News!
This single bike project is turning into a twin bike project. We'll be making 2 minibikes, which will be copies of each other. One will be the "General Lee" minibike and the other will probably be a "Herbie" minibike. Herbie, as in the VW beetle with number 53. "Probably", because things are not certain, yet. Because they'll be the same, progress on both minibikes will be reported here.
What happend since last post?
One Mikuni/Chikuni carburator arrived.
I have imported the carb from the USA (will this give me some likes?

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Because the Mikuni jets don't fit in the jet holder/emulsiontube (M5x0,75 thread doesn't fit in M5x0,8 thread), I will modify the jetholder/emulsion tube in a way that I can use Mikuni jets.
With the use of this carburator the governor will also be removed from the GX160 engine. Because of that, I have ordered a 1.75Lb billet flywheel.
A billet connecting rod, 18Lb springs, gaskets, etc have also been ordered at GX tuningstore UK. That's in Europe.
At the moment I have 4x GX160's (3x QMDS, 1x QX4) and 1 GX140 (SE). And after a compression test on all of them, I took the worst performing engine for this project(s).
This will be my first Honda GX160 to tear down (by the way).
This is engine nr. 2; it made only 5 bars (75psi) compression. After taking the valve cover off, I noticed the exhaust-valve to slightly open on compression stroke. This afternoon I had no idea what could cause it to open, during compression stroke. Now I know. (Keep reading...)
Compared to the new Mikuni VM-22 the original carburator has a tiny hole. That will make some noticeable difference, when the Mikuni is installed.
This cylinderhead came off. After some searching on the interwebs and OldMiniBikes, I think this is a 18CC head? I could be wrong...
I've seen a lot of GX parts go by on internet and this engine seems to have a flat top piston. Or this is standard on a GX160 of this age (prior 2003).
Flywheel removal; well that went easier as I expected! A prybar and a hammer (with the nut on the crankshaft) did the job.
Thanks to an earlier thread here on OldMiniBikes I knew there is a lighting coil in the 3 QMDS-type engines I have. This is one of those QMDS type engines. I took the lighting coils off and they won't go back.
At this point I did find why the exhaust valve opens during compression stroke. I thought the engine might have a damaged/bend camshaft or something, but it appears there's a decompression mechanism on it. Another lesson learned on this sunday afternoon. Perhaps this caused the poor compression testresult, too. I have another engine, which makes 8 bars (116psi) compression. Makes me think that engine's decompression mechanism isn't working? Or stuck.
I know...; no gloves for me, as I'm no surgeon.
I took out the piston, connecting rod and crankshaft and started measuring.
Crankshaft O.D. measures 29,90 and 29,92 mm (1.1771" and 1.1780"). According to the Honda service limit and the connecting rod instructions, this crankshaft needs to be replaced.
Piston also needs to be replaced as it's to loose in the cylinder. With the piston almost at the top, I was able to put the tip of a feeler gauge of 0,008" between the piston and cylinder. According to the .pdf document I have; the piston to cylinder clearance service limit is 0.005".
This could also be because of a worn cylinder, but I've measured the piston with a caliper and a micrometer and both measurements indicates that the piston needs to be replaced.
With the bore gauge I was not able to measure the cylinder, because I need some washers for it. I will get those this week. A measurement with a caliper, indicated that the cylinder was within specs. But I want to measure it with the bore gauge, which is more accurate.
The cylinder needs a little hone job. It is to smooth.
Pistonrings; will be replaced, too. Piston ring end gap was to big.
Well...and that's just for 1 engine. The "Herbie" minibike also needs an engine. I think I'll tear that one down pretty soon. So I can safe on shipping costs! Don't feel sorry for me, I like this kind of work. It gives me more satisfaction as to buy a new engine and run it.
If you have any comments, remarks; feel free to post!
"Stay tuned".
John