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319
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3/7/2008
Location
Tigard, OR
US
Edited Date/Time
8/8/2019 9:56pm
I could really use some guidance and I’m hoping to find an answer here.
The lower bearings sound a little rough and probably need replacing. Is this something I should consider doing myself or is splitting the cases beyond your average backyard/weekend/amateur’s ability?
I’ve done top ends and have always have had good luck but the lower end’s a different ballgame. The dealers/shops here in Portland aren’t accepting motor work until fall.
What to do?
The lower bearings sound a little rough and probably need replacing. Is this something I should consider doing myself or is splitting the cases beyond your average backyard/weekend/amateur’s ability?
I’ve done top ends and have always have had good luck but the lower end’s a different ballgame. The dealers/shops here in Portland aren’t accepting motor work until fall.
What to do?
Beyond the tools you probably already have like a torque wrench, rubber mallet, etc, a few inexpensive tools make this job so much easier. A Tusk flywheel puller, case splitter, crank puller, clutch/flywheel holder combo and simple handheld propane torch. Well under $200 in tools you can use a lifetime and you will still have huge savings in labor on just one job (and get it done before fall.)
Can you do it without some of these tools? Yes, did a few as teen decades ago. But its a WHOLE lot harder and wouldn't recommend a newbie try it. Just not worth the all the extra effort, chance to get stuck or f up, and frankly, the right tools are cheap.
The hardest part is putting the tranny back into the cases....and that isnt that hard if you take your time. Like every motor, there are lots of tricks to make the process pretty pain free.
BTW, in my experience if the main bearings are going your big end bearing isnt far behind if you dont already have a relatively low hour crank.
If you want more info or tips when and if you move forward, happy to respond with what I know from my experience. There are also a few of us who are on thumpertalk consistently who have built a lot of these YZ250 motors.
Good luck and well within your ability!
The Shop
I get some dry ice from the local supermarket and set the bearings in there before dropping them into the heated case halves. -109F shrinks the metal a little more than a freezer set around 10F.
Also, I got a really HD heat gun instead of torch. Works great.
Some folks use more heat, and I have read arguments about metallurgy, too much heat etc.... I've always believed 250 degrees to be safe and more than enough heat to do the job. I'm neither a pro wrench or scientist though. Lol
Reverse process when installing. I leave my bearings in the freezer overnight at minimum and they just fall into the hot case. I've had to revert to dry ice only once when we needed to freeze them fast (cough, somebody forgot to put them in the freezer the night before.)
Pull the crank through the right side case first. If you dont have a puller, a torch or heat gun to warm up the main bearing will work. Set case flat on it sides over a couple scraps of 2x4's on your bench to make putting the tranny in easier.
If you have never done this before, it can be helpful to test fit the cases a couple of times cold with the transmission to get the feel for it without the crank.
I looked around today for some of these tools and with so many products available I have no idea which brand/style I should get;
“ A Tusk flywheel puller, case splitter, crank puller, clutch/flywheel holder combo and simple handheld propane torch. ”
Can you direct me to some name brands you prefer? I get/saw the Tusk but the others?
Case splitter here and can also be used to push the crankshaft out of the right side of the case after splitting (never use a hammer to knock a crank out.)
Clutch holder that also doubles as a flywheel holder here is helpful in removing the basket and holding the flywheel when taking off and installing the bolt on the end of the crankshaft
Crank puller here
Flywheel puller here double check that it fits your year YZ.
You may be able to find some cheaper versions on ebay... but I have used and trust the Tusk brand from Rockymtn for budget level tools. Been my experience with some of the cheap Harbor Freight or Ebay tools is they simple dont work well or break... like a blind bearing puller I tried off ebay some years ago. Its not a rule, just been my experience.
Tools I use more often, I'll upgrade to brands like Motion Pro. All my suspension tools are Motion Pro. The tools I have linked are in my tool box, have been used multiple times, and work on a budget for the hobby mechanic like myself.
You should also consider making yourself a two stroke leakdown tester (different tool and process from the four stroke tool - they are not interchangeable) to ensure your motor is tight when done. You can make them from parts available at any big box store like Home Depot for under $30. Also very useful in diagnosing and repairing your two stroke, not just rebuilds. The Motion Pro version is $260 which I hope to add some day. But the home made ones most folks use work just as well and only take 20 minutes to assemble.
Good luck with the project and keep the thread updated with your progress. We all have gone through this the first time once before and had plenty of questions!
His channel also has a 3 part video series on reassembly. He goes over EVERY step. Have your phone on your work bench, follow along, pause when you have to. Got my YZ rebuilt easy with this!
Pit Row
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