78 cb750 f2 chain conversion

[Clifford Mcdonald]

I am doing a build on a 78 CB750 super sport. I want to swap the 630 factory setup to a 530 chain but I am having trouble finding the parts. Is the front sprocket model year specific or can I use one from another year? I have found rear sprockets but for some reason front sprockets seem scarce.

 

[Rod]

You will have to find one off a 1972 to 1976 and see if it fits.

 

[Clifford Mcdonald]

I went ahead and ordered a 76 sprocket and the 1972-1976 will work. The only difference is that the pre 77 front sprocket bolts thru two holes and the 77-78 has one bolt that threads in to the counter shaft. It works but there are two empty holes in the sprocket.

 

[Rod]

Why are you going to 530 chain from a 630 chain?

 

[Clifford Mcdonald]

There are more options for gearing.

 

[Rod]

Ok makes sense.

 

[dirtdigger]

Another big reason to go to 530 is simply weight. 630 chain is not needed now days. The 530 chains of today are stronger and last longer than they did years ago. Takes a lot more power to turn 630 chain.

 

[Rod]

True

 

[Snider1970]

The '77-'78 sprockets are different. They are built with a spacer. This is evident when going to a wider rear tire.

 

[hinksy]

I went ahead and ordered a 76 sprocket and the 1972-1976 will work. The only difference is that the pre 77 front sprocket bolts thru two holes and the 77-78 has one bolt that threads in to the counter shaft. It works but there are two empty holes in the sprocket.

Hey clifford , how did you go with the sprocket ? I am going to do this to my 77 F2 when I get it going . What gearing did you go with ? I was told 16-45 would suit mine but am finding it difficult to get that size rear , so might go 48 , greg

 

[madmtnmotors]

The earlier sprockets are thicker with a raised shoulder on both sides while the later K and F models (77/78) only have the shoulder on the inside with the outside of the sprocket being smooth with no shoulder. The outside shoulder of the early sprocket will extend out past the end of the output shaft by about 2mm. I have used a head nut washer behind the big washer to keep from deforming the big washer on the sprocket bolt when tightening down. The front sprocket for a 79' CB650 is a correct 530 sprocket for the 77/78 CB750's in that it only has one raised shoulder on the inside and the sprocket will finish flush with the end of the output shaft. I use the CB650 front sprocket on my dragbike.

 

[Snider1970]

The earlier sprockets are thicker with a raised shoulder on both sides while the later K and F models (77/78) only have the shoulder on the inside with the outside of the sprocket being smooth with no shoulder. The outside shoulder of the early sprocket will extend out past the end of the output shaft by about 2mm. I have used a head nut washer behind the big washer to keep from deforming the big washer on the sprocket bolt when tightening down. The front sprocket for a 79' CB650 is a correct 530 sprocket for the 77/78 CB750's in that it only has one raised shoulder on the inside and the sprocket will finish flush with the end of the output shaft. I use the CB650 front sprocket on my dragbike.

What do you use on the rear?

 

[madmtnmotors]

What do you use on the rear?

I am using a 52 or 53 tooth rear sprocket on the dragbike from Sprocket Specialists, but for the street I would use something from the rear sprocket offerings that were used on the earlier CB750's that came with the 530 chain.

 

[Snider1970]

I am using a 52 or 53 tooth rear sprocket on the dragbike from Sprocket Specialists, but for the street I would use something from the rear sprocket offerings that were used on the earlier CB750's that came with the 530 chain.

I was curious. I am using the stock sprockets on my '78 because I am running a 160 tire on back. The stock '77-'78 sprockets allow for a tire that wide with no modifications or spacers. Unfortunately it runs the 630 chain.

 

[madmtnmotors]

I am running a 160 tire on back. The stock '77-'78 sprockets allow for a tire that wide with no modifications or spacers. Unfortunately it runs the 630 chain.

It's not the sprockets that determine the maximum tire width, it is the placement of those sprockets. The 77/78 F and K models have an output shaft that moves the front sprocket outward by 10mm and a rear sprocket carrier that is taller than earlier models and also moves the rear sprocket outward by 10mm. The 630 and 530 chains are the same width, only the pin to pin distance (link length) are different. O-ring chains are wider than standard chains to accommodate the o-rings.

 

[Snider1970]

I was curious about that because Cognito moto sells the kit with sprockets for the early models to run a wider tire. The '77-'78 have no need for the sprocket conversion. I always assumed it was d/t sprockets not the shaft output.

 

[madmtnmotors]

I was curious about that because Cognito moto sells the kit with sprockets for the early models to run a wider tire. The '77-'78 have no need for the sprocket conversion. I always assumed it was d/t sprockets not the shaft output.

You have to watch chain clearance at the chain guard as well as the rear shock when using the offset sprockets on the earlier models. The rear shock on the chain side is also pushed out another 10mm when compared to the early models. The front sprocket covers are different on the later models as well and I have seen early model front sprocket covers that were "self clearanced" by the resulting chain rub. The painted cover is the later model, and the extra relief in the screw head boss area is a distinguishing feature:

 

[Snider1970]

Nice! I'm staying with all original parts. Not changing anything in the line of drive except a wider rim and tire.