Shifting problem.

[762SPR]

I'm finally putting my YZ250's motor back together. I have the case halves bolted together, they went together real easily, I just had to do a little tapping with a rubber mallet to get it on but it seated with no binding.

The problem is when I try to run through the gears. I installed the ratchet mechanism, and slid in the shift shaft and lever to test it out. The problem is it keeps hanging in between gears. Sometimes it will shift just fine, sometimes it will hang, and a downshift then upshift will work, sometimes the index wheel will be stuck on either side of the peak and it won't go further without a bunch of shifts... Sometimes, If I just shift quickly it will snap into place, other rimes it will get stuck... It almost seems like a lubrication thing, but I don't want to bolt it together only to find out I need to tear it down again.

The gears and shafts had a light coating of WD40 on them to keep them from rusting when it was apart, and they all seemed to slide well when they were apart. I also greased all of the shift fork shafts and holes when I put it together.

If I pull the ratchet mechanism off and try to rotate the drum by itself, it seems to rotate freely, but you can sometimes feel it hang up. When it hangs, it feels solid like something is stuck...

I have already split the case halves and checked... everything looks good but I'm totally stumped on this one... I'm also rotating the shaft while I try to shift.

Any ideas????

[arnego2]

It is a continous mesh gearing so the complete assembly will be in movement making the shifting possible. When I did it it also hang sometimes as the gear box was open. When closed and filled with lubricant it went through the gears like a hot knife through butter.

[762SPR]

Yeah, it's so random I think that must be it. If it would always hang in one particular spot, then I would think it was something mechanical getting hung up. Thanks for the reassurance. I'll get this sucker put back together and hopefully fire it up!

[s14 2510s]

The bike will shift a ton better when its turning fast and running. If it shifts into every gear id say run it. They always shift crapy once you first bolt the lower end together.

[tim512]

Im about to reassemble my bottom end this week, any tips on getting the trans all back together? I've got the yama manual and a clymers so I'm hoping I can get it all right cuz the last thing I wanna do is have to tear it all down again

[762SPR]

Well, the manual shows some guy magically holding the gears, forks, and drum in his hands and just putting it in... Maybe I'm just dumb, but I couldn't figure out how to do that.

What I ended up doing was putting in the drum, then the gears and forks. Then you need to sort of lift up on the drum to get it aligned with the forks. The gears and drums won't be all the way in, but then you will need to adjust the forks so they are all in their grooves and their shafts are aligned with the holes in the case. Then you just slide all three assemblies into place. It can help to tap them lightly with a rubber hammer.

Don't forget to lube the shift fork shafts first. It's a giant PITA, and the Yamaha engineer that decided to make the forks pinned to their shafts instead of sliding freely on them should be shot! I can't think of one reason to do it that way, but a bunch of reasons not to...

Good luck!

[hardhitwarrior]

wait!just WD40? you are in for a cold start waering of the gears. you should have lubricated the gears before closing in the halves.

why not fill the motor with oil and tumble/shake the whole motor and doing it upside down to really distribute the oil thru the components before bolting back the motor?

[762SPR]

I'd think that running the motor will do all the required tumbling and shaking. The WD40 was just a light spray to keep them from rusting until I put them back into the engine. If the gear assemblies can't get sufficiently lubricated by soaking in the oil that's in the case right now and running a little bit, then I have bigger problems...

[hardhitwarrior]

yes but still. its shearing the gears. if i were you id do what iv just decribed above.

[tim512]

Just starting to get my cases back together and I'm worried there is an issue in my trans...

tl;dr - when putting my cases back together I can shift through the gears until I install the shift pawl thing then it seems like it is locked up and I can't shift gears at all even if I spin the shafts

I installed the shafts and the shift forks and shift cam into the clutch side of the case halves, and can rotate the cam with my hands while spinning the shafts and it goes through all the gears.

I can then put the case halves together, bolt in the star detent thing (thing that bolts into the back of the shift cam) and also the stopper level and torsion spring, and it can still shift through the gears.

However once I put in the shift pawl into the star detent, its like it locks up and I cant shift gears. Even if I install the shift shaft and lever, it still wont budge.

Is this simply because the engine isn't running? Once all back together and running it should be fine?

Edited October 25, 2011 by tim512

[s14 2510s]

I have had my 250's apart tons of times. They always shift hard when there not running. If you could shift it in all the gears at one time your fine. Spinning the shafts by hand and shiftig fast wont get the dogs to properly lign up and you will have binding. What hapening is the dogs are contacting the faces of the gears and because the trans is going so slow it just pulling the next gear along with it and not properly enguaging. When you could slowly enguage the gear it worked because you were not forcing it to shift the next gear untill it was properly aligned. Like I said before just put it together and it should be fine. Make shure your installing the Shift pawls correctly. They realy can olney go one way if you ruel out were everything else get placed. Best thing is to get a manuel with pictures if you dought yourself on reasembly. Dont forget to loctite the bolt that holds the gear on the crankshaft. Ive had one come loose before because I failed to do so. Loctite 243 is perfered but comin 242 with is blue medium will work if you dont want to order 243. 243 is just like 242 but its made to be used in oil saturated places. Most stores wont carry 243.

[tim512]

Cheers for the help

I have both a factory manual and clymers and I've followed both, and yea I studied how the gears engaged while everything was apart (I enjoy learning about this stuff, been a good experience ? )

Everything seems to be back together fine and good, but as soon as I put in the shift pawl thing it won't shift at all, it really seems like something is wrong.

Considering I can rotate the shift drum fine maybe up a gear or two... then put in the shift pawl and it's all locked up and wont budge, that to me indicates there is something wrong :worthy:

[762SPR]

All my problems went away once everything was soaked in oil.

For me, it was really random when and where it wouldn't shift, that's what convinced me it was a lubrication problem, not an assembly one. It worked fine some spots some times, but then randomly wouldn't... That and the fact I pulled it apart several times and everything seemed to be working fine.

[tim512]

yea at the very least I'm certain the transmission and shift cam is in correctly, so I'm currently in the process of sealing up the cases. Worst comes to worse when everything is installed back in the bike if it still doesn't shift (unlikely IMO) then I can just pull the clutch side cover off and work on the external shift mechanism.

Right now my problem is this liquid gasket stuff, I got some stuff from my local shop but the stuff dried in like 5 minutes?!!?!?!! So while I was struggling getting the crank to go in, the stuff dried and so I had to scrape it all off, bit of a disaster everything considered.

I did some research on here though and I think I used too much anyway and I don't think the stuff I have is a great engine gasket (its Permatex Red RTV) so I'm gonna go down to my local automotive shop and get a better, proper engine gasket, then give it another crack tonight.

[Maple Leaf MX]

yeah the cheap permatex stuff never seems to work as good

i like threebond 1194 or yamabond...both high quality

[762SPR]

I'm not sure what stuff we use in the shop. It's white, in a green tube and we keep it in the fridge. I think the cool temperature slows it's curing, or maybe it is just for long term storage.

I had the same thing happen to me with it curing... Then I got ir right and had the shifting problem and had to split the cases again...? So that makes three times I did it on that engine. On the bright side I got pretty good at it by the end, and i discovered that the easiest way to apply it is with your good ol' booger hooks! That's right, a dab on the tip of the finger and smear it on. Just make sure there are paper towels handy!

Make sure you have the dowel pins in, you don't want to forget them! Have a mallet handy, too.

[s14 2510s]

I use threebond 1194 because it semi drys and its a million times easyer to deal with then rtv. I order it off ebay most times I have 2-3 tubes in my shop. I use it on my race cars too. I put some in a small cup and apply it with a small paint brush. You should have the crank pulled into one side already when you start applying the threebond. Then you just slap the empty case half on quick. I use the tusk crank puller to pull my case halfs together after there all coated. It helps to find another person to help apply sealant to one case half as your doing yours then its still wet. You olney need a real thin wet coat as most of it will ooz out.

[tim512]

I use threebond 1194 because it semi drys and its a million times easyer to deal with then rtv. I order it off ebay most times I have 2-3 tubes in my shop. I use it on my race cars too. I put some in a small cup and apply it with a small paint brush. You should have the crank pulled into one side already when you start applying the threebond. Then you just slap the empty case half on quick. I use the tusk crank puller to pull my case halfs together after there all coated. It helps to find another person to help apply sealant to one case half as your doing yours then its still wet. You olney need a real thin wet coat as most of it will ooz out.

thanks for the tips ?

I pretty much learnt the hard way what you said above haha

I'm gonna have a crack at it tomoz after I get some threebond or something

[tim512]

sorry for the epic thread hijack too lol

[762SPR]

Haha, no problem! My problem is pretty much resolved, so we might as well work on yours!