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Swingarm strength-will it break?

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I have swapped a YZ450F swingarm on to a YZ250....turns out the linkage is off ever so slightly. I recently swapped a 250F swingarm onto the YZ250 and solved the alignment issue, but have since noticed a difference in the dimensions of both the forged section and the axle dropouts. I am not as concerned about the front forged section, but am concerned with the dropout difference as it relates to strength. The YZ250 and 450F swingarm are 1.4 cm wide in the axle dropouts. The 250F is 1.2 cm wide in the dropouts. On the YZ250 dropout, the extra 2cm comes from a steel plate, which I assumed was for wear purposes, not strength. There is a difference in axle diameter from the 2T to 4T swingarms of 2mm.

 

Should I be concerned with breakage is the dropout?

 

Photos are 250F, 2502T, 450F.

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Doubtful you have to worry about strength. But you have to make it fit properly. Change wheel bearings to suit the correct axle, shim for the missing steel or fabricate them. The 250 2S is less 'updated' than the 4S version and parts used on it are 'in stock' vs 'new and updated'.

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11 minutes ago, William1 said:

Doubtful you have to worry about strength. But you have to make it fit properly. Change wheel bearings to suit the correct axle, shim for the missing steel or fabricate them. The 250 2S is less 'updated' than the 4S version and parts used on it are 'in stock' vs 'new and updated'.

What He said. Unless you do Huge jumps all the time I can't see it failing. Even then I doubt it'll be the rear bits that are a problem, swingarms usually fail near the linkage mount, that has the highest loading.

As William mentioned, change out the bearings to fit the bigger axle (don't forget the internal spacer), but I'd just spin up some new spacers to suit the new arm without the steel bits.

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No huge jumps, mostly fast desert and some woods riding, occasional track day.

I have been running the 450F arm for a few years, but noticed it was pushing the connecting rod up against the drive side mount. It all lines up when nothing is torqued, once you torque it all down it is offset to the drive side. Enough that it had started to mushroom out the mount.

The 2011 250F arm lines up straight (the 250F was still carbed vs 450F fuel injection). So I already had a 450f rear wheel brake carrier etc. All three swingarms measure the same between the dropouts, the outside measures different though. I am stumped on one thing though. The axle, hub, etc all have the same part number for the 250F and 450F for all years 2010 on, the only difference is in the brake side axle block for the 250F. I have aftermarket axle blocks and the threads on my axle stick out about 1/4 inch. Might just add an extra washer as everything else lines up.

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