Introduction: Motorized Bicycle DIY: the Hard Way

About: I'm an ex-RPG400 programmer, now working in a Fabrication shop as a LASER cutter. (go figure) I've always had an interest in building things: Model Airplanes; circuits; and such... My current obsessions are:…

Squishing a Honda DHX50 Engine into a 24" Boys Huffy Cranbrook Beach Cruizer

Step 1: Motorized Bicycle DIY: the Hard Way

Squishing a Honda GXH50 into a Huffy 24" boy's Cranbrook Cruiser Bicycle.

Oh good gawd! More Updates:

The replacement engine decided to separate the piston from the crankshaft! (luckily, I caught it before it was trashed). [nasty loud noises can be a blessing sometimes]

As long as I had it all disassembled, I decided to to a full overhaul. The rear frame has been re-centered (it seems that I did a "less than accurate job" of that initially); The seat post has been reclaimed and lengthened (I can pedal it now!); and the engine has been repaired.

I hope to have it back on the road by the end of the weekend! (Woo Hoo!)

/# end of update - BACK TO THE SHOW!

170 MPG - Really?

Short answer: NO - not for me, I drive full throttle almost all the time (30 mph), and I'm getting 110-130 mpg (depending on the wind)
Long answer: YES - if you're just going for a leisurely putt around town and aren't in a hurry - yes, it will get 170 MPG!

uh oh... the short answer was longer than the long answer... (sorry!)

The "Other" Answer?


OK, enough with all that!

We now return you to your original programming-in-progress...
(Sorry you were so rudely interrupted by this tacky updatey-thingy)


As of 2012, the Minnesota statutes have re-classified Motorized-Bicycles as MOPEDs and are
now required to be registered and plated. BUT!!! (and this is the part that makes me angry)
The DMV/DVS will NOT register "homemade" MOPEDs without a federally approved MSO (Manufacturer's Statement of Origin)
a.k.a. built in a federally recognized and registered factory.
Since *I* am the manufacturer, there is no way I can possibly do that.

I am currently pursuing registering it as a "Specially Constructed Vehicle" - lumped in with Choppers, Street-Rods, Reconstructions, and all other modified vehicles. These people want RECEIPTS!
When I started this project a year ago, it was a BICYCLE and I didn't bother keeping any receipts (who could have known?)
Do yourself a favor: SAVE ALL RECEIPTS!

OH NO!!! MORE UPDATES!!! (run away! run away!)

Update 2013/09/02:
I've added some recent pictures of her:

New "Tail-feathers" (she now has "running lights")
New buckboard (strangely attached)
New Collapse-able Saddle Basket (she's now a workhorse! - I can actually carry sh*t now!)

Update 2013/08/25:
The lighting circuitry is still a work-in-progress...

With the addition of 2x 1N4001 diodes in a "Y" configuration, the lights are now powered by the batteries while it's not moving (a.k.a. "stand lights")

AND, when it's moving, everything is now powered by the dynamo!

Also, it now has additional "running lights" and a re-designed (and removable) tail light assembly.
Updates to the circuit diagrams are forthcoming as well as new pictures - when I can find the time.
(it's been a busy summer!)

Update 2013/06/02:
After much frustration with the electrical system involving 2x 2.7v 82f "SuperCapacitors" in series, I have decided to dump them all together due to the fact that "THE LIGHTS DON'T COME ON UNTIL THE SUPERCAPACITORS ARE CHARGED".

I've done my best to find a way to overcome this problem, but hey: I'm not an EE.

(Driving 1+ miles in the dark until they charge is totally unacceptable)

The system is now split into:

1: The Headlight is exclusively powered by the Dynamo running through the rectified/regulated circuit.
1a. The voltage regulator has been changed to an LM7806 (+6vdc).
1b. The addition of a 1000mA BuckPuck current regulator.

2: The "Tail Lights" (one word: BATTERIES)
2a. The "Tail Lights" refer to every other light on the bike - and I want to be ABLE to light it up like a christmas tree!
2b. I hate batteries.
2c. Batteries DIE.

3: This thing has TWO POWER SOURCES (unacceptable!).

4: There has GOT to be a way to recharge batteries from the "other" source.
4a. I thought supercapacitors might be the answer...

5: HELP!

Older Update: The comment section contains the instructions for "getting it registered & plated"
Many thanks to all the people who have helped me in this quest.

/# end of updates. (whew!)

ANYWAY, as I was saying:

This bike project started out as a request from my wife:

She has a 4 mile hilly terrain commute to work (and she's very frugal)

We saw a youtube video of a motorized bicycle in action doing 30+ mph and getting 170 mpg.


She said: "Can you build one of those?"

I said: "Hell yes!"

Then she said: "Well then, go ahead and build one for me"


(For the record, I think I have just about the best wife on the planet)

The 1st picture was a current (September, 2012) view of our new "MOPED". *updates forthcoming

1: It's got all the "legal" stuff taken care of... (it's been inspected, registered, plated, and insured)
2: The seat has been repositioned just as low to the ground as possible.
3: The headlight and all of the electronics have been upgraded - (see the schematic).
4: The turn signal/brake/horn switches have been upgraded.
5: The brake lights and turn signals have been upgraded.
6: The fuel filter has been upgraded.
7: The air filter is in the process of being upgraded.

It's DONE, FINISHED, COMPLETED, etc, etc, etc...


I've come to the realization that: THIS IS A NEVER ENDING PROJECT !!!!!

(run away! run away!)


The 2nd (or is that the 10th?) picture is how it looked right out of the box around May, 2011 (*some assembly required)

The 3rd picture was a recent (March, 2012) view of how far it had come over the last year or so that I've been working on it.
- A very upgraded version from before the "long, cold, winter of 2011 - that never happened in Minnesota"

It has come a long way since then!

(updates to this site are forthcoming - REALLY!)
I just need to take more pictures, measurements, figure out a way to dis-mount the tail-light structure from the seat, add running-lights, and hopefully design a rear frame-cage that can support the new tail-lights and baskets or saddlebags.

The rest is, well: A (very) detailed log of my work in progress...

Buy the ticket, take the ride...

(I hope you enjoy the trip!)

Step 2: Stripping/Chopping

As you can see in the photos, my original intent was to make a "V-Line Slash Cut" on the bottom of the frame parallel to the ground @ .375" above the chain wheel (plus and minus the .25" for the mount itself) .
It's hard to explain, but I think the pictures do a pretty good job of that. (see pic #3)
Then bend the forward frame to meet the "forward end" of the motor mount - to be welded later.

After the cuts were made and it was bent into shape, I decided that it didn't look quite sturdy enough.

So I drew up the plans for a 1/4" steel motor mount assembly in autocad, cut it out on the laser at work, and had a couple of the boys there weld it all together for me.

(again, I'm one lucky guy!)

Step 3: Test Assembly #1

Here's just the basics: just to test the alignment.

Step 4: Sprockets - and the Battle

Here's the project with the soon to be gone "Rag Joint" sprocket on the LEFT rear side of the bike.

This method of attaching a sprocket to a wheel is at best problematic... I could NOT get it trued.
I took it for a test "pedal" drive after I had it all put together, and it threw off the motor chain after about 10 feet...
It was really that far out of alignment...
I'm really glad the motor wasn't running...

So I bought an HD hub from a reputable dealer in Canada who has been VERY supportive.

(Thanks Terry - you warned me!)

Step 5: Semi-Finals

Here she is - Nearly complete (or so I thought a the time).

24" Huffy Boy's Cranbrook.
Honda GXH50 engine
EZ Q-Matic drive system.

The sprocket pictured here is the still the original "rag-joint" sprocket.


The next step is to replace it with an HD hub/sprocket kit that attaches directly to the hub - NOT the spokes (like a rag-joint)

Yes, it requires a total rebuild of your rear wheel (it's called "Re-Lacing")
And, as I found out - the rear forks would have to be widened by 0.50" on each side. (quite a stretch for a 24" bike)
I spent quite a bit of time investigating the local bike shops in my area and found that most of them were pretty leery of the "Dishing" that is required on this type of hub.
Luckily, I found an excellent bike shop in my area did that did for me for around $50.
The "Dishing" required on this type of fat tire hub is quite surprising - and quite an education in itself.
It's worth the extra bux... (please! don't even waste your time with a rag-joint!)

Step 6: Miscalculations

Here's the replacement sprocket.

(sorry I didn't take any pictures of the rag-joint sprocket at this angle - It would have spared me a lot of 'Splainin)

Due to my miscalculations on the "Dish" I asked for when I had the rear wheel rebuilt. (they did an excellent job btw - be careful what you ask for...)

The Stock (read: Chinese) sprocket that came with the kit did not have enough dish to clear the tire.

So, I had to go into "engineering mode"...

I wasn't going to pay another $50 to have the wheel rebuilt AGAIN, so I felt it was my DOODY to fix the problem myself...

So... I drew up a 72 tooth sprocket designed for a #41 chain in autocad...

** .dwg/.dxf files may be coming to a www.interweb site near you soon! - just add water, it makes it's own sauce! Quantities are limited!  So call before midnight tonight and order yours today for the low, low introductory price of...

The bottom line is:


So I made one!

Step 7: Semi Finals Part 2: the New Sprocket

Here's the new 72 tooth, 3-piece, 10 gauge stainless steel sprocket.
Fresh off the laser.

Terry and I decided that a 72 tooth would be the optimal speed vs. power ratio count for the sprocket.
The more teeth you have, the more power (aka:: hill-climbing ability) you have.
(Thanks again, Terry)

I needed a "variable dish" on the sprocket - to get the teeth as far away from the tire as I needed.

A 3+ piece sprocket design came to mind:

1) A Receiver Ring that bolts on to the HD freewheel hub.
2) A tooth ring to handle the chain.
3) A Spacer Ring (or two, or more) that fits between the two...

The Spacer Ring was the "AH HAH!" moment I had...
I could conceivably push the dish of that sprocket out to at least .50" if I needed,
or none at all, and everything in-between. (or even backwards).
I just had to choose the thickness of the spacer ring(s): INSTANT VARIABILTIY!

But, since I was working with 10 Gauge at the time, that's how the prototype was built.

Once I cut out the three parts out of 10 Gauge, and after some quick de-burring and rounding of the teeth - with a little "grinder-art" for effect.

I bolted it all together, and It was good to go....

I Installed the sprocket assembly on the wheel that night and test fit the wheel assembly on the bike in the morning.

I was expecting to have to do some "re-shaping" of the frame, but it turned out that the assembly fit AS-IS!

Step 8: Carburator Settings: Another Battle

I didn't want to do it, but:

A replacement carburator was needed because the stock carb on the Honda GXH50 has a "Set And Forget" type of throttle.

This engine is designed and set up to run at a constant speed ALL DAY LONG!.

The adverts for a GXH50 suggest that this unit can be WORN ON YOUR BACK! (I'm not kidding!) - HD leaf blowers; Brick-Layer Vibrators, and the like...

There was no linkage on that carb that could handle a normal "twist handle" throttle.

SO, I RE-WIRED IT! (arrh arrh arrh!)

A HuaSheng "142F-CC" clone of the Honda carb took care of the linkage problem.

But then, there were other issues:

Once I had installed the new carb, and tried to fire it up for the first time:

I could get the motor started with the choke on, but once I took the choke off - the engine would always die.

The air/fuel mixture screw was poorly manufactured.

The "notch" that a screwdriver blade is supposed to fit was so poorly manufactured that it was just barely a scratch on the surface of the brass screwhead.

A Dremel cutting wheel solved that problem.

I'd been told that the correct setting for that screw is supposed to be 3 turns up from zero.


After a trip to a local small engine repair shop (backlogged as they are this time of year).

He didn't even want to look at it due to it's Chinese modifications, but suggested that "TOO MUCH AIR" was my problem.

So I removed the HuaSheng carb from the engine and COMPARED It to the original Honda carb...

On the Honda carb, I could clearly see the tip of the needle valve sticking out of it's hole from the inside.

It became obvious... Three turns out from zero was WAY over the limit.

The Bottom line:

Just over one half of a turn out from zero (on THIS particular carb* [caveat emptor]) solved the problem!!!!

* Your mileage may vary, check your local listings for news and official information.

Step 9: Layback Seat Modification

Here's the newest modification of the original seat-post.


The last version turned out to be too high for my diminutive wife.

That style is known as a "LayBack" seat-post.

Intended for "vertically challenged" individuals.

But, It was still too "tall" for her, so I had to make some modifications.

I abandoned the original "LayBack" seat post design..

If I was going to lower the seat, it would have to be right down to the bare metal frame.

So that's what I did...

These pictures should 'splain it all..

It now measures 28.5" from the center of the seat to the ground - Good Gawd I hope that's short enough!!!

[more to follow]

Step 10: Spring 2012

Winter 2011/2012 - such as it was, is over...

The squeaky, melting rubber caliper brakes have been replaced by drum brakes with a dynamo.

The "new" springer front fork came from a little "dumpster diving" - The difference in the way it rides now is AMAZING!

It now has everything required by law to be "road-worthy":

Mirrors & Reflectors,
Front & Rear Brakes,
Front & Rear Lights,
Brake Lights,
Turn Signals.

(Brake lights & turn signals on a BICYCLE?  - gimme a break!!!)

But wait!  There's more!

Now that the powers that be, in their infinite wisdom, as of 2012 have re-classified the "Motorized Bicycle" as a MOPED:
It suddenly needs to be registered, plated, and insured - not the case when I started this project in the spring of 2011.

I'm fighting an up-hill battle to get it on the road "legally".

But, they flat-out refuse to deal with the "homebuilt" issue: by citing their federal MSO requirements.
(apparently, if it did not come from a "factory", it can not exist to them)

Henry Ford is rolling in his grave!

I have been tipped to a little known class in my state's statutes:  "Specially Constructed Vehicles"
putting it in the came class as Choppers, reconstructions, street-rods, and all other "non-factory" modified

Currently, I am pursuing that avenue...

Stay tooned to this channel for nooz and official disinformation...