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.
 

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