Lard-*** mini bike build

[andrecht]

Wheels..... dam wheels...... It always starts with something......

Im building a Edge X2 double seat sand rail, and a mate of mine donated some hubs, break lines and other parts when moving his workshop. Amongst the donations were two 10" aluminium rims with fat tyres.
The front break setup on the rail is made to fit 12" rims, so these are just lying around...
Wheels..... dam wheels...... What to do with two perfect...pretty... useful wheels.....that haunt me at night..... dam wheels that speak to me when I walk past...

One morning after repackaging my workshop the two annoying aluminium rims stood just in such a way (about 5 foot apart) that it jumped to mind!!!

And so the idea was born... Im going to take time off from the sand rail...and humour those dam aluminium rims and build a lard-*** mini bike!!!

 

[andrecht]

Had some hubs cut to suit the rims 100X4 PCD
Being a fat rim, habe to make extender tubes to take the wheel bearings.
Extended tubes 32mm OD 28ID
Bearings are standard 28x12x8...that fit perfectly inside extender tubes

To prevent the bearings from sliding deeper into the tubes, I inserted 28mm steam pipe, drilled the extender tubes and welded them into place...

 

[itsid]

single side swingarm please

Oh uhm, family frendly forum and such, you might find some of your words censored ..
maybe good to avoid these

I wonder if a single sided front 'fork' from a scooter might be able to hold a wheel of such width *headscratch*

Ah well.. I'll be following this ... sounds like a fun project

'sid

 

[Hellion]

There's always someone who is innovating and not following the herd. This project shows promise and I will be watching too.

I think big wheel trail-type mini bikes were popular in the 60's and 70's but we shall see if this is forging ahead or following the rut.

 

[andrecht]

Single swing arm rear....sounds tempting...

 

[chancer]

Great design on the simple bearing hub holders.
I have done similar work with Go kart front spindles.
Thanks for sharing.

 

[andrecht]

Front fork assembly, two plates 350x150x6. Two 1"DOM tubing 550mm long, inserted through and front axle tabs tack welded into place.

 

[landuse]

There's always someone who is innovating and not following the herd.

There are a few of us left.......

Most of us are in South Africa

 

[SoBored]

Nice work! Now I have an idea on how to my my own idler hubs! Thanks!

 

[ML-TOYS]

Is there a mini bike from like the 80's that was a fat tire bike ?

I am liking this build. Gets my brain goin with the big tires i got here. But too many projects right now.

Cant wait to see it complete

 

[andrecht]

Fork pivot tube
Similar trick with 32mm tubing with 28mm schedule 40 tubing inserted as bearing collars.
Bearings standard 28x12x8

 

[itsid]

What? no single arm front fork

hehe, JK!

looks nice.. proceed..

OHHH if you need a frame idea..
How about the Carter Transformer
http://web.archive.org/web/20101120160707/http://carterbro.com/transformer/transformer_slideshow.swf



'sid

 

[andrecht]

Sid, I thought you were talking about single rear....

 

[andrecht]

Amongst the pile of goods donated to me, there is this obscure single stroke engine. I assume Its a old Classic racing kart engine, but looks really sad...
Can someone help Identify it, and will it be any good to use on a mini bike?

 

[Denny]

Rotax engine, direct drive only. It would haul butt, but suck to try and stop because no neutral.



Denny

 

[itsid]

NOT Rotax ...
indeed PCR (TS54 I think)...
.. IIRC based off a iame Parilla or Sirio maybe BM Atlas.. (elongated cooling fins)
(although that crankcase looks alot like Rotax indeed...)

rotary valve 100cc with what looks like a motoplat ignition and in it's more glory days roughly around 17-20 horses worth of oomph.

If you do not have a plugged reed valve port on the crankcase (next to the coil);
the rotary valve is indeed your only intake, and thus you will not be able to just mount a clutch..
not without fabbing up something to extend the crankshaft (incl support...)
so it indeed is ment to be direct drive only.

I'd be happy to see what you could come up with to mount and support a clutch without interfering with the intake

But to be honest.. it'll be a pain on a mini bike like that..
it's a low torque high rpm racing engine, that's not too happy to climb a hill or see many load changes over the course of the day..
and worst: it'll require tons of maintenance... (every 4-6hrs of driving time)
with at least 15k rpm you will have a hard time even fitting enough gear reduction
to make it move properly with wheels like these.


'sid

 

[andrecht]

Sid, your bank of knowledge is astounding!
For ease of use, I will probably opt for a 6.5hp powerplant and recycle the kart engine at some other point.

---------- Post added at 10:43 AM ---------- Previous post was at 10:26 AM ----------

Started the frame fabrication today, had some "off "from my wife's list of usual Saturday DIY jobs.

Im using standard 1"(25.4mm) dom tubing, and bent the basic rear end shape....
I have previously posted a thread about my bending machine... Can be seen here:

http://www.diygokarts.com/vb/showthread.php?t=31464

This is a pure winging it project.. I have no preconceived idea of what I want to end up with, just making it up as I go along

A simple technique I learnt for notching tubing without using a hole saw or any expensive tooling, is simply a grinder with a rough flap disc...

Hopefully I am allowed to continue my flight tomorrow

 

[chancer]

Here is a cool tool for notching.
http://api.viglink.com/api/click?fo...rum&txt=http://metalgeek.com/static/cope.pcgi

you still have to grind but, well check it out. it tells you where and how much metal to remove.

 

[andrecht]

Eric, that is probably the most accurate way of getting the perfect profile at the end of a tube.

---------- Post added at 03:04 AM ---------- Previous post was at 02:54 AM ----------

Question :
How does the rake angle affect steerability?

Im building this for agility rather than speed, perhaps a backup or reconnaissance vehicle...so my concern is that too much rake will ruin that..

 

[bob58o]

http://www.motorcycle-superstore.com/4125/mngr/rake-and-trail-explained.aspx


The Practical Application of Rake & Trail

Rake and Trail enhance stability, so bikes with lots of both, like modern cruisers and heavy touring bikes, which typically have rake angles close to 30-degrees or more and a trail measurement of maybe 5- to 7-inches, tend to be extremely stable. They generally have impressive stability in a straight line and are able to maintain their composure through long sweeping corners.

On the downside they are often less maneuverable than we might prefer, especially at low speeds. These type of bikes usually require a stronger hand on the bars to initiate and maintain a tight turn. As an aside, this is one reason why cruisers have such wide bars, because the leverage reduces the steering effort. Obviously, other factors including the bike’s weight and of course, wheelbase also plays a role here but all things being equal, the more Rake and Trail we build into a motorcycle, the slower it will respond to rider inputs and the more stable it’ll be in a straight line.

As Rake and Trail are reduced, the bike will become more maneuverable and quicker to respond to steering inputs. It’ll also develop a lighter feel at the handlebars.

Unfortunately, it will also lose some of its stability. Pure sport bikes with their steep rake angles and short trail measurements, Rake measurements of 24-degrees (or less) and Trail measurements down around 4-inches aren’t uncommon, tend to turn and handle extraordinarily well. But their overall steering demeanor might best be described as nervous, twitchy, light or darty.

Though highly maneuverable, they also have a tendency to feel a little twitchy or unstable at high speed, so a steering damper is a good way to prevent things from getting out of control. But, let me digress here and point out that the last sentence shouldn’t be construed to mean that sport bikes aren’t stable at high speed they are in large part because while Rake and Trail play a critical role in the way a bike handles, they aren’t the only things that affect it. A well-developed chassis and properly designed suspension are also crucial. As are things like centralizing the bikes mass, engineering the right wheel base and so on, so in and of itself, the steering head numbers - while highly important -obviously aren’t the only things that impact a bike’s handling characteristics.

The bottom line here is that the more Rake and Trail we have the more stable the bike will become, although both steering and maneuverability may suffer for it. Conversely, when Rake and Trail are reduced, the bike will steer quicker and become more maneuverable, though it’s usually at the expense of some stability.