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fraser

'10 YZ450 missing gears

11 posts in this topic

Earlier in the year I posted a problem with my 450 finding a false neutral going up through the box. I found the post but it wouldn't let me reply to it for some reason. As I wasn't the only person to suffer this I thought some people might like an update.

Ok, after a big off a few weeks back and a concussion I decided to have a few weeks out from racing. Ideal chance to get to the bottom of this gear shift issue. Despite being told on here it was basically operator error the problem has been getting steadily worse. Last cpl of weeks it would find a false neutral between 2 and 3rd I think, most times I change unless I really clunk it hard, but you forget to do that in the heat of battle.

So, faced with quotes of around $400 labour from Yamaha dealers just to look in the gearbox I decided to do it myself. It was a bit daunting, particularly getting it back together correctly but I did it with no parts left over..

Anyway this is what I found- nothing much in there to look at apart from a bit of polishing between the dogs on these two gears, wear was minimal, and a couple of scuffs on the back of this fork which to me indicated maybe it was bent though again not by a visible amount.

So I replaced both gears and fork for around $200 and put the whole thing back together. Nervously went out to test it yesterday but I'm pleased to report that no more issues with missed gears. Bike ran perfectly, the problem has gone away. I'm amazed that such a small amount of wear could cause it to miss gears, but there you go. So anyone else finding that neutral, here's your problem-

gear4.jpg

gear3.jpg

gear2.jpg

gear1a.jpg

gear1.jpg

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I don't want to burst your bubble, but none of that wear will have contributed to missing gears. The problem that you unwittingly corrected would have been a binding condition related to the replaced shift fork, either between the shaft and the crankcase, or the way the drive peg on the fork ran in the cam. I may even have been something other than that that you fixed without realizing it, but the illustrated wear did not cause it. I've had any number of them apart with far more wear on them than that, and not one problem with missed shifting as a result.

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Fair enough, not worried about bubble bursting! However there were no other signs of wear or seizing or anything in there, and its now working so as far as I'm concerned I'm please with the result. But I guess if it starts missing again I'll have to look elsewhere. I wonder why the other two forks have bearings on but this one doesn't? Maybe it was sticking in the cases as you say.

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I'm not a big fan of the approach Yamaha takes to the shift forks, actually. I think that Honda and others have the right idea by having the rails fixed between the cases and the forks sliding on the rails, rather than the rails being fixed to the fork and sliding in the case. I understand the reasoning, but I disagree, nevertheless.

But most of the time, they wear in and work well after an initial period of being a bit sticky. Probably all yours would have needed would have been time, but there may have been a fault with something, too.

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The fault developed from 35 hours and got progressively worse to the point at around 60 hours where I went in, so I don't think it could have eventually gone away, but who knows. Thanks for your thoughts anyway.

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The fault developed from 35 hours and got progressively worse to ... around 60 hours ...
That does make it a little different. Odd.

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mine was doing that to at about sixty hours i thought it was rider error and my son kept riding it guess what exploding transmission now i need new motor busted cases all trans broke cylinder and top end destroyed im done with yamaha now i need to buy new motor so i can sell this pos!

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mine was doing that to at about sixty hours i thought it was rider error and my son kept riding it guess what exploding transmission now i need new motor busted cases all trans broke cylinder and top end destroyed im done with yamaha now i need to buy new motor so i can sell this pos!

I don't think you're going to find a more reliable brand for 450cc mx bikes then Yamaha. Especially when you continue to use your machinery even when you know there is a problem.:eek: But you're right, that must be Yamaha's fault.

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i dont know but after 60 hours with those kind of problems i have had yamahas 4ever and none of them have been reliable i should of known better than to continue with that brand you are right.

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was it hitting a fake neutral between 2nd and 3rd then skipping to 4th from 2nd? i have an rm and it seems to be doing that but only when you dont back off the revs, im still using the clutch though

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