sprockets

[cobra]

Hi I have just bought a CB750 engine and a pair of wheels, the engine sprocket has got 15 teeth, and the rear wheel sprocket has 40 teeth, and both sprockets are very thick, a standard chain wont fit. the rear wheel sprocket has a label on it (azusa engineering) my question is what was this bike being used for. and why were these sprockets fitted.

[K2-K6]

When they were more current various suppliers made up kits to use a bigger chain size (630 i think) in the belief that it would last longer/be stronger etc, so they were fairly common but probably not really required.

The best mix nowadays I feel would be standard sized sprockets and use an O-ring type chain (not available when they were new) as it's easily able to match the expected performance.

Some of the original intent, to use bigger chains, was a fear of chain brakeages and subsequent crankcase damage from early model stories. I've never seen this occur with properly maintained good quality chains used.

[cobra]

Oh ive not come across this before, i thought it may have been used to pull a sidecar, looks like a expensive bit of kit,looks like its made of a treated aluminium.

[K2-K6]

The rear sprockets were often in alloy that had been hard anodised, quite often black.

There were also some "conversions" that used a duplex twin row chain as well.

Think they were all in response to chain snapping stories that came through the mists and formed myhtical status. But then I guess if you look at what came before this bike and suddenly there was nearly 70bhp available and you didn't keep on top on chain maintenance you could run the risk of damage.

To me the big chain conversions just appeared to add kilos and not really do much.

[Seamus]

It was fairly well known for chains to snap and wreck engine cases. Early chains were nowhere near as good as they are now and I suspect that in their day, the owners worked the bikes much harder than us modern day CB750 riders

[hairygit]

Don't know about tha, I still ride mine in the spirit the manufacturer intended, thrash the nuts off it, live at the red line! CB750 F1's had "SUPER SPORT" on the tank, so I ride it accordingly, and use regular 530 non O ring chain, never broken one yet!

[Bryanj]

The 630 was standard on the 750F2 and the CBX1000 and used as the life before change was extended as long as you read the book and only used hypoid 90 to lubeb it

[hector2800]

I think those sprocket sizes are right for an F2 so maybe you picked up some f2 wheels and engine.

[Spitfire]

In the 1970's I got fed up with ruining chains on long runs to rallies and bike race meetings, bombing down the mororways flat out, stopping at the services, buying a can of oil, pouring it onto a rag and soaking the chain to get the kinks out,  so I fitted a Renold 3/4" conversion to my CB750K1, worked great, still have the sprockets somewhere.

Cheers

Den

[Hinomaru]

Hi I have just bought a CB750 engine and a pair of wheels, the engine sprocket has got 15 teeth, and the rear wheel sprocket has 40 teeth, and both sprockets are very thick, a standard chain wont fit. the rear wheel sprocket has a label on it (azusa engineering) my question is what was this bike being used for. and why were these sprockets fitted.

Perhaps you have one of the old aftermarket conversion kits like this one:

[K2-K6]

"Renold" is usually a premium grade of material and I would guess have advantages over unknown quality kit even for standard sizes.

I have seen the wrong spec used (low speed industrial machinery grade) with all sorts of difficulties as you'd expect.