05 WR450 chain slapped out a piece of crankcase, options?

21 replies to this topic
  • AMS2015

Posted August 09, 2016 - 10:28 AM



Got a sweet 2005 wr450f that I used as a daily sumo. Love the bike, but to use it to its full potential took it off-roading in the weekends. Last weekend however the chain snapped and took a piece out from the crankcase, exactly where the clutch cable connects to the block. I noticed it immidatly as there was no drive and when turned my head down to look at the sprocked i saw oil spitting out. 

As I saw oil gushing out i turned off the motor, so the internals should be ok. What are my opitions now? Since there is a piece already out of the crankcase any chance of an easy plastic weld repair is out of the question?

So Im guessing I got to strip down the whole engine and replace the crankcase? However from what I've read so far, people have said i should replace both sides, or can I just change the left side that has a hole in it?

Attatched some pictures of the damages aswell.

Any help and suggestions are highly appreciated.

Greetings from the Netherlands!

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  • stevethe

Posted August 09, 2016 - 10:36 AM


Big bummer center cases are a matched pair.

Edited by stevethe, August 09, 2016 - 10:37 AM.

  • bikedude987

Posted August 09, 2016 - 10:42 AM


might be able to have it welded, but it's thin there and you may have to restore the bearing and seal bore afterward.  


Best bet is a new set of cases, but you're splitting cases either way, so guess it's time to get to it... 


I may have to beef up the case protector on some of my bikes if that's all the stocker was good for.  How fast were you going when this happened?

  • stevethe

Posted August 09, 2016 - 10:52 AM


Before you split the cases there is a very low temperature aluminuim welding rod that might work. The problem will be trying to get the outside diameter of the seal to work. Take it to a very good welder and ask. I have had cases welded in the frame with the low temp rod.

  • AMS2015

Posted August 10, 2016 - 03:18 AM


Thanks for all the replies.

I managed to source a bottom end locally for a lower price than i would just pay for the empty cases shipped from overseas. Hopefully i can just swap the top end to it and it will work. Although I have a question inregards to this. My bike is an us model and the bottom end is a eu spec one. There shouldnt be any difference right?

and bikedude, this happened going around 30kph, 2gear, with a whack of throttle, although not wide open. Surprised me aswell. 

  • Summit

Posted August 10, 2016 - 03:57 AM


What caused that, how did that happen?

  • knuckleduster271

Posted August 10, 2016 - 06:11 AM


Ive seen cases broken numerous times from chains coming apart.
I bought a plastic case saver because the oem one is about useless for absorbing any kind of shock.

Edited by knuckleduster271, August 10, 2016 - 06:12 AM.

  • toten

Posted August 10, 2016 - 06:26 AM


What kind of chain were you running? Did a link break, did a master link fail, did it fall off the sprocket, or what exactly?

  • AMS2015

Posted August 11, 2016 - 01:52 PM


What kind of chain were you running? Did a link break, did a master link fail, did it fall off the sprocket, or what exactly?

To be honest i dont even know what chain it was, it came with the bike, but i converted it to sumo and for this i bought a new chain. For offroading i used the old one and the masterlink failed. 

What kind of case saver would you guys suggest to prevent this from happening again?

  • Summit

Posted August 12, 2016 - 04:53 AM


Was the masterlink a clip type?

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  • knuckleduster271

Posted August 12, 2016 - 06:10 AM


I run the tm designworks-


  • AMS2015

Posted August 12, 2016 - 07:08 AM


Yes the masterlink was a clip type.

Got a used bottom end today. Unfortunetly wont have time right now to work on the bike for this week.

I probably need new gaskets and what else? . And should i also change the piston if im digging in or judge when i see it?


  • stevethe

Posted August 12, 2016 - 02:18 PM


Cam chain and you probably should put piston and rings in it.

  • AMS2015

Posted August 15, 2016 - 11:53 AM


Sorry, if its a stupid question, but why do you advise me to change the cam chain?

Also, if i decide to change the piston, how do I know which size to order?

This thread will keep going as this is the first time for me to do engine repairs as substancial as this. But we all got to learn somehow, so a bunch of questions and pictures will soon follow!

  • stevethe

Posted August 15, 2016 - 12:14 PM


Cam chains on old bikes wear out and can skip teeth and cause major engine damage.

You would need to take your barrel to a competent machinest to determine the piston size.

  • DeepPurplishBlue

Posted August 15, 2016 - 12:41 PM


Cam chains on old bikes wear out and can skip teeth and cause major engine damage.

You would need to take your barrel to a competent machinest to determine the piston size.


If it is a stock Yamaha cylinder, there is only one size to order for piston and rings...  standard.     The cylinder is plated

and is not designed to be bored or receive oversized parts.


If the cylinder measures out of spec it will need to be replaced.     Depending on how worn/damaged it is there is the

possibility of replating but the cost is normally pretty close to a new cylinder so I usually just go for the new one.

  • stevethe

Posted August 15, 2016 - 01:14 PM


Yes if it isn't a big bore or some such other. Check it for bore size against the shop manual to see if it is worn out or a big bore.

  • knuckleduster271

Posted August 15, 2016 - 07:37 PM


Stock bore on a 450 is 95 mm iirc.

  • AMS2015

Posted August 20, 2016 - 12:01 PM



However when looking for a piston, there are still different sizes on offer, that is the pistons are categorized as A (94.93)  B (94.94) C D (Vertex pistons) , how would I differentiate between these? 

  • knuckleduster271

Posted August 20, 2016 - 02:22 PM


Measure your ring end gap or have your cylinder bore mic'd- if your close to the service wear limit then use the larger piston

Edited by knuckleduster271, August 20, 2016 - 02:23 PM.


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