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Fusedbrain

2000 WR400 Rear wheel locked up in 5th gear

6 posts in this topic

Hi guys,

I was riding my WR home after a day on the trails and the rear wheel locked up on me in 5th gear. I was pretty close to full throttle. When I finally came to a stop the bike started with the clutch pulled in but the rear wheel was still locked up. I then shut it down and got the bike home on a trailer.

I'm in the process of taking the bike apart for an inspection to find out what broke. I drained the oil and the oil was grayish and cloudy. The filter had some metal particles on it but not much.

I now have the engine on my workbench and when I went to knock the pin out of the piston after I removed the clips. What was interesting and alarming is that the pin was stuck to the piston. The metal from the pin had sort of welded itself to the piston. Now I'm going to need a piston and pin I'm afraid. What I'm wondering is how do I tell if my cylinder is bad? It's got some very light swirl marks in it but I think that's when I was puling the cylinder from the crankcase. There are no up/down score marks anywhere in it and it seems smooth to the touch.

Any of you here ever had this kind of failure? I'll take the rest apart tomorrow after work. I need a tool to remove the stator nut and I'll probably need a puller as well to remove it. I'm going to have to split the crankcase so that I can get to see what happened to the transmission. I'm thinking that it got pretty hot because of the piston and pin situation that I just explained. Any tips and thoughts you might have would be appreciated.

Thanks,

Eric.

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Yikes! That sucks. If you're wondering if your cylinder is pooched you'd have to measure it in several different spots (inside diameter) to see if it's warped or out of limits at all. A siezed wrist pin points to some sort of lubrication failure. Was it siezed into the con rod too? I would think it would have to have been to lock up the rear wheel.

You said the oil was grayish and cloudy, sounds like water contamination.

If it was me I'd measure the I.D. of the cylinder, replace the piston and pin, change the oil and give it a try. If/when it fires up run it for a while then pull the screen and filter to look for metal. If you find more metal you'll want to look deeper into it, but I doubt you will need to.

Frequent oil changes save alot of grief! :thumbsup:

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I don't know if they have have a needle roller or bush in the conrod little end, but on other motors in the past I have had to heat the crown of the piston to expand it enough to allow the gudgeon pin to slip out considering that alloy expands heaps with heat.

Hope this might help

Wayne

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I don't know if they have have a needle roller or bush in the conrod little end, but on other motors in the past I have had to heat the crown of the piston to expand it enough to allow the gudgeon pin to slip out considering that alloy expands heaps with heat.

Hope this might help

Wayne

No its not a bearing or a bush at all....the pin just rides in the rod small end and this is the weak link of the 400 engine. I replaced my 400 rod with a 426 rod which is larger on the small end...look like you are going to have to do the same. Replace the counterbalancer key while you are at it.

Consider yourself lucky the that rod did not break.

The cylinder sounds fine but if you go 426 you can replace it with an ebay 426 cylinder and piston!

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The piston pin is a press fit in the piston. You need a puller to remove it. Don't bang it out with a hammer! You can make a puller from a bolt two washers and a socket and nut. Did you ever find the problem? Grey oil means your water pump seal was leaking coolant into the crankcase which is typical on higher mileage YZ/WR's.

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