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john munt

wr 426 hot spot on crank should i split the case

24 posts in this topic

was sitting at a light it was about 105 out bike shut off with slight back fire let it cool down started to kick it over felt slight metal to metal binding but  it started shut it off because of that got it home tore down the top end this is what I find should I split the case and replace the bearing ? anything will help

wr 426 crank.jpg

Edited by john munt

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was sitting at a light it was about 105 out bike shut off with slight back fire let it cool down started to kick it over felt slight metal to metal binding but  it started shut it off because of that got it home tore down the top end this is what I find should I split the case and replace the bearing ? anything will help

 

 

Is the rod moving smoothly and freely? That's actually normal discoloration from heating during factory assembly...looks like they replaced the other crank half.

 

Does the motor rotate freely or does it bind?

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rotates freely no binding

There's a side clearance measurement for your rod, might as well give that a check too.

How about when you kick it over? If so, pull your clutch cover.

How's your piston/cylinder? it's possible it may have heated to the point of seizure as well.

Edited by jeffdanger

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everything else looks great besides the valves having normal carbon build up checked the rod play its were it needs to be the barrel has no scaring needs a set of rings though piston is in good shape no sign of over heating there but since I have it off going to put the wisco set in just for good measure just was not sure about that heat spot just didn't look right all I can think now is that the decomp must have got stuck due too it getting hot and probably would not hurt to put a new water pump in

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Does it feel like it binds when you kick it over?

There may be someone else with some more insight. I'd give them a chance to answer as well.

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If you use it for street riding, I would recommend a fan kit to keep that air flowing at the traffic lights...

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there was slight binding when I first tried starting it but after it ran and tried starting it a second time it was gone but I didn't want to ride it without taking the head off and taking a look inside and that is what I hade found which made me come to the conclusion that maybe the barring might have been going causing it to heat up on the one side in turn making it slightly weld itself to the piston rod but with no heat discoloring to the piston rod makes me think that it is the bearing being scared but again not sure thanks for your feed back

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I would say that's normal from crank manufacturing , but it's only on one side . Are those cranks machined solid with one web welded on ? 

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I honestly don't know i'd like to though ,  :thinking: Obviously you have damage somewhere i would rebuild it if i were you , of course if you have the funds but you are halfway there now . It probably had a small seizure, that i couldn't imagine getting any better by just putting it back together with new gaskets. 

Edited by Beau 88

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I would say that's normal from crank manufacturing , but it's only on one side . Are those cranks machined solid with one web welded on ? 

  

 

7u77hb2.png?1?5387Multi piece. My guess is they heat the daylights out of them so they can assemble them quickly.

I would LOVE to work in a YZ manufacturing plant.

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in that case shouldn't the other side have the same discoloring ??

That was my point :) and reason for saying more investigation is needed and if i took it all apart all the bearings would be replaced . 

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in that case shouldn't the other side have the same discoloring ??

Correct...unless it was replaced with a new one. I'm not sure it's common, but I remember doing it with some 250R fourwheeler cranks back in the day with some broken off flywheel threads. I've also heard of some of those older thumper cranks cracking. 

 

To reassemble them, you don't have to heat them til they're blue...i was sayin...the factory probably does it that way so they can do it in 12 seconds 

 

EDIT: I agree though...I'd keep investigating...clutch cover...

Edited by jeffdanger
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7u77hb2.png?1?5387Multi piece. My guess is they heat the daylights out of them so they can assemble them quickly.

I would LOVE to work in a YZ manufacturing plant.

Too lazy to look it up right now , thanks  :p

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Too lazy to look it up right now , thanks  :p

If there's such thing as dirt bike nerds...we are them.

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