Building another Minibike - recommendations appreciated.

[LMUdave]

Hi guys,
Been a bit since I’ve been on the forum. A few years back I built a nice bonanza from pretty much scratch pic included just because. Found a slightly butchered “invader” frame and plan on building it on the cheap with what I can find.
Looks like the scrub brake has been cut off. Also not sure what wheels would be best. I have some old Azusa spinner 8” but they seem too big. Any recommendations. I have a nice running Briggs 3.5hp that should pair well. Thinking of getting 5” wheels and a 60tooth sprocket. Not sure about the brake though. Any recommendations or ideas are appreciated!

 

[t555trailblazer]

If you haven’t bought the wheels yet, search… Minibike 5” rear wheel drum brake kit.You will find several options for sale. Some other options would be…brake caliber on the rear sprocket, rebuilding the scrub brake or a band brake on the clutch. Those are just a few ideas, you have many options. Good luck on your build.

 

[Minimichael]

Looks like you'll need to weld axle tabs on, at the very least. Some sites (including this one?) have lots of those. There should be some affordable new wheel sets out there – maybe even available with hub, sprocket, brake design and even tires included – since you're looking to $ave. Keep in mind ebay isn't your only source. Motor already looks good in there. I appreciate your frugality, too. The concern in shopping online these days is always one of quality, or at least adequacy. But no doubt a resourceful builder like yourself can modify and improve some of these to get the job done.

Check this out - https://www.aliexpress.com/item/1005008785571701.html

 

[Triley41395]

Hent also sells 6 inch Astros and Tristars. And you can get compatible brakes for them.

 

[Minimichael]

Just in case you're still searching ...
https://hent.com/wheels/steel-wheels/6/

 

[DaddyJohn]

I usually use a clutch brake rather than trying to build something from scratch into the rear wheel assembly. They’re usually $40 or so, bolt right on, and include a clutch cover.

 

[Powerband83]

I've used the clutch band brakes plenty of times on drum style clutches, with great results! The shoes last for many miles, and the cable is adjustable. I always use a drum clutch like a Noram GE, hilliard or max torque. I'm partial to the GE from the WKA kart racing days. It is very tunable with the springs/shoes, and affordable.
One thing to take note on said brake, is your chain tension. Too much slack in your chain will make it pop off, and there goes your brakes... If you're novice, I highly recommend a tensioner while using a band brake, especially with no jackshaft. Quite a few options for a tensioner that require no welding in today's world. The bolt on one's work great.

All from experience here

 

[Minimichael]

A word to the wise: the smaller your wheel the slower your roll. And I prefer drum brakes, myself. Pretty sure those Honda dax and monkey rims share standardized hubs, too. Plus I have seen them 8-inchers with drum hub cast into the rim itself.

 

[forcefed86]

Might try an EV powertrain. Opens up a whole new aspect. UNique, quiet, and the power/tq is absurd compared to 2-6.5hp setups generally used.

 

[Havasu Dave]

Might try an EV powertrain. Opens up a whole new aspect. UNique, quiet, and the power/tq is absurd compared to 2-6.5hp setups generally used.

Not that unique. I can't search for stuff anymore without having to sift through endless electric bike stuff. I built one years ago on a micro frame. My grandkids rode it for years. They still have it, though painted wings and giant's rings have made way for other toys. Like girls and cars.

I've used the clutch band brakes plenty of times on drum style clutches, with great results!

I'm also not a fan of clutch brakes, because Jim Donovan says it's a bad idea. You're heating up a device that already needs to shed heat as part of it's life, and putting the weight and inertia of the machine and rider against the bronze bushing when braking. It's an easy solution for engineering challenges, so do with that what you may.

That's my two cent's worth!

 

[LMUdave]

The EV idea is cool, but I’m looking to build an old school one to teach my 12year old about motors and mechanics. It’s how I learned when I was a kid. I’m thinking of getting a rear drum brake that fits inside the sprocket. I’m worried that if the chain pops off we won’t be able to brake with a clutch brake.

 

[Havasu Dave]

72 Tooth AZUSA Astro Sprocket & Wheel Kit AZ2218-ID-1128 that Hent sells, along with the AZ2208 brake assembly. You'd need 5/8 axles, nuts and spacers of sufficient width, as well as brake cable, R_264 and lever AZ1731. AZ2360 wire clamps or a clevis AZ2366. Front Azusa Astro too with axle. Edit: The reason people like the clutch brakes so much is that minibike drum brakes suck. I found that by arcing them on my lathe, they work a lot better, and that goes with any vintage bike with a drum brake setup.

 

[forcefed86]

There are EV bikes that "work"... and there are EV bikes that are actually fast and fun lol. BIG difference! I hear ya on basic mechanics though. Gas is cheaper and easier... longer range for sure. I figure by the time my 9 year is older, everything is gonna be EV anyway.

I do low 4 sec 0-60's out accelerating most sports cars and still top at 80-90mph. Not necessary for everyone I know, but you can tone it way down and its still a blast compared to gas. The tiny little blue kids scooter does a 4 sec 0-60 as well. (w big goofy 220lb rider) Its just ridiclious performance for the size.

o

 

[Havasu Dave]

I am not new to electrictromotive force- I was a tron guy most of my life and used to follow that fellow in Portland with the electric drag car. This was decades ago. What I see there is a lot of good engineering. Form following function. I realize a lot of that is big motor and battery bank, but I do appreciate very much the chassis work involved! Great job!

 

[Triley41395]

The EV idea is cool, but I’m looking to build an old school one to teach my 12year old about motors and mechanics. It’s how I learned when I was a kid. I’m thinking of getting a rear drum brake that fits inside the sprocket. I’m worried that if the chain pops off we won’t be able to brake with a clutch brake.

You don't necessarily have to use a clutch brake. There are other band brakes like on a trailhorse. You might have to engineer a bracket though.

 

[Minimichael]

minibike drum brakes suck. I found that by arcing them on my lathe, they work a lot better

What is this voo-doo the shaman from Havasu conjures? Arcing? Does this mean grind the interior til true? Any non-lathe solutions out there in our miniverse? Despite the wheel wobble legend of Azusa, the vintage drum design is already old as the circle, and with shoe size standards scattered like half moons across the after market, I just like em

 

[Havasu Dave]

What is this voo-doo the shaman from Havasu conjures? Arcing? Does this mean grind the interior til true? Any non-lathe solutions out there in our miniverse? Despite the wheel wobble legend of Azusa, the vintage drum design is already old as the circle, and with shoe size standards scattered like half moons across the after market, I just like em

Spinning the entire brake assembly (shoes and backing plate installed) in a circle and removing brake material. However one can accomplish that will work. There are some home built machines out there using a dremel and a fixture to circle the brake as well. The rationale is that this allows a tighter brake adjustment without making partial contact with the drum, as well as more brake surface contact. Google Hodaka Brake Arcing and you should find a nice tool a guy made.

Here's my friend Greg out here in the West.

 

[Minimichael]

Wow that's great information. Thanks for this advice and the time, @Havasu Dave. And for all the part IDs and tips, too. I do like the drum/shoe design for its mechanistic simplicity and always felt more approachable than braking with liquids.