21 sp GT LTS 3 Build

Discussion in 'Photos & Bicycle Builds' started by ArtemisJones, Oct 18, 2014.

  1. ArtemisJones

    ArtemisJones New Member

    1st mockup. There is lots to do. Custom motor mount, modify tank mounts, install shift kit, lights and ignition - and the list goes on. I am glad I took the time to do the research.

    It will be a nice basement project, for lousy winter days.

    It has hi compression head, ported/polished cylinder, balanced crank, race carb, hot CDI ignition and expansion chamber exhaust.

    FYI - I also posted this to my FaceBook page. One comment I got: Is it electric or gas? I just had to shake my head...LOL

    My GT LTS 1.jpg
    Last edited: Oct 18, 2014

  2. Bzura

    Bzura Member

    That's a nice setup! I especially like the head :cool:

    Does the gas tank flop around much with the rear suspension? I really like that older GT frame, and I've been eyeing one up on Craigslist. The price keeps coming down. Any weakness that you can tell me about the bike itself?
  3. ArtemisJones

    ArtemisJones New Member

    I got the frame in yesterday. I just mocked the motor in to see what i needed for a motor mount. I think I am going to make an adapter plate and attach it to the water bottle mounts. They are very solid. The tank will require some engineering. I really wanted a rear tank, instead of a front mount 'nut buster'; clean lines and rider comfort LOL. I am also getting a hard shell triangle bag. If fill fit up front, in frame, and house ignition and battery for lights.

    With all LTS bikes, worn rear suspension bearings can be an issue. The previous owner redid them 5 yrs ago and stopped riding it 2 yrs ago.

    Needless to say, I am pumped. I will do by best to keep a journal and pics of the build. I am busy right now, and can't get to it for a month.
    Last edited: Oct 18, 2014
  4. KCvale

    KCvale Motorized Bicycle Vendor

    A GT jackshaft is pretty easy.

    This is a hard tail I built this way back on 1/2012 but the same center and front geometry.



    The 7-speed finally broke so he showed up with the bike and a Nuvinci hub for it 8/2014.
    No biggie, lacked it in, changed the controls, and he's motoing again.



    I suggest just get the SickBikeParts jackshaft kit (with the tools if you don't have them), their Small front motor mount that fits your downtube, their expansion chamber exhaust, dual pull brake lever, and grab an NGK Iridium plug.

    Your bike has 3-piece cranks but what kind? Shaft and bearings, or a cartridge?
    All your motor and pedal power rotate on the freewheel sprocket mounted to your right side pedal shaft.
    The SBP kit comes with a cartridge, see if that's what you have and if not get the SBP threaded BB bearing cups with the shift kit.
  5. ArtemisJones

    ArtemisJones New Member

    Hiya KC - really like some of your bikes and appreciate the expert level imput.

    The posted pic was just a mockup to see engine position. I have the SBP Shift Kit and all of the rest; as well.
    There is a member on this forum [not current] named 'gasbikeproject'.
    He has built 3 different GTS bikes, using the Shift kit, while maintaining the 3 original front gears. Here is an example


    I would have been happy with the back 7 gears. The prospect of having 3 different gear ranges [hill climb, 'round town, open road] has me intrigued. I have written him here, as well as his website; no reply, so far.

    I am currently moving, so all of this will be on hold. I have all winter to complete this project. I am in no rush and plan on doing it right; first time.

    Last edited: Oct 19, 2014
  6. KCvale

    KCvale Motorized Bicycle Vendor

    I looked at the example, what he didn't show is how offset the drive chain is at extremes or his handlebars.

    Yes the freewheel bearing will allow you do all kinds of sprocket things with 5 hole sprockets and spacers, but why?

    Bike gears are for people power and all pretty much have the same lowest gear reduction and high end overdrive gear ratio.
    The difference is the number of steps you can choose in between them, and for most every application I find a simple 3-speed internal hub (lowest-middle-highest) to be the best with engine power but that's not my point...

    My point is besides not needing any more ratios than a 7-speed cartridge what would you do with your handlebars?

    My stance on this is no more than 2 levers and twist controls.
    To that end I:
    1. Strip the handlebars of everything.
    2. Remove the complete front derailleur system.
    3. Put a dual pull brake lever and throttle on the right.
    4. Put the clutch and 7-speed rotary shifter (upside down) on the left.
  7. ArtemisJones

    ArtemisJones New Member

    KC - using a single front sprocket was my original plan; may stick with that. I already have the dual brake handle. I also have 9/10/11 tooth sprockets for the jackshaft. If I go with the single front gear, I will experiment, to find the sweet spot.

    Thanks, so much, for your input......
  8. KCvale

    KCvale Motorized Bicycle Vendor

    Good plan and my pleasure, but you can also just change the size of pedal drive sprocket with much less hassle, it's just the final drive chain to mess with.
    I've run 32-42T depending on the bikes gears and it beats aligning jackshaft chain.
  9. 052.jpg Sorry I did not get back to you sooner. Well it would seem KC is not a fan of my 21 speed bikes. To build the 21 speed cluster and mount it you must use the wider 153 mm crank cartage instead of the stock one the comes with the deluxe shift-kit from SBP. And yes on the road there are way more gears than you need, but off road I use them all.
    FurryOnTheInside likes this.
  10. My bar setup is fairly simple clutch on left and both shifters as well. I use Rapidfires lever actions. Gas kill and dual brakes on the right .
  11. KCvale

    KCvale Motorized Bicycle Vendor

    A CNS carb as well. Most people don't like them but I had good luck with them.
  12. IMG_20121202_111808.jpg IMG_20121202_111739.jpg All my 21 speed builds. Red was the first. 4 gt lts's.