YZ426F/YZF450 questions

[Kyledvor61]

Just picked up a houser 250r/yzf426 hybrid. I checked the bore and stroke, and its 95mm bore and 63.4mm stroke. The bore is regular, but the stroke is longer. It's a 449cc. I'm assuming its the WR450 or the yzf450 crank? is there any way to tell without getting it out? I'm just curious to know which one it is.

Also, I popped the head, and theres some damage. I need a new one. I'm assuming the yfz,yzf,and the 426 head are all the same? I know on the yfz's they did some updating in 06 or 07. but thats fine its going to be a ported one anyway.

so my question is, are the heads the same? and also what are the differences between the yfz and the 426 motor?

thanks everyone

[grayracer513]

There is very little interchangeability between the 426 and any 450, and the YFZ crankcase will not bolt into any of the bike frames. The head will also not interchange, nor can you use either a 450 cylinder or crank in the 426, to my knowledge. So, if it says 449, it's more likely a 450 engine. Pics?

Casting numbers on the head, cylinder, etc.?

[FinchFan194]

Gray you blow my mind sometimes where do you store all of this stuff? I can't even remember what I had for dinner last night!

[Kyledvor61]

Gray you blow my mind sometimes where do you store all of this stuff? I can't even remember what I had for dinner last night!

+1 no way in hell id be able to remember all that.

So it must be a stroker crank then? about 2 mill, 61 stock to 63.4.

The guy told me it was a 426 motor, but it had a 450 cylinder. obviously he's wrong since there all the same, and the stroke is different. He didnt know very much about it, the guy who had it before him did all the work to it.

I'll post pictures of the cylinder and motor in a minute. head is going out to get an estimate to be fixed.

[Kyledvor61]

Cam Journals-the damage

Cams-looks good to me?

Valves-picture makes it look darker than it actually is*

Cylinder-looks good to me. smudges at the end are from my fingers*

[grayracer513]

If you want the parts identified, you'll have to back out a little and also bring them into focus. The cam bearing damage to the head can be repaired. The cams may be usable if the journals are refinished.

[Kyledvor61]

I went to take some other pics and the camera died.

Any clue what companies could repair it? Someone reccomended CT racing to me. and if its a 426 motor, ill probably be getting a yzf450 exhaust cam for the decompression and an aftermarket intake cam

[grayracer513]

Engine Dynamics Co. or Millennium Technologies.

[Kyledvor61]

Thanks. what do you need pictures of to identify everything?

[grayracer513]

Top and front of the cylinder, and the whole bottom of the head. Left side of the crankcase, and stator cover.

[Kyledvor61]

The heads currently in my Dads truck but I think I got everything else you asked for. If not I can get more.

[grayracer513]

Well, it's unquestionably a 450 cylinder. And it is also an '02 or earlier lower end, making it most probably a 426, too. It is news to me that a 450 cylinder will sit on the 426 cases, but you learn (or should learn) something every day.

The next question is the head. If I could see the whole gasket surface of that, I can tell you whether it's a 426 or 450.

[grayracer513]

Well, it's unquestionably a 450 cylinder. And it is also an '02 or earlier lower end, making it most probably a 426, too. It is news to me that a 450 cylinder will sit on the 426 cases, but you learn (or should learn) something every day.

The next question is the head. If I could see the whole gasket surface of that, I can tell you whether it's a 426 or 450.

BTW, it also has a wet sump conversion kit. Change oil often.

[Kyledvor61]

So the guy wasnt lying when he told me it had a 450 cylinder. hmmm. I just figured he meant crank since the cylinders are all the same sizes. Why would you do this? Put a 450 cylinder on a 426 motor....

and I can get you a picture of the head gasket right now, since I dont have the head in my garage currently.

[Kyledvor61]

Gray is this the pic you wanted?

[grayracer513]

Yes. That looks like a 450 head, too, which makes sense, because the 426 head won't fit the 450 cylinder.

[MuDPoUNdeR]

So if you changed the head on a 426 motor with a 450 it would basically be like boring the motor out in a since, yes?

[Kyledvor61]

So...its a 426 bottom end, 450 cylinder and 450 head? without a doubt?

Thanks for all your help so far!

[Kyledvor61]

So if you changed the head on a 426 motor with a 450 it would basically be like boring the motor out in a since, yes?

How would it be boring it out? I dont know the differences between the heads, but it wouldnt be the same as boring it. Boring is making the cylinder larger. Stroker is longer crank. I dont know the advantage of a 450 head. Maybe Gray could explain why someone would do this.

[grayracer513]

Maybe Gray could explain why someone would do this.

Because the 426 head won't fit the 450 cylinder.

As to why they put a 450 cylinder on it, I have no idea. I could not possibly guess the motivation for some of the bizarre concoctions some quad riders cob together.