My thoughts on a possible mini bike build

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danssoslow

Active Member
#1
#1
I've been wanting to build a mini bike for quite a while now. I finally got my kart in a rideable shape; now I'm contemplating changing directions during the winter months to have both a kart and mini bike completed by next Spring.

If I may, I'd like to share some of my thoughts and pre-plans; and welcome any and all advice!

The frame I'm wanting to pick up is one of the Motovox MBX10 rollers. I'm really digging the Jesse Rooke look to them. I'm also wanting to stretch the front end out, and contemplating picking up a replacement set of Motovox MVX70 front forks and seeing if it's possible to pick up the tripple trees while I'm at it.

I'd like to run a 10" scooter wheel up front, raise the rear axle into the frame to level the bottom line of the frame; and maybe run a taller and wider tire in the back.

Engine plans I'm leaving open; but it will probably come down to a predator or a EX17-20 if I can find one on the cheap (love my Subies). I'm not really worried about haw fast this bike will go; rather I'm concentrating on the looks without sacrificing ridability.

As said before, suggestions are welcome. If anyone has a better suggestion on a front end, by all means, please speak up. Raw fabbing is gonna be out of the question. I may be able to do some mods myself, and I'll be subbing any welding out; but bending metal is far out of my league.

Thanks for your time guys!
Daniel
 
M

MKW

Active Member
#2
#2
"raise the rear axle into the frame to level the bottom line of the frame"

This is one thing that I am definitely going to do when I build a Motovox this winter. I don't think I've seen anyone do this, but IMO, it desperately needs it. That would change the look/stance of the bike a lot...for the better.

Mike
 
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danssoslow

Active Member
#4
#4
I love taking pics, that I will guarantee to satisfy you guys with!

I spent a good while last night peeping back and forth at Rooke bikes and that frame. :D i'd love to fab up one of his sprung forks; but alas, no tools, and I can't bend spoons with my mind, much less tubing without kinking it. :(

I have a machinist friend that could make me the gooseneck; soooo much work to get the rest done.

If there is anyone in the Louisville Ky area that would like to help me make this a reality, please speak up! Take my money!!!
 
D

danssoslow

Active Member
#5
#5
Now that I've been looking into it harder, the more I'm wanting the complete Schwinn look, including the springer front forks. Gonna do some investigating on how to make this happen.

Again, any help is appreciated!
 
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danssoslow

Active Member
#6
#6
So, the project log will be starting soon, as I have purchased a used Murray Track II off of Craigslist. Bee doing a lot of research on mounting a Schwinn springer fork, and choosing wheel sizes which will help me arrive at the look I'm shooting for. It's going to be a lofty project, which will make it slow going; but in the end, it should be possible to turn out as I envision.

In the meantime, I'm having trouble coming up with an available rear wheel. I'm wanting to run a 230/90-10 tire on the back, and finding a 3.5" width rim is troublesome. If anyone has a good idea on a wheel/hub combo, live or dead axle, please share!
 
zombiewoof

zombiewoof

New Member
#7
#7
If you do use a springer, make sure you buy a high quality unit. I may be new to the mini bike scene, but I am a bicycle/Whizzer collector. The cheap springers are IMHO very dangerous on even a motorized bike. They are not designed to take the abuse of riding at speed. I built a Felt 1903 and after just about 100 miles on our washboard smooth Indiana roads, the main bolt that goes through the crown had worn down to half its diameter. If it would have snapped at speed, I would have been seriously injured.

Here is a pic of the crown:


Here is the bolt:

And here is a pic of the bike:


If you really want a springer I would suggest a "Monark" style.

Here is what the Felt ended up getting:
 
charliechaindrve

charliechaindrve

Member
#8
#8
zombiewoof said:
If you do use a springer, make sure you buy a high quality unit. I may be new to the mini bike scene, but I am a bicycle/Whizzer collector. The cheap springers are IMHO very dangerous on even a motorized bike. They are not designed to take the abuse of riding at speed. I built a Felt 1903 and after just about 100 miles on our washboard smooth Indiana roads, the main bolt that goes through the crown had worn down to half its diameter. If it would have snapped at speed, I would have been seriously injured.

Here is a pic of the crown:


Here is the bolt:

And here is a pic of the bike:


If you really want a springer I would suggest a "Monark" style.

Here is what the Felt ended up getting:
Click to expand...
Truer words have not been spoken. When it's in the subject of forks, cheaper means you get less. I had a pair of forks just like that do the same thing, I fixed it by welding a washer over the hole in the yolk and then replacing the bolt. Frequent checking Is KEY! (off subject, sorry :p )
 
D

danssoslow

Active Member
#9
#9
Thank you plenty for the warning!!! This is exactly the kind of info I'll need moving forward here.

I'm set on the Schwinn type; but the head tube on this Murray is going to require that the forms go through a bit of fabricating. If the strength of some parts are an issue, I may have to have the whole shebang fabbed up. The head tube is so long on this mini bike, I'll have to use a 26" Cruiser steering tube to make the distance. At this point, I'm figuring I'd have to use a 26" forks with 20" fork bars, and have the forks recrimped to suit. This will be done just so that the spring setup sits in the correct position.

Are you familiar with Bicycle Designer's parts? What brands in particular are considered good? I've seen some in the $80 range; but I don't know if price and quality go hand-in-hand in this situation. Any more information you can provide would be highly appreciated!
 
zombiewoof

zombiewoof

New Member
#10
#10
Bicycle Designer mostly sell stuff made from Chinesium (cheap stuff from China). A Felt Springer uses a 1 1/8" head tube (like most modern mountain bikes). The "standard" springers are 1". I would want the bigger head tube.

Sun makes a decent standard sporinger. A good condition vintage Schwinn springer would be a decent starting point.

Just keep in mind you are using a part for a purpose it was never designed for. It was designed to withstand cruising at 5mph on smooth surfaces. At my age road rash and busted teeth just don't sound like that much fun.

I look forward to seeing what you come up with, but I do urge you to be carefull.
 
D

danssoslow

Active Member
#11
#11
No doubt, safety first. I'm picturing this being a very long term project, and will sacrifice the time and money (read:more time) to ensure it turns out rock solid.

This is what I'm shooting for, sans paint and motor:



I have a "friend of a friend" that is a welder; but I'm thinking I'm going to have to befriend a fabricator to get this one into shape. Fingers crossed! I've nailed down the wheels I'm going for, so I'm going to be purchasing those and tires over the next two weeks. I'll get those laid out and see where the fork and rear end have to lie.
 
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danssoslow

Active Member
#12
#12
Ok, first pic!!! I'm gonna keep this one here, as it's not quite project worthy. Call it a proof of concept, if you will. It doesn't much pove anything, other than maybe a solid view at my direction. Hopefully it may be some help to someone who knows how to fabricate. Btw, pardon the mess.



Mmmm, electrical tape.
I used 3/4" EMT to mock the parts up, which is right at .90" o.d. It appears that the mini bike's tubing is a bit over 1 1/4", 32mm according to my cheap analog calipers. The bicycle tires measure right at 20"o.d., within 1/2" of the o.d. for the rim/tire combo I have in mind for both front and back.
If the rear axle lands in that exact location, I'll be looking at 6" of ground clearance; does that sound about right?

The lower axle bar will have to be shortened to a pick up point closer to the end of the mini bike's lower rail to avoid TAV2 interference; but I figure the angles are about right. That bend at the mini bike/lower rail is 45*, the ends where the axle is located are 60* and cut to come to a point. The upper rail will look better with a bend transitioning into the pick up point. I was anxious to see what it will look like before bending that portion.
And of course the backbone will need that extra piece to complete the "tank" silhouette!

The front tire is sitting about right, which will provide about 2 1/2"-3" of trail. Any closer to the body, and it looks too close. Wheelbase is at 45".

So there you have it so far guys. I promise that the final product will be free of any taped joints. :D
 
D

danssoslow

Active Member
#15
#15
A bit of a progress update, and a little ranting/forewarning mixed in.

The front wheel came in on Tuesday. Didn't bother taking a pic. It's a 17" spoked front rim off of a 80cc Yamaha dirt bike, with a decent shaped rotor. It currently has a knobby tire on it. Hopefully tomorrow brings about a change there.

Today, the rear rim finally showed up. I ordered a flat black 14x6" ITP rim with a 4/110mm bolt pattern on Nov. 24th from Powersports Superstore, along with a street tread front tire for the dirtbike wheel. Last Friday, I called them; as the status of my order was still in the Pending state. I was told it was going to ship this past Tuesday. I also noticed neither the rear wheel nor front tire were on their site anymore.
Googling them, I came to learn that not having up to date inventory isn't a big deal to them; as they are quick to send what they do have, and play the run-around to deny making any issues correct.

It would appear that I am no exception. Here's the rim they sent; and according to UPS tracking, the tire should be here tomorrow.





At least they got the bolt pattern/size right. I'm going to keep the rim. The brush finish looks better in person than on the internet pics; and it keeps me from having to worry about having the front wheel powdercoated in black and re-laced.
Hopefully, the front tire isn't way off.

And it appears that I found a fabricator. A local welding school has been advertising on Craigslist for students and projects. I've contacted the school, and they are willing to take this project on. After the wheel debacle gets sorted out and tires mounted, I can take the frame to them with solid height/length dimensions for the rear axle. If the rear goes well, I'll have them scratch build me the front forks.

One more thing. In the midsts of my cousin moving, I have been acquiring quite a bit of shit from his garage. Included in this Sanford and Son starter kit, a near spotless Briggs Flathead. Mocked up on the bike with a 15* motor mount, the engine looks the part; as I have been desperate to come up with a front facing jug. The engine packages well without interfering with the soon-to-be extended backbone, and leaves plenty of room for the expectant gas tank/location.
 
D

danssoslow

Active Member
#16
#16
Progress report:

I finally have the tires mounted on the rims. I received an order from BMI for the majority of the rear axle parts; and the order was made for the rest of the rear axle pieces from ARC, mainly the hub to make the wheel work with the 1" axle.

I'll take a couple pictures of the wheels this afternoon. The front looks to be right around 22" in diameter, and the rear is right at 20". This 160mm tire looks pretty sick on this ATV rim. Goodyear had to use one of those handheld high pressure tanks to get the bead to sit on the 6" wide rim. You could see the fear in the installer's eyes! That device is freaky!

We should be close to starting on the frame, and finally be in a position worthy of starting a build thread.
 
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D

danssoslow

Active Member
#18
#18
jdogg said:
This is good to hear Dan! Glad the school is willing to work with you on this! Now picts of them tires mounted please!! :laugh:
Click to expand...

You'll have to squint hard to make them look mounted. :p

You reminded me also, I have found someone else willing to help get the frame done. He's a memeber here, and I'm going to wait before revealing his name. I'm not sure how he'd feel about me saying it out in the open (simply being respectful). I'll admit that the school kinda scares me. I can't expect a single teacher to watch closely over every student all the time. I'm afrad something might get missed/overlooked.
 
D

danssoslow

Active Member
#19
#19
Pics!!!!!


I hate that the front tire is sitting so close; but in order to keep the ideal 2-3" of trail in the front end, I'd either have to raise the frame, (nope) or rake the head tube (even more expense!).

Here's a pic of the rear tire width compared to the frame.
 
LSCustoms

LSCustoms

Moderator
#20
#20
NICE! can you put a greater bend in the front fork setup to move the tire out further away from the frame, like rolands front end... also are you staying with that front wheel?
 
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