80 KZ400 18\" on 81 Z750-M1

Should I have any problems with this wheel.

80 KZ400 18" on 81 Z750-M1

Thnaks in advance!

In the US, the 750M1 was a 82 model KZ750 twin. So if yours is a 750 twin then I think you will find the 400 axle is smaller than the 750 axle.

The US didn't get any 1981 750 twins, in 81 they were all fours and there wasn't a M1 model 750 four.

Yep it seems its an 82'.
Is there any easy fix for using this wheel or should I sell it and try something else to get the 18 inch front I'm after...

In the FileBase (under the "KZ Information" tab at the top), there is a list of KZ wheel bearings that tells you what bike uses what bearings. Check there to see what front wheel bearings your bike uses, then look at the KZ400 and KZ1000P to see if either one uses the same size bearings. The KZ1000P (at least some years anyway) uses a 18" mag wheel.

If you want a wire spoke 18" wheel, you could have a 18" rim laced to your hub.