Anything Goes! Another Dutch minibike build from scratch.

SAT

Active Member
#21
Hello,
Short update on the projects;
Some more parts have arrived and others are on their way.

Both minibikes will be equipped with torque converters, so now I have 2 at home. In the background (on the box) is 1 of 2 seats, that we'll be using.

Both minibikes will be using thumb throttles. These aluminium throttle housings came for €4,-/each.

I'll modify them to make it more comfortabel to operate. And to meet my quality standards.
They standard Chinese clearance/play on the shaft is resulting in poorly behaving and sticking throttles.
I'll replace the cast aluminium shaft with a stainless steel one (cut off part of 14 mm bolt). And with a reamer I'll make the housing bore 16 mm. In the housing I'll place some thin wall sliding bearings. They will not misbehave themselves anymore...

For a total of €6,- (=approx $7,-)! I have ordered, all new, quality, hardware for:
Cylinderhead studs + nuts
Side cover studs + nuts
Valve cover studs + nuts
Exhaust manifold studs (SS) + brass washers + brass nuts.
Intake manifold studs + nuts
And a new M14x1,5 nut for the flywheel.

"Stay tuned"
Nice project.
Concerning the number of bikes...
It takes one to ride, two bikes to race, and three for the future “group ride”.
Fine work on parts received!
 
#22
All throttles have been modified.

The milled down handle, stainless steel shaft and I have milled some aluminium of the housings. The throttles are operating very nice, now.


I just need to make an adapter so I can make use of this adjuster for the throttle cable. The handles are mounted to the shaft with the use of green Locktite 270. I think it will hold.


As the torque converters are not available with a sprocket for #219 chain, I will make the sprockets myself. So I can make use of the chains and rear sprockets that I already have. This way I don't get all sorts of different chain types and sprockets in the workshop.
I will have the red colored part lasercut. with the lathe I will cut of the sprockets that came with the torque converter and on the remaining part I will tag-weld the lasercut sprocket. At least that's the plan...
 
#23
Adapters for the throttle cable adjusters have been made.

I used some black, round bar PVC that I had laying around. It turned out nice and works great.


4 new, steel rims have arrived. They are 4,5" wide and are the same as I used on my previous minibike. the 145/70-6 tires will be mounted tubeless.

There's a "side project" in the workshop.

It's a Suzuki ALT125 trike. For some reason, somebody had cut of the primer pump on the carburator. Since then the trike was hard to start. That's about 5 years ago, or more. I ordered a new primer pump for it and I am pretty sure it will run when it's mounted. Also need to clean the entire fuel system. The gasoline had been sitting to long.

All drawings for the minibikes are ready and I took them to my work, where the parts will be lasercut. So actual building is soon to start!
 
#25
Actual building is soon to start, so this weekend I decided it was time to make an adjustable frame jig. This will make it easier for these 2 minibikes, but also for future projects.
As I already have a 3-D drawing of the minibike it was easy to create a frame jig around the frame. Just another advantage of 3-D designing.

This is the design I came up with. There's a neck support, which is only adjustable in height. If I need another rake angle, I can replace this part with another part with the correct angle. Frame supports can be adjusted in length and in height. I have attached welding nuts to make use of bolts to secure the adjustable supports.


After cutting all the square tubes, I have tag welded it all together, which should be enough for a frame jig.
If someone is interested in the free drawing (.dwg file), here's the link to it: Framejig.dwg
 
#28
Last week I started to make the front-, rear- and neck axles for both minibikes.

They're not finished, yet. Need to drill and tap holes in them and make some flat sides on them. The flat sides will prevent them to turn, when installed.

I also continued working on the GX160 engine.

Because I remove the governor I need to close the hole of the governor arm on top of the crankcase. I have glued (Locktite) a piece of 6mm steel bar in it.


The hole of the low oil sensor is also closed with a 10mm steel bar and some Locktite.

Because I have ordered several new engine parts, like pistons, rings and pins. I wanted to know if there's any diffrence in weight.

The old piston is being reused with a new wristpin and new OEM standard size piston rings. I do have some aftermarket ringsets, but I'm not sure about their quality. I might try it later in another engine.
Ring end gaps are within specs.

Because the governor is being removed I've installed a billet connecting rod.

Because the old crankshaft was not within specs I have replaced it with a new one (aftermarket). I checked bearing clearance with plastigage. All was within specs given by ARC.
The first new aftermarket crankshaft (to fit a GX160) I tried to fit, gave me some problems. It hit the piston on BTC and on TDC the piston was way outside the cylinder. Somebody must have swapped a GX200 and GX160 crankshaft before sending it to me. I will have this crankshaft replaced with another.


After measuring and checking the bearing clearance again on another new, aftermarket crankshaft, I have installed this one. And it fits. Torqued the rod bolts down with the use of a inch pounds to Newton meter converter and a torque wrench.

I installed the side cover studs and cylinderhead studs, which I ordered at a hardware store.

The studs are ordinary DIN939 studs. M8x30 for the side cover and M8x60 for the cylinderhead. I did mount them "upside down". It leaves enough thread for the new nuts.

Even more bling-bling installed on the old "not-so-clean" GX160 engine.
This is an "ultralightweight" flywheel, as they call it. No better way to see if it works, as to buy and try it. So, I did.
It accepts a plastic fan and recoil starter.

A billet flywheel from ARC. I bought it together with the billet rod at a store in the UK, no import charges for me. After lapping with valve grinding compound it fits the new crankshaft perfect. For now it is installed with the stock key in the crankshaft.

After the new parts had been installed, I had to see how my homemade degree wheel would fit.

It fits!

Cylinderhead is the next thing. No big changes there, I only tried to clean it and it will be equipped with 18Lbs springs.
"Stay tuned"
 
#29
Well, the engine runs by now.
I've lapped the valves a bit and installed them with the new 18 lbs springs. Installed the head and for now put the original carb on to see if it would fire.
It was hard to start, but it ran after a few pulls.
So far for the good news...
The bad news: when the engine ran low rpm's/idle it stops and puffs back through the intake manifold?!
Sometimes it did start and other times it didn't and pulled hard on the cord. While smoke came out the intake.
Since then I broke a recoil starter and from another recoil starter that I installed I broke the cord...
I was thinking that maybe it was a malfunction of the decompression release. But I figured if that part would malfunction it would always be hard to pull. That wasn't the case.
Today I thought it would be wise to pull start it with ignition switched off. To see if the ignition timing might cause the occasional pull backs on the cord. It had no pull backs with the ignition off.
I have no timing light, yet. But the flywheel was installed with the stock key in the crank.
I took the key out the crank and installed the flywheel back on and retarded ignition timing by 14 degrees, just to see if it would work.
It started with half throttle and ran ok. Even on idle.
When the flywheelmagnet is complete under the coil, my degreewheel tells me it is at 20 degrees now. With the key in the crank this was at 34degree.
But I am not sure what the position of the magnet regarding the coil would be when it sparks.
I think I will have to order a timing light.
 
#31
I have uploaded a video to Youtube of the running GX160. For this occasion it's fitted with the old gastank, and carburator again.
This was before I retarded the ignition and before I broke a recoil starter and a rope...
 
#32
A timing light is ordered and on it's way, but in the meanwhile I couldn't resist to run/test the engine with the retarded (20 degree btdc) ignition timing.
This engine now has a thin metal head gasket which gives a higher compression ratio, compared to the standard "thick" GX160 head gasket. I also replaced the stock spark plug wire and resistor boot with a solid core wire, and boot.
To test the engine under load I installed it on my other minibike.
First run, it ran ok. I had expected more of it, but maybe that was because of the retarded timing.
2nd run it ran worse, 3rd run it was even more worse. It didn't want to go way up in rpm's. No tachometer installed, so no precise numbers, but I guess it revved up to around 4000-4500 and no further. On load or unloaded.

Troubleshooting began: I checked the spark plug, which didn't look to bad. It is running the stock carb with stock jetting. I would have thought that it would indicate that it would be lean. I did check the main jet, which was clean. Compression test gave me >6 bar. Valve lash was still okay.


I did some "internet research" and pictured above would be the point where the spark should occur. Correct me if I'm wrong.
When I checked this with my timing...


...It indicated that I was running an ignition timing of 6 degree btdc... The flywheel must have travelled, without the key installed. I did set it at 20 degree btdc, without a key before I ran it 3 times.
Well, happy me! I did find something that could contribute to the "not willing to rev high engine".
I took the flywheel off, filed a keyway a bit down and installed the flywheel back on. This time with the keyway.
Set the timing at 28-30 degree btdc.
I took the clutch off, to hold the crank while torquing the flywheel to 54 ft lbs.
Put the clutch back on and installed the other parts. I did replace the BPR6ES (resistor) spark plug with a new BP6ES spark plug.
Started the engine and ran the minibike like I stole it...
Yeah! Now it was running. It revved up like I wanted it to do. I ran it a couple of times down the street and enjoyed the sound of the open exhaust untill...


...I found out I forgot to tighten the "hold the clutch in place bolt", the hard way. The chain came of and got stuck between the frame and sprocket. Leaving a flat spot on the tire. No injuries, besides a dent in my ego.
Good news: The new sparkplug reading now shows it's running lean. It's white coloured. So I'm on the right way.
I'm wondering how much harder it will pull with the Mikuni carb on it, as that bore is a way better match with the intake of the GX160.

Weather forecast this week is good, so I will test the engine a bit more, before I tear down another engine for the 2nd minibike of this "2 minibikes" project.

*Minibike in pictures above is not 1 of the minibikes of this project, it's just a minibike to test the engine (for this project) under load.
 
#34
Several parts have been lasercut this week.

Pictured below is (with it's thickness):
-Front-fork plates (is that the correct name?); 3mm
-Seat support; 3mm
-Engine mount front and rear; 3mm
-Sprockets for #219 chain conversion of torque converter; 5mm
-Front- and rear brake caliper supports; 3mm
-Fuel tank supports; 3mm
-Fender mounts; 5mm
-Mikuni-, exhaust- and intakeflanges; 5mm
-Rearwheel sprocket supports; 8mm
-WD-40
-Junk
-Etc.

Missing in the picture is the stainless steel sheetmetal parts for the fueltank.

I know I have to many flanges for the intake and exhaust, but that's always handy if I decide to make another intake or exhaust.
 
#35
This is the time where the 3-D drawing time starts to pay of.
Now the lasercut parts have arrived, it's time to do some bending of the sheetmetal.


Initials of my last name cut out in this part. These parts will be a support for the 15mm thick aluminium engine mounting plate. This will be mounted on the back side, between the frame rails. Slightly slotted holes will help with mounting the yet-to-make engine mounting plate.


I bought this tool for around €20,-. It's clamped in the vise with magnetos and with help of the vise I'm able to bend small sheet metal parts up to 2mm. This part is 3mm and it worked, but hardly. Not recommended for 3 mm parts, but I like the tool.


Sheet metal parts for the rear engine mounting support ready to be welded together. I think it looks strong enough, but time will tell.


Front- and rear brake caliper mounts also ready. If I make no mistakes with tube bending, it should fit perfectly. 2 of each, because of the 2 minibikes to build.


Stainless steel sheetmetal parts (1,5mm thick) for the gas tank. Why stainless steel? Why not... I don't like rust / corrosion in a fuelsystem.

For the neck I started with a very thick walled steel tube.

On the lathe I turned it down and made room on top- and bottom end where the ball bearings will be placed. I used ball bearings in my other minibike, too and that works very good. No lash and it steers very gently. Ball bearings can handle the axial load easily.

It took some time to make these neck tubes, but as I know they will last long and will perform well, it's well worth the time.

Next job: making parts for front- and rear axles/hubs.
 
#38
Hello again,

I have done to little to the project lately, but here's what's been done:


I have machined the parts for the front- and rear axles. Pictured above is drilling an tapping holes in the brake disk adapter. These adapters will be welded to the CrMo tubes of the front- and rear axles. They will carry a ball bearing on the inside and the brake disc will be mounted (and centered) on the outside.


These are all front- and rear axle parts, before welding. The CrMo tubes have been machined to fit ball bearings on the inside and other parts on the outside.


After I welded the parts to the tubes, it was time to do some more machinework on the lathe.


This is a rear axle. I just turned down the sprocket hub, this helps the sprocket to be centered perfect.


Front- and rear axles/hubs ready from machining. Finally...


The shafts for front- and rear axles and for the neck had been given flat sides to them on the Bridgeport mill. Together with a "anti-rotating" plate that has been lasercut, this will prevent the shafts from turning. I don't want the shafts to be able to turn, because if a shaft is turning the mounting bolt might come loose. The "anti-rotating" plate also is some extra body which "unloads" forces to the bold. It will also help to keep the mounting holes round for a longer period of time.


Several parts ready from machining. And the 20mm thick aluminium (6082) plates will be machined soon. They will become the engine mounting plates, which I need before welding the frames.

When machining parts is done it's time for some tube bending and welding. Can't wait.

"Stay tuned"
 
#39
I got some things done past weekend.

I started with making #219 chain sprockets for the torque converters. As I couldn't find a torque converter with these sprockets standard, I thought I would make them myself.


I took the standard #35 chain sprocket, that came with the torque converter, and cut of the teeth. I had some #219 chain sprockets lasercut at work.


Welding the lasercut #219 chain sprocket to the cut of #35 chain sprocket. A shop press holding the parts tight together.


2pcs #219 chain sprockets for the torque converters welded and cut down on the lathe.


#219 chain fits!


Machining adjustable engine mounting plates on the Bridgeport mill.


2pcs adjustable engine mounting plates done, except for deburring.


The top and bottom parts for the gas tanks. I TIG welded a M10 fine threaded nut in the bottom sheet metal part. The fuel petcock fits in this nut.
I also welded a short piece of tube on the top sheet metal part. The filler neck will be welded on this later on.


Gasttanks tacked together.

"Stay tuned"
 
#40
Hello,

All tubes for the frames have been bend. The manual tube bender did a nice job in bending the 22mm diameter, 3mm wall thickness, tubing.
For bending I used mathematical formula's to calculate length of tube to cut and where to start bending each bend. This worked out pretty good.
I cut the tubes to (over)length and with a marker I marked where each bend has to start, before making any bend.


Pictured above is the left-frame-side-tube being bend.
1 Tube, consisting of 3 different bends in 3 different planes. This means a lot of checking and keeping attention to the job. Luckily I made no mistakes.


Frame upper tube being bend. This tube will be located under the seat and travels forward to the neck. Also 3 bends in 3 different planes.


All tubes bend. Including the front fork tubes.
The printed out drawings helped out a lot.

Next thing is some milling to the front forks, cut off the over length of tubes and tack everything together with help of the new frame jig.

"Stay tuned"
 

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