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

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:

Fork:
RST CAPA
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.

 

[Donavan321]

nice build, im in the middle of a similar build, its way cool to have the support of a local bike shop

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!

 

[KCvale]

nice build, im in the middle of a similar build, its way cool to have the support of a local bike shop

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.

 

[KCvale]

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)

http://KCsBIkes.com/pics/GT2firstLook3motorBase1280.jpg

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.

http://KCsBIkes.com/pics/GT2firstLook3base2-1280.jpg

http://KCsBIkes.com/pics/GT2firstLook3base3-1280.jpg

http://KCsBIkes.com/pics/GT2firstLook3base4-1280.jpg

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...

http://kcsbikes.com/bPics/2_BigRed21280R.jpg

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.

 

[KCvale]

Last Previews!​

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

This is how the base mount turned out.

http://KCsBikes.com/pics/GT2lastLookBaseMount1-1280.jpg

http://KCsBikes.com/pics/GT2lastLookBaseMount2-1280.jpg

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.

http://KCsBikes.com/pics/GT2lastLookLeft-1280.jpg

http://KCsBikes.com/pics/GT2lastLookRight-1280.jpg

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.

 

[KCvale]

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 ;-}

 

[BigBlue]

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


Chris
AKA: BigBlue

 

[KCvale]

The 142F and new 4G cover to cover is 11".
The base mount has to drop the engine in between this 11.25" pedal ID.

http://kcsbikes.com/pics/4GbbCartridgeInstall3.jpg

That sets the base mount parameters.

 

[KCvale]

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 ;-}

 

[cj!]

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?

 

[Robot]

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..