how to tell if a crank assembly is good??????

21 replies to this topic
  • bakeyz426f

Posted September 10, 2009 - 05:29 PM


got the cases split and they look good
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wondering how to check to see if the crank is still good.
it has extremly little to no movement side to side or up and down. think ill see if the engine place by me can check it.
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  • mxmaddman

Posted September 10, 2009 - 06:39 PM


The crank teeth look like they have some wear, but its really hard to see from the pics. A crank is not something you can really eyeball either. Take it to a shop and have them see if its "true". It doesn't look too bad at a glance. However if its stock its not something i would reuse on a 01

  • bakeyz426f

Posted September 11, 2009 - 01:45 PM


it was bought new in 05 so only ridin for four years. i called two dealers and their service guys said they would be about 100% sure that the crank would be fine based on what happened. timing skipped and broke valve on piston. one guy said same thing happened to him ,his was fine it his 450. they said its unuasal that it would get bent and if it was you would be able to tell. i think im going to reuse it. the teeth are in good shape with normal wear. ill replace the bearings and get new seals and lock washers for the rest of the bottom end. do i just use a big socket and hammer out bearings? one my first picture of the case is the rough spot around the bearing somthing to be conserned about? should i smooth it over with jb weld or somthing?

  • Pincushion

Posted September 11, 2009 - 02:28 PM


Might as well have it rebuilt while its out. My local builder charges $35 plus parts for a crank rebuild/truing. Cheap insurance from having to split the cases again in 6 months.....

If the cam chain gear is showing any wear then dont even bother putting that crank back in.

Why did it jump time? Chain too worn?

  • sacfelix

Posted September 11, 2009 - 02:45 PM


I would have the crank rebuilt since it's out and throw in some new bearings.

  • yz007f

Posted September 11, 2009 - 04:20 PM


I would for sure change the lower rod bearing + rod if it showed any wear.. Plus make sure the crank is true, also like said above if the teeth are worn then there is no point to reuse it!

  • bakeyz426f

Posted September 11, 2009 - 07:30 PM


do my teeth look worn? what do the teeth look like when worn, sharp?

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  • bakeyz426f

Posted September 11, 2009 - 09:14 PM


it jumped ethier from a worn chain or bad tensioner

  • rufusz

Posted September 11, 2009 - 09:33 PM


Use your cameras macro function for such closeups so you will get nice clear pictures, not such blurred ones, that you can't tell anything apart on them :busted:
And try to not use the flash for such shiny surfaces. Better take it outside if the sun shines or just use some other lighting.

  • bakeyz426f

Posted September 11, 2009 - 09:58 PM


these any better? wat do u think?

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  • mxmaddman

Posted September 12, 2009 - 05:53 AM


Too blurry, I cant see anything. If you at least stand back farther you can crop in. It will be sharper if it is allowed to focus. It cant focus that close.

  • rufusz

Posted September 13, 2009 - 12:07 AM


Macro function? You didn't use it.... It's icon is a tulip if you don't know what I'm talking about.

  • TD-3

Posted September 13, 2009 - 03:00 AM


If I where that far into the engine, I would replace the whole crank assembly. The difference between having it rebuilt, and new, is probably around $100 to $150...........easy decision to me.

  • bakeyz426f

Posted September 13, 2009 - 04:38 PM


took the crank to a dealer and the repair guy looked at the teeth and said a few teeth have some wear. he said i could use it but if i was plnning on keeping the bike to replace it. he had a 2006 yz450f leftover for 4300. i figure he will take 3500 this winter when no one buying bikes. starting to wonder if i should fix the 426 or just stop the bleeding. i estimate 2 grand to fix the 426. is 4300 too high on a left over 2006 yz450f

  • azlodaniel

Posted October 19, 2009 - 10:29 AM


I would be careful with the Cranks, I had a valve drop on my 06 and it bent the rod just slightly. you couldn't tell by looking at the crank but if you put the piston and tdc, with the Cylinder on you could see the difference in the height of the piston on the side that was hit, compared to the side that didn’t get hit by the valve.

Just my 2 cents.

  • Florida_426

Posted October 19, 2009 - 02:01 PM


If you have a Yamaha shop manual it has the tolerances for the crank and rod so you could check them. the macro visuals of the cam sprocket teeth is a good idea. Maybe Grayracer will see this thread and put in on the condition.


  • grayracer513

Posted October 19, 2009 - 02:04 PM


If the engine dropped a valve, broke the piston, and destroyed the head, the crank was almost certainly damaged.

  • Aka.Goose

Posted October 19, 2009 - 03:56 PM


$4300 is high for an 06...
Keep in mind the crank tolerances are very very small...
I had mine skip time (tensioner failure) and had piston slap the head/valves...
I got lucky and got a brand spanking new motor for $2000
with CDI, carb, cables, pegs, kick start, everything...
I then sold off the stuff I didn't need and basically got my money back...
You can still find deals on ebay (people parting bikes out)
that may be a better deal than fixing your old motor...
Then sell your old cases, etc...
I saw new motors on ebay for $2500 when I got mine, but
I just did a quick search right now and only saw some used ones...
Just another route to think about...

  • bakeyz426f

Posted October 19, 2009 - 04:12 PM


that bikes long gone now guys. i sold it for 750 bucks and stopped the bleeding. i now have an 01 wr426f. i put the 02 yz426f suspension on it though. (forks and shock) bought those parts from the guy who bought it back for 150 bucks. picked up this pretty nice 01 wr426f for 1600. i think it might still have the throttle stop though. how do i check to see if it does?
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  • 02WR426Cali

Posted October 19, 2009 - 04:24 PM


The throttle tube will only move like a half inch or so and will feel much different than your YZ. Also get a manual so you can find out where some of the parts are. The throttle stop is a allen head bolt on the upper back right part of the carb behind the plastic cable cover. On the right side of the bike it will be on the upper left of the carb while you look at it. Take it out measure it, then look through that shiny new manual to get the specs. Or do some searching for the free mods on the 426 and try to do all or most of them and you will find that this WR is just as powerful as your YZ.

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