Kymco ZX86LQ

[dexameth]

So.... last year I blew a hole in my 82cc Kymco ZX50. Was using a Charmo cylinder kit (SSP-G) air cooled with a Tecnigas NextR pipe that I had a larger header pipe welded on to. 24mm PWK, had thousands of miles on it then put on a Jiso pipe that woke it up big time, and a few weeks later a hole was in my piston. Maybe I did need to upjet...

I was gonna rebuild with a fresh piston, but when I rebuilt it with new bearings I noticed some wiggles in the crank. Slapped a drive face on the spline and spun the crank, cases sealed together with new bearings and seals, and it was visible to the naked eye: a bent crank. The scoot has always had some crazy vibration... I wonder if this was it the whole time? Oh well, not gonna rebuild with this crank. Start shopping...

Well, I sprung on a little upgrade. Got a 44mm stroker crank, another 50mm bore cylinder kit but this time it's liquid cooled. Purchased everything from tunescoot.site with 3 DAY SHIPPING FROM CHINA. Yeah, Taiwanese parts still ship from China. Got a kit that came with everything I needed for the top end, then a cooling kit with a radiator, 12v pump, hoses etc... everything! I still need gauges, everything in my CVT (hoping to go overrange variator and grind the walls away around the bendix that's non-existent) and probably a few other things here and there. Gotta mock it all up and see what, if any, grinding needs to occur. 

I'll get photos at a better time, my workspace is not photo-worthy at the moment haha but here's a couple quickies:










shorter piston, shorter cylinder, longer stroke? old cylinder with replacement piston on left, new stuff on right

[oldgeek]

I wish I had known you were interested in that kit. I have the same one sitting on a shelf I doubt I will ever build up. Since I built my 120cc LC naked Kymco I cant see building anything less. LOL!

[dexameth]

So with what little time I have, I've been tinkering here n there trying to get this thing ready. Found out the piston skirt was about .5mm too long, had so shave that down. I ported out my cases a little bit more, and got all the shavings in my new bearings. DOOHHHHH. Luckily the new kit came with fresh bearings. I reset everything tonight... new bearings then pulled the crank in, then assembled the top end and wouldn't ya know: the piston hits the head. I didn't even get port timing numbers as I was too excited to get this top end on the case and kinda seal everything up.

The way this kit was described, I thought it would be a bolt-on and ride kinda setup...

Gotta get a stack of gaskets and some solder then spend some time with my degree wheel and digital caliper. I was really really hoping this would be together tonight!

[oldgeek]

You might want to take a look at this thread It is the air cooled version of the kit you have. I have the AC version and the LC version, they are very close to being the same.

I had a time setting up a stock stroke crank with this cylinder, it seems to need less than 41.4 stroke. A 44 stroke crank will be even more challenging.

[dexameth]

Mar 19, 2024 21:46:43 GMT -5 oldgeek said:

You might want to take a look at this thread It is the air cooled version of the kit you have. I have the AC version and the LC version, they are very close to being the same.

I had a time setting up a stock stroke crank with this cylinder, it seems to need less than 41.4 stroke. A 44 stroke crank will be even more challenging.

Yep! started reading into that thread again and it's totally the air cooled version of this kit. I'll have to revisit when I have more time, looks like we are doing quite a bit of the same stuff! 


The 50mm bore I had before, in the first pictures, was from Charmo as well... weird how it's so much taller, it bolted right up with no modifications and ran amazing!

[dexameth]

Was able to cut up 2 of these before work, then after work I fitted them and got a squish measurement of .35mm hehe I think that's a bit tight... maybe one more base gasket.

[oldgeek]

Multiple base gaskets will compress over time, you really need a spacer but they can be a PITA to make.

[hippo008]

I think what you have there is a Peugeot Speedfight cylinder. I’ve not measured it myself but supposedly the Speedfight uses the same bore, stroke and has the same stud spacing as a Honda AF18E and the Speedfight came in LC variants. Seeing as you have the ZX50 motor which is a clone of a AF16E American motor you have a hypothetical match. I would be careful though, Tunescoot and BWSP are known for selling parts of dubious quality and passing them off as good stuff.

I’ve seen Speedfight ignitions and cylinders used on Honda setups before but they are always stock stroke. IMO there was a lot more engineering that happened with those engine systems and they supposedly have much higher quality aftermarket parts than the normally available Honda stuff. The builds were always more involved though, never saw the port work myself but always assumed some timing stuff had to be done there to make it work just right. I’m not certain but I think the Speedfight may also have a centrally located intake and not a side intake like the vertical Honda platforms, that could present a problem too.

You are going to need to do some pretty serious port work and spacing to get that bad boy to play nice with that crank. If you decide to go that route please document it here, that’s a rare setup outside Europe. I’ve not seen one online before.

If I were you I would consider returning the Stroker crank. The 44mm stroker cranks are known to be meh quality. I’ve had two develop unacceptable amounts of play around their conrod. Plus with the additional work required to get everything timed right and playing nice I think it would be in your best interest to go a stoke stroke route. The OEM Honda cranks are known to be tough. But if you want to go aftermarket the Athena crank is a known quantity as well as the TWH stock stroke replacement from ScooterTuning.

I’m keeping an eye on this one. Very interesting.

[dexameth]

Just keep in mind... I work SLOWWWW. Real slow. I have little time to tinker, so be patient with me. I have ran this "brand" stroker crank in a Minarelli build with no issues, but that crank had the plastic inserts while this "dio" crank is full circle. Looks very good quality to most other cranks I've seen...

With 4 base gaskets (the two included with the kit, and the two I had cut) I was able to get a squish of .35mm. I didn't check port timing, but I will as soon as I know the amount of gaskets needed to get the correct squish, THEN I'll see what they got the port timing at. As far as the spacer setup, every one I've seen for sale has a boost port WAY too big for even what I have cut into my cases, which would lead to an air leak. So, I figured I could build for around 1mm squish, then during break in retorque the cylinder bolts and maybe end up with .8mm of squish... but idk maybe tighter? I'd rather have a spacer but I'm building this mostly on a budget / little time / crappy tools.

Stay tuned!

[190mech]

Home made cylinder base spacer fab;

49ccscoot.proboards.com/thread/2250/base-gasket-spacer-fabrication

[dexameth]

So no measurement of gasket thickness, but I cut a couple thicker oil/gas/water proof gaskets and paired them up with the two gaskets that were included with the kit. Got a solid reading of .88-.9mm squish (tool error) and here's the timings:

Intake 130­°
Exhaust 180°
Blowdown 23°

Seems legit... was hoping to get those exhaust numbers a bit higher for this pipe, but I think these numbers will be just fine.

Now to seal it all up and run to home depot for the leak down tester supplies...

[dexameth]

Here's a pic of BDC.

[oldgeek]

What type of head gasket came with it? The one that came with mine sure as hell would not work.

[dexameth]

oldgeek mine came with the same head gasket my air cooled kit came with, a standard aluminum flat crush gasket. BWSP found me on WhatsApp and messaged me asking if my order looked good and had EVERY part laid out on a table. I asked about the head, if it came with o rings for sealing the coolant and it took them a day to respond "yes sir everything included all gaskets". I used fuel/coolant/oil safe gasket prep just in case. 

[dexameth]

Here's a photo of the stock variator, notice where I was grinding on the bendix retaining wall...




Got this variator when I worked at Partsforscooters. Designed for Minarelli, but they came with a special boss to fit the Mina crank. A standard Kymco / QMB boss fits perfectly! 95mm diameter, I squeezed it in there. Now to determine appropriate belt length. Stock is 723x18, I've ran 729x18 since I got the scoot. Now I'm wondering if the 729 will be long enough or if I'll need to make the jump to 738x18.



The posts in the variator that guide the back plate are cut shorter than a typical variator to fit with the minarelli starter clutch, so I was lucky enough to find a back plate that had what seemed to be lower than normal guides. So, as the rollers push the variator away from the back plate I shouldn't have to worry about the back plate coming off! I tested full roller travel vs my longer boss and it should work just fine. Mucho gear ratio!