missing plug

I have an 03 WR450 and there is a plug (or something missing from just about the exhaust exit on the engine. If it were a street bike I would guess it was the connection for the tachometer. I was changing the oil and when I removed the exhaust pipe I noticed it. Crazy thing is I thought the radiator was leaking, I had it pressure tested and didn't notice this until now. I've only been out once with it like this and every time I stopped I was getting smoke off the pipe and it looked like it was dripping down from the radiator. Now I am sure that it was oil accumulating on the radiator and dripping down. Luckily I was going to run over to 380 and check that out and see if there was still a radiator leak but I figured I'd give her an oil change before going for a run.

So does anyone know what went there? If no one knows I will probably just run over to Richardson Yamaha to see if they can help me. The service manual is all hand drawn and I can't find what that was anywhere so I think it was a simple plug.

The hole is where a manual decompression mechanism used to be on the earlier WRs. The later models still use the same head though so the hole is still there, but should be plugged with a rubber plug (I think). The problem is the plug can be blown out by high oil pressure, which is probably what happened in your case. You can buy a replacement plug from the ThumperTalk store which is held in by a bolt so can't blow out. This seems to be a common occurrence on the later model WRs, which begs the question; "why didn't Yamaha fix it on the '04?".

The plug from the TT store works great. Once installed go easy on the set screw that holds it in. Very easy to strip. Make sure the vent hose coming off the top of your valve cover is not pinched. That will cause the pressure to blow that thing out.

Thanks for the information! I did find the part number in a manual under the "WR Performance Index" but luckily you guys responded first, I'd rather get an aftermarket that works better than get the same part again. Also it's good to know why it's there. I was seriously questioning why they would put a plug in that area.

Definately get an aftermarket plug. When my '04 was new I blew out the original plug on the first ride. I took it back to my dealer (not knowing any better at the time) and (after a week) I got the bike back with a new plug. I blew that one out on the very first ride again! By that time I had discovered TT and was able to fix it right. I have the TT plug in mine and it works great (and looks good too).


Get one of these but be careful when you tighten the bolt that holds it in as it strips pretty easily.


Thanks, I actually just jumped over to the store and searched for "plug" and that was the first hit. You guys absolutely saved me the cost of buying the stock one and having it happen again. I'd say that this absouletly falls in the category of "it should have been a recall" and they provide you a replacement that looks/works like the aftermarket one! With all the engineering that went into this bike I can't believe that they left something like this with a cheap rubber plug. But all is good since I have it on order and I was doing an oil change anyway.

Thanks again for the assist!

I have been trying to find this plug everywhere and finally a friend sent me over here.

My story is that I flipped the bike and kept running upside down, gas and oil were coming out everywhere. I knew oil had gotten on the radiator fins and was dripping into the pipe. After a while I thought it just would burn off. It never stopped. I took the radiator out to clean it good and when I was putting it back on I noticed the whole. Cranked it up and saw that something was coming out of there. Put my hand and it was getting oil.

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