Jackshaft Kit Considerations...

jolfstn

jolfstn

Member
Having a bent rear axle, I replaced it today, and upon accerlation, I felt a POP!, then a pronounced wobble, accompanied by a sickening crunchy sound as the wheel turned. I pulled the wheel off and ball bearings began falling out. I brought the wheel to the bike shop and he asked if the engine was driving the bike's cassette. It does, with the SBP Jackshaft. The kind of freewheel cassette I have, or had, on the Greenline BC-706 M, is not a seperate assembly, but the harder one pedals, the farther it drives the casssette assembly into the wheel. With the tourque provided by a 66cc engine, this was sufficient to drive the cassette through the wheel, demolishing the bearing assembly. $80 for a new wheel and cassette. And I have to wait until Wednesday for parts. Before you add a jackshaft kit, be it SBP, Dax, or some other option I'm unaware of, be sure of the freewheel cassette type you have, and change it as necessary. One of the reasons I chose the bike, was gasbicyclekits.com (Motorized Bicycles - Gas Bicycle Motor Kits and Gas Powered Bikes / Mopeds - Austin) Jackshaft cruiser. scroll down about half way, I have the exact same bike, except my motor is black, slant head. I assumed that the bike would be ideal, as these professionals are selling the exact same set up for over $1000 assembled. and excepting the cassette issue, it is ideal, but that is pretty major, dangerous issue. I've mentioned this in previous posts, I am not a bicycle mechanic nor a small motor mechanic, although with my experience in the past few months I probably qualify now. Be sure of what you are doing. Post here, ask questions, and most of all, BE Patient! I know it's not easy. For the amount of time I've spent trying to get this thing to work, I could have had a full time 2nd job. For the ammount of money I've spent, I could have a crappy but drivable car! Be safe. -J
 
I just emailed gasbicyclekits.com aka texasmotorbikes and told them of my experience.
To whom it may concern: I would like to address an issue with your product the "Jackshaft Cruiser" made from the Greenline BC-706 M. I was so impressed with the one on your website, but didn't have $1000 to shell out all at once, so I built my own. I found a black Super Rat GT-5 66cc engine on ebay, purchased the BC-706 M from ocbeachbikes.com (now out of business) and the jackshaft kit from sickbikeparts. All the various and sundry other bits I've ordered from a dozen other vendors. I assembled it, and got it running. After maybe 15 miles, the rear wheel began wobbling. I replaced a bent axle, and got it running again. Today, I felt a nasty POP! back there, then a really pronounced wobble, accompanied by a sickening crunchy sound as the wheel was turning. I removed the wheel and a bunch of ball bearings began tumbling out. I brought the wheel to the bike shop, and they said the engine driving the rear cassette is to blame. Instead of the rear cassette being a seperate assembly, the design on the BC-706 is such that the harder one pedals, the farther it drives the cassette into the wheel. Add the tourque of a 66cc engine, and that is sufficient to drive it into, eventually through the wheel. In my case, it demolished the right side bearing assembly inside the wheel, and now I have to pay $80 for a new wheel and cassette. From the photos on your site, I'm assuming you are leaving the original rear wheel/freewheel/cassette assembly as it comes from Greenline in your finished product. According to my experience and what I was told by the bike mechanic, this assembly cannot be safely driven with a jackshaft. it WILL eventually fail, and at higher speeds (the main reason one uses the jackshaft, enabling shifting) this could obviously be exceedingly dangerous. I urge you to replace the rear wheel with a cassette/wheel assembly that is seperate from the wheel, the cassette on the one I'm buying sits over the freewheel, isn't part of the cassette. According to my bike mechanic, one could add all the tourque one wants on this set up, and although it is possible to overwhelm, it will not ever drive the assembly into the wheel the way the original on that bike would. You might consider at least letting the customers to whom you've already sold these models to as to the danger they could be dealing with. I know this isn't good for sales, and I'm sure you have some disclaimer somewhere that states "motorbicycling is inherently dangerous, etc, etc,..." but as a vendor of finished motor bikes, instead of just selling kits, don't you have a responsiblity to somewhat mitigate potential known dangers, or at least point them out? Thank you for reading.
 
It is very well worded. Let's hope that they actually take the time to read it and follow through on correcting a potentially deadly flaw in their bike!
 
The email I sent to [email protected] bounced back, there is no other email on their website for contact, nor can I find the new site for gasbicyclekits.com which is according to them texasmotorbikes.com. No site with that ip on google. Does anyone know a valid email for them? I would like for the powers at that company to read my email.
 
The shift kit will bend and break standard or hollow QR (quick release)
axles. You need to make sure your axle is chrome moly.

If you speed shift without letting off the throttle momentarily when shifting
you will inevitably bend or break axles. I know I've bent and broken 3 of them.
I've learned to baby it a little.

Also it's vital that the pre-load on the back wheel bearings is set just right.
Too tight and it will grind the bearings up. The cups and axle cones will wear prematurely and get scored up. That results in quick failure.

Too loose and the wheel will wobble a little and wallow out the bearing cups,
get deformed and self destruct.

Make sure the jamb nuts are tightened against the axle cones using a cone wrench. If the 2 nuts turn as one, then they will turn on the axle under load, which will tighten or loosen the bearing pre-load depending on which side works loose. You'll forever be adjusting the rear wheel bearings if they don't fail first.

You also will need to re-pack the bearings with good axle grease on a regular basis. It's a not fun job, especially on the gear cluster side.

If you have the single piece freewheel and not a freehub they will thread on quite tightly onto the axle hub. I would definitely recommend using anti-seize compound before threading a new freewheel onto the hub.

Ultimately it's up to you to minimize the potential for failures on your bike.


TiM
 
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