Gramps needs help -

[WB4RT]

I want to build a simple mini bike like I had in 1960. I'm saying it's for the grandkids, but I just want to try to build it and expect I'll be the main one to ride it.

I know I can buy a used one cheaper, or even buy the frame cheaper and easier than I can build it, but I'm a fair hand at welding, and well, I just want to do it myself.

I know I should have the main components before I build the frame, but I thought I could go ahead and bend and weld the two side frames, then adjust the width to fit the wheels when I get the kit before i weld the sides together.

i'm thinking I will buy the Azusa 5" or 6" kit without frame so I can get all the hardware in one shipment. Then I will use a HF Predator 212 cc engine.

It seems 7/8" tube is the main choice for the frame. Will that support up to 220#'s?

My questions:
1. Does this sound like a good plan? Other suggestions?
2. Should I buy 5" or 6" wheels?

3. ** MOST IMPORTANT ** - can someone provide a drawing and/or dimensions on the frame? I have searched here and all over the internet without finding what I need. I want to know the length and height of the frame (or at least the minimum length and height to fit the engine). Also the bend radius.

Any help in getting my project started is much appreciated.


Burt

 

[OzFab]

Welcome to the forum Burt

1. Does this sound like a good plan? Other suggestions?

It does, apart from one thing (which also partly answers Q3), get your engine first! There's nothing worse than spending days, weeks or even months building a frame only to find that the engine doesn't fit. The dimensions of the engine will determine the size of the frame

2. Should I buy 5" or 6" wheels?

That comes down to two things:
1. Riding terrail &
2. Personal choice

3. ** MOST IMPORTANT ** - can someone provide a drawing and/or dimensions on the frame? I have searched here and all over the internet without finding what I need. I want to know the length and height of the frame (or at least the minimum length and height to fit the engine). Also the bend radius.

There are loads of mini bike plans all over the net, here are just a few:

http://www.vintageprojects.com/mini-bike/mini-bike-plans.pdf
http://www.smartkartparts.com/freeminibikeplans.pdf
http://pmlamon.tripod.com/

 

[WB4RT]

Hi, Fabroman.
Thank you for your reply.

So if I buy the Predator engine, I still need to know how much clearance I need from the top of the engine to the top frame. Say the engine is 11" tall (I'm just guessing), should there be 2", 4" or more clearance so total inside the frame needs to be 13" - 15"? That is what I need to know. Then, from the engine to the rear wheel probably requires some minimum distance. Again, I'm guessing maybe there needs to be 12" from the engine shaft to the rear axle. If I knew those minimums, I can draw out the 2 side frames.

From the plan sites you show I can figure the front fork and how to attach the rear wheel. Then I can fabricate the engine mount plate and other pieces based on the wheels.

So if someone can help with those minimums, I think I could start the project.

Thank you for any assistance.

Burt

 

[OzFab]

The minimum height dependes on a few things too:
-will you leave the tank mounted to the engine or mount it to the frame? If you leave it on the engine, you need to have clear access to it bit, if you mount it to the frame, the frame can be lower...
-do you want to be somewhat comfortable or have your knees in your ears?

Sorry I can't give you any numbers, I'm more of a 4 wheel guy

 

[WB4RT]

OK, you are helping me think this through.

So if I want the frame a little larger, so my "knees are not in my ears", as long as I measure the engine, allow enough room for it and the gas tank, and give it a little to be sure there is clearance I should be OK. Maybe someone who has used the HF Predator 212 cc engine will have a good idea of the overall height.

If I am thinking about trail riding, would the 5" or 6" wheels be better? You said personal choice or terrain, so anything to add?

BTW, we were in Australia around July 2001. We really enjoyed Sydney, the Opera House, zoos, etc. Also got to dive the Great Barrier Reef - wow!

Thanks for your comments. Maybe other members will have some thoughts too.

Burt

 

[mckutzy]

if your already decided to build a bike, go get the motor, and build a bike around that.
I got the motor then the tires, everything was germinated off of that.

A good idea I used, was an office chair to judge a good seat height. Sit and find a good position. Measure that(or have someone else measure that).

At that position, put your hands where you would like them and measure.

Pick a wheelbase and you have a basic bike to think about, for all the other details.

 

[OzFab]

For trail riding, I'd use 6" rims but, it depends on how mini the rest of the bike is; 6" rims may look out of place on a really small bike...

Does that help

I'm glad you liked my home town, I haven't met many people who don't

 

[WB4RT]

I have spent a lot of time reading posts and learned a lot along the way.

Finally, I found what I was looking for from DocSprocket, 11/4/12 post #19.
http://www.diygokarts.com/vb/showthread.php?t=19580

Wheelbase- 36"
Rake (caster)- 30*
Width (at widest point of frame)- 10 1/2"
Height- (bottom of frame to top of frame)- 17 1/2"
Handlebar height (from axle to top of bars)- 30"
Tires- 145/70-6

Since I read a lot of posts asking for some basic dimension information, maybe you would consider making this a STICKY?

This gives the newby, like me, a frame of reference and now I feel I can start. I plan to modify this to suit my build, but this is a great help.

When I finish, I could try to get my son to do an Autocad with actual dimensions of the final product and some pictures to help guys get started, if you think that would be beneficial.

 

[OzFab]

Do you mean make this thread sticky or the reference thread?

I'll consider it but, it needs a few more to agree...

 

[porsche930dude]

definatly go with 6" wheels or even bigger if your trail riding with no suspention. you definatly want to design it so you atleast have shocks on the seat. consider it a must or you wont want to ride it much at all. you are correct most frames are 13-15" inside. Check out oldminibikes.com youll find much more info there

 

[landuse]

I have been searching my PC for diagrams from r_chez that he sent to me with the dimensions of his minibike, but I just cannot find them. If I do I will post them up

I found the thread r_chez made. If you look from about page 5 you will see some dimentions posted.

 

[WB4RT]

OK, I have welded up the two sides of the frame. Inside dimension is 17.5".

I am planning to put gussets in the back lower corners with a 5/8" hole for the axle. Just wondering, if the two frames are spread at an angle, does that create a problem with the axle holes? Will I have to round them out a little? Maybe it is not enough of an angle to cause a problem.

Going with a 8" wheel kit and a Predator 6.5 hp engine. Is there anything special I have to do to the throttle on the engine? I think I need a spring to pull it back but is there a kit or something?

Also, the kit lists 5 bushings 5/8" id x 1" od. Not sure where they go. I know on the axles, but are they just spacers or do they sleeve the axle holes in the frame and fork? Sorry, I'm just confused.

Thank you for any help.

 

[WB4RT]

Update: I have my Predator 212 engine, and my Azusa 8" kit arrived last night. So far I think everything is coming together pretty well. Still a lot of work to do. I cut off the forks to right length and almost finished fabricating the front fork tabs. Still got to cut out the slots for my engine mount.

I know square tube is a little unconventional, although I have seen some bikes made out of it, but it is what I had. So far all I've bought for the frame is the tube for the fork and some bolts.

I'll probably turn my engine mount over so the diamonds are underneath and have a smooth surface for the engine to sit on.

Any suggestions or recommendations?

 

[landuse]

Looking good to me!! I wouldn't worry about the square tubing. It doesn't look like the "traditional", but it will serve the same function.

Personally I would not bother turning the motor mount round. The engine will bolt on fine with no worries. If you turn it round you might find it hard to weld because of the ridges (diamonds). You will not have a totally smooth surface to lay your bead on

 

[WB4RT]

Finished, except I have no brakes. The cable in the kit is too short so I will pick one up today and it will be complete.

I rode it around some last night - what fun!!

My wife and I made the seat. It's big enough for two to ride.

All scratch built from scrap in the shop. I had to buy the tube for the handlebars and some 3/16" flat bar for the front axle tabs.

 

[Poboy kartman]

Nice- Reminds of the days as a young boy drooling over the pics of mini-bkes in mags and dreaming wistfully about owning/building one.....

EXCEPT -They were never yellow. ...Of course I'm so old even the porno mags back then were black and white.....and only showed ankles....

 

[landuse]

Nicely done. That thing looks store bought.