My Murray Monterey Build

I thought I'd try to share my experience with motorizing this Murray Monterey Cruiser that I found on Craigslist. I used to be an avid cyclist, but I suffered from a medical condition in 2010 which has no cure and makes it excruciatingly painful to walk or pedal a bike. I haven't ridden since then. For mobility, I often use an adult Razor kick-scooter. I can use my right leg to push, and my left leg is essentially motionless. This is much less painful than walking and allows me to get around when I have to go places like my daughters' softball or volleyball games. I hope that this project can bring the joy of cycling back into my life. I'm sharing a little of my backstory so you will understand some of my motivation and also that I have major financial constraints. (Despite this, I intend to survive this project and will make safety a priority.) It is my first motorized bicycle attempt. My physical limitations also mean I won't be able to spend all day in the garage doing assembly. I have to pace myself and can work only in short intervals. I received my kit a couple of days ago. It's a generic kit from an eBay seller in California.

My first step was to begin installation of the rear sprocket rag joint. My kit came with the 3-piece collar and a 9-hole 44 tooth sprocket.
I plan to retain use of the coaster brake, and add a front (and possibly rear) rim brake.

Kit Hardware is GARBAGE!!
One thing everyone seems to agree on about these kits is that the included mounting hardware is worthless. As I began torquing down the 9 bolts around the sprocket I quickly proved this again by stripping the threads on several bolts.

My kit came with M6 x 1.00 x 40mm bolts. As I removed the bolts, I noticed the "spring" washers had no spring after being compressed and remained flattened. All of it went into the garbage. I don't have a good hardware store nearby, so I went to Home Depot. While metric fasteners were available there, they were outrageously expensive. (Just the bolts were sold individually at like $0.70/each.) So I opted for 1/4" hardware.
Since the rag joint had already been compressed, I was able to easily use shorter 1 1/4" long, 1/4" bolts. I also used new flat washers, spring washers, and nylon lock nuts. (These bolts about 32mm long vs the 40mm bolts from the kit. This left about 6 threads extending past the nut, vs about 14 for a neater installation.)
Without having any experience with this rag joint, I used my best guess about how tightly I should torque the sprocket. I just kept it as even as possible and adjusted any run-out by tightening an additional 1/4 turn or so on the bolts near the "high" side.

Coaster Brake
This bike has a Bendix coaster brake. My sprocket is dished or offset. I installed it per the instructions with the teeth closer to the wheel. My sprocket center hole was large enough to not interfere with the coaster brake cover. However, I did find it necessary to re-shape the coaster brake arm to clear the heads of the sprocket bolts. This was easily done by placing the arm in a vice and tapping on it convincingly with my favorite 3-lb hammer, "mini-Thor." Two main bends are required: 1 just beyond the square drive opening to let the arm clear the bolt heads. Then another near the anchor strap position to realign the arm with the chain stay. I'll take a photo of this and post it in the next day or so if I get to work on the bike.
I reversed the anchor screw so that the threads extend to the outside of the bike because I thought there might be interference with the drive chain.

Conclusion:
I think the result so far is satisfactory. I was able to achieve a reasonably true installation I believe (though if I had the money I'd probably use the 1.5" hub adapter and replacement sprocket.) I question whether I'll have adequate clearance between the tire and drive chain, and between the chain and coaster brake hardware, but I'm sure these issues can be addressed if/when they arise. I can reverse the sprocket if necessary, but I think in my case the "concave-in" arrangement will work best. We'll see!

 

[junglepig]

So, I'm cruising (not far from home) today after putting on a better clutch lever (The kit lever broke) and suddenly there's a very wrong noise from my HT motor. I check everything drivetrainwise that could hurt me, and then head home. I pulled my plug and it looked like maybe the piston had just kissed the end of the plug electrode, so I pulled it off and took down the top end. I'd been meaning to do this anyway to see what kind of rod and piston were in this engine anyway. I found nothing wrong. While I had the jug off, I got my Dremel out and cleaned up the transfer ports which were ugly, ugly, ugly from the factory, and put it all back together. I had noted a crack earlier in my clutch cover. I'm pretty sure this was the source of the noise. A chunk of aluminum had broken off the edge and fallen down into the gears. And there were crushed aluminum shavings all in there. I blew it out with lot of air and regreased the gears. No troubles now. The minor work I did on the transfer ports had no discernible effect on how the engine runs.

 

[junglepig]

Ha! If you have an old lawnmower they usually have good quality boots. Maybe a junkyard

I've got some boots and terminals and wire and plugs ordered. Of course, I got to reading last night about the whole resister vs non-resister debate, and whether not having any resister components (wire, cap, or plug) would be harmful to the CDI. I've decided to run it with a 5K resistor boot. I think that's what's on it now, and what most CDI ignitions spec. Then I can run it with non-resistor plugs. I've ordered several styles and heat ranges to experiment with while I'm playing. My wire will be copper core with a dressy fabric exterior.

In better build news today, my front brake came, so I drilled out a mounting hole for it and got it installed. I feel much better now. I had been reaching for a brake lever with my right hand all the time, and it just wasn't there on this old cruiser. She stops so much more reliably now!

Next steps will be lighting. I got a little headlight that runs on 3 AAAs, or 4.5V right now. If it's bright enough as is, I'll set it up to run on either 5V (USB) or 12V. I also have a 12V tail/brake light to install. But before all that, I'm going to attempt to put my own lighting winding on my stator. The new style stators don't have a lighting coil on them. Some have a white wire, but it is just soldered to the same lug as the blue wire, not to a second coil.

I think there is room on my stator to wind a coil of 26ga magnet wire that will provide at least 7.5V and 500mA nominal. 3 W should be plenty for my LED lighting, and will not be a significant burden to the engine. Specs I have found here and elsewhere for the original coil design is 300 turns of 26 ga, and a resistance of about 2.3 ohms. At 41 ohms/1000ft for 26 ga wire, this works out to 56ft of wire and an average diameter of 0.71", all of which passes the feasibility sniff test. (Normally the lighting coil is underneath the CDI coil. I don't think either will suffer too much if I wind the lighting coil on the outside instead. I plan to rectify the output of that and use it to charge an inexpensive li-ion USB pack. I'm thinking a 3 or 4 cell pack of 18650s. I'll use that (with a boost module) to power a 12V system for lights & horn or other electronics. I figure having a fully charged USB powerbank on the bike is a bonus in the event of a dead phone battery.

I'll share details of what I do and how well it works. I hope this little project will be helpful to others. All the components are readily available and require no special tools or skill beyond soldering. Probably won't get into it much 'till after Turkey & Shopping weekend.

 

[junglepig]

I wound 300 turns of my 26 ga magnet wire over a stator from ebay. I scraped the ends and soldered one end to the black ground tab. The other end I soldered to my white wire, and covered with heat shrink tube.

300 turns on the outside of my coil is a lot of wire - about 3.4 ohms, or about 83 ft. And, it may be just a little too much to allow me to install it. I hope to try it tomorrow.

If it won't sit flat, I'll have to remove a few turns and try again, but it's close.

Things are busy this time of year, so I just thought I'd make a note here of what I did in case I don't get back to it for a while.