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What To Check in YZ250 Bottom End

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About to split the cases on my 2005 YZ250 as it has started vibrating more than normal with RPM, plus I would like to go through it to know where I stand. Crank is getting sent to Ken Oconnor and will be getting new KOYO crank bearings. On the transmission side, what should I inspect? As in what particular areas? Any key items need to be replaced?

I would like some advice on the best way to pull the cases together also. I will measure the gap on each side of the crank so I know how far to pull in the crank on the first crank half, but how do you pull the other case half on and have no residual stress on the crank or bearings after torquing the case bolts?

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Vibration has more to do with engine mounts than with crank although the latter also causes vibration when not running true. The seals come to mind. 

Tranny: check all bearings and look for rounded dogs on the gears. 

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2 minutes ago, arnego2 said:

Vibration has more to do with engine mounts than with crank although the latter also causes vibration when not running true. The seals come to mind. 

Tranny: check all bearings and look for rounded dogs on the gears. 

All of the engine mounts were checked for torque, even swingarm bolt. Not loose.

What is the expected life of tranny bearings? About the same as crank and crank bearings or longer?

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6 minutes ago, arnego2 said:

Far longer, mine have hundreds of hours. I'm in the third crank so far.  

Awesome, I will check out of caution anyway. What is your preferred method for removing crank bearings and leaving transmission bearings (if using heat)?

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I use a little heat and a large socket/sledge method and they pop out with a few taps on a 4lb sledge (not massive force).

Along with doggs and bearings check the shift forks for wittness marks of wear. C-10 usually the worst. 

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7 hours ago, arnego2 said:

Vibration has more to do with engine mounts than with crank although the latter also causes vibration when not running true. The seals come to mind. 

Tranny: check all bearings and look for rounded dogs on the gears. 

No man, it's fine. Send it!

20170708_175715_zpsbggvhfcv.jpg

This was my gem. Found this carnage this past weekend.

If you were not the first owner of the bike, I highly recommend replacing all bearings and seals if they feel like they have the slightest bit of drag or hesitation. This way, you'll know what's what and how many hours on the bottom end. It's what I'm doing to my poor donkey. 

Edited by AnimalMother85
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After removing the clutch side seal, I found this gouge in the OD sealing surface of the seal. I do not think I did this as I use a hook to pull the seals out, although anything is possible.

Is this a major issue? Can I just put some yamabond in the scratch and OD of the seal to make sure it doesn't leak?

IMG_3602.JPG

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4 minutes ago, LumberjackLloyd said:

After removing the clutch side seal, I found this gouge in the OD sealing surface of the seal. I do not think I did this as I use a hook to pull the seals out, although anything is possible.

Is this a major issue? Can I just put some yamabond in the scratch and OD of the seal to make sure it doesn't leak?

IMG_3602.JPG

Is it deep? Otherwise no bige deal. If it is deep, yes a little bond will help... 

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Not severely deep, because it is a wider scratch it makes it look deeper in picture. I will take off any sharp edges with some crocus cloth and use Yamabond upon assembly.

Do you run across many cases like this with all the rebuilds you do @P84ONE ?

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1 minute ago, LumberjackLloyd said:

Not severely deep, because it is a wider scratch it makes it look deeper in picture. I will take off any sharp edges with some crocus cloth and use Yamabond upon assembly.

Do you run across many cases like this with all the rebuilds you do @P84ONE ?

I have found cases that had little fish hook gouges that were only in the center of the sealing surface. Like some knucklehead was digging at the seal with a hook. Nothing that went from one side to the other. seals do have a little layer of "flexible" rubber on the outside to fill in slight deviations, so if its deep, it possibly will be a problem, if shallow a smear of bond wouldnt hurt.

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Here is a better picture after hitting with crocus cloth.

It seems that it did not really get the edges, but did go most of the width of the sealing surface. Is there any JB weld type product I could use to fill in the scratch that I could trust? I am a perfectionist, so little things like this bother the heck out of me.

 

IMG_3603.JPG

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49 minutes ago, LumberjackLloyd said:

Here is a better picture after hitting with crocus cloth.

It seems that it did not really get the edges, but did go most of the width of the sealing surface. Is there any JB weld type product I could use to fill in the scratch that I could trust? I am a perfectionist, so little things like this bother the heck out of me.

 

IMG_3603.JPG

That doesn't look bad at all. If you do JB, you might go the other way. I would leave that, put a smidge of Yamabond, it's not going to leak. 

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After a long day at work, I dropped the crank into the case. Out of habit from my old 125, I dropped it into the clutch side case and not the flywheel side.

Will this cause alignment issues? If so, will pressing the crank out of the crank bearing damage it to the point of replacement? I have always tried not to side load ball bearings, but I want to try to avoid buying and replacing another $35 bearing...

Edited by LumberjackLloyd
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3 minutes ago, LumberjackLloyd said:

After a long day at work, I dropped the crank into the case. Out of habit from my old 125, I dropped it into the clutch side case and not the flywheel side.

Will this cause alignment issues? If so, will pressing the crank out of the crankcase bearing damage it to the point of replacement? I have always tried not to side load roller bearings, but I want to try to avoid buying and replacing another $35 bearing...

That's the way you wanna do it :thumbsup:

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