Topic: Put a 72 cb750 engine in my 78 cb750. Need to align sprockets.

[specialone70]

I swapped in a 72 rear sprocket carrier but now I assume I need to add some spacers so the distance from the swing arm to the middle of the wheel stays the same, and to take up.the extra room on the shaft so the nut can tighten down on things properly. So my question is: how much of a spacer do I need/ what's the difference in width between the two sprocket carriers? Thanks!

[70CB750]

They way I understand it, the 72 sprocket lines up the chain and no spacer is needed on the left side. The new sprocket takes care of the 10mm difference between 72 and 78 shaft.

Line it up and measure how much you need on the right side, it may take few iterations to get it right.

[turkey4me]

Take a look at the cyclex site regarding this.  Seems like they have a couple options for offset sprockets front or rear plus a good description of the carrier difference

http://cyclexchange.net/Chain%20Sprocket%20Page.htm

[Patrick]

You don't need a fancy offset sprocket. You just need the sprocket carrier from a '72 back wheel. It's shorter and lines up with the front sprocket.

Patrick

[seanbarney41]

Yes, he says he got that...you need an extra 10mm spacer and I think it goes on the sprocket side.  Ironically, I don't think any oem setups use one, but it is easy to grab a spare and trim it down.  Best to face it off on a lathe but it could be done by other more backyardish methods with care and attention to detail. ...could also swap in the entire '76 and earlier swingarm

[Patrick]

I put a '72 750 in my F3 frame and used the original F3 rear wheel. The chain lined up. I'm trying to remember if I did anything special to make it work (sold the bike a couple years back). Maybe the right mix of K7-8 spacers and K2 sprocket holder? I just remember I did not need anything custom. Does the K7-8 have the same swingarm as the F3?

[specialone70]

Added 10mm of washers and everything worked out perfectly! Thanks, guys!