GasBike Lowest Price Transmission Chain Stretch Fix for HS-142F

Discussion in '4-Stroke Engines' started by bakaneko, Jun 21, 2016.

  1. bakaneko

    bakaneko Active Member

    Hello. I thought I share what I did to "fix" or compensate for chain stretch in my GasBike transmission box. The chain in the GB transmission is very small and I think the BikeBerry one is small too but probably not as small. After normal use, the chain will stretch and might jump the drive sprockets in the transmission rendering the transmission useless. I think I am probably the only HS-142F rider with the lowest price chain transmission box so not sure how relevant this is to other HS-142F riders, but to compensate for the chain stretch I bolted in a chain guide to the bottom portion of the drive chain that also moderately increases tension.

    The chain guide consists of a steel bolt, nuts, spacer, and washers. A 2 inch bolt with no threads (until the end) is the drive shaft with the two spacers being the chain guide and a spacer being the bearing. These are offset using nuts so that the guide portion is aligned with the drive sprockets. There is about 1/8" play for the chain in the chain guide. I drilled a hole into the transmission to place the chain guide with low chain tension. The nuts, spacers, washers diameter is slightly larger than the bolt. And, all material is stainless steel.

    This has been working well for almost 200 miles and there is some additional noise due to the spinning washers I think. The spacer as a bearing is okay, but it would have been better with a stainless steel ball bearing. Problem is the cost for those bearings are around $10 and the transmission is $50 new. This setup cost me $5. I put a bunch of high temp grease inside the transmission. Not the prettiest fix, but I don't have great tools and yeah its a $50 transmission.

    Here is a simple diagram and pictures of it. Yup, my bike is a dirty mofo. :eek:

    Attached Files:

    Last edited: Jun 21, 2016

  2. dougsr.874

    dougsr.874 Active Member

    That transmission is inherently a bad design....throw it away and get a 4g from
  3. bakaneko

    bakaneko Active Member

    The design is extremely simple. This fix was probably the most straight forward though not adjustable way to do it. There are probably much better ways including using steel ball bearings and springs. I cruise comfortably at 25 and hit 30 at slightly beyond mid throttle. I would recommend the lowest price GasBike transmission if you are on a budget and understand that at some point you will have to compensate for chain stretch. No need to throw it away.
  4. skyash

    skyash Active Member

    I made a bigger sprocket 1t more at work and got a heavy duty chain no problem since. I found my box was bent put a ruler on the side and see? and I blame having the drive chain to tight. And what size back wheel do you have I find this box to be way to overgeard even on a 20inc wheel I have to pedal to take off like half a street . For $10 get a pocket bike box and swap the shaft over thay seem stronger and 1 mm shorter and comperd to $50 for a 4 stroke there the same box just different sprocket to the back wheel. Thay are made for pocket bikes with small wheels so on a 4 stroke 26inc bike thay suck bad should not even sell it with a 4 stroke kit
  5. skyash

    skyash Active Member

    Kit with the bad box $200 kit with good box $350 ➕ all so where you put a chain gide I was going to put a block of nylon like thay use on dirt bikes
  6. CrazyDan

    CrazyDan Active Member

    Those cheap boxes will eventually fall apart, had one that eventually got huge play in the output shaft. The spot that held the shaft bearing in the outer case got warped so it allowed that bearing to move around. I first noticed when looking down as I opened my throttle, watched as the shaft bent back at an awkward angle.

    Needless to say I'm running a 4g now, loving its 5:1 initial reduction. Them cheap boxes run a 3:1 reduction, you need at least another 5:1 reduction to be usable, 6:1 even better. So with a 10 tooth output sprocket with a 50 tooth rear sprocket will give you 15:1 reduction at the rear wheel, a 60 tooth will give you 18:1, good for hilly areas.
    Last edited: Jul 16, 2016
  7. bakaneko

    bakaneko Active Member

    Yeh, I noticed a slight tilt in the output shaft as you mentioned but it hasn't been a problem for me or has not reach that stage yet (~1500 miles). I am also a lighter rider but in no way am I babying it; I do crank it up to 33mph on a 44T on flat roads and about 22-25 on hills depending on the gradient. I think the cheap box is fine; you will have to account for the 3:1 reduction and chain stretch though which I did by bolting an internal chain guide in the transmission box. I am sure 4G is great but I am not paying that price when the cheap box is fine with modifications.
  8. CrazyDan

    CrazyDan Active Member

    I got lucky and purchased a bike for $150 that needed some work but had a very good 4g and a motor that lasted another 1500+ miles. Owner guessed he had over 10k miles on it already.

    I had around 4k miles on that 3:1 box before that tilt was bad enough to go from perfect tension to chain jumping off at full throttle. I guess if you managed to fabricate a cover out of more durable metal that box can be made to last. Gotta say 43 mph was fun with the stock low reduction I had with the 44 tooth.
    Last edited: Jul 16, 2016
  9. KCvale

    KCvale Motorized Bicycle Vendor

    Nice score!
    A new 4G is $140 here
    I build a lot of 4-strokes and the 4G is the best transfer case available and all I use.
    Do your best to make the garbage gasbike/kings sells if you want, just don't expect anything you do to make up for lack of quality and design to make it better.
  10. CrazyDan

    CrazyDan Active Member

    Mine is the one with 20-100 reduction, 6 holes on the big sprocket and freewheel 12 tooth output, had to replace the original belt after about 1k miles. Was already torn when I bought it, surprised it lasted so long :D. Didn't come with a cover so just gotta watch out lol :p.