Top end Rebuild 03 WR450F with YZ parts

[latitude777]

So heres a quick run down.

I graduated from Uni 18 months ago and as a grad present i bought a 2003 WR450FR. Yay me! Anyhows, after a full $450 service and going over by the local Yamaha dealer i bagan riding. After only riding it 3 times, i found out (the hard way) that i had a blown head gasket.

Turns out I had a siezed head, busted valves and enough imprints on the top of the piston to make a grown man cry.

So i started pulling it down for the rebuild.

Now with a tight budget and a small amount of mechanical knowledge i'd like to get it up and going again!

I've sorced a reasobably priced complete ported and polished serviced head for a YZ450FS (04) which i've been told is the exact same print as the wr head. Only differences being cams and maybe valves (correct me if im wrong). The head gasket is definately the same according to yamaha so i should be heading in the right direction. I didnt aim to use YZ parts but they were cheap and now will hopefully save me money.

My questions are:

Is the crank the same on YZ/WR? Ie do i need to change to the yz one to maintain the use of the YZ cams etc?

I know the stroke bore and compression ratio is exactly the same between the wr/yz (according to yamaha) but is the crank lighter on yz?

Do i need to change cam sprockets to run yz cams? YZ cam chain etc?

And finally im assuming i'll have to change jetting etc to get this all to run properly together? I've heard the enduro guys use YZ heads on wr's all the time but havent seen any write ups etc that may point me in the right direction.

Any help in this area would be grealty appreciated. I phoned a few local yamaha dealers and i cant get a straight answer from anyone whos done this before. only bits and pieces that im trying to put together.

thanks.

[grayracer513]

In general, the only difference between a YZ450 head and a WR450 head in any given year is that there is no provision for an air injection system on any YZ, and of course the '06's were two different engines.

The crank is definitely different, but only the left axle, which is longer, etc. to accommodate the e-starter. There's no problem using the whole YZ top, with the possible exception that some people have reported difficulty with the electric starter being able to start the engine with the YZ exhaust cam.

And you probably will need to tweak the jetting a little, but you should wait to see how it runs first unless someone has a proven setup to offer.

[latitude777]

In general, the only difference between a YZ450 head and a WR450 head in any given year is that there is no provision for an air injection system on any YZ, and of course the '06's were two different engines.

The crank is definitely different, but only the left axle, which is longer, etc. to accommodate the e-starter. There's no problem using the whole YZ top, with the possible exception that some people have reported difficulty with the electric starter being able to start the engine with the YZ exhaust cam.

And you probably will need to tweak the jetting a little, but you should wait to see how it runs first unless someone has a proven setup to offer.

Thanks for the heads up. Not familiar with an air injection system though?!? What's that?

[dgcars]

The air injection system or 'AIS' is the anti-smog system. If it is still on your bike, there will be a rubber pipe from the air box, a pipe from the inlet side and one from the barrel beside the exhaust header. They end up in an alloy unit under the fuel tank. If you don't need it for emission controls, take it off.

[miweber929]

AIS wasn't until 05 or 06 and yours is an 03 so you should be just fine.

[latitude777]

Haven't seen it. I bought the bike seco d hand so it may have been removed already.. OR it never came out on the Australian model. I'm not sure.