My Bike Build

Hi. Welcome to my bike build thread and first ever post on ADV.

I’m building my own bike largely because I think that I can. Na, I know I can. I am a mechanical engineer by trade which means I can crunch numbers, work computers, inspect workmanship bla bla bla bla. What is does not mean is that I can weld, turn assemble or any other craft type skills. Much of this I will be learning and increasing my skills in as I go. That is not to say that I can’t weld, just that it is not something that I ever do for my job or have ever done any significant training for or qualifications for.

So, what to build?

Well, 8 or 9 years ago, I had a really interesting job in a very small design firm in Christchurch, New Zealand. One of the more interesting projects we did was an ultra light motorcycle. It weighed in at about 55kg (about 120lbs), was fitted with a pit bike engine (angled up to increase clearances), Down Hill mountain front forks, pit bike air rear shock. My job was to design a frame, swing arm and subframe to tie all these items together within design parameters (shape, form, construction method) prescribed by the client. I also designed the fuel tank and rear hub.





You can check them out and even buy one if you want from here:

www.fxbikes.com

Ever since then, I have wanted to make one for myself but with my design parameters.

First off, some things that this bike will NOT be!

An adventure-touring bike suitable for long multi day rides,

A motocross race bike set to take on Suzuki, Honda, KTM etc,

A trials bike that Toni Boa will want to compete on,

Your ideal bike!


Now, here is what I want the bike to be:

Light! The goal is 50kg, anything lighter than 55kg will be acceptable,
Air cooled. I don’t want to deal with radiators during the build or riding,
4-Stroke. I want to run straight gas,
Tuneable. I want to be able to use engines that very from mild to wild (well, to less mild),
Sized to fit an adult of about my size (176cm),
Make-able. I don’t have a mill or presses to create monocoque frames etc,
Fun! To both build and ride.

The idea for the bike is sort of an ideal recon bike. Light enough to lift over a fence or carry across a water crossing. Fast enough to have fun on while trail riding with mates and will hold its’ own when ridden with friends on typical dirt bikes. The bike is designed with heavy-duty bicycle components where possible to keep the weight down.

So here are some of the bits that will be used:

Honda XR 100 engine (6hp wu hu!),
Kitaco 145 engine kit (18-22hp! That is in the realm of a stock XR 250),
Marzocchi Monster T 8” travel forks,
Fox air rear shock,
CR 125 seat,
Bicycle front wheel,
Home-made rear hub laced into a motorcycle rim,
Formula disk brakes,
Home-build cromoly tubular frame and swing-arm,
Home-build aluminium fuel tank and air box,
A Clake. www.clake.com.au to operate the rear brake and clutch in one unit,
I still have a couple of the FX Bike parts such as the rear fender so I’ll use those also.

See you next time when we get into the design in the CAD system

Nice, very interested to see this happen. Cool parameters too

Ok,

One of the things I do for a job is to create CAD models. Well, I did in a previous job. So I used a CAD system to layout the design for my bike also.

I create the bike frame, swing arm and sub frame as one part that I can then subdivide out into all of the individual components necessary for the build. I then get all those individual components, add all the cuts, threads and hollows and reassemble them into assembly files.









Solid model including jigs from the frame and swing arm ready to be subdivided out into separate components

Now, to make any given component, I can go to the individual components part file and make a drawing of that part.



And now all the individual components are added back into an assembly file.

This process takes many hours, many changes and lots of design decisions.

Also, because I am building my frame from scratch, I will make jigs that will position the critical components and hold them while the interconnecting frame members are added and join everything together



The almost complete assembly file of the whole bike. I won't be bothering to include items that I won't be making or that do not interface with items that I will be making such as the handle bars and controls

last pic for today



When designing the FX Bikes, we did a link-less rear suspension design. It caused some design decisions that I was never happy with so I have made mine with a linkage to drive the rear shock. This will also allow a measure of tune-ability by being able to change the geometry on the linkages. Much more complicated but it's my bike and I want it.

Just what I've been thinking about making for the super tight trails here in Indo. Too cool.

Sounds like what I built a few years ago.



138cc Pitbike motor
Downhill Bicycle Forks
Bicycle rims
8" Double disk front brakes
8" Disk Rear brake
Fabricated bicycle hubs
Stainless Spokes
Adjustable Head angle
Competition Motocross Air shock (1)
Street Legal with License Plate
130 Pounds plus Gas

So then I wanted one that was more suited for offroad.



160cc YX160 Pitbike motor
KX85 Forks
17" & 19" Alloy rims
8" Double disk front brakes
8" Disk Rear brake
Fabricated bicycle type hubs
Stainless Spokes
Adjustable Head angle
Competition Motocross Air shock - Under Seat
Street Legal with License Plate
A little heavier - forks, rims, tires

Don

Welcome to ADV!

Do you have a budget in mind?

I love this idea, and have been toying with one of my own. I have designed and fabricated a bunch of downhill bikes, so this piques my interest in many ways. I don't want to question your intentions at all, just curious about part spec:

Why a Monster T? Is it because you have one laying around? Furthermore, why a fox air shock? Same as above?

If you already have them I understand that. If you were starting from scratch I would consider more modern fork options; A Rockshox Domain, for instance, has the durability of steel stanchions, coupled with all the spring and damper options of a Boxxer (including 3rd party like Avalanche). It would weigh much less than a Monster T, and even less still with the air spring.

The air rear shock is a head scratcher... While there are several nice options out today (CCDB Air, RS Vivid), the only fox offering suitable for speeds is the RC4 air and they are unreliable. The rear shock is not somewhere to cheap out for weight's sake, and (personally) I would choose a coil every time. Even if the intent is to reconnoiter, a bike with an xr100 motor will be capable of sustaining 30+ mph speeds on dirt, and a platform valved air shock (rp23 etc) just won't cut it. From an engineering standpoint, the less leveraged the shock is the better it will perform as well, so if you are putting 8" in the rear wheel to match the front, a 10x3.5" stroke shock would be best. 9.5x3.00 is the most common on DH bikes, and I'm pretty sure platform air shocks are usually in the 1.5-2" stroke range tops. Sorry for using imperial.

Well free advice is worth what you paid for it. Good luck, I'm subscribing to this and anxious to see your CAD drawings!

Edit: pics just loaded up of the bike drawings. Very interesting-- I have more free advice but I think I'll shut my mouth for awhile

Well this should be good. An engineer with limited build skills. Usually, at least in my case, it's build "skills" with no formal engineering knowledge.

Good luck.. I love the idea.

Exciting! I'm watching this thread for sure!!!

If the honourable MrBracket is in then so am I! (actually I subscribed earlier today:d) Been waiting for my FX for too long and no end is in sight yet, so it's do it yourself time....

Not really. It would be nice if it came in a half the cost of something new but things like the Kitaco kit are not cheap. I'll keep track of the costs.

You are right, I had both items already so I used them BUT..

The Monster T fork, while heavy, is ultra reliable and has a nice damping systems. I like the Aluminium stanchions as my experience with every steel stanchion is that they end up rusting. However, I have not kept up with the latest fork offerings for DH bikes.

On the rear shock, I am using a Fox MXR with 76mm (3") of stroke designed for motorcycles. I had the same concerns that you have raised.

Great build plan.

I'm in!

Salsa, those are a couple of interesting bikes.
Thanks for posting the pictures.

Yep im in and i like the concept

food for thought maybe

http://www.motorcycledaily.com/wp-content/uploads/2004/06/062104pic3.jpg

I had a ducati cucciolo on a mountain bike frame 1951 /52 t2 model but always wanted more

Bruce

I picked this one up on E-bay. DRZ 125 with a modified frame , warmed over motor , 17" wheels , etc. Set up as a flat-track bike.
Little remains of the stock frame , just the steering tube and downtube plus the the tube where the footpegs and swing-arm attach.
It's a fun little bike, but, the gas tank is only about 1/2 gallon so no long range travel.
Good luck with your build, the frame looks strong enough for 500 cc of hot motor !

Hi, I really like your build idea! I've thought about someday building something with a similar concept. As a mechanical engineering student I am very interested in seeing your plans come together. You made it sound like you might be fabricating many of your own components like controls, parts, etc, is this correct? If so, are you going to be designing the entire bike and all of its parts as an assembly, or designing and building one portion at a time?

Good luck! I'll be checking back on this one!

I decided on a Honda XR 100 engine as the power plant. This engine was chosen for a number of reasons including:
• Small. The 100 is considerably smaller in size than most if not all of the 150cc – 200cc options.
• Performance parts availability. There are heaps of hot up parts for this little engine including big bore kit, 6 speed transmissions, twin cam heads.
• Air cooled. No need for a radiator.
• 4 Stroke. No need for mixing gas.
• Available brand new or (as in my case) 17 years old with very little changes.
I looked around on eBay but didn’t see much that I liked. Most cost more than I wanted to pay. Because I always intended to use a Kitaco 145 big bore kit, I did not need an engine that was perfect.
Finally, through a post that I put up, I found what I was looking for. A 1995 XR100 that has been beat to within an inch of its life!

No photos of the frame but here is the engine, remove from the frame so I could create a rough CAD model.





I fully disassembled the motor. The oil screen was full of grass seed.



Most of what I wanted to keep looks good but I am amazed the motor ran long enough to wear the ring gap to almost 3mm!

The cases look like they have 15 years of oil build up on them.













So I send the off for cleaning to bloke that does vapor blasting on the side. They come back looking like new.





I remember years ago when my neighbor had a VFR750 which had these gold coloured cam covers. I loved them so I decided to paint mine gold also. I also painted the left and right engine case covers the same gold.



Love the cam cover colour but not sure on the side covers yet. They can be repainted if I don’t like them.

With the increased performance, I opted to put in a higher volume oil pump so I had to drill the oil port.



At some point in the engines life, the chain has come off and broken the left side engine case. Nothing structural but the case can not be sealed now so I will rebuild the case with JB Weld. Will this work or just fail after some heat cycles?

Next post: Lets make a frame

Jb weld should hold up ok if you clean and rough everything nicely before you put it on.

I had an Xr100 as a kid and beat on it just like the one you ended up with, and most of that life was lived with Jb welded cases because of a snapped chain lol.

I think a case saver would be pretty much a must have on that engine.

Got some more photos of the engine internals…both old and new.

I didn’t really have to look over the old top end because it is all going to be replaced anyway. However, it is a good indication of how the engine has been looked after and a great chance to see the difference between a standard engine for a AU$3500 bike and high performance components to release the potential of that engine.



Here are the basic items being replaced.



Check out the ring gap on the old upper compression ring! I measure it at 3.5mm. That’s more than 1/8th of an inch! I am guessing this bike was hard to start by the end.


Head looks ok. Lots of carbon buildup on the valves but not to bad.



Old piston looks ok to me. Minimal scrapes, no hot spots. Just worn rings?



Here is most of the new stuff that will be going in. Cylinder, head, piston, rings, crank, carb, clutch plates and springs, output shaft, kick starter shaft, gear selector shaft, cam chain, cam sprockets, cam, oil pump. I wont bore you with photos of all of that.

But here are some of the more interesting bits.



I like girls that wear short skirts and this new piston wears a short skirt.



Here you can see the difference in piston diameter. The crank also has a longer stroke to take capacity from 99cc to 145cc.



Not only does the new piston have a short skirt, it is not wearing panties! To get higher rpm, you have to reduce reciprocating mass.



The Kitaco conrod is beautifully polished



Nice new head with increased valve size and a new cam with increase valve overlap and duration.



I can’t wait to have a play with this new engine. I’ll have to find someone with a stock XR100 to compare.

I did not rebuild the engine straightaway cause I want to use the cases as a jig for the placement of the engine mounts on the frame. Once that is done, everything will be ready for the rebuild.

But! Talk is cheap and I I am here to build a bike, not reassemble an engine with some new bits. You are not reading this to see me buy some bits and make some pretty pictures in a CAD program of what the frame should look like. So lets hurry up and get into cutting some steel!

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