8849.JPG

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Yey! :D

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