Kymco ZX50

[Calothrix]

Sid, persistence feeds the bulldog!

[sidthesloth]

Okay, going to work last night when I stopped I heard a rather loud rattle at idle, so, when I got home this morning I pulled the jug to check, would rather a cracked piston than a bent conrod. Compression only 95psi. Cylinder and piston show heat colouration as would expect with my poor setting up initially. The piston was ok apart from some scores down the skirts. I did a squish test without the head gasket and got a rough measurement of 1.17mm. (using 1.2mm solder), head gasket is 0.52mm. When I put it back together I stripped the thread on one of the head bolts (stripped the thread in the crankcase), so off to buy some recoils, that done I got it back together. The rattle is still there, is there anything behind the flywheel/stator that could come loose? I am hoping that is all it is. I have taken pics of the bits and will try to get them up a little bit later.

[sidthesloth]

Hey Calothrix, sometimes I think the bulldog is feeding on me. Shall persevere, is a little frustrating but rewarding none the less.

[zombie]

I would order another piston for starters. The squish also has to come down to .8mm to get the performance the kit was made for so a head shave is in order. 1mm off the head should do it. These kits are close from the factory but due to machining tolerances they are not all in perfect shape. I had .5mm taken off my malossi. There is nothing behind the stator but it may be the flywheel itself. It cannot hurt to pull it apart, and re check it all. There are 2 other possibilities, The rollers, and a resonance from the pipe. You may be hearing an echo from the cyl. in the pipe. Try wrapping some of that header insulating cloth around the first 12-15" of the header tube to see if that is it.  I crashed my computer  (again) , and missed the "fuchs". Keep at it w/ a smile! Once it is done you will love it. If you give up and sell it, the next guy will put in a plug tighten a bolt, and have a Fuchin' kick a$$ scoot. Did that needle ever get there? I just thought about it today!

[sidthesloth]

Yeah mate, the needle got here complete with your hound's DNA, sorry, but I havent gotten around to sending it back yet, will get onto that soon, the rattle is not an echo through the exhaust, it is deffinately coming from the engine, I only heard it for the first time last night, I have this weekend off, so I will pull it apart then and see what I find. With having put in a larger pilot jet yesterday, Original was 45, new one is 48, could that cause bogging at full open throttle, I sort of got into a bit of a do~it frenzy, (I blame it on night shift).

[zombie]

All good. The pilot does nothing after 1/2 throttle. It is way good to have it rich on these scoots tho. You want to here the engine firing when you are at speed and, let off the throttle. When you have it opened up check for any play in the crank bearing. They are tough as heck but could be worn/damaged. 48 sounds good for the pilot cause I had a 44 in a 28mm delorto that was too small. so I think I am at 46ish now.

[sidthesloth]

Yeah I just had to give it a go, if ya dont try/ya dont learn, the main jet is dead set simple to change, the pilot jet is a bit different, you can see it through the plug hole, you can almost get a screwdriver onto it but you can't get it out without removing the bowl. This scoot has just clocked over 14,000 kms last week.

[zombie]

The km's don't matter as much as what the scoot has been thru. Even a grain of sand sized bit of trash is enough to trash a bearing. Not to worry you, just throwing ideas!

[sidthesloth]

Yeah, not the best scenario but if it needs new bearings then I will replace them, just another excuse to buy or make more tools. This is the photo of the head, though it looks like the piston was touching it there are no marks on the piston crown. I may be able to get some more pics on.

[zombie]

The photo w/ the scoring on the piston; Is that the exhaust side? How does the dome look? is it still smooth, or is there a rough patch on it?

[sidthesloth]

All that crap cleaned off the side with wd40 and 600 wet and dry. the piston crown looked good, an even coat accross, black, if anything I would say a little rich but that does not go with what we saw on the plug. what do you think of the clean patch on the head?

[zombie]

I cant see anything. Maybe slinger can dl, and fix it up. There is too much clearance for the piston to have hit it. Is it symmetrical? Or maybe just a hot spot? I wish I new how to use photo editing software. I'll save it, and try to figure it out.

[sidthesloth]

Here is another pic of the head, hopefully a bit larger.

[sidthesloth]

Have a happy Easter everyone ,be careful and stay safe.

[zombie]

I don't see any "impact" marks! 2 things I do see are the clean spot on the head is where the electrode is facing, and starting your burn. Your flame front is bouncing off the top of the cylinder, and hitting the fuel from the opposite side from the squish zone. That is most likely the biggest factor in the detonation problem. If you mill 1mm off the head it will force the timing of these two fronts closer together, and lessen the effect. Also "index your plug". That means using a copper shim instead of the "gasket" that comes on the plug. You want to have the electrode facing right at the exhaust port. That will prevent 2 separate flame fronts. I know this sounds like a bunch of hi tech. hog wash, but in fact I believe that is what is happening inside your cyl.. The main cause is the increased bore, and no increase in stroke. There is a much larger surface area to allow these opposing forces to develop. Give that a shot, and I think w/ the jetting where you have it your troubles will be over.