Topic: CB750 Rear Sprockets - 48 tooth (Update 10/11/09)

[HondaMan]

OK, Honda says they have discontinued this, so I'm taking up the project...

The 48T rear sprocket for the CB750 is a special design, with a larger-than-standard base circle and teeth that are tapered all the way from the root of the arc. This was done to (greatly) improve the life of the chain and sprocket, and it also puts more horsepower on the ground, compared to standard ASA-1 or ASME sprockets.

I talked with Martin Sprockets here in Denver, and they said they can make them if I make an "official" drawing. So, I'm starting on that tonight, and will take it to them next week. I don't know yet if I have to make a batch of these and buy them all at once, or if they can be bought a few at a time. Martin does not normally stock sprockets, but makes them to order. However, they are also in the process of changing their business model, since the marketplace is also changing, and this project is one of the first for their new "model".

This will be a steel sprocket, as they, like me, do not think aluminum is appropriate for this application.

So, here's my question for y'all: if you want one of these from this first batch, or one sometime this year, please reply here so I can make a count. I won't have a cost until they accept the drawing, but I'm sure it will be less than Honda's last price of over $68 that I paid.

Edit 6/26/09

Finally, this project is moving forward again...I finished the required drawings and delivered them to Martin Sprockets today. They are supposed to quote back to me next week, so stay tuned. The pricing issue will probably depend on how much they want for the tooling, if it must be built specially for these unusual sizes.

Other bikes: a whole bunch of you have asked me to do the 500/550 sprockets, too. If I can get this act together (i.e., enough buyers for these 750 sprockets to recover costs soon), I can start on the 500/550 ones, too. They were made the same way by Honda, with an oversized base circle to improve smoothness and power transfer, while reducing chain wear.

Martin is going to quote the following specs back to me:

1. 48T in 1040 steel.
2. Hardened teeth, about R40 (the chains are R65 or so).
3. Per my drawings, which includes:
- the same tooth pattern as my last OEM sprocket,
- radiused tooth profile to allow for sprocket misalignment at high torques,
- base circle .024" (0.6mm) larger than ASA-1 or ASME standard pattern,
- shortened tip length to prevent chain tripping on entry and exit.

Options that may or may not happen, depending on cost:
- Black oxide finish. The jury is still out on this one, as it would NOT be vintage.
- Lightening holes, like Honda's own sprockets. I'm in favor of bigger ones than the stock setup, made possible because I am NOT recessing one side of the sprocket for the splash guard, which prevents your being able to flip the sprocket for another new day. While a heavier sprocket is not a better one, I don't yet know their cost difference for this feature. I would like to reduce the weight by 45% over a solid sprocket, which would put almost 0.5 HP more on the ground.

(Update 9/30/09):
Martin Sprockets did not seem to be interested enough to work with us, so I recruited another machine shop in town who does both one-off and full-production parts. I've worked with them for over 20 years, good people.

The first 4 sprockets are done today. The first will go on my bike, #2 and #3 on other's test bikes. Number 4 is not claimed, yet. These sprockets are "flippies", meaning they are NOT concave on one side. This will let you flip them over for double the life without any chain alignment penalties (I expect 40,000 mile life from these). You could not do this with Honda's sprockets, and the JT Sprockets are just like Honda's: concave on one side. Honda did this to clear their "splash guard", but the JT sprockets are made wrong and won't fit that guard (!). If you flip either of those sprockets over, you must space out the sprocket to align the chain, or else the chain is subjected to side loading. (The JT Sprockets (EMGO) are made to ASME specs, with the resulting noise and chain wear issues that were a real problem when these bikes first appeared. I just measured a set of those sprockets to confirm this.  ).

On my new ones, they are symmetric, and the teeth have the original Honda +0.5mm base circle profile: to the uninitiated, the teeth will appear to be "short". To the educated: that's how they were supposed to look. 

The "production" version of these sprockets will have different hole shapes for the lightening holes: they are done on CNC machines, so I can customize them. The final holes will have a 'tombstone' appearance to them: a parallelogram with the narrow end toward the center. This should lighten them to be less than the OEM sprockets.

[andy750]

Sign me up Mark -Ill take one if its less than Honda.

Great project!

cheers
Andy

[kghost]

As always....Your the man Mark

[Gordon]

I'd like one from the first batch.  Thanks Mark!

[noisebomb]

I would defiantly like one.

[grumpy]

I'm in for one!

[GammaFlat]

I'm in for one and possibly two. 

Thanks!

[fuzzybutt]

any idea what the timeline for these will be? i would like one, only question is will i have the money when the time comes?

[jaknight]

Hello Mark,

Yes!  I will most emphatically take one.  When they are actually available......... if I have the extra money..... I would like to opt for 2.

If that opting for a maybe 2nd sprocket causes a problem, then drop the 2nd sprocket........ But definitely one.

~ ~ ~ jaknight ~ ~ ~

[Ricky_Racer]

I'm in for at least one, Mark. Any design is good, but it'd be nice if they were black with lightening holes...    RR

[754]

Just a few thoughts.
 Should try to get one on a high miles members bike, to try to get at least 15k on it for a test this year.

Was going to ask if they were to be stock cad plating.

Then I was going to suggest that a few done in the goldy Zinc plating might look cool..

But now it sounds like we need black , too..

[GammaFlat]

Just a thought - the design should maybe be "off-spec" some because after all, this is a different design. 

[cb750k7]

Hi Mark.
I would like one.
Will you make the front 16 tooth  sprocket as well?

TNX

Jona

[HondaMan]

Hi Mark.
I would like one.
Will you make the front 16 tooth  sprocket as well?

TNX

Jona

Jona:
Does your bike have the 530 chain? These will be 530 size. Most CB750K7 had 630 chain. 

[imamotohead]

I'm in for one as long as its cheaper than the Honda price.  +1 on the black w/ lightening holes if we have a choice.  When do you think they'll be ready?  Oh , and THANKS for putting this together H-man! 

[cb750k7]

Hi Mark.
I would like one.
Will you make the front 16 tooth  sprocket as well?

TNX

Jona

Jona:
Does your bike have the 530 chain? These will be 530 size. Most CB750K7 had 630 chain. 

Mark,

Yes it does.
I guess that some time in the past the PO has changed it to 530.

TNX

[nokrome]

put me down for one.......black with lightening holes, please

[imamotohead]

Hey H-man,

ANy progress on the sprocket project?  Inquiring minds want to know!   

[heyjones]

Sign me up, too!

[HondaMan]

I finally have a good quote, am waiting for the local distributor to ante up as to whether they will commit to nationwide stocking at their various locations. It seems they have about 6 major distribution centers in the U.S., and would be shipping from stock at the nearest one to your location, when you ordered one.

I have to find about $800 for their up-front tooling charges, though, to get this rolling for the first piece. Then, it's going to be about $6k to $7k to set up the initial stock in their warehouses. I can probably get the $800 from an interested local party, but right now, that next figure stumps me. I'm looking for investor(s) for the long haul.

Right now, this particular vendor strikes me as being half-hearted, wanting me to carry all the costs despite their eagerness to get into bike sprockets in general. I'm not ruling out contacting JT Sprockets themselves at this time, to ask if they would clone the design I now have: they sell things at a much more reasonable price than some of the vendors I have talked with. The market for these sprockets is unlike most other bike markets, as these bikes have a far greater (and more 'loyal') following than most bikes enjoy. That's a little hard to get across to non-biking sprocket builders. The Brits have an appreciation for the importance of this issue, so JT might end up being our vendor, at least our next quoter.

In any case, I'll be contacting them in a couple of days: the local people wanted to sell them to their distribution people at $68 apiece, and a California builder wanted more than twice that figure. Both would incur someone else's "cut" on top of that: I consider neither of these options to be acceptable, at this time. The target price should be below $70 into the rider's hands, if this is to work, and it should include the special offset dimensions that Honda used. Without that, there is no advantage, and the performance will be less than a standard ASME or ASA sprocket.

I can get one-off sprockets made for under $100 on any local CNC machine in Denver, for Pete's sake...

[Really?]

If you are able to get this going, I need a sprocket.

[754]

If Honda cut them with Hobs, then  that is the major cost, try to find someone that has them.
 Sounds like they want you to foot the whole bill and assume all risk..
 better to sell 25pc at 125.00 than to be sitting on 60 pcs unsold..

[HondaMan]

If Honda cut them with Hobs, then  that is the major cost, try to find someone that has them.
 Sounds like they want you to foot the whole bill and assume all risk..
 better to sell 25pc at 125.00 than to be sitting on 60 pcs unsold..

I don't think they would go unsold for more than 1 season, myself: I just don't have the $$ (I'm still unemployed in this bust out West) right now. If I were employed, I'd already have this whole thing running, because I know the $$ will come back.

I would like to see these sprockets selling for a max of $80, $70 would be better. That could require a lot of volume, or a large order. I can inventory them in my garage or something (would consider sending half to Gammaflat to reduce postage for those riders out East) if I can just get them...

[HondaMan]

OK, here's the first step:
I have a local shop, and financial backer(s) to help out. I'm having 4 test sprockets made, starting on Monday (8/24). But, I am still awaiting my next job to start (been out of work several months, now), so I can't pay for these and just send them out to y'all for testing, need your help.

I have 3 available from this batch for testing (I will use #4 myself), need someone who lives where they will continue riding for the next several months and can afford to pay $100 for one, and I'll cough up the shipping (in the lower 48 States, at least). I'll need pix about every 1000 miles from you, and a report on how much chain slack you are seeing as the sprocket "settles in" (typically the first 3000 miles or so). I need to get these tested before this year is over, need at least 3000 miles on the sprocket, more would be better.

These are 48 tooth rear sprockets for CB750K0-F1 bikes, 530 chain size. If you have a new(er) chain, it would be best. I don't need the sprocket back, just need the pictures and reports or some sort on how well they are holding up. I do need to know:
1. What chain you are running.
2. What chain lube you are using.
3. What countersprocket you are running (17T/18T, Honda or non-Honda).
4. What sort of riding you are doing with it (around town, commuting, touring, etc.).
5. You must set the chain slack to 3/4" to 1" to start, and report how often it needes to be adjusted back to the same amount, the mileage when the adjustment takes place, and how much slack developed when it needed adjusting.

Any (richer than me) takers?

If I can get permission, I'd like to make these the "SOHC4.net" sprocket(s), with the next ones being the 500/550 rear units. I may be able to have that engraved on them, so we can use them as "fundraisers" to support this site (like my gas tank pins).

If you are interested, please also drop me an e-mail so I can "track" with you: mgparis@concentric.net.

[HondaMan]

OK, here's the hard part:

As Zorba the Greek used to sing, "If I were a rich man..."
If I were, I'd find those of you who wanted to be Testers and send you each a sprocket for this winter's testing (those of you who ride in winter, probably you Southerners...). But, I have been out of a real job all summer (due to economic conditions in this area), and need someone out there who can afford to buy each sprocket and report back on the schedule I have for them, so we can check the wear rates. I'm not making any $$ on this deal, and even borrowed the monies from someone to make these first 4 sprockets. One will go on my bike, but there is limited riding here between now and Spring. So, there are 3 more that need to be tested, preferably more than 3000 miles by Spring.

The cost would be $114 to put one in your hand. If you wish to help us all by being a Tester, and can afford it, please contact me ("Us" being this forum, where these sprockets will ultimately be "marketed" for near-cost price, plus $1 each for the Forum itself, which I send in for each unit, like with the Gas Cap Pins and Ignitions).

The machine shop tells me that in quantities of 25, the price will drop about 20%, which will bring these in line with Honda's last price before they quit making them last January.

For those of you who may have just entered this "conversation", here's why I'm doing this:
Honda's sprockets were a special design for the 750, 500 and 550 bikes. The design was done to improve the power transmitted to the ground, to quiet the chain noise, and to [greatly] extend the life of the chain and sprockets. The standard sprocket (known as "ASME" or "ASA-1" standard tooth) design, when used on the 750, results in very short chain and sprocket life: in 1969-1970 the sprockets were lasting about 5000 miles. The secrets: the base circle (where the chain settles against the sprocket) was increased 0.6mm (some say 0.5mm) and the tooth profile was modified, radius-tapered, shortened and machined instead of cast. These changes force the chain to deliver the power to the sprocket over nearly 1/3 of the diameter (the rear 1/3 of the sprocket, as mounted on the bike), instead of just on the last 5-7 teeth as the chain leaves the top of the sprocket. This change in torque causes the force to push forward on the swingarm instead of imparting an upward twist to the end of the swingarm, which improves handling under power, too. It was a real smart change, on Honda's part, at the time. Now, it is lost with the EMGO/JT sprockets, and no one else is making the "right" ones (until now.  )

The chain situation was even worse: the chains often did not make it even 5000 miles. By the time of their famous "Shop Bulletin" regarding the special [and at the time, secret] redesign of the sprockets to include a 0.5mm base circle oversize, the sprockets and chains were exceeding 10,000 mile life. When Diamond and Reynolds chain companies comleted their new chains for Honda (and Harley), this figure became 30,000 miles or longer on a set of properly lubed Diamond/Reynolds chain and Honda sprockets. This dramatic difference also shows up on the dyno: typically a full additional 1 HP (occasionally a little more, in our tests then) appeared on a rear wheel dyno on the bikes where we switched from "standard" sprockets of ASME design to the Honda sprockets. The best overall combination was (and is) the Diamond Powersport chain with the Honda-style rear sprocket.

My sprocket now goes one step further: Honda's sprockets were one-sided, because they recessed the outward face so as to receive the tin "splash guard" on top of the sprocket. This made the sprockets fit only one way, unless you went to a lot of trouble to make a spacer for flipping the sprocket over to even out the wear, then ran without the splash guard. My sprockets do not have the recessed face (and in any event, the ones from JT Sprockets/EMGO don't fit the guard, anyway), so these can be flipped to double the wear life. You don't use the splash guard with mine, unless yours just happens to still fit (some were thinner than others).

Below you will see 2 pix of the Honda vs. the EMGO (which is marketed by JT Sprockets of the UK) sprockets. You can clearly see the difference in tooth profiles and surface finish: the EMGO sprocket has the as-cast, rough surface finish and the Honda sprocket is the smoother one. (Note that I manually offset the Honda sprocket inside of the EMGO on the face-forward picture: the Honda actually does have a larger base circle than the EMGO in this image.) As soon as I find my hi-res camera (lost in the house!), I'll post a shot of the new sprocket against the others, so you can see the differences.

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