Sprocket won't fit rear hub

G'day, I ordered a set of sprockets and a chain for my KZ750B twin and when they arrived I thought great today is the day I finally get to do the job. To my surprise the rear sprocket won't fit. The centre hole in the sprocket on my old one is 63-64mm and the center to center distance of the diagonally opposed bolt holes is 90mm. Ever since I had a new tyre put on the rim I have had a funny feeling that the whole rear hub/tyre set up is not original. I will take some photos later on today to put up here to see if anyone knows what sort of setup is on this bike.
Any ideas what this rear sprocket belongs to. It is 63.5mm hub 90mm bolt centre to bolt centre 38Teeth for a 530 chain, regards Neil

Photos might help.

Stock would be an 80mm center hole, 6-bolt holes and 104mm center-to-center on opposing bolt holes.

How many bolt holes on your old ones?

Drum or disk on the back?

I looked up our references and there's nothing with the dimensions you mentioned - check the dimensions again. Also look for any markings on the sprocket. Most aftermarket sprocket suppliers stamp the sprocket series number and tooth count on each sprocket.

G'day, so I took some photos of the strange rear wheel on this 1980 KZ750 twin. The hub has the two smallish sealed bearings fitted to the outer extremities of the hub, they look like rather small bearings for a 750 hub. the only thing I can find on the actual rim is a T and a M above it and somewhere else A199 in small numbers. The tyre fitted to the rim is a Battleaxe 130/90 - 16 m/c

Here are a couple more pictures, I re measured the hub again and it is 64mm which converts to 2.5 inches and the center to center hole is 90mm. The sprocket is a 37 Tooth alloy/aluminium the only markings being 37 stamped into it.

That looks like a Morris Mag wheel.

2.5" center (63.5mm), 3.5" (89mm) center to center. Search for a PBI sprocket for the morris mag wheel.

Its definitely a Morris Mag. The sprocket also has what they called a "cush drive" setup. Save those nylon spacers, and the inner collars. I don't think you will get they when you order a replacement sprocket.

Back in the day you could order your Morris Mag with non-cush drive, or with cush-drive sprockets. Make sure they know you need the cush-drive rear sprockets. I would like to find a spare set of those cush-drive nylon spacers and collars for my Morris Mag.

Jeez this forum is great, thanks fellas I had never heard of a Morris mag wheel I will do a search of what is available here in Australia but I have a funny feeling I might have to either get one from the USA or get one made up. I'm definitely not going to get one made of the same material as the old one, 7500 miles and it's shagged one tooth missing and the others horribly worn, I don't think the PO was really keen on lubing the setup. Thanks once again, regards Neil

Morris Mags are one of the more desirable wheels from that period. There are road and race versions. The race versions are made of mag alloy and are VERY light - you can pick the wheels up with your little finger... Those are worth good money if in perfect condition. The street version was cast aluminum and much heavier.

The wheels themselves are interchangeable across bikes as different adapter plates for the brake and axle bolt to the hub of the wheel.

Aluminum rear sprocket is probably all you are going to find - and yes, it's likely you'll need to order from the USA to get these. PBI is one brand that still makes sprockets for the wheel.

You might also consider selling the wheels and buying KZ750 wheels - you will likely make some good money with those Morris Mags.

3cav84a wrote: G'day, I ordered a set of sprockets and a chain for my KZ750B twin and when they arrived I thought great today is the day I finally get to do the job. To my surprise the rear sprocket won't fit. The centre hole in the sprocket on my old one is 63-64mm and the center to center distance of the diagonally opposed bolt holes is 90mm. Ever since I had a new tyre put on the rim I have had a funny feeling that the whole rear hub/tyre set up is not original. I will take some photos later on today to put up here to see if anyone knows what sort of setup is on this bike.
Any ideas what this rear sprocket belongs to. It is 63.5mm hub 90mm bolt centre to bolt centre 38Teeth for a 530 chain, regards Neil

Neil
Sent you a PM, let me know if it helps!?
TennesseeZ ED

Jeff.Saunders wrote: Morris Mags are one of the more desirable wheels from that period. There are road and race versions. The race versions are made of mag alloy and are VERY light - you can pick the wheels up with your little finger... Those are worth good money if in perfect condition. .......

Was there a problem with the race versions cracking when they got old? I though I read someplace that the magnesium alloy didn't hold up over many years of use, but I could be thinking of some other wheel manufacturer. Ed

650ed wrote:

Jeff.Saunders wrote: Morris Mags are one of the more desirable wheels from that period. There are road and race versions. The race versions are made of mag alloy and are VERY light - you can pick the wheels up with your little finger... Those are worth good money if in perfect condition. .......

Was there a problem with the race versions cracking when they got old? I though I read someplace that the magnesium alloy didn't hold up over many years of use, but I could be thinking of some other wheel manufacturer. Ed

With true Mag Alloy wheels, I don't think it's so much getting old as hitting bumps and pot-holes. I cracked an SMAC front wheel a few years ago hitting a curb - two of the six spokes had cracks all the way through... I was VERY lucky the wheel didn't collapse on me. They should not be used on the street - but many of us did...