Mystery Solved

[the Ferret]

Ok both have had a chance to respond to each other. We will not turn this into a peeing match between forum members online. You are welcome to PM each other and "discuss" all you want.

if this thread degrades, we will lock it down. Comprende?

[kennyw]

rbike, if you reduce the OD on the sprocket, you will not change the bolt pattern that attaches the sprocket to the hub. You would still have the exact same, less than a mm clearance. You could end up with higher stress in the reduced section between the teeth and nut. This could be fix by reducing the size of the "speed holes".

The stock Honda sprocket has the exact same nut to hub clearance with a thinner sprocket that gets wider at the teeth (shaped like an I beam if you look at cross section).

[rbike_imp]

Thanks Kenny. You are 100% correct! I was in a brain dump mode after receiving a 37T instead of the 35T I had ordered. I was trying to figure out why he did not do the 35T I had ordered. I shrank the inside vs outside edge - my bad. Even I make mistakes - you caught me on a rare moment- lol. Maybe I will get a 35T someday.

[kennyw]

The sprocket you purchased only reduces the section as a C'Bore because it is cheaper to build it that way than to machine the entire surface to match the Honda profile.

The only feature I could have an issue with as a Mechanical engineer is the speed holes in the aftermarket sprocket. They greatly reduce the strength of the sprocket compared to stock by relying on a smaller section area to carry the load compared to the original resulting in much higher stress concentrations. Some of that material is not heavily stressed and safe to remove, but those slots are fairly large. Without running the numbers I do not know if it is an issue for this application though.
If you want to see some interesting sprocket design... Wisconsin Racing posted a video showing the load paths of a sprocket under acceleration (engine braking would act in the opposite direction meaning you can't make your sprocket look like this and expect it to work in the real world).

[url=https://www.facebook.com/photo.php?v=398611056823668&set=vb.141092665908843&type=3&theater]https://www.facebook.com/photo.php?v=398...=3&theater

[rbike_imp]

Kenny, Thanks again! In between these post, I recontacted the actual manufacturer and they are going to build me another sprocket-I can't say enough good about them. This time it will be a 35T! AND it is not going to have any cutouts. It will be full strength. I should have it relatively soon too. It is not going to take 4 months this time. I'll post the pics when I get everything.
This brings up my original concerns though. Thankfully, I have all the parts required to shorten the chain (will be necessary) to a correct length, but will utilize the local store for the chain break/mate tools.

I'm crossing my fingers regarding having enough clearance from the slider. With a couple of links removed, it should assist with that situation - time will tell if enough. I'll keep all updated. If everything works out, I'll have a new 37T available if someone ....

[pekingduck]

The sprocket you purchased only reduces the section as a C'Bore because it is cheaper to build it that way than to machine the entire surface to match the Honda profile.

The only feature I could have an issue with as a Mechanical engineer is the speed holes in the aftermarket sprocket. They greatly reduce the strength of the sprocket compared to stock by relying on a smaller section area to carry the load compared to the original resulting in much higher stress concentrations. Some of that material is not heavily stressed and safe to remove, but those slots are fairly large. Without running the numbers I do not know if it is an issue for this application though.
If you want to see some interesting sprocket design... Wisconsin Racing posted a video showing the load paths of a sprocket under acceleration (engine braking would act in the opposite direction meaning you can't make your sprocket look like this and expect it to work in the real world).

[url=https://www.facebook.com/photo.php?v=398611056823668&set=vb.141092665908843&type=3&theater]https://www.facebook.com/photo.php?v=398...=3&theater

I have not seen a sprocket fail as you describe on a bike - the chain will break first or rip the teeth off first. I don't think they can generate enough traction.

[kennyw]

The link I shared was to a formula SAE team. They use a motorcycle engine in a small racecar. With an aero package creating down force and sticky racing tires, that is where you would start to see failures because the sprockets are loaded higher than on a motorcycle. It is also an engineering design competition, so it is important to go through the small details of every part of the car design.

On a bike, I would need to know more to know the limiting factors and actual loads. But, most factory sprockets wear out at the teeth first and they are likely designed that way intentionally for the intended applications. Most of that wear is from dirt and grime getting in between the mating surfaces.

In an aftermarket sprocket, you can cut material out of the center safely up to a critical point. The load will redistribute to the remaining material. The more material you remove means higher load and greater deflection (bending, twisting, stretching) on the smaller cross section that remains. All metals have an elastic region where all of that deflection can be recovered once the load returns to zero. As long as you don't exceed that linear limit, the material will go back to its original shape.

Then there is fatigue, bend a paper clip back and forth until it breaks and you have experienced a fatigue failure. The reduced sections on a sprocket will bend more than a sprocket without a cutout. They will then fail from fatigue faster than a sprocket without cutouts.

I cannot tell you if a sprocket will fail first from normal wear at the teeth or catastrophic fatigue in the reduced section without first knowing the geometry, material, and load parameters. I can only tell you I am concerned enough to say it is worth checking if you design a new sprocket.