Topic: Fixing improper sprocket install.

[maxheadflow]

I suspect that the reason why I had to weld the case is that the sprocket came loose and off the output shaft.   It got wedged and dug into the case. First pic shows the front sprocket setup as I found it.  This bike is a 78 cb750K that had been converted to 530 chain. For some reason the guy left the holding clip for the earlier bikes in place.   The main washer could not stay tight due to the space underneath.  After losing the sprocket the next fix was to add washers underneath so the bolt had a seat to set on. Sprocket stayed on but notice the sprocket wear. It's out of line with the rear chain.  Hunting around I found a drawing for a 630 sprockets from JT.  The only difference is that the back side of the sprocket needs to be cut down.  Removing the clip and machining the back will allow the sprocket to line up better.

One unfortunate thing I found was that the gearing is sort of messed up.  It has a 17 tooth JT sprocket on the front and a 40 tooth sprocket in the rear.  I guess this is one of the reasons why the bike was pretty doggy when I was riding it.  The chain is still in pretty good condition so I expect I'll go to a 15 tooth front sprocket until the chain wears out then go 17/48 with a new chain. Unfortunately I probably have to take a link out of the chain.

[bryanj]

DO NOT go that small on a front sprocket, one of the reasons Honda went to the 17 tooth is they reconed the 16 was too small for the chain to go round without excess stress

[Jerry Rxman Griffin aka MuthaF'er]

Use a 650 front sprocket 530 and only one shoulder.

[maxheadflow]

Thanks for the advice. 

I'll look for a cb650 front sprocket.

I'm not sure it is "excess stress" as it is the amount of chain flex. The pin in the chain has to rotate.  Smaller sprocket tooth counts have more rotation on the pin than a larger one... While honda figured out that, I would figure that they had to learn it..   After all the 630 chains had a 14 tooth front sprocket.  Chain pitch makes no difference on the amount of flex, tooth count does.

I think the point to remember is that the current chain and sprockets are actually pretty good, what is the lower cost way to use use these parts and lower the gearing? 

[754]

 I doubt you have the  rear sprocket in line. earlier wheels will bolt on but the sprocket carrier is 10 mm close to frame center .
 the way your front is worn heavy on one side indicates that rear one is over too much toward center.
 77 and 78 motor, maybe early F and Auto, are long sprocket shaft motors.

[bryanj]

It was one of the reasons Honda gave for the early chains breaking and wrecking crankcases, they spent millions on r&d so i tend to believe them

[Don R]

 I'm a big fan of 18/48 but I don't compete for acceleration, I'm more of a, gear a 50 year old bike for 75mph on the 4 lane guy. 

[maxheadflow]

This sprocket was case hardened.  It was too much of a pain to cut all off.

[754]

you better check your rear sprocket alignment.
the hard sprocket  you can disc grind it, and flatten with sandpaper.

[maxheadflow]

It cut just fine.  Inner part is within 0.001 of the gear face.   BTW the alignment is much better on the chain.  Moved the sprocket in about 2-2.5mm.

[maxheadflow]

BTW, Found the rear axle spacers reversed also. Chain lines up even better.  Chain guard centers on the sprocket better.  Will see how long the chain lasts with a 15 tooth sprocket. Got one for a CB650.

Man, there has been more screwed up stuff on this bike.. It's running real  well tho.