KC's 4-stroke 3-speed on GT2A-S gas tank frame

Discussion in 'Photos & Bicycle Builds' started by KCvale, Jan 19, 2014.

  1. KCvale

    KCvale Motorized Bicycle Vendor

    I have been itching to build a high end bike from the ground up on the cool Grubee GT2A frame designed specifically for motorizing from the in-frame 2.5L 2/3 gallon tank to the engine friendly frame geometry and I finally have my chance.

    I have a customer that wants a 4-stroke 3-speed shifter like Big Red, but without the 'barnacle' gas tank.


    I went through all the common options but as his budget grew so did the options until we got to GT2A frame which made for a ton more options.

    Anyway, other than a base color theme and look I had him start with from the options of 3-speed wheel sets I have a big pallet to work with.

    After an hour in my local bike shop with nothing but the bare painted frame and wheel set I got it on it's feet and rolled it out the bike shop door yesterday.


    The is no easy way to explain how cool it is to have great little small business bike shop around corner that has actually grew to accommodate my business needs with MB enthusiasm.

    They have a work space for me to do things so I looked at tire options and finished the wheels and then moved on to picking the right fork, headset, handlebars and seat post by trying them on and looking at it.

    But back to the build...
    I had my local auto painting place paint the frame, chain guard, all the SBP 4-stroke shift kit parts and other misc parts to exactly match the rim color.

    They did a nice job.
    3 coats of primer, 2 coats of paint, and then 3 coats of sealer on everything.

    Some parts specs:

    Weight 1980g
    Axle to Crown Length 460mm
    Crown Race 30.0
    Brake Type Cantilever, Disc, Linear Pull
    Wheel Size 26"
    Travel 80mm
    Front Hub Spacing 100mm
    Front Axle Type 9x1
    Spring Coil
    Wheel Mount Center Offset 0mm
    Steerer Type Straight

    KORE headset with 5 1/2" forward offset and 'just right' beach cruiser handlebars.

    Tire Parts:
    Standard inner liner.
    Sunlite 6321 HD thorn resistant tube.
    Thick 'special material' outer liner.
    Kenda K1008 Flame 26x2.125" Cruiser Tires.

    I really like Kenda tires and the cool flame tread design and not just because my wife's name is Kenda ;-}

    Obviously more to come but I couldn't resist posting about this new build as it comes along from this point ;-}

    *Note I made a topic here http://www.motoredbikes.com/showthread.php?42525-GT2A-S-in-frame-tank-frame-for-MB-s
    with pics and specs for a real close up look at what th4 GT2 frame is and what is really required to build any MB with this frame as the base so please refer to it for frame details.

  2. LR Jerry

    LR Jerry Well-Known Member

    Can hardly wait to see this build. As for tires here's a company you may want to try in the future. The V99 tires come in different colors.

    BigBlue likes this.
  3. wheelbender6

    wheelbender6 Well-Known Member

    I'd love to do a build with that GT2A frame. However, with our nebulous motorized bike laws in TX, I fear the local law men would consider it a "motorcycle" because of the in frame tank. and require me to tag it.
  4. Pablo

    Pablo Motored Bikes Sponsor

    I do like that frame!!
  5. KCvale

    KCvale Motorized Bicycle Vendor

    It really sucks being a perfectionist sometimes, and it's not firgg'n cheap or a one man job in cases like this either, but that's what it takes to meet my standards and I start from the ground up.

    I know, bla bla bla, until you look closer and see the progression of how you fit stuff as you go as it sucks to go backwards and why we spent all day just getting the JS pedal drive train perfect, the wheel aligned perfect, and then perfect fitting 3-point mounting fenders on it.


    It doesn't look much different than my first pic which was the whole point, I'll post the details later but here is a tip for getting stickers off.

    Just use the end of a lemon which is easy for me, I have a big lemon tree full of ripe lemons.


    To me it's all the little subtle stuff you can do as you go and why I including it as I go for all you guys that think you might want to use this frame and I hope it helps ;-}
  6. KCvale

    KCvale Motorized Bicycle Vendor

    It turns out the SickBikes 4-stroke Jackshaft kit motor mount base once all the muffler clamp parts are in place is over an 1" longer than the direct drive 4-stroke base the frame was designed for thus moving the engine position up to the point of the top bar interfering with function.

    We spend the morning fabing some mount changes that should work and as the parts paint drys outside we went to work on getting the bike ready to just drop the mount and engine in and hook it up.

    Pictures just don't compare to looking at it person and even riding it around as a pedal bike but I did what I could to get some pics from my alternative photo wall for this late time of day.






    Needless to say we are chomping at the bit to get the engine in and ride it tomorrow ;-}
    Hamzsim likes this.
  7. Donavan321

    Donavan321 Member

    Wow! I can't wait to see the outcome! also I noticed it looks like your fork can accept a disc caliper. Going to run a front disc brake down the road? Looking forward to more pictures!
  8. KCvale

    KCvale Motorized Bicycle Vendor

    The hub doesn't have a disc mount so the chances it will ever get a disc are slim as dual V's work great here in Phoenix but the option is there should the customer ever want a front disc.

    Here are the pics above in 1280 wide versions.

    Image: http://KCsBikes.com/pics/GT2secondLookLeft1280.jpg

    Image: http://KCsBikes.com/pics/GT2secondLookLeftTurned1280.jpg

    Image: http://KCsBikes.com/pics/GT2secondLookLeftTurnedClose1280.jpg

    Image: http://KCsBikes.com/pics/GT2secondLookRight1280.jpg

    Image: http://KCsBikes.com/pics/GT2secondLookRightRearTurned1280.jpg
    Hamzsim likes this.
  9. Donavan321

    Donavan321 Member

    You'd have to buy a wheel that could accept a disc or build your own with a disc hub. You probably already knew that.. But as long as the brakes are working fine, great! In my experience, it seems that the MAB's chew through pads quickly, only happens with some of my builds not all. So, I just try braking as little as possible to avoid excessive wear and tear.
    Hamzsim likes this.
  10. ez dave

    ez dave New Member

    nice build, im in the middle of a similar build, its way cool to have the support of a local bike shop
    Hamzsim likes this.
  11. Donavan321

    Donavan321 Member

    It's really rare to have support from bike shops! Most of the guys that work there don't support gas bikes, and the whole "defeats the whole purpose of a bike" thing. I've heard it all lol. I like motoring I refuse to ride an empty-framed bike. I can pedal when I want, save gas, or just cruise. Plus, they're fun to build and upgrade...especially when you get to do it with some buddies and take a cruise!
  12. KCvale

    KCvale Motorized Bicycle Vendor

    Very cool indeed, I love my little bike shop around the corner (1/8 of a mile) and we have a great relationship.

    I setup shop here about 3 years ago and when they doubled there showroom 2 years ago I asked them to stock some of the bikes I like to build on and it has really helped us both.

    Most everything I build is a custom job and since my prices are based on a set price for the type of motorizing they want + the bike I encourage the customer to stop by Try Me Bicycles and pick out a bike, test ride it in the parking lot, have it adjusted to their preference, pick out any other goodies they may want like a rack, basket, HD tubes and lines, etc. and pay for it.

    They don't even have to load it up, Try Me will hold it for me to pick up.
    Then they drive around the corner to my shop and we work out how they want it built and pay me and we get to work.

    But I stray from the topic...

    After a lot of trial and error we finally found the best way to mod the SBP shift kit base to fit in so the HS 49cc would fit in as that frame is smaller than it seams and the petcock for the gas is the major reason why.

    I'll post the pics of how I did it later as I haven't processed them yet but I think we can wrap this puppy up today.
  13. KCvale

    KCvale Motorized Bicycle Vendor

    The fix was to move the engine forward and to that it had to go up.

    Here is the mod to the JS base I did.
    (big pic links under pics)


    To spread the 2-part SBP base wide enough the bottom plates middle slot for the set screw needs to be made longer in the back, long enough so the engines 2 front mounts only sit on the lower plate for this frame.

    Note we tried to do it just a little shorter first and cut the top plates front slot all the way open, you won't need to do this is you go this wide.

    When that it is done flip the base over and outline the bottom plates rear 2 slots on the top plate and make the slots that long.

    We just drilled a slot size hole at the front end and then just worked the material out between the hole and slot but you don't have to do that either, all you need is rear motor mount bolt size holes in the top plate at the back.

    In short with the motor mounted as far forward on the lower plate as it will go all you need to do is drill holes in the back of the top plate at the farthest forward point of the lower plates slots.

    Since the front engine mount bolts won't help hold the the part base togeter and I don't trust just that single middle set to do much we put a couple of spot welds on the bottom to make sure the 2-part base stays together but if don't have a welder I would think a generous amount of JB Weld between the two plates and then clamping them together for 24 hours would do the job.

    The result is the stock HS 142F on the GT2A-S frame with an SBP 4-stroke shift here.




    This of course renders the engine and the base unmovable so go ahead and locktight your 4 engine bolts in well.

    Today we tackle the tensioners on both sides as they will be needed to match the 4G's output to the actual jaskshaft on the left, and from the other JS side down to the BB sprocket.

    The right side is easy, I put a hand made one using a gear from a 7-speed derailleur, a piece of metal, a bolts and some spacers and a spring on builds like this all the time...


    There is a kit for this, maybe even SBP has one, but I like to fab things like this myself with what I always have 'laying around' so I don't need to buy parts ;-}

    I'll try to detail that process as well so everyone that attempts a build like this in the future can get some advance tips.
  14. KCvale

    KCvale Motorized Bicycle Vendor

    Last Previews!

    (Note, click link under pic for 1280x view)

    This is how the base mount turned out.



    Though most of that base will be covered with other parts, my object with all the detail paint work was to make the engine look like it belonged there and though I am only ~95% done, this is a 'pretty close to finished' bike.



    The drive chain and tensioners need to be put on and the chain guards done and we could have if I hadn't realized the back rack wasn't on yet.

    I'll save the rack mount story for another post and and make another for the other views of it so you an even better idea of how it looks in person.
  15. KCvale

    KCvale Motorized Bicycle Vendor

    This ended up being a nightmare to make the JS chains work with the JS base.

    Though a fine frame equipped similar to this for a a 2 or 4-stroke direct drive and a blast to ride, if you want to build a 4-stroke shifter on this frame, or maybe any frame, you might want to hold off to see where my new HS 142F and 4G combo mount goes, it was re-inspired by this shifter build but well over a year in the works.

    In short I want to directly move the output of the 4G outdrive to right side on the actual engine mount base and dispense with all the left drive sprocket, chain, and stuff behind the seat post.

    Just a 'Sneak Peek' of the mock up for a build sitting here waiting it for it as I await the last of the parts I need and of course my custom frame base.



    The really cool part will be it can be used for direct drive and fit nice, and for the add-parts make it a JS shifter without even un-mounting the engine or base ;-}
    Last edited: Feb 9, 2014
  16. BigBlue

    BigBlue Active Member

    Great idea!!! Can't wait for a report on how it works out.

    AKA: BigBlue
  17. KCvale

    KCvale Motorized Bicycle Vendor

  18. KCvale

    KCvale Motorized Bicycle Vendor

    My new 4 stroke base with jackshaft is pretty cool, it ran with the 80T 4G pulley but 1st gear wasn't much lower than a direct drive, I have some 100T 4G pulley systems coming that should make the design fly on a 26" wheeled bike ;-}
  19. cj!

    cj! New Member

    Really nice build, love the detail of the big pics.

    Do you think it would take Schwalbe's Fat Frank 26x2.35's?

    What headset does this frame take?
    Last edited: Dec 3, 2014
  20. Robot

    Robot New Member

    Yeah jack shaft kit on it the idea that it will run as a single speed will only disappoint if you take the same exact bike and compare it with one running a 3 speed final drive off a jack shaft which I see appears to be partial installed on that looks like a Nexus setup the bike should run well.I'm working on one currently.Yet I'm not content with the braking system and unsure of one I'm attempting to complete I'll probably be behind your build at least a week..I've got chains to link together cables and wires yet ... The featured bike is nice should work well powerful bakes not really one the one above maybe maybe not..

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