21 inch wheel on a 1976 sportster ?

a friend has a 21 wheel from a 78 fL cant remember anyway it has a 1'' axle od can this work on my 1976 iron head sportster ?

Nope, it's like oil and water, it will not work.....

what do i need to make a 21 fit my bike ?

Not an expert but the stock axle is 3/4" I'm guessing so you'd need to either reduce the new hub somehow with either smaller ID bearings or turn down the 1" on the ends to fit into the stock mounts. Or...masked your stock mounts bigger without compromising the strength. I can't help you with the actual process but I'd go with an axle that's been turned down on the ends to fit into the stock holes or see if you can get different bearings. But that's with no brake modifications. I have no clue there.

Sportster axle is 5/8?
Big twin is 3/4 up until recently some changed to 1"

So.......5/8 axle..........with a 3/4OD sleeve inside.......or swap the bearings.......just measure the OD of the bearing.

If you post a pic of the front end that the bike has on it.. would make the question easy to answer... If it has a 35mm narrow glide on it the change over is as simple as getting a narrowglide 21 and the appropriate spacers etc (3/4 axle). If you have the earlier 33.4mm front end (drum front brake) you would not really want to make the change as you would have to do so much machining it would be pretty...errrrr... pointless.

You could find a sportster hub laced to a 21.That's what I did.Or you could do it yourself .

Change bearings to fit the axle you currently have, or you can sleeve the axle

can i take the bearings i have and swap them from my front wheel to that front wheel would that work or do i need another set of bearings to swap into the 21.?
could i just pop out my bearingd and matching axle and use that ?

If, by some odd chance, they are the correct outside diameter and the spacer on the inside is the correct length.

Are the hubs the same size?
If they are that might work............but sleeving the axle may be the easiest route.
Just find a tube that fits over the smaller axle and fills the larger wheel....dig?