Special tool(s) needed to split the case?


6 replies to this topic
  • flyinguitars

Posted August 23, 2006 - 07:53 AM

#1

My neighbor is having a problem with 3rd gear on his 2 stroke 05' yz250. It only has about 20 hours.
He's had a couple of crashes from over jumping and flat landing.....we're assuming that he bent a shift fork during one of the landings. When shifted into 3rd, it grinds then jumps to neutral.
He pulled the engine out of the bike and has it on his work bench. I've never been into the transmission of these bikes and was wondering if there are any special tools needed....ie - gear puller, bearing puller, arbor press, etc...?
He asked me yesterday if I knew how to take the trans apart....I told him "no" but I'd check for tips here.
Thanks,
Mike

  • grayracer513

Posted August 23, 2006 - 08:09 AM

#2

Most of the time, a good mechanic can work around not having the specific tools listed, but in their absence, good skills and common sense must prevail. Some tools, such as a flywheel puller, can't really be done without, and are worth the money to buy, or to have that task done professionally. But for the most part, the job can be done with just the basic stuff and, occasionally, a little ingenuity.

BTW, the problem is worn locking dogs on the sides of the two gears that lock 3rd to the trans shaft. The fork will almost certainly be damaged, but is usually a result, rather than a cause.

  • flyinguitars

Posted August 23, 2006 - 09:11 AM

#3

Most of the time, a good mechanic can work around not having the specific tools listed, but in their absence, good skills and common sense must prevail. Some tools, such as a flywheel puller, can't really be done without, and are worth the money to buy, or to have that task done professionally. But for the most part, the job can be done with just the basic stuff and, occasionally, a little ingenuity.

BTW, the problem is worn locking dogs on the sides of the two gears that lock 3rd to the trans shaft. The fork will almost certainly be damaged, but is usually a result, rather than a cause.


Thanks!....He has a flywheel puller at his shop, so we'll be covered there. i just got back from vacation so I haven't had time to devote to a plan for his trans......so I figured I'd cheat a little by aking here :thumbsup:
Are the locking dogs the three "nubs" that protrude from the sides of some of the gears?
Thanks!
Mike

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  • grayracer513

Posted August 23, 2006 - 09:56 AM

#4

Are the locking dogs the three "nubs" that protrude from the sides of some of the gears?

Yes, that's them.

  • flyinguitars

Posted August 23, 2006 - 10:52 AM

#5

Yes, that's them.


OK, thanks... I haven't been inside one of these transmissions before, so this will be a first. Typically, are there several parts that need to be R&R'd for this type of problem?....like a paticular gear(s), fork(s), etc...?
A couple others questions - Is this a common failure? What could be the cause?
Thanks!
Mike

  • grayracer513

Posted August 23, 2006 - 12:55 PM

#6

Shifting in a generally sloppy, non-assertive manner that allows the gears to clash or grind as they engage is one cause. Just plain old wear is another. The locking lugs are originally made with a slight undercut, or dovetail, to make them hold in under pressure. As this undercut wears, it reverses, and the gears start forcing themselves apart, which in turn bends the shift fork. If the shift fork gets bent first, it can cause the problem by incompletely engaging the gear in question, giving the lugs a reduced overlap area to hold with.

There is a lot of stuff on the outside of the cases, but inside, there is only the crank, two gear shafts, and the shift cam and forks, which I suppose is enough. When only one gear is misbehaving, you would typically need two gears on one shaft, and the associated shift fork. In this case, it's 3rd and 5th on the output shaft (counter shaft) and fork 3, I believe. But you should carefully examine the lugs and other surfaces of the remaining gears for similar wear that has not yet reached the point of causing a problem, and replace those too.

  • flyinguitars

Posted August 24, 2006 - 09:50 AM

#7

Thanks for the tips and your time grayracer513! We'll probably open it up, inspect everything, and order parts this weekend. I'll try to get some pics posted here for future reference.
Thanks!
Mike





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