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Crank and bearing question

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Hello guys,

2006 KX250

Doing my first bottom end rebuild and have a question. 

 

I baked my cases, started at 200 degrees, and had to keep going up all the way to 350. None of the seals would budge until I hit 350 then they all came out with light taps of a socket and hammer. All of the new bearings dropped right in (crank, transmission) without any issues. On my particular bike, the seals have to go in first. I was in a bit of a rush and never oiled/greased the seals. Once they were all in and the cases cooled down, and checked them all out and the crank and transmission bearings WITH seals were a little hard to turn. They spin nice and smooth, just a little stiff. Is this normal with new bearings/seals? I am worries if I install the crank with the bearings like this it will also be stiff. 

 

None of the bearings look visually out of place/ misaligned. If anyone has any info on this that would be great,

 

Thanks

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I've got the exact same bike as you, and have just done a full top and bottom end on mine as well. I used assembly lube putting everything back together, but if you got your bits to go in nicely without it - we will ultimately end up in the same place. This is because my bike will dilute and/or burn off the extra lube I've used during the run in, and will then utilise the transmission fluids and pre-mix. Yours won't have to burn off extra lube, it will just go straight to using the transmission fluid and pre-mix. If you know you torqued everything to spec and checked that clearances and tolerances are to spec like I did - you're good to go.

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3 minutes ago, ItsJuniorJ said:

I've got the exact same bike as you, and have just done a full top and bottom end on mine as well. I used assembly lube putting everything back together, but if you got your bits to go in nicely without it - we will ultimately end up in the same place. This is because my bike will dilute and/or burn off the extra lube I've used during the run in, and will then utilise the transmission fluids and pre-mix. Yours won't have to burn off extra lube, it will just go straight to using the transmission fluid and pre-mix. If you know you torqued everything to spec and checked that clearances and tolerances are to spec like I did - you're good to go.

What I was worried about was having the bearings not seated properly, but I would think these would be visually out of place.

 

Yes I will use ATF and premix to start lubing stuff up. Hopefully the bearings free up a little but 

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Out of curiosity, roughly how hot were the casings when you dropped the seals in? If they were too hot, that's not good for your new seals. That said, if you can spin everything with just your hands, you really should be fine!

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Like I said I had to get the heat up to 350 in the oven for the bearings to drop out. If you just did the same bike then you know the seals have to go in before the main bearing. So the cases were pretty close to 350 when I dropped the seals and frozen bearings in.

Even if the new bearings are a little stiff (but smooth) it is nothing to worry about?

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Awesome, I will hopefully get the crank in tonight when I get home. 

Another question,

Do you attach the shifting mechanism to the transmission prior to attaching the cases to make sure it shifts good? I have all of the gears / forks in as per the manual and it all move together smoothly. I just want to make sure i do this right the first time

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2 hours ago, motorboatinjesus said:

 

Even if the new bearings are a little stiff (but smooth) it is nothing to worry about?

good to go 

2 hours ago, motorboatinjesus said:

 

Another question,

Do you attach the shifting mechanism to the transmission prior to attaching the cases to make sure it shifts good? I have all of the gears / forks in as per the manual and it all move together smoothly. I just want to make sure i do this right the first time

i did this just to make sure , do it for your own piece of mind

on a side note , 

the 2 dowels that align the 2 case halves when putting together , put them in the holes on the bottom case . one of mine feel out from the top case and got kicked side ways and i had to push the cases apart again and remove all the sealant and then reapply it because it starts to skin quickly .

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10 minutes ago, kxrob said:

good to go 

i did this just to make sure , do it for your own piece of mind

on a side note , 

the 2 dowels that align the 2 case halves when putting together , put them in the holes on the bottom case . one of mine feel out from the top case and got kicked side ways and i had to push the cases apart again and remove all the sealant and then reapply it because it starts to skin quickly .

Now that I think about it I actually couldnt find my dowells...

 

That is a good point though. I am going with the freeze the crank, heat the inner race with a hot socket approach so I need everything ready to go quickly. 

 

I appreciate the help guys

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31 minutes ago, motorboatinjesus said:

Now that I think about it I actually couldnt find my dowells...

 

That is a good point though. I am going with the freeze the crank, heat the inner race with a hot socket approach so I need everything ready to go quickly. 

 

I appreciate the help guys

i just heated the cases up to 200 on my bbq and froze the crank in freezer over night and had no issues assembling and i did it on a 100f day 

you will need those dowels

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I put seals in the cases when they are cold but then I put em in a 400° oven so the temp your at is not a problem . The only time I've ever seen a problem with heat is when people use torches , broken cases ,burnt seals etc

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Yeah that makes sense.

 

Those who have been in my situation before, would you recommend throwing the cases back in the oven to install the crank? Or only heat the inner race with a hot socket so I can get the liquid gasket on?

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I put just the right side back in the oven so I can pop the frozen crank in the right side after  that let cool down before I use case sealer and I use longer bolts in several places to pull the cases together to get the left side in I don't use heat on the left side .

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44 minutes ago, Greenwrench said:

I put just the right side back in the oven so I can pop the frozen crank in the right side after  that let cool down before I use case sealer and I use longer bolts in several places to pull the cases together to get the left side in I don't use heat on the left side .

I have read about this online for hours.. and most people said never to use the bolts to pull the cases together. You havent had any issues doing it this way?

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You can buy a crank installer tool. Uses the crank  to do the pulling , and I've probably done 40 bottom ends (never a problem using bolts to pull em together , obviously you need to use caution in doing it evenly , in  all reality it doesn't take much pressure to pull that crank into the bearings 

Edited by Greenwrench

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