Big end failure

Lately my '98 WR400 began getting more and more engine noise. After 2500 hard trail miles since brand spanking new, I decided I better investigate (especially after riding a YZ426 with only 600 miles on it and hearing the difference). I removed the flywheel cover, and found excessive play and a clunking noise while rotating the flywheel back and forth by hand. I suspected the rod bearing and after dissasembly confirmed it. I change my oil frequently (less than 500 mile intervals), never have run low or without oil, never submerged the bike in water and introduced dirt into the crankcase, service the bike regularly, and have never had to shim my valves since it was new. (I'm still on my orginal brake pads!) The top end still looked very good, but the rod bearing was quite loose. I do not use a synthetic oil, and the dealer thought because I ride single track in Michigan, that I may have been breaking down my oil from excessive heat (low speed). However, the top end does not show any sign of poor lubrication. Is this typically what I can expect for rod bearing life? Do I need to run synthetic oil (probably will anyway)? Did I get a deffective engine (It was one of the first '98 WR400 to arrive at my dealer)? I'm quite dissapointed that Yamaha seems to blow me off when I call, because I feel this is not acceptable.


Good Luck on getting Yamaha to do anything, especially to a 98, factory defect or not.


Yamaha customer support is an oxymoron.


My bike is also a 98' and sounds like a washing machine lately. looks like I'm going in.....

I have split my cases once already.

have you finished the project???

any special hints???

All I did was tear down the top end and take the cases to the dealer. They are going to split the cases, press the crank apart, and install a new pin, bearing, and rod. Right now they are still waiting for parts. I have no hints for you, but I am curious about a few things. What kind of oil did you use? How often did you change it? How many miles are on your bike in what kind of riding? Maybe we can get to the root cause of these failures.

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