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Handy Andy

07 yz450f crank bearings shot

28 posts in this topic

I took the flywheel cover off to figure out the noise my bike was making and found that I can grab the flywheel and pull back and fourth (axial play) on the crank quite a bit which is causing the noise. It looks like the crank moves within the inner race of the bearing. Is this typical? I figured the balls had just worn and created play in the bearing, I didn't expect the crank to slide back and forth in the bearing. I was hoping to replace the bearings and be good...am I looking at a whole new crank? Thanks.

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Before we can really have this discussion, we need to know how much end play you actually have.

Bear in mind that normal annular cartridge ball bearings do usually have a fair amount of end play to begin with, ant the real measure of their condition is is better taken as the vertical (radial) play. How much does the crank move up and down?

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Axial end play: .016"

Radial: .003-.004"

I'm sure that radial is out of spec and obviously axial is but as I said when you pull the crank back and forth it makes a clunk sound consistent with the clunking sound when it's running. I'm just trying to avoid having to buy a whole new crank but if that's what I gotta do then so be it. I'll tear it apart this weekend and evaluate but any educated opinions beforehand are appreciated.

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.004" is pretty loose. The main bearings can be replaced without replacing the crank, of course, but you should check the rod bearing against the specs, too. The specs and measurement method are in the manual.

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Have you ever seen or heard of an instance where the nut on the crank on the clutch side comes loose causing excessive side to side movement of hte crank?

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Yes, but in that case, the inner bearing races would not move with the crank. Besides, they should be a somewhat pressed fit, and you still have the radial looseness.

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I too noticed on my 250f that my crank was able to slide back and fourth within the inner bearing race. I saw it the first time I replaced the timing chain and posted about it being normal or not too. The only answers I was real able to get were that almost everyone who had split their cases said that the crank pulled out of that bearing very easy, didn't need to be forced or pulled. I had some side to side play and could barely feel some radial play I decide to leave mine alone since it didn't sound any worse then my friends brand new 450. That was 50+ hrs ago and right now I have it apart for the timing chain again. The play doesn't seem to be any worse then it was 50 hrs ago.

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Hmm that's quite interesting. I'll have to listen to another one to compare it... It sounds abnormal to me though. My 250f and 426f don't sound like that.

I too noticed on my 250f that my crank was able to slide back and fourth within the inner bearing race. I saw it the first time I replaced the timing chain and posted about it being normal or not too. The only answers I was real able to get were that almost everyone who had split their cases said that the crank pulled out of that bearing very easy, didn't need to be forced or pulled. I had some side to side play and could barely feel some radial play I decide to leave mine alone since it didn't sound any worse then my friends brand new 450. That was 50+ hrs ago and right now I have it apart for the timing chain again. The play doesn't seem to be any worse then it was 50 hrs ago.

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I just started the job of replacing the timing chain on an 08 450 that has 40 hrs on it, not ridden very hard and very well maintened so I'm confident there's nothing wrong with the crank or bearings in it. The crank has the same side to side play as my 250 and makes the same clunk noise, but it takes a little more force to get it to move when I push and pull on it and I don't think I can feel any radial play. I don't have a puller for this flywheel yet but when I get it off I let you know if the crank is sliding within the inner bearing race.

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I just started the job of replacing the timing chain on an 08 450 that has 40 hrs on it, not ridden very hard and very well maintened so I'm confident there's nothing wrong with the crank or bearings in it. The crank has the same side to side play as my 250 and makes the same clunk noise, but it takes a little more force to get it to move when I push and pull on it and I don't think I can feel any radial play. I don't have a puller for this flywheel yet but when I get it off I let you know if the crank is sliding within the inner bearing race.

Can you measure the side to side play and let me know how much there is? I'm pretty convinced that the play and resulting sound is abnormal. I pulled the side cover off to see if the nut was loose on the crank and it wasn't.

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When I said side to side play I ment the axel end play, just want to make sure we're talking about the same thing. The only measuring tool I have at home is feeler guages. How did you measure the axel end play on yours? Did you use a dial guage for the radial play?

I put the bikes side by side last night. I'd say the axel end play was the same, I mentioned before that I thought the 450 took more force to get it to move in and out but now I'd say their the same. There is a definated thud or clung sound when I do it on the 450. The clunck is similar sounding on the 250 but maybe more click then clunk sound. But I can hear a lot of noise from clanging between the drive and driven gears for the balancer when ever I move the crankshaft. If I grab the balancer and rotate it back and fourth I can feel way more slop between the gears then I can on the 450 and it makes quite a bit of noise. 450 hardly any noise. I'm sure on the 250 alot of the noise I'm getting is form gear lash between those 2 gears when its running. The little bit of up and down play I could feel in the 250 has me worried now that I can't feel any at all in the 450, and it also concerns me about yours too. I think I'm going to split the cases on the 250 tonight and at minnimum replace the main bearings and most likely the crank as long as I'm in there. I'll let you know what I see. I should be able to tell if the crank is wearing were it sits in side the bearing.

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Yes, I'm talking about the axial end play, I measured it with a dial indicator. I pulled the engine and am going to disassemble it this week some time to assess the situation.

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I split the cases and pulled the crank last night. Crank pulled out of both bearings with out a puller, just my hands. The fit was snug but it didn't take much force. The main bearings feel real smooth when I turn them but they fell like they have to much play if I grap the center race and rock it back and forth. The crank looks good still but I'm replacing it. I'm realy glad I went in there though cause a transmission bearing for the main axel barely spins, very rough. I'm sure the axel was spinning inside the bearing so hopefully thats not to worn cause thats $90.

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I split the cases and pulled the crank last night. Crank pulled out of both bearings with out a puller, just my hands. The fit was snug but it didn't take much force. The main bearings feel real smooth when I turn them but they fell like they have to much play if I grap the center race and rock it back and forth. The crank looks good still but I'm replacing it. I'm realy glad I went in there though cause a transmission bearing for the main axel barely spins, very rough.

Left side, I'll bet.

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Yep, the one right behind the push lever, but after inspecting the others closer a couple of them felt a little rough so I'm replacing them all.

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I was talking about this with a friend and he told me that the two halves of the crank need to be pressed together the correct amount to adjust the axial play. He said if I'm measuring .016" play now then find out what it's supposed to be (say .003 just as a guess) pull the halves apart (professionally done) by .016-.03 = .013". Then put in new bearings and put back together.

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Your friend is wrong. The end play, or side clearance, of the connecting rod can be set this way on some cranks, and some others have shouldered crank pins that have the two halves of the crank pushed together until it bottoms.

The axial play in the crankshaft is controlled entirely by the internal clearance in the right side main bearing. The main bearings are pressed into the case and held fast by retainers. The crank axles are a snug slip fit to the bearings, and what locates and holds the crank in place is the primary drive gear nut. The torque on the nut clamps the right side main bearing between the crank cheek and the drive and balancer gears, holding the crank in that bearing to locate it axially.

Since there is very little thrust (ideally none, but realistically very little) placed axially on the crank, the axial play is not really a matter of any concern except as an indicator of the condition of the right main bearing and/or when it starts bumping into things. That's why you don't see a specification or wear limit for it.

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OK, is it possible that the bolts for the retainer on the right side have backed out and the bearing subsequently did the same? There's no shim or thrust washer or anything like that behind the primary gear, correct? I'll disassemble tomorrow and figure out what's wrong.

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No shim or washer. It is possible for the retainers to come out, and it has happened. However, there are two independent retainers on each bearing, the screws are held in with red Loc-Tite, and there isn't room for the screws to back all the way out with the crank in the engine without rubbing on the crank and making a LOT of noise.

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