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yz 250 bottom end time

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Well it looks like I'm goin in. The right side crank seal is leaking and has to be replaced. I've never split the cases on a bike before but I feel confident. Watching the rmtv videos and I have the manual, so I'm gonna give it a shot. While I've got her open what else do you guys suggest I check/replace. Bearings, seals, rod, crank, etc. While I'm not made of money, I do recognize this is the time to rebuild entire lower end . I am now seasonally out of work so money is tight. I would like to get most of the parts ahead of time, over the next couple of months. Plan to rebuild over the holidays. So anything you guys think I will need will be considered/ prioritized. Thanks for any imput.Also are there any must have tools you guys recommend?

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FYI you dont need to split the cases to change the crank seals.

However splitting the cases and doing some routine maintenance is definitely a good idea.

Essential tools (costs if you order off RMATV)

flywheel puller - $10

clutch/flywheel holder $15

case splitter$60

crank puller $60

also need a torque wrench.

My recommendations to replace:

- All gaskets

- most oil seals (at least both crank seals and the drive sprocket seal and shift shaft seal)

- At least main bearings and drive sprocket bearing.

- Fresh top end.

While in there check:

- Clutch basket - grooves and/or notches = file or replace.

- Shift shaft - make sure its straight and goes into its groove without resistance (although if you currently have no issues with gear shifting then it should be fine)

Check out all your transmission parts, including:

- shift forks - any burring or signs of wear at all = replace (they're only $30 each and splitting the cases is a decent task so I would recommend it)

- trans gears - again look for signs of wear etc, particularly on the dogs.

Crank - get a yamaha manual and make sure the crank is in spec (basically no more than 2mm side to side movement if I remember correctly).

They're the main things.

One other thing I recommend you look at inspecting/replacing if there's any wear is the shift pawl square arms and the back of the shift cam drum that the arms go into. These were slightly worn on my yz125 and it caused me a lot of shifting issues. These are both part of the 'external shift mechanism'

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havin the right tools is 50 percent of the job. even more actually. ya want a case splitter, crank installer (or jig if ur pressing), flywheel puller, impact screwdriver (absolute must), good torque wrench, maybe the odd bearing puller/separator

its really easy. nothing to it...take ur time and bag/label the parts

should i say that again? label ur parts....

yup label ur parts eh

need a good case sealant (i like 1194) and patience

check out ur crank...and id put in new main bearings, seals obviously, and id go fresh crank to, cus im ocd

u can make summa ur own tools...but....

any other questions? lot easier doin it then splainin it

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Just to reiterate, replacing the right crank seal is a 45 minute job if you know what you're doing. No need to split the cases. It will probably take you 2-3 hrs the first time if you have to walk through the manual step-by-step. Theres not much opportunuty to mess anything up, just be careful of race that the seal sets in (don't scratch it).

Going through the bottom is a great idea. But if you're tight on funds, just fix the seal and ride for now; start collecting the tools and parts in the meantime, for a later date.

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Id recommend just replacing the seal and leave the rest alone, uless your bike has a LOT of hours on it.

FWIW - IF you do split the cases, replace crank bearings and seals. BUT dont install the RH crank seal until you press the crank into the case. I put the seal in first and when I pulled the crank into the case I found the lip on the seal had turned inside out and the spring had came off it :busted: LUCKILY I was able to pull the crank back out and fix the seal with no issue. I waited until I pulled the crank into the case and reinstalled the seal - much better that way.

You WILL need the proper tools to do the job, I know some guys cobble stuff together to do the job but I wouldn't after having done it myself. You damage a crank or engine case and youre out a lot more money than it would have been to buy the right tools in the first place.


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Thanks for the replies. I was not sure about having to spilt the cases, and was preparing for the worst. I had not checked my manual before I posted. Thanks again guys.

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