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Yz250 Motor in YZ426?

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Anyone ever put a YZ250 motor in a YZ426 Frame? I have a 98 YZ250 motor and I found a cheap YZ426 with a grenaded motor (Imagine that!!). :lol:

I know that any swap is possible, but some are more of a pain than others.

I have no idea what kind of problems I'd run into with a 4-stroke frame. Not sure if a 2-stroke expansion chamber will clear the front of the frame, if the swingarm axle holes will have to be bored....etc.

I'm just looking for some info from someone who has seen or heard of this kind of swap.

Maybe it isn't even worth trying?

As most of you know, it's fairly easy to find a 4-stroker with a blown motor dirt cheap. I guess they freak out when they see the estimate from the dealer?

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I used to have a '00 YZ426. They carried the engine oil in the frame backbone and front down-tube. I am not sure that your stock pipe will be able to clear the front of the frame. If you can get that to work, then the rest of it, while being labor intensive, would certainly be doable.

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Probably better off just swaping the suspension and brakes over to the 98.

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Wow! I just looked up some pics of the 426 frame and saw the oil line. That is a weird design. It looks like part of it can be removed, or even cut off to make a little more clearance.

I already have a slightly modified pipe for the YZ motor. It was made to fit into a blaster frame. It has already been cut and welded, so I could probably mod that one to bend around the frame if I had to.

I don't have a complete YZ to swap the suspension and brakes on to. I only have the motor.

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The major problem as others have stated is going to be the pipe interference with the frame cradle. Luckily that frame is steel so if you get creative you could probably make it work. That said... I doubt that the YZ426 frame will be a big upgrade if any over your current frame. Certainly not worth the trouble. A newer fork swap may be worthwhile.

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Personally I think going to the thumper frame is a step backward, but I agree that it can be done. Finding a proper 1998 frame and using the 426 suspension and body work would be a little better due to flex characteristics, etc. But you're probably looking to build an inexpensive bike with what you have and that's pretty cool/resourceful.

Here's some info that may help you:

-Swing arms are interchangable between 2002-2008 YZ-F and all 2002-2012 YZ250.

-I think the older 1999-2001 two strokes had a smaller swing arm pivot bolt.

There are seel bushings in the center-cases for the swingarm pivot bolt. Perhaps there's enough meat in them to bore them out to fit.

I think you can probably get the center-case bushings from a 2002-2012 YZ250 and put them in your 1998 cases to fit the 2002+ frames.

I agree with the other guys that the huge thumper frame will present clearance issues with your exhaust. Steel frames are easy to weld with MIG or TIG equipment.

The clearance between the pipe and radiators/hoses may also give you issues. Some of the swaps I've seen have required modded radiators, or creative adaptation of the two stroke radiators.

You will probably have to do some serious mods to the airbox and find a two stroke air boot. Check up on some of the aluminum YZ-F frame swap threads for some great photos and ideas on how to address that issue.

You'll have to change the whole throttle assembly out for one off a smoker since the thumper uses that push-pull style. I'm sure the 426 also used a different clutch cable vs the 1998 YZ250.

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I don't have a complete YZ to swap the suspension and brakes on to. I only have the motor.
That said... I doubt that the YZ426 frame will be a big upgrade if any over your current frame.

He doesn't have a YZ frame.

Personally I think going to the thumper frame is a step backward

Sounds like a fun project, so that's worth something, right?

Why would you want too?

Why did Sir Edmund hillary want to climb Mt Everest? Because it was there. And when he gets there he can haul a$$ on his frankenbike!

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