WR450F Bad Oil Leak

A buddy of mine has a 2004 WR450F. We went riding today and just a few miles into our ride he had smoke and oil leaking everywhere. I towed the bike back to our home and couldn't find anything that could be leaking. But today I noticed up on the front of the cylinder head a little round hole near the exhaust. It looks like a cap of some sort has came out of this hole. Is that normal? Any ideas?

the manual decomp plug fell out. Fairly common issue.

the manual decomp plug fell out. Fairly common issue.

I own an 04 ...as far as I know...there isn't any manual de-comp on this model year

Not really familier with the 04' models, but on my 07', that would be where my AIS block off plate is.

Could that AIS block off plate came off?

I own an 04 ...as far as I know...there isn't any manual de-comp on this model year

It may not have a decomp lever, but i think there weren't many changes between the 04' engine and older models and the decomp hole may have been blocked off from the factory on the 04's. Not 100% sure though.

On my 07' that location would also be near where my AIS block off plate is, but I did a search, and it looks like the 04' models didn't have AIS?

Edited by mikewrf18

I also think it sounds like the place where the AIS block off plate goes. Got any pics?

It may not have a decomp lever, but i think there weren't many changes between the 04' engine and older models and the decomp hole may have been blocked off from the factory on the 04's. Not 100% sure though

My 04 does not have a decomp lever or AIS fittings. Now mine is a Canadian model...but I believe the AIS did not appear until the '05 model year.

However mikewrf18 could be spot on with the idea that in the '04 model year, the factory just plugged the hole in the cylinder head for where the decomp lever used to be in earlier model years.... and that this "plug" may have been whats fallen out.

Definitly a picture is the way to figure this out.

None of the 450's had manual decompression, but all the Gen1 engines ('03-'06 WR's) have the machine work in place to install one, and it's listed as available in the parts books. The plug that blocks that off is a wimpy little plastic thing that will pop right out if the breather line gets pinched or if the weather's wrong. Replace it with something better.

Read:

http://www.thumpertalk.com/forum/showthread.php?p=1522419#post1522419

http://www.thumpertalk.com/topic/858331-decompression-plug/

Sorry, maybe I should've been more specific.. yes, yamaha had a manual decomp lever already machined into the head from the previous generation WR's, unfortunately they never changed the casting for the head when they went to a Auto Decomp system, instead, they installed a "wimpy plastic plug" to block off the hole. If the main breather hose gets restricted and/or plugged, it creates too much pressure in the cylinder head, thus blowing out that wimpy plug and unleashing a whole lot of oil just above the exhaust header.

There is aftermarket alternatives for that plug on Ebay.

There is aftermarket alternatives for that plug on Ebay.

There are aftermarket alternatives right here at the TT Store (see the second link I posted). You can also use an 18mm "freeze plug" from an auto parts store, but they can be a challenge to install with everything assembled. Some have just used the OEM plug and glued it in place, but I wouldn't trust it.

There are aftermarket alternatives right here at the TT Store (see the second link I posted).

I tried the link earlier this season and just now and get nothing.

Haven't found any in quite a while not OEM.

Mike

Just search "Decompression Plug" on ebay, you'll get like 17 hits in various colour options

I used an 18mm freeze plug on my 04 WR450. 6 years later no issues with leaking or coming out.

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