2.5L Rocket Stroker Engine Kit with 6 Speed Transmission (R&D)

[Rocky Raccoon]

...I really wish that 6 speed had come to production... would solve a lot of problems I'm going to have next year.

I also have been dreaming of the 6-speed.... he says it will take $100K if we can get 100 buyers to tool up and produce them.

 

[R-III-R Turbo]

So here's the design, free to one and all.
I've brought it this far, feel free to go get someone to make it for you.

This was demonstrated to work in a prototype/proof of concept way, so it isn't perfect, but it's 95%+.
Needs a gear manufacturer and a guinea pig to finalise.

It's been a few years so hopefully I haven't forgotten anything pertinent, or mixed stuff up any.

The secret/trick was using the same gear pair as 3rd, but in reversed positions.
I.e. 3rd is 23T input and 33T output, and this 6th is 33T Input and 23T Output.
The principle was beautiful in its simplicity really.
The rest was about fitting it all together.

This is quite overdriven and will result in cruising at a touch under 2200rpm in 6th at 80mph, as opposed to over 3000rpm in 5th.
Will raise top speed potential (i.e. provided you have the power to get there, or are on a dyno where there is no wind resistance) to 220mph at stock 6300rpm, or 320mph if you spin the motor to 9000rpm.

Gear Ratios
Primary 1.034:1
1st 2.929:1
2nd 1.947:1
3rd 1.435:1
4th 1.160:1
5th 0.964:1
6th 0.6969:1
Secondary 1.043:1

I'm sure there are more interesting tidbits I've forgotten.



Parts List

0. Heavy Duty Wider & Deeper Groove Circlips

1. Input 3rd & 4th Gear

2. Input 6th Gear Splined Bush

3. & 4. Input 6th Gear Splined Washers

5. Input 6th Gear - 33T Straight Cut Spur Gear

6. Input Shaft inc 14T integral spur gear

7. Output 1st Gear (modified existing)
(-1.0mm off front face, -3.45mm off front face of centre boss)

8. End Washers (2)
Input 2nd Gear End Washer M30x42x1
Output 1st Gear End Washer M25x35x1.5

9. Output 2nd Gear (modify existing)

 

[R-III-R Turbo]

10. Output 6th Gear
(23T straight cut spur gear on dog ring)

11. Output Shaft

12. Selector Drum

Drum Track Map

13. Selector Fork A (modify existing OEM)

14. Selector Fork B (modify existing OEM)
(-5.0mm off dowel end of cylinder)

15. Selector Fork C

16. Selector Fork Shaft (modify existing OEM)

And last but not least, the CAD files >>> LINK TO DOWNLOAD
Enjoy!


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[Joesmoe]

I drool for this. If anyone takes the torch, I'm up for an order of the resulting kit.

 

[Joesmoe]

Here you go, @Sparky59

 

[SpazOnaR3]

I'm willing to devote up some time to cutting up as many parts as I can. It'll be a slow going, piece by piece sort of affair, but I can make/modify a lot of those parts.

Do you think a stock shift drum could just be modified by extending the existing tracks, or does a whole new piece need to spring into existence for that one?

 

[Idaho Red Rocket 3]

Just a thought that occurred to me now .... would any of these needed components be compatible with the corresponding parts in the 2500 transmission ?

 

[R-III-R Turbo]

I'm willing to devote up some time to cutting up as many parts as I can. It'll be a slow going, piece by piece sort of affair, but I can make/modify a lot of those parts.

Do you think a stock shift drum could just be modified by extending the existing tracks, or does a whole new piece need to spring into existence for that one?

If I remember correctly, no I'm afraid. Initially I thought you could, as in weld up the blank space where the fork tracks for 6th gear positions should be (the stock drum has space for a 6th gear track, as the detent wheel already has 1-N-2-3-4-5-6 positions), but then found that the tracks need to shift left or right a little to facilitate making space for the 6th gears.
So a new drum might be as economical as welding up the stock drum, turning it back down and re-machining out the fork tracks.

Just a thought that occurred to me now .... would any of these needed components be compatible with the corresponding parts in the 2500 transmission ?

I'm afraid that would be a no.

1. Rocket 3s have a helical cut gear set whereas the Rocket IIIs have straight cut spur gears. Various reasons under this point say not possible.
2. The centres of the input and output shaft would need to be exactly the same, which is possible but unlikely imo.
3. The parts needed (and everyone only ever focuses on the "6th gear", not realising there are many parts needed to combine so one has a 6th speed in the trans) would have to happen to be the exact dimensions and design
4. If you mean just lift the input and output shaft assemblies out of a Rocket 3 and drop into a Rocket III, again the centres and locations of the input, output, fork shaft, selector drum etc would all need to happen to be exactly the same, the overall length of these assemblies and their bearings etc, and the size of the compartment in the block would have to happen to be exactly the same, which is ridiculously unlikely.
5. The Rocket 3s' 6th gear is practically the same in terms of rpm per speed / road speed capability as the Rocket IIIs' 5th gear anyway... so all of the above become moot points.

Rocket 3 gearbox

Rocket III gearbox

 

[SpazOnaR3]

Hrm. This has me thinking that cutting up 2 different torsion gears would be a whoooooole lot easier way to get a lot more mph out of the bike. For all the turbo/SC guys, we have more than enough torque to make 1st gear absolutely useless; why not just stretch out the overall ratio of all the gears instead? With the extra rpm that the carpenter/higher rev limit folks have it I don't think they could pull the stock gearing all the way out, but it would reduce cruising rpm down a bit.... just flipping the ratio on the torsion gears would be really close to 8% more gear.

EDIT: Good grief, that torsion gear set up would have a huge impact... if you could squeek something like 42/52 in there (as opposed to the 48/46 stock), it would stack 23% on to each gear.
1st: 65
2nd: 98
3rd: 133
4th: 165
5th: 198
...on a small tire. it would drop about 725 rpm off of the cruising rpm @ 75mph. Bike has the torque to pull the first gear for most of us, for sure. And honestly, less shifting is more enjoyable... and generally faster, than extra shifting.

 

[R-III-R Turbo]

It was something I looked at some years ago when examining the transmission first. Like flipping the 3rd gear pair to give the 6th gear pair, you can indeed also flip the output helical gear and the torsion damper helical gear and not have any centres challenges.

However my feel at the time was, one would have to get 2 new gears made (the torsion damper one is a bit special as the torsion damper follower has to mate with it), and one would also have to get 2 gears made for the 6th gear too.

Having gone further down the road it became apparent that several more parts were needed for the 6th gear, but still only 2 gears needed for the output/torsion rearrangement.
But the 6th still yielded much much greater results in terms of speed capability and rpm drop for cruising (and let's not forget making use of the 6th gear spot on the detent & shift drum), so onward Christian soldiers we went.

Kind of kept the torsion gear flip as a further enhancement in the back pocket, for when the 6th gear was not quite enough, this could be added on too for extra excess.

Sort of like oversize pistons and custom liners was next, after completing the stroke job.