Build a Fun 4-wheel Buggy on Your Own!

Modifications & Improvements
03/21/2005 Updated


I noticed (as of June 2004) that I have enjoyed driving my buggy only for 2 times since I got it completed back in September 2002.
The primary reason might have been that my Toyota van that I had and used as a transporter of the buggy has gone due to an emission raw which was taken place here in Kanto region around Tokyo, but at the time of the months I have not been motivated in starting to work on several unfavorable points once I had got it completed.

Now I just took off the cover that I have put on the buggy for about half an year, and started again to work on it.
I would like to get all the work completed before it goes into rainy season.
Followings are the points of modifications and improvements.

1. Kick pedal re-design
2. Heat shield plate in front of exhaust pipes
3. Knuckle arm extension
4. Front fender add-on
5. Silencer replacement
6. Reinforcement around ball joints of front-lower suspension arms
7. Repair of bent drive shafts
8. Repair of broken front axles & Offset change of front wheels
9. Replacement of ignition coil, spark plug wire & the cap
10. Repair of broken front axles (Vol. 2)
11. Steering angle adjustment of inner & outer wheels
12. Fuel filter relocation


Kick pedal re-design

Pull-up lever has been the method to start the engine, however with this method I was convinced at the first run in September 2002 that it did not secure required angle of rotation of the crank shaft, thus starting the engine was quite a hard job.


First thing I did in October 2003 was this.
A steel rod with a kick pedal at the end, supported by a automotive jack.
This worked but it redundantly took time to put on and off every time of starting engine, furthermore, every time engine stops somewhere far away from the base I had to push it back to the place or to come back just to take the pedal for re-start. It was nothing but painful.



After number of months have gone, I re-started to work on it.
I purchased an used kick pedal for motorcycle (type unknown, 100yen) and welded it onto the rod I originally put in place.
As a replacement of an automotive jack, I made a foldable supporting structure in "A" shape and put onto the frame of the buggy.
The material was from a leg of a beach bed being disposed, thus the cost was zero.
Difficulty to make it complete was that the thickness is only 1.2mm therefore it was a hard job not to get it melted due to excess heat coming from my DC battery welder.



I got the all painted, and made a few small components for completion.
An "A" shape structure and the kick pedal itself are designed to be folded and tied up onto the frame of the buggy when it is in driving.


Then all the things come out at simple operation when it is needed for engine start.


Heat Shield Plate in front of Exhaust Pipe

My back gets heated when I drive the buggy.
This is because of the heat comes from exhaust pipes coming close to the seat.
A shielding place is needed to block the heat.


Exhaust pipes coming closer to the seat (approx. 40mm in between).


The material I chose was a steel plate originally used an air conditioner at my home.
I interrupted this being disposed at sometime before because I thought it could be used for the heat shielding purpose.
The thickness is only less than 1mm thus easy to work, and also it is pre-plated with zinc that I can expect sufficient anti-rust performance.


Completed. Appearance is fairly poor but it is OK as this is just behind the seat back.
The performance of heat shielding will be checked at the next run.


Knuckle arm extension

Since the heavy operation force of steering and the angle less than 90 degrees for lock to lock, I extended the length of knuckle arms for slower steering and restricted the operation angle of steering.


I put some pieces of materials by welding, painted, and the extension has become completed.
For steering angle restriction, I re-iterated the stopper that I made sometime ago.


Front fender add-on

Two years ago when I had the first run, a lot of stones and sand are rolled up by the front tires turning, and they hit my face.
Also the stones and sand are stuck up on the seat until the end of run.
I decided to make a pair of fenders for the front tires at the opportunity of taking the knuckle arms off from the buggy.


The material I chose was a front fender I found at a shop of used motorcycle parts. The original use is not for sure, and the price was only \100.
I cut it into two pieces, made the corners rounded, and a pair of fenders become completed.


I then made all the necessary metal structure to support the fenders.
The material was several pieces of steel rods in diameter of 3mm that I got from a beach bed which had not been in use. Thus, the material cost was zero.
I put flat steel plates at the top of the rod to install the fenders. The flat plates came from junk, thus they were also zero cost.


I got all the steel components painted, and put the fenders by bolts and nuts.


Completion.
The width of the fenders are slightly narrower than that of the tires, but this should be still better than having no fenders.


Silencer replacement

I have used a silencer from Kawasaki ZXR250, 4-cylinder motorcycle, and the feeling on it has been that the acceleration in a certain range of engine revolution goes less powerful possibly due to uncongeniality of the silencer with the engine.
I thought another silencer from a single-cylinder motorcycle should demonstrate better performance because the engine of my buggy was from XLR250R, single-cylinder motorcycle.
Thus, I decided to replace the silencer with another one to see what will happen.


The one I found was a silence originally for Suzuki motorcycle.
I found it also at the same shop of used motor cycle parts, and the price was only \300 although it stays at a good condition and less number of scratches.
Connection with an exhaust pipe is slip-on, and the diameter inside perfectly matches the exhaust pipe of my buggy.
A ring gasket is still intact and in place.


I made a metal band to hook the exhaust pipe. The material I used was a band originally for automotive catalyzes.
I also made a bracket (the material was from junk) and welded it onto the frame of the buggy. End of the exhaust pipe is then supported by the band that is fixed onto the bracket.
Silencer is slipped onto the exhaust pipe, and tightened up with a band already placed on the silencer.


A metal bracket to hang the silencer, connected to a bracket already in place.


Completion.


Reinforcement around ball joints of front-lower suspension arms

First of all, I observed carefully the portion broken at the experiencing drive held on July 24, 2004.


Thread of the nuts welded inside the bottom of king pings (if I call them so) were completely destroyed.
In contrast, thread at the link balls marginally stayed fine although the bolts themselves were slightly bend due to an excess stress.


Lower arms were also bent as shown.

I just noticed one thing that could become a trigger of the failure.
Sometime ago, after I enjoyed the driving, I found the tightening of this portion became loosened.
The fact should have told me that the bolts were kept stressed radially during the drive, and possibly the thread was mechanically damaged without being noticed as a result.
Right before the drive on July 24, I re-tightened the nuts and looked well tightened, however due to the failure of the thread of the bolts, the tightening torque of the nuts might not be secured properly.
The possible story of the failure is that repetitive stress applied on the bolts kept leveraging the thread, and the stress finally destroyed the thread at the nuts (which were not heat treated thus relatively weaker than the bolts).

Now, 3 improvements that I identified are as follows.

(1) Replace the nuts welded inside the king pints with another ones having smaller pitch of thread and larger size for the lower fixation of king pings
The current nuts (M10X1,5) will be replaced with another ones (M12X1.25) for more stable tightening performance.
(2) Eliminate usage of nuts at the bottom of king pins, and weld bolts instead
Bolts in size of M12X1.25 are to be welded at the bottom.
(3) Replace rod ends in larger size and with different type
Replace the rod ends with closed-end type, in size of 12mm. The rod ends are to be inserted into the mentioned M12 bolts, and tightened with 2 nuts per side. Security pints for anti-looseness will be also put in place.


Bolts and nuts in size of M12X1.25, and rod ends in the corresponding size.
Both of them can be found hardly at DIY centers.



To secure wider angle of operation for rod ends, I machined the head of the bolts and perimeter of nuts.
I put them on my milling machine, and got machined with hand file.


I welded the machined bolts carefully on the bottom portion of king pins.
Rod ends will be inserted into the bolts, and tightened with nuts machined.



Next objects to modify are lower arms.
I got long nuts in size of M12 (but with no thread that I eliminated by machining) welded onto the lower arms.
M12 bolts will be put through the long nuts to fix the rod ends.


I got all of them painted, and brought into the garage for assembling into my buggy.
I paid much attention to this particular modification because failure of such portion at the front directly connects to flip-over accident that I experienced.
Rod ends adjusted approximately, and I finished today's work.


Completed.


Repair of bent drive shafts

Right after completion of repair of front suspension, I found that right-rear tire looks not in the correct direction.
I then noticed that the drive shafts are bent.
Supposed root cause is that, during the drive on July 24, the right-rear tire got excess force in thrust direction from the ground when the right side of the buggy hit the ground after the rear tires jumped up because of the right-front suspension broken and hit the ground.


I put off the whole assembly of the drive shaft in the garage where I could hardly stand the thirsty because of the temperature in the mid of summer.
I brought it back to my home and observed it on the work bench, and recognized that it is certainly bend.
No deformation found on wheels, fortunately.



I put the bent portion back to the original shape by using hydraulic press.
The deformation were successfully eliminated.


Lastly, I strengthened some minor portions for completion.

In overall, the drive shaft assembly still looks not strength enough.
I would be interested in making it reinforced more, but I expect that the workability is quite poor because the shaft assembly is no longer serviceable structurally.
Complete remaking of it would be also another tough job.


Repair of broken front axles & Offset change of front wheels

Right-front tire flew off at the experiencing drive held on September 20, 2004.
Because the dirt track is an oval turning anti-clock wise, tires at right side are always stressed higher than for left, however the failure must be solved otherwise the buggy will never be able to come back on the ground.
One suspected root cause is that the moment applied on the axle might be higher than the limit of the material.
The surface of inner bearing stays almost in the surface of side wall of the tire.
Bending moment applied on the axle should become less if the surface of the inner bearing comes toward inboard, I thought.
I started looking for the alternative wheels having the inner bearing placed more inboard, while maintaining the same tread as current.


From left to right, a wheel with a worn tire (but in good condition) that I purchased for 500Yen at a used part shop, and another one with some moss that I found in a garbage box at a junk yard.

Probably both of them were originally for Yamaha Jog, 50cc scooter, or something like that.

A guy of the junk yard said it would not be recommended, but I thought it quite OK because I observed no deformation in the thrust direction while rotating. I did not care about the condition of bearings as I intended to replace all of them anyway, and I got it for free of charge.



Comparison between the previous one (from Honda Dio ZX) and the one I procured.
Although it is not clearly shown in the photos, the inner bearing of the alternative wheel is placed outboard by approx 15mm from the wheel rim, despite the current wheel having the bearing placed inboard side by 15mm.
Thus, the difference of the inner bearing placement is 30mm which could be said as offset if I talk about wheels for automotive.
Width of the wheels are same each other.


I pulled out all the bearings of the alternative wheels and checked the total width including a spacer in between.

The width of the current one is 81mm, and the alternative one is 51mm. The difference is 30mm like I observed in the inner bearing placement.
Based on those facts above, it can be judged that the location of the outer bearings of both wheels are common each other.


To pull out the bearings, I had to purchase a puller shown in the photo.


I made spacers having length of 30mm and welded them onto the king pins.
For the material, I used long nuts having M10 thread (that I eliminated by milling).
The length I choose was 50mm to maintain the tread as current.
The objective of this modification is to alleviation of bending moment applied on the axles, while maintaining the current tread.


The wheels originally looked like garbage (one of them was actually a garbage as it was found in a garbage box) drastically improved the appearance after re-painting I did.
I scrubbed the surface to get it rough, and painted with head-resistant silver paint that I have had.
I got both of them painted for common appearance.


I put new bearings into place. I choose sealed one because the original dust seals are no longer fine for use.
One negative impact I got in this modification was that weight of the new wheel was 2.7kg, instead of 2.0kg of the original one made with die-castled aluminum.


Completion.


Repair of broken front axles (Vol. 2)

Right -front axle got broken again at the experiencing drive held on October 24, 2004.
Things come to the point that no more durability of the current 10mm bolt can be expected any longer no matter what kind of material is chosen.
On the other hand, when I looked at the front axle installed on a Zerohan car, I found that the size had been increased to 17mm from the original 10mm. This lately told me that this has been the way I had to take for failure prevention.


For the axles, I choose rear axles for intermediate motorcycles which have 17mm of diameter, and the corresponding spacers.
I ordered 2 sets of rear axles and the crown nuts for Yamaha SR400, and 3 spacers for Kawasaki ZRX-II.
The reason of the choice was only because the cost, and the only criteria was the diameter.
Bearings I chose were 6903 manufactured by NTN.


I cut the spacers into length required for the spacer to be inserted between 2 bearings of each of the wheels.
The length of the original spacer installed in the Yamaha Jog wheels were 33mm, within a tolerance of +/-0.05 according to the measurement I did.
I thought a lathe would be necessary to achieve such tight tolerance, but I decided to try my best only by utilizing the equipment that I have at home.
First of all, I cut the spacer into pieces longer than desired by approx 1mm, then grinded one of the surfaces carefully by using a side surface of an electric grinder, while the length is kept measured on a frequent basis to make sure the both surfaces are in parallel each other within the tolerance of +/-0.05 for the distance.
The point I paid attention in the grinding was that I kept the spacer continuously rotated in order not to get it grinded unevenly.

Lastly, I polished the grinded surface with a sand paper to make it shine like the original one.
I measured and observed that the tolerance of the 33mm distance of both surface is within +/-0.05 like the original one.
I lately remembered one thing that it has not been recommended to use a side surface of an electric grinder for safely reason...


The remaining length of the purchased spacers were supposed to be used for caller inserted into king pins.
I put holes of 25mm diameter on the king pins and inserted the caller by press.
Although now shown in the photos, I made it completed after welding and painting.
No photo is available for the completion process because I accidentally dropped my digital camera into the ground and failed.


Upon the completion of all the components, I tried to assemble all.
A space located between 2 bearings in the photo will be place inside wheel.
The diameter of the axle looks impressive compared to the original broken one having only 10mm of diameter.


Bearings and spacers placed inside the wheels.
I checked that the rotation of all the bearings is good.
The bearing shown in the right photo is placed back inside the wheel itself, and to fill the space a spacer made by using M16 nut will be put in place.


For completion of front axles, I cut the shafts into length, and welded M16 nuts that I removed thread.
The right photo shows the condition of the placement of the wheel and nut.
After getting all the components painted, things become completed.
As a trade off, the weight around the front suspension became heavier than before, however it would be fine if I encounter no failure.



Relative relationship between front axle, wheel, and fixation nut.
After putting a wheel into the front axle, a spacer made by using M16 nut has to be inserted, and tighten them with a crown nut, then put a security pin for anti-looseness.


I checked that the wheels rotate smoothly even after tightening the nuts, and got all completed and became ready to run.


Replacement of ignition coil, spark plug wire & the cap

Here is an ignition coil, wire, and the cap that look suspicious and that I believe original since the manufacture of the XLR250 motorcycle.
The external insulation material has become degraded and lost flexibility, and at each time of spark plug service the wire was significantly bent at the root portion of the coil side, thus I was wondering if the strands inside might have been mechanically cut or damaged.
Another fact is that I had peeled the external insulation to get it free from the poor flexibility, and in the operation I damaged something inside the wire. The wire runs next to the frame and I suspect that some electrical leakage might have happened since.
Engine stalls sometimes during the drive, and some of the mentioned elements could have been the root cause.


This is the original one.


An alternative one that I got. This was originally installed on a Honda 50cc scooter, however the resistance value that I measured is the same as that for XLR250.
Resistance measured both at primary and secondary was good, with no electrical failure.
I got the spark plug wire and the cap only for 100Yen at a used part shop close to my home.
Resistance value of the cap including the wire was good as well.


Completion.
Because the spark plug is L-shape, serviceability became better than before, involving less chance of getting the wire bent.


Steering angle adjustment of inner & outer wheels

The inner wheel should have been steered larger than that of outer when steered.
The reason is in order not to get the trace of inner and outer wheels crossed on the way ahead.
However, looking at my buggy I noticed that this has not been taken into place. It must be corrected.


I replaced the fixation points of tierods toward outboard direction.
Displacement that I took was approximately 12mm according to the simulation that I did on a piece of graph paper.
Hopely this modification will work to improve the cornering behavior of the buggy.


Fuel filter relocation

In the past experiencing drive events, I have encountered a phenomenon that the engine revolution drops suddenly that I felt something might happen at somewhere on the fuel delivering system.
I noticed one potential root cause of it by looking at the place around the fuel filter, and I made it corrected.
The fuel cock was place in between a fuel tank and a filter, and the cock has blocked the air inside the filter getting outside toward the fuel tank, therefore, the fuel itself could not smoothly come into the filter then into the carburetor.
I relocated the filter into the place before the cock, and the air started getting up to the tank while the filter started being filled with the fuel.

... To be continued.

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