Topic: Sprocket problem.

[ericsaeter]

I have a shredded sprocket. It has NO teeth left, and no, I'm not still riding it. I managed to break a whole number of teeth when hauling another large body as a passenger up a hill, although it was already showing wear. It's a 1978 cb750F, and it's mostly stock. I believe it has the 630 chain but I'm not really knowledgeable when it comes to chains and sprockets. The rear sprocket that is now shredded is a 35 tooth, and you can tell by looking at it that it doesn't fit right, as there are incosistencies where the chain links meet up with the teeth. I was told that what I need is a 48 tooth sprocket for the rear, but I think that would be too many teeth and also cause the chain to grip it incorrectly or land on the teeth, chipping them. Or is it just acceptable to have mild misalignment? I took pictures of it so you guys can indentify the chain size and see my little teeth worn down to nubs. My question is what sprocket would be optimal for my bike?




Thanks so much. I don't know who to ask, my manuals say NOTHIGN of the sort of information I need, and everything online seems to have a vastly contradictory story, and I can't ride the sucker to a shop.

[Gordon]

The optimal size sprockets for your bike would be the stock sizes, which for the '78 750F should be 14 front, 43 rear, and a 90 link 630 chain (at least according to cycle-re-cycle). 

The "inconsistency" between the chain and sprocket is most likely due to the chain being worn way beyond it's serviceable limit.  The spacing of the teeth on the sprockets is the same regardless of how many teeth there are. 

To sum it up, you need two new sprockets and a new chain.  If you only replace the rear sprocket, the worn chain will quickly tear it up.

[merc2dogs]

 If the chain doesn't land in the grooves right either the chain and sprocket should have been swapped years ago, or the sprocket and chain doesn't match.
 a chain should lay on the sprocket smoothly, otherwise you'll break chains or bust teeth off
 tooth count realy won't affect  how the chain fits the sprocket, only effects final drive ratio.

 I'd replace both front and rear sprockets and the chain.
the bright side is that now you can fine tune your gear ratios!
 
ken.

[ericsaeter]

Awesome. Thanks guys. The chain must be mismatched, then. I got it about 8 months ago from a guy who had put it together himself. I had assumed it would need a considerable amount of work. Several months after I bought it, a vintage Honda mechanic told me the chain and sprocket looked like they all matched fine but I knew that was wrong when it started chipping really bad.

Some of you ahve converted to a 530 chain. What are the advantages to that?

[DME]

Awesome. Thanks guys. The chain must be mismatched, then. I got it about 8 months ago from a guy who had put it together himself. I had assumed it would need a considerable amount of work. Several months after I bought it, a vintage Honda mechanic told me the chain and sprocket looked like they all matched fine but I knew that was wrong when it started chipping really bad.

Some of you ahve converted to a 530 chain. What are the advantages to that?

Go for a 530 chain.
The 630 chain is heavier, more expensive an totally over-the-top for a CB 750.
In the seventies it would have been right but stuff has evolved in the chain manufacuring-business as well.
A 530 will deal with up to 180 hp, no sweat.

[TwoTired]

A 630 chain has 3/4 inch pin spacing vs the 530's 5/8 spacing.  This makes the sprocket teeth spaced farther apart on the 630 setup.  So, be wary of 630 and 530 sprocket tooth count comparisons.

The Honda Micro Fiche calls for an 88 link 630 chain for the 78 Cb750F, endless type.
Rear sprocket - 43 T.
Front sprocket - 14 T.
This gave a final drive ratio of 3.071

I agree, with damage like what you've shown, I'd replace both sprockets and chain.  I would also consider changeover to a 530 type chain along with the sprockets. Modern chains can have tensile strengths beyond the older 630 chains, are lighter and more readily available.

If, for example you were to select an 18/48 combo in 530, you would have 2.667 final drive.  The higher tooth counts (and sprocket diameters) make for a longer wearing set of sprockets and chains.

A 17/48 combo in 530 would be 3.101 final drive, and give the more spirited acceleration it had from the showroom.  However, touring would be "buzzier".

Cheers,

[Tim.]

Go to Bikebandit.com and check out sprockets/chains for your bike.  Even if you don't order from them you'll see the sorts of things avaiable, including 530 conversions.

[ericsaeter]

Do the conversion kits just bolt on or is there some sort of adapter? I suppose I could mill one myself if I needed.

I actually found the old 630 size sprockets and chain to be a mere 40$ more.

[smashme33]

 As far as what sprockets to use...I can suggest to try the stock setup for your bike first, and then see how it works for you. If you want to adjust the ratio, I think you should do so in small increments. For example...say your stock sprockets are 14/43 and you want lower highway RPM...maybe try a 15/43 or 15/42(assuming those sizes are available to you). Not a huge decrease in RPM, but likely not a strain on the bike from a standing start. My CB650 came with 16/39, and I thought it was a little too buzzy on the open road. I am currently running a 17/38(see, not a HUGE change) and it shaved a few hundred RPM off on the highway...I am very satisfied with it because I am saving just a little more gas, the engine sounds perfect at cruising speed, and it's still producing decent power. On the other end of the spectrum, if you wanted a buzzy acceleration machine, increase the amount teeth on the rear.

[eldar]

Remember, when you change your sprockets, 1 tooth in the front is worth 3 in the rear. Also do not use a tiny front with a large rear.

Also, the smaller the front, the more accel OR the larger the rear, the more accel. More topend, you just flip around what I said. Larger front and smaller rear.

If you want a bit different gearing, you can do the ration of the 78k  15t/41t  which comes to about 2.73. Not too low but not too high either.

But if you like what you got now, dont stray to far then.

[ericsaeter]

Thanks for all of the great info. You guys have given me a bunch of different, tremendously helpful starting points. As an inner-city bike, I think I'll lean toward a greater low-end ratio. My highway RPMs were nice and smooth but a little low yet.

I came across some broken sprockets for easy switch-out, too--a completely unnecessary and wonderful option! : )

[ericsaeter]

Whoops, more q's. How long does my 530 chain need to be for a conversion? Over a hundred bucks cheaper than a 630, a standard 116 link 530 is $17 (bikebandit.com). There are also O-ring, heavy duty, and X-ring options. I'll read up on them when I'm back home later, but do you guys have any personal notes on any of the types? I don't mind spending extra for quality.

[Duck]

Talk to Jeff at Z1 enterprises. He'll fix you up with a 530 kit. Got one for my kz1000 at a good price including high strength O-ring chain. The O-ring seals the roller-pin interface against outside elements like road grit. The X-ring has a double seal. You chain doesn't 'stretch' with age. What happens is the roller and pin grind away at each other making a bigger hole in the roller to ride on a smaller pin. If you take off 0.02 inch per link off 100 links that's two inches over the length of the chain or an inch on the tighteners. It's not hard to do this over 2000 miles with the old unsealed 630 chains if you don't wash them out with kerosene and and lube  them every 200 miles or so...

You need no special adapters.
If the 750 has a single large nut holding the sprocket on you may want to tighten up your old chain enough to hank on to what;s left of the rear sprocket and use it and the brake to hold your front sprocket. Learned this the hard way. Had to make a special tool because my chain and rear sprockets were already off and gone to the scrap yard. Also, check the manual for any lock washers or retaining plates that may go on the front and/or rear sprockets and order these to if the old ones are missing or in bad shape.

[ericsaeter]

A 630 chain has 3/4 inch pin spacing vs the 530's 5/8 spacing.  This makes the sprocket teeth spaced farther apart on the 630 setup.  So, be wary of 630 and 530 sprocket tooth count comparisons.

The Honda Micro Fiche calls for an 88 link 630 chain for the 78 Cb750F, endless type.
Rear sprocket - 43 T.
Front sprocket - 14 T.
This gave a final drive ratio of 3.071

I agree, with damage like what you've shown, I'd replace both sprockets and chain.  I would also consider changeover to a 530 type chain along with the sprockets. Modern chains can have tensile strengths beyond the older 630 chains, are lighter and more readily available.

If, for example you were to select an 18/48 combo in 530, you would have 2.667 final drive.  The higher tooth counts (and sprocket diameters) make for a longer wearing set of sprockets and chains.

A 17/48 combo in 530 would be 3.101 final drive, and give the more spirited acceleration it had from the showroom.  However, touring would be "buzzier".

Cheers,

I'm not understanding the math here. I thought the ratio was deduced from the division of the rear by the front; final drive assuming a constant wheelsize and such. That makes a 17/48 a 2.82 final (16/50=3.125), right?

For innercity driving I want to stick to more low end. One of the reasons is because I have a 15/35 setup now with my 630 chain and this gives me a powerband between 15 and 50mph or so, which is awfully tempting on arterials and I'm hoping I can just nurse my accellerative desires on a hoppier, low end. I'm always driven to lay the powerband out on the road but I quickly get in excess of 70 and I only have one long kid-free, non-freeway, empty road to do it on within 50 miles.

Also, I've been reading a lot of past posts and other internet sources for chain conversions and without calculating radiuses and pin spacing, and etc, I can't find the length of chain I need in 530 links or an easy enough formula to figure this out. I'll probably buy a couple links overhead anyhow, for security.

[TwoTired]

I was actualy trying to relate crankshaft RPM to rear wheel RPM.

The primary and trans ratios varied among CB750s with the year and model.  And, I thought the Honda specs included that difference in their printed specs for final drive reduction.  But no, incorrect assumption.

Your math is correct for the final drive sprocket ratios.  It will only be off by 0.017 for crankshaft speed on your particular bike...I think.

I picked the 17/48 combo, since that was what the 76 Cb750F had in 530.  Then I added the primary reduction difference from the 77K model 1.708 vs 1.986- 78 750F.  But, I can't justify the reasoning now and was probably wrong.    Maybe, I was just flipping the wrong pages when entering numbers.    Or, possibly just a senior moment.

Anyway, go ahead and talk amongst yourselves. I can maybe find something more useful to do...

Cheers,

[ericsaeter]

Thank you. As you can tell, I'm learning this stuff, so my intention wasn't to correct, but to understand.

Any notes on 530 length?

[eldar]

I have been waiting to do a 530 conv but my 630 is good yet and why waste a good chain. But I was told to get a 110 link chain and remove what I dont need.

[hcritz]

I'm still trying to find a front spocket for the 530 conversion for the 77k
No luck so far for one listed that fits!

[dusterdude]

please dont hurt yourself tt.

[ericsaeter]

I'm still trying to find a front spocket for the 530 conversion for the 77k
No luck so far for one listed that fits!

Rear http://www.bikebandit.com/partsbandit/product~pf_id~5265421~dept_id~2164079.asp
Front http://www.bikebandit.com/partsbandit/product~pf_id~5260777~dept_id~2164079.asp

Those are 530 conversion sprockets for the '77 750K. Really well-priced ones, too.

[hcritz]

Thanks Viking...
Dennis Kirk doesn't list that sprocket in their JT sprocket section!

[ericsaeter]

Thanks Viking...
Dennis Kirk doesn't list that sprocket in their JT sprocket section!

Good luck then. Check out the rest of what they have to offer. There were 15 or so sprocket choices for that year by JT on their site. If you have the patience to go through all of the lists and mfgs, you can find annyythingg. I even found chrome pod filters for $5 or something like that.

[Boomologist]

>>>The primary and trans ratios varied among CB750s with the year and model.  And, I thought the Honda specs included that difference in their printed specs for final drive reduction.  But no, incorrect assumption.<<<

Am I to assume that transmission gears are different between various years CB750/4's? Could that be why I have such a high gear ratio? Are transmission gears interchangable between various years? If so it would open the possibility of having a lower 1st gear and a higher 5th by mixing years.

On the topic of chain, in the past i would use the least expensive non-"O" ring chain I could find. Without fail they would stretch badly within the first 200 miles or so, then I would be adjusting the chain every 200 miles after that. Once I even had a chain snap the side of a link.
Now I run only 530 non-"O" ring chain made by "DAIDO". I put on a fresh chain just before our trip and after 900 miles it still doesn't need adjusting! The cost is a little more than the cheep ones but they last much longer.