Thoughts on Internal Shifting Hub?

[Steve Best]

Hey Gino,
I've souped up my Grubee Skyhawk with enough power to see 44mph on a single speed. I have no doubt it would have broke 50mph with proper gearing. I also had a jackshaft kit on my 50cc bike working through a conventional 7 speed derailleur. Here are my impressions:

A properly ported and rechambered China Girl (PK80 or Grubee) will easily make more than enough power, especially with a tuned pipe (I have not even started with tuned pipes yet) to achieve 50mph with the right gearing.

The jackshaft plates, shafts and sprockets are all heavy steel. With the chains, I found the jackshaft kit added a lot of weight to the bike, more than 10 lbs, almost as much as the motor. I kept the sprockets in close so while I did widen the pedals slightly for mine, but I could have kept the original pedals if I really wanted.
I didn't like:
1) having to "kick-start" the bike, but got used to it.
2) the extra weight of the jackshaft kit,over 10 lbs.
3) extra complication and chains to set tensions on extra chains
I did like:
1) no pedal start-away on hills, just release the clutch in low gear
2) quiet cruise at low rpm
3) noticed an improvement in fuel economy
4) no hill too steep even with a stock 50cc

If the jackshaft kit plates were made of aluminum and shaft kept short and the sprockets lightened and drilled you might get the jackshaft kit down near 5 lbs. The kick-start will still be required

I am riding mostly street with my 50cc so I removed the jackshaft and am running single speed again. With a little porting and head work it does 30+mph with the 50cc and that is plenty fast on a light bike. I like that I can lift it over fences and carry it up stairs.

 

[gary55]

I have the shimano nexus 4 speed internal on this bike. It came with the bike used, and has performed well for 1500 miles so far. I used the SBP heavy duty j shaft kit. I also bought one that was built by someone else with a 4 stroke j shafted to a strumey archer 5 speed internal. The 4 stroke looks really nice, but is a complete dog on hills. The 2 stroke bike is super heavy, but it does everything I need in a MB.

 

[Street Ryderz]

im going to try doing the pedal chopper set up for jack shaft and my own devised gearing! i just ordered form Stanton inc, 15 tooth 415 chain gear for left side,16 tooth z72 free wheel for right side.12 tooth z72 drive gear for right side,10 inches 5/8 keyed shaft,shaft collars,free wheel adapter,keys,and bearings for under 100 bucks! and here is my proposed gearing 1st just slightly higher than a stock 44 at 4.5,2nd is 3.8,3rd is 3.5 ,4th is 3.1, 5th is 2.8, 6th is 2.5, 7th is 2.4, my thinking is these ratios will give the best all around performance for acceleration,speed,mileage,longevity the only thing is im not sure how the smaller z72 chain will handle the load

 

[Street Ryderz]

Hey Gino,
I've souped up my Grubee Skyhawk with enough power to see 44mph on a single speed. I have no doubt it would have broke 50mph with proper gearing. I also had a jackshaft kit on my 50cc bike working through a conventional 7 speed derailleur. Here are my impressions:

A properly ported and rechambered China Girl (PK80 or Grubee) will easily make more than enough power, especially with a tuned pipe (I have not even started with tuned pipes yet) to achieve 50mph with the right gearing.

The jackshaft plates, shafts and sprockets are all heavy steel. With the chains, I found the jackshaft kit added a lot of weight to the bike, more than 10 lbs, almost as much as the motor. I kept the sprockets in close so while I did widen the pedals slightly for mine, but I could have kept the original pedals if I really wanted.
I didn't like:
1) having to "kick-start" the bike, but got used to it.
2) the extra weight of the jackshaft kit,over 10 lbs.
3) extra complication and chains to set tensions on extra chains
I did like:
1) clutch starts on hills
2) quiet cruise at low rpm
3) noticed an improvement in fuel economy
4) no hill too steep even with a stock 50cc

If the jackshaft kit plates were made of aluminum and shaft kept short and the sprockets lightened and drilled you might get the jackshaft kit down near 5 lbs. The kick-start will still be required

I am riding mostly street with my 50cc so I removed the jackshaft and am running single speed again. With a little porting and head work it does 30+mph with the 50cc and that is plenty fast on a light bike. I like that I can lift it over fences and carry it up stairs.

how does clutch start on hills work doesnt the free wheel prevent that?

 

[gary55]

Trying to start going up hill is a chore with a j shaft. You have to kick start it with the pedal while the clutch is out.

 

[Steve Best]

Trying to start going up hill is a chore with a j shaft. You have to kick start it with the pedal while the clutch is out.

I edited that line to: no pedal start-away on hills, just release the clutch in low gear
I meant moving the bike with a running engine, not starting the engine.

 

[gary55]

Hay Steve.Been thinkin a lot about that squish band stuff. Checked out how the piston relates to after market heads.. From what I could round out with using h/2+w2/8xh=r it worked out to the piston being at a radius of 3.60" and the head cut at 11 deg.. The piston marked with a sharpie would only touch at the half way point on the squish band which led me to this wonder why. A radial surface and a straight cut surface. See what a picture of sand paper glued on top of a piston leads to. It's all your fault. Watch out for them bobcats.

 

[Street Ryderz]

Hey Gary you use a jackshaft kit do u use a regular bicycle chain on drive (right)side? and has it held out out well ?

 

[KCvale]

Hey Gary you use a jackshaft kit do u use a regular bicycle chain on drive (right)side? and has it held out out well ?

Good single speed 410 chain works well for internal shifting hubs, 7-speed chain works but you need to use some finesse when shifting as a bad shift can break the thin chain.

 

[Steve Best]

Hey Gary you use a jackshaft kit do u use a regular bicycle chain on drive (right)side? and has it held out out well ?

I've used regular 410 chain for both the jackshaft kit sprockets and for the primary drive off the motor.
I also use it for the single speed kits. As you know, the final drive takes the most torque.
If the thin 7-speed chain can handle the final drive, there is no problem with 410 chain.

I suspect the guys using 415 and 41 chain are compensating for inadequacies in other areas!

Seriously, the 410 chain offers significant advantages in economy, weight, centrifugal effect and wear on other components. I like KC's analogy of using a ship's anchor chain for a dingy. 410 (BMX or single speed bike) chain is available at any bike shop ($10) and more than strong enough for our application.

Like KC mentioned, a rough shift with a derailleur shifter can damage the chain and sprocket teeth.
I had a few rough shifts where it jumped as I opened throttle and could see the effect on the rear sprocket teeth.
More power causes more damage.

Steve