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Discussion Starter · #1 ·
I know this has been discussed a few times in the passed but i recently noticed some different solutions.

Chris at MCCycles seems to leave his adhesive to cure overnight - not sure what type he is using.

Pierre at Bear racing seems to have a larger bolt that can take a higher torque rating.

Has anyone tried Chris or Pierre's solutions and how many people are still having the issue?

I know Turbo329 has had some issues with his SC bolts backing out, not sure if he has a permanent fix as yet?
 

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I can tell you I was using new OEM bolts torqued to spec with red high temp Loctite and it sat for about 2 weeks while I was waiting on my ECU to come back. That was back in December and it was around May or June that the head of the bolt broke off. So while mine didn't back out, it did however break. I've seen one other that had the same thing happen as mine. So I'm not totally sure a higher torque value bolt will be the end all but its worth a try I guess. The only issue people have brought up about the bolt Pierre offers is that it doesn't provide a proper channel for oiling like the OEM bolt does.
 

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Discussion Starter · #3 ·
I can tell you I was using new OEM bolts torqued to spec with red high temp Loctite and it sat for about 2 weeks while I was waiting on my ECU to come back. That was back in December and it was around May or June that the head of the bolt broke off. So while mine didn't back out, it did however break. I've seen one other that had the same thing happen as mine. So I'm not totally sure a higher torque value bolt will be the end all but its worth a try I guess. The only issue people have brought up about the bolt Pierre offers is that it doesn't provide a proper channel for oiling like the OEM bolt does.
WOW!!!

So what is the solution?
 

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The "solution" that I'm using is to leave well enough alone. I've yet to hear of a stock one breaking. This also means that I haven't seen or dealt with these sprockets in my own hands. But ... the engineer (and former mechanical designer) in me says that with the style of shaft connection that these sprockets use and with torque reversals due to vibration, there must be absolutely no backlash between the outer splines on the shaft and the inner splines on the sprocket; if anything, this has to be a press-fit. And it has to be a press-fit along the flanks of each spline (so that the torque goes straight through a solid backlash-free joint), not a diametral press-fit (which would still allow relative rotation). If you test-fit one with the shaft coated in machinist's dye, it should rub off along the flanks of each spline. It may still be there at the tip and base of each tooth, that doesn't matter so much. If there is any dye left along the flanks of the teeth, there is rotational backlash, and that is A Bad Thing.

In machinery design if there were torque or direction reversals I avoided splined or keywayed connections with a center bolt/nut like the plague. Taper-locks of some sort were much more reliable.
 

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Discussion Starter · #6 ·
The "solution" that I'm using is to leave well enough alone. I've yet to hear of a stock one breaking. This also means that I haven't seen or dealt with these sprockets in my own hands. But ... the engineer (and former mechanical designer) in me says that with the style of shaft connection that these sprockets use and with torque reversals due to vibration, there must be absolutely no backlash between the outer splines on the shaft and the inner splines on the sprocket; if anything, this has to be a press-fit. And it has to be a press-fit along the flanks of each spline (so that the torque goes straight through a solid backlash-free joint), not a diametral press-fit (which would still allow relative rotation). If you test-fit one with the shaft coated in machinist's dye, it should rub off along the flanks of each spline. It may still be there at the tip and base of each tooth, that doesn't matter so much. If there is any dye left along the flanks of the teeth, there is rotational backlash, and that is A Bad Thing.

In machinery design if there were torque or direction reversals I avoided splined or keywayed connections with a center bolt/nut like the plague. Taper-locks of some sort were much more reliable.
I agree with you, but if it is a "press fit" from Kawasaki surely it would be quite difficult to remove for the people doing the upgrade e.g. they would have to use a small sprocket puller, which i have not heard anyone mention.

Bottom line i guess is Bear Racing did a good job but its not quite perfect, so we need to go back to the drawing board and get it made with much tighter tolerances.

Could very strong adhesive also be used on the splines or is that not possible due to lubrication?

I do think this is a serious enough issue that it needs more engineering to find a better more permanent solution!

I am not comfortable losing a motor due to an aftermarket SC gear coming lose!

Maybe we need to enlist the help of "ze Germans" since they arguably have the best engineers in the world with excellent 'state of the art' equipment.
 

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When you change the sprocket drive ratio to speed up the supercharger you are also increasing the torque that it takes to drive the supercharger by the square of the amount that you change the drive ratio, and you are changing the inertia of the supercharger reflected back to the drive sprocket (which is the bottom one) by the square of the amount that you change the drive ratio. It is entirely possible that the clamping force of the stock bolt is enough for the torque and inertia of the stock design to be transmitted entirely by friction against the flange that it's clamped against without actually relying on the splines, in which case backlash won't matter as much - but it is a marginal design, and speeding up the supercharger goes past what it can take. There is a limit to how much clamping force that can be applied through a bolt of a given size.

The crankshaft of a normal in-line 4 cylinder engine doesn't rotate at a uniform speed. Halfway between TDC and BDC the pistons are moving fast and this has taken some kinetic energy out of the crankshaft, then at TDC and BDC the pistons are momentarily stopped and that kinetic energy has gone back into the crankshaft ... so twice every revolution the crank is going faster than average at TDC/BDC and twice every revolution it's going slower than average ... and superimpose the compression and power stroke forces on top of that, and superimpose torsional vibration of the crankshaft on top of that! The bottom sprocket is gear driven from the crankshaft and gets all of that. The top sprocket has the chain in between, which acts something like a vibration damper.
 

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@GoFaster

And dont forget compressor surge that occurs even with the vented (recirculated) air, and thats connected via chain to the crank. So its got another tug of war thats occurring at moments that are not predetermined in the cycle of operations.

NOLA
 

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Discussion Starter · #12 ·
So what are some solutions?

There must be some serious lateral forces to take the head off that SC bolt, does that mean the stock SC bolt to SC gear tolerance is different to the aftermarket one, in which case would a shim help the situation? Perhaps even a custom shim that fits on the splines, that may take some of the stress off the bolt head?

OR

Make the SC shaft a 'sacrificial one' and weld the SC gear to the SC shaft. I know that creates numerous nightmare scenarios when it comes to engine dismantling but at least the SC gear will stay on the SC shaft!

I would really like to find a viable solution for this problem as the SC gears provide too many benefits to not have a reliable solution.
 

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Anybody on here try a brand new bolt from Kawi when they installed the lower gear ? Instead of reusing the old one ?

I am wondering if that would help. Can the OEM part only take being torqued once and then its got to be thrown out. I can tell you a couple OEM manufacturers have Titanium bolts in their engines that are single use only. If the engine gets modified or rebuilt they have to order all new bolts, as they are single use and expensive.

Yes, I realize Fe vs. Ti are two diff metals, but the Fe part has oil paths drilled in it. Possible its too weak after the initial torque set ?

This is just talking out the box.

NOLA
 

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Thank you, NOLA!

Is there a reason to not just use the "Stage 3" top gear rather than the Stage 2 pair of gears? The change in ratio would be almost the same, and would eliminate having to change the lower spricket and the attendant issue.

?

Loss of chain tension from dropping two teeth overall, while the "Stage 2" method drops one from top and adds one to bottom, and "Stage 1" and "Stage 3" drop just one overall?
 

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The SC lower drive is off the counterbalance shaft , it gets a little free damping than it would on the crank and a slight ratio change
IMO the bolt is only to stop the gear sliding off the shaft, there is no way it can stop any rotational movement in either direction between a loose fit gear to shaft , even the original has enough movement to surprise me considering the method of securing it
I also think Bears new bolt has merit, i dont mind the oil passing along the recessed thread area , strength wise it looks sound compared to the "banjo bolt" style of the original , but it does make it possible to block with enthusiastic locktight application
 

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Discussion Starter · #17 ·
Anybody on here try a brand new bolt from Kawi when they installed the lower gear ? Instead of reusing the old one ?

I am wondering if that would help. Can the OEM part only take being torqued once and then its got to be thrown out. I can tell you a couple OEM manufacturers have Titanium bolts in their engines that are single use only. If the engine gets modified or rebuilt they have to order all new bolts, as they are single use and expensive.

Yes, I realize Fe vs. Ti are two diff metals, but the Fe part has oil paths drilled in it. Possible its too weak after the initial torque set ?

This is just talking out the box.

NOLA
yes, read post #2 in this thread.
 

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Discussion Starter · #18 ·
I can tell you I was using new OEM bolts torqued to spec with red high temp Loctite and it sat for about 2 weeks while I was waiting on my ECU to come back. That was back in December and it was around May or June that the head of the bolt broke off. So while mine didn't back out, it did however break. I've seen one other that had the same thing happen as mine. So I'm not totally sure a higher torque value bolt will be the end all but its worth a try I guess. The only issue people have brought up about the bolt Pierre offers is that it doesn't provide a proper channel for oiling like the OEM bolt does.
How the H*E*L*L did you get the rest of the bolt out of the inner spline after using red loctite or did you just buy a new shaft, which for $95 is a good deal!
 

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Discussion Starter · #19 ·
Perhaps have a new shaft made while reversing the thread on the spline so the threads turn the opposite of the rotation?
 

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If you are going to make a new shaft then make a new supercharger drive sprocket to go with it ... and use a tapered connection and NO splines and NO keyways, and don't forget to design in a method of pulling the taper apart.
 
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