Heads Up: don't ditch your crankcase gasket.

[SEANIA]

EDIT


So, found out the real reason as to why it wouldn't fit.

I went to rebuild the engine top to bottom with higher quality parts.

After I pulled it apart, it seems it's already been rebuild once. However, whomever rebuilt it, decided not to use a gasket, and opted to use Hondabond/Yamabond in place of it.
Using a small amount of it is a ok idea to aid a gasket, but it's not a replacement for it. Why? In engines not designed for it, the gasket adds spacing between the two halves. Spacing that, is enough to make cylinder skirts not fit if removed.

Would explain all the apprentice marks that were in/on it.

Bad news is that there also appears to be case cracking in the crank case. Hopefully it's just mold cracks, and not case cracks. If it's case cracking, buying a new case might be required. I could fill in the cross section suports on the outside of the halves with J.B.Weld to add support, and hopefully stop them from getting worse/plug them. I know people do it for reinforcing Zuma cases before a 100cc bore, but not sure how much it'll help after damage is already present. They'll do it before porting cases too, and even grind into the J.B.Weld a bit with success. Hope it'll be fine.


Yeah, so
It is not compatible with the 1999-2007 US models at least.
It was a tight fit, even with lube, which is unusual for most bore kits I've used on other scooters. I hadn't done a Kymco engine before though, and figured that might've just been the norm for them.

Again, very exacting fit, but did fit. Unlike other bore kits too though, the first few warm-up-break-in starts required excessive force to kick over the cylinder. Keep in mind this is with a lubed cylinder wall to have helped with install.  Also with a new piston pin needle bearing, correctly matched new gaskets, and being bolted down to 10 pounds of force. Everything by the book for a new cylinder.

It eventually did wear in after a few break in warm ups, and was easily started with the starter after. I disabled the auto mixer, and used a pre-mix of 1/40 using 2 stroke Yamalube. I know local region effects jetting, but, I used a 120 main jet (which runs it rich for my area), and kept the idle mix/enricher heavy enough to slow down the idle a bit.

But, after 100 miles or so, it lost compression, and I got what you see in the pictures.

Here's the imgur link for the pictures: https://imgur.com/a/71TetVx

Sent a message to the store I got it from, asking them to remove the people 50 from their compatibility, or to specify which one is compatible (Ima assume the shorter harder to find variant).
I doin't think they'd ever refund me it or send the Malossi bore, but hopefully can save others the inconvenience and cash by having it removed from the list.

[dan v.]

I'm not sure why you say it is the "wrong" cylinder. For Kymco 70cc units there are three kits - a liquid cooled one, an air cooled one, and one that is for the Honda designed vertical cylinder.  Obviously you installed the correct kit, so there is not a compatibility issue.

When you received the kit, did you do the proper prep work - as in checking the ring end gaps and chamfering the ports?  Without the rings installed, did the piston slide in the bore properly?

When you say it took excessive force to kick over tells me that something went wrong with the install.  Did the cylinder slide on easily when installing - should have gone on easily with just finger pressure holding the rings in place.  You should have been able to turn the engine over easily by hand without the plug installed.  Did you check that?

How about the carb and pipe?  Did you replace either or run stock?  What plug did you use?

From what I see from the pic, it looks like a typical seize.  What does the piston look like?  When did it die - were you running at full throttle, a long run downhill with the throttle closed, or what?

We are missing some important details here, lets see if we can help.

IMO, the Polini cylinders are of better quality than the Malossi, so I wouldn't put the blame there. I prefer to use Polini parts over Malossi for most of my tuning for several reasons, but both are of great quality.

[SEANIA]

Checked bore/piston fit before install- checked out

The cylinder, with no piston, was hard to test fit on. I had it lined up properly, but, was really hard to slide in, especially the last 1/8th inch or so.

Plug or no plug, did not want to turn over easily the first few times.

Pipe was replaced with a LeoVince TT, carb was jetted up to 120, and the intake de-restricted on the stock 17.5mm carb (which polini listed as useable). Disabled the automixer, and premixed the entire time. Used Castor oil to help build a initial coating of it on the outside of the various parts.

Cylinder was nikasil coated, so wasn't as easy on it as I would've been with a bare iron cylinder that'd need a cure.

For plug, used one of NGK's, either iridium or platinum plugs. I got like 20 of them for 1$ a piece on clearance from a local Yamaha power sport dealer (was in there to pickup more yamalube 2t). I know you hate me now.

Had died at "full" throttle. Varried the throttle a lot, cause, nikasil break ins, but was at full at the time.

Pictures of the piston are in the link I provided.

Hmmm this is what the crank looks like though

[dan v.]

Something doesn't add up here.  For a new cylinder kit, it sure is rusty.  Did it come in a sealed box?  There are also some weird "ring" shaped things at the mating surface at the holes for the studs.  There are no marks on the very bottom of the cylinder, so I don't  understand all the gouges inside the case and at the edges of the crank.  What the heck was going on in there.
If you have the Polini box, what is the part number of the cylinder kit?

I asked but you did not reply about chamfering the ports.  It does not look like it was done.

Pictures show a bad seize.  That is from running lean and/or lack of lubrication.  What was your premix ratio?  You used Yamalube 2 stroke oil for the premix?

You state your carb is stock, but the stock Kymco carb is 12mm, (maybe 14).  Yours is 17.5?  So not a USA model People? 

I don't understand "Used Castor oil to help build a initial coating of it on the outside of the various parts"  Please explain.

Curious - what NGK number plug was used?

I'm pretty sure that Polini does not nikasil plate their cast iron cylinders.  Are you saying that you had it plated after you got the cylinder?

So what do you know about this engine?  Did it run before you changed out the cylinder?  Something had happened in that engine at some time, judging from all the gouges and marks in the cases.  I notice that the cases were filed down or something at the edge of the  bore and the transfer ports, and there is some damage down there - like some stray metal parts, like a broken reed,
were loose.
 
Odd that the cylinder would not go easily into the case.  I think that some of that damage kept it from seating properly.

Any other info would be helpful.

[SEANIA]

chamfering the ports-
Didn't need to. Polini seems to do that for you as apart of their production process. If you don't believe me, I have another new in box Polini cylinder (for a zuma 2t) I could take pictures of. 10/10 looks NICE.
The Arisal I got for my 03 Aprilia also had this done from the looks of it. The Stage6 I had didn't. It's a hit and miss, and alot of people say you shouldn't need to do it, and that the rings will cut them as apart of the break in process.
Not to say it isn't necessary sometimes, but unless it's horrid, lot of people say you don't need to if you break it in properly.

Rust? What are you-
Ohhh that's copper gasket spray. I cut a cork gasket to shape, and sprayed both sides of that to help prevent it from leaking any. The head gasket was, quite literally, brown paper bag, coated in gasket spray.
When opened up- neither had showed any signs of having leaked. Worked 10/10.

The carb-
Kymco made a few variants/revisions of the People 50 for the US. The earlier the model, the less restrictions there seem to be. The newer it is, the more emissions regulations there were in place making them limit it in more ways.
You can get a stock 17.5mm people 50 carb. It's rare, but possible. Mine may have not come with it, but the one that was on there when I got it was a stock brand matching carb. So either someone spent 100$+ on a carb for it, or it came with it. Mine is a 05 production model.

Castor oil doesn't burn completely, and seeps into everything. If you run castor oil- you'll find the outside of your engine coated in the stuff. It gives everything a sticky yellow looking tint, which most people think is bad, nasty, ugly, and bad- but in reality it'll protect various parts from corrosion and oxidization.

I was running castor oil for my pre-mix at somewhere between 1/35 and 1/40 (human error and all). Normally I run yamaha lube (one of their dealers is 1 mile from where I work), but use the castor oil for break ins.

The plug is a B7EVX. So, a heat range of 7, and is platinum. Before you ask- yes the Polini head uses a 3/4" plug length.

Engine ran 10/10 before I stuck in the cylinder. Runs fine after too now that it's back on the stock cylinder.

The "gouging"-
You didn't look at all the pictures? Should be obvious what caused that.



See that huge chunk missing from the piston. Yeah, that piece broke off, but stayed pinned between the piston and the cylinder, scrapping up and down with each stroke. It did not fall into the casing. Only fell out once I removed the cylinder from around it. Have the missing chunk, somewhere, prob lost it by now, but yeah that's what did a lot of the damage I'd imagine. The other half being done by the slammed/pinned side of the piston that got its ring melded into the piston.

I'm going to try to have the cylinder re-honed, and have already ground down the base of the skirt that had no cylinder wall on it (bout a 1/8th an inch, maybe more). Ordered a off-brand replacement piston with no piston ports just like the Polini one that came with it (has a bit less height, but can always lower the head to compensate for that). I'm, pretttyyy sure the issue was that the skirt was too long. Since it's at the last 1/8th inch or so that the cylinder was being difficult.
What else.....yeah Ima probably throw the bikes crank soon with the amount of RPMs I'm throwing at it. I'm right at the edge of stable, but oh boy does the TT exhaust love to give more power when given more RPMs. Can't wait to throw it to the wall when I get in some new taller tires. Aiming for **actual** 60mph stock 50cc bore. Already can do a real 50 (spedo reads, 55 or somthing higher, is blank by that point).

*police officer pulls me over*
"Do you have any idea how fast you were going. I pegged you going 60 in a 45"
Officer, not to be rude, but this bike only has 50ccs. Are you sure your gun was dialed in correctly this morning?

I don't think it'll get me out of a ticket, but, in brightest of fantasies it gets me out of a ticket on the pure absurdness of it. Can't wait to push my people 50 more <3

[dan v.]

Thanks for the quick reply.  It sounds like you have been around 2t tuning for a while.  I got into it about 2001.  A little more serious a few years later.  Bought  a '05 super9, and went with the Airsal, Arreche, and Technigas bits that most were running at the time.  Still have it - had burned up an Airsal, and Malossi, and went back to Airsal.  Changed to Dellorto and Motul; been good since.
Have hot-rodded a couple of Minarellis and Piaggios since.  Anyhow.....

Chamfering the ports - Last cylinder I did was a Polini.  Pretty sharp edges at the ports.  Big exhaust port. Breaking the edges a bit is good insurance.  Matter of opinion if they are good enough from the factory - I prefer to err on the side of caution and chamfer.  I have as set of small die maker's files for this.

Gaskets - You made a cork gasket?  For your base gasket?  Why?  That will throw your port timing off a bit, and did you check squish?

Carb - After I posted found the Kymco service manual.  It states the carb is 16mm.  If you say you have a 17.5, so be it.  Can you adjust the needle height to change midrange mixture?

Oil - Castor oil? Que?  You mean you used Beano, or did you have old school Castor oil like way back in the '70's dirt bike stuff? 

Plug - the NGK 7 is a little hot.  In my experience most kits run the #9 or #8. 

I saw the piston picture.  You stated the piece did not fall out.  The gouging I refer to is in the engine case.  Any idea as to what caused that?

Back in the heyday of 2t tuning, it was the opinion of the guys at Moped Hospital Racing and others in the know that the stock Kymco crank is fine.  No need to change it out if it is in good shape.  You should be good for 10k rpm.  Now for Minarelli - that is another story.

I've always found it cheaper to buy a new cylinder kit rather than repair when one is burned up.  A piston will often cost half the price of a new kit, and you need gaskets and cylinder work, too.  Just never seemed cost effective to me.

Do you do leakdown tests on your engines before you run them?

Thanks, and good luck.

[SEANIA]

Huh, didn't notify me of the post. Came back after idly looking at the cylinder, noticing something very nice.

 The apparent gouging near the exhaust port? Turns out, not actually gouging. That's all material from the piston. Ground off the piston, and apparently, melted onto the wall. Picked at it with my nails a bit, and a few pieces on the edge just flaked/chiped off like they had melted on top of the beginning of the cure, and not into the cylinder! Might still be gouged a bit underneath it all, but, for the most part, seems like I should be able to recover the cylinder with minor damage. Damage minor enough, that I hope a solid cure layer can compensate for it. (Got hot enough to make the piston melt instead of destroying the iron XD my luck 10/10)

Was going to send it off to a machine shop to be re-honed, but might do it myself if the one-use honing tools are any good...given they're like 15$ vs probably at least 50$ for a machine shop.

ALRIGHT BACK ON TOPIC

Cork Gasket: Yep, made one for the base, and is why I went with the brown paper for the head gasket. Tried to sand down the head a bit with some paint graded 600 wet grit to compensate, but, it didn't seem to make any progress on the aluminum. The cork compresses quite a bit anyways, so whatever difference it would add to thickness, wouldn't be much. If anything using the paper on the head with the cork at the base would've raised my ports a bit for more power, but, again, is/was minuet. Reason? cork sheet/roll I can cut to any size gasket on demand- get 6 feet for 10$. A new specific use gasket I have to wait 2 days to a week, or even two weeks to receive?- varies, but lets say at least 3$. By the time you've bought 3 of them, you could've just bought a roll, made 30, and have gotten a fitted gasket in under 30 minutes (I put on some netflix and take my sweet time OCD measuring and cutting one though x3)

Carb: I got the bike 3rd hand from a ex kymco dealer. I guess they had it in the shop when the owner moved to another state or somthing, or they didn't want to pay the repair and just ignored it before moving? I duno, but apparently one of their guys had been messing around on it it bit, and I noticed one or two minor non-stock parts on it. They could've changed it out before it was sold to me. Oh, btw, this guy had a huge storage locker filled with kymco bikes, kymco stock parts, kymco performance aftermarket, and who knows what else. He had a super 9 in the back apparently (thing was so crammed full you couldn't step in) ,and I should've asked if he'd sell me that instead, but oh well. Still have his number, might be on the forum if he has that much stuff.

Even with a 120 jet, the top end seems to run lean. Don't know why. If I richen the idle, let it sit and fill the case a bit before taking off- my acceleration will be way better. Been playing around with needle size. Oh, stock needle on it isn't adjustable, same as the Roughhouse. Didn't stop me from modding the needle mount to take regular ones though. Will see how that goes later. Im going to give in one day and by a electron pumper carb to make jetting easier. 

Oil: Haven't run straight raw castor oil (yes the bean oil). I use Maxima Castor927, as, it's the easiest to get modern equivalent of it, and they apparently add in things to deter some of the sludge build up that castor oil usually makes. https://www.amazon.com/gp/product/B000GZV25G/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1
Is pre-mix only, as, it'd clog a auto mixer, and is more sensitive to being at a set mix as opposed to a varying mix like most synthetics. Since it is thicker, and leaves more/quicker build up- it's a bit of a cheat for break ins if you want to push the cylinder a bit more during that time. Could probably do a endurance race on a brand new cylinder using it without destroying the cylinder, but, the cure would be awful. Also reportedly adds a few hundred RPM too, but, eh, I'll just call that good curing vs ok curing. If someone went out of their way to buy castor oil- then I'm sure they'd spend the time to do a good break in too.


Plug: The 7 is a little hotter, but it's also one that's more immune to high heat in general. So high heat resistant+foul resistant I think is a trade off for running the whole thing a notch hotter. Plus, and I know it's wrong compare them, but, the morini and yamaha minarelli 2 strokes, as well as tons of others, usually use 7's. An 8 or 9 may be better for this, but, it shouldn't hurt it to be outside spec by 1 when using platiniums like that.  Oh, burnt out/semi-melted a E3 in it. Was carbon build up on the melted bits too. So not like it was lean. Guess their plugs aren't actually rated for what they say they are! (generically claim, I think, 6,7,and 8 heat rating, and say they're better at dealing with carbon build up) Haven't burnt out a NGK in it yet though. Have gone through a few new ones to troubleshoot,but never a failure as of yet. I have a 2 stroke specific 3/4" NGK spark plug for 2 stroke racing I'll throw in at some point once it's all dialed in for the 70cc bore (BR9EG).

Case Gouge: actually have no idea. Was partialy like that when I first opened it up. The Polini may have added a bit, but, yeah most those were already there surprisingly.

Crank: Really? I mean I'd be throwing 8k-9k at it the entire time to stay in the peak for the TT. Hmmm, though not sure of the condition mine is in either, and an OEM replacment costs more then getting the Jasil one. NO idea what the Jasil crank is stable up to. Can't find user info on it anywhere.

Kit: Buying a replacement piston meant specifically for that kit, is pricey. Buying one of the same size? With sh/h, 20$. It's not the exact same piston, and performance might suffer a hair, but it'll work, and doesn't cost half the price of a new cylinder. The one I got seems like it'll make a hair less compression, but I can always lower the head height for that (there's a decent chunk of the heads height that's not the compression area), as heads are cheap too.

Leak Down: Nope! Which is bad. That said, all the gaskets I've made, and have looked back at after use, haven't had any signs of leakage from them thus far. I do use a torque wrench though on anything with a gasket, since I don't trust my "feel" for that.

MISC:I have a analog torque wrench, but- On most parts of bikes I use a low-powered 3/8th impact wrench (what?)- I use a corded "matrix system" (every company calls it somthing else) base "gun", and slap on the impact wrench geared end for most any bolts. Can take off the CVT cover in under 30 secs, and slap it back on in the same amount of time. Seat is off in all of 10 secs. Extenders and adapters let me get to most things.  The amount of time I've saved on it 0_o  Helps with stuck spark plugs too (carbon/caked-n-baked oil in threads). Makes me feel like a Nascar pit stop x3

[dan v.]

After all this, I see nothing that shows that the kit you installed is not the proper one for your scoot.

What you have shown is that you had a bad seize, and something caused the piston to break.  The seize is from running too lean/hot and/or improper lubrication.

So is it too small of a carb, jetting wrong, or air leaks?

Without doing a leakdown test you may never figure it out.  Using a leakdown test, I have found leaks at cylinder base, and manifold/reed case joint, places that were easily sealed with Yamabond.  Air leaks could also come from bad case sealing and crank seals.  Leaks in any of those areas could lead to seizing.  So could poor carb or exhaust mounting, warped head, and bad gaskets.  Careful assembly, bench work, and leakdown testing are all necessary.

Good luck with the project.

[KymcoRockr]

Cylinder was nikasil coated, so wasn't as easy on it as I would've been with a bare iron cylinder that'd need a cure.

There's no nikasil in that cylinder.

[KymcoRockr]

Yeah, so
It is not compatible with the 1999-2007 US models at least.


Sent a message to the store I got it from, asking them to remove the people 50 from their compatibility, or to specify which one is compatible (Ima assume the shorter harder to find variant).
I doin't think they'd ever refund me it or send the Malossi bore, but hopefully can save others the inconvenience and cash by having it removed from the list.

Hard to believe they didn't take your advice instead of the fitment information from the company that actually makes the part.  If what you are saying is true, either you are the only person who bought this kit and tried to put it on a People 50 2T or everyone else who ever bought one over the years decided not to mention that it doesn't fit this model. 

[KymcoRockr]

It sounds like you have been around 2t tuning for a while. 

Not really. Anytime someone makes pronouncements like the title of this thread, it's obvious they don't know what they are doing. There have been a lot of those Polini kits installed on People 50s over the years that didn't grenade. But most of them weren't installed by people who make head gaskets for two strokes out of paper bags.  How many times did you ask yourself, "why would anybody do that?"

[SEANIA]

If what you are saying is true, either you are the only person who bought this kit and tried to put it on a People 50 2T or everyone else who ever bought one over the years decided not to mention that it doesn't fit this model.

Legitimately might be, as all the posts and videos I've seen have them using the Malossi kit for their 70cc bore.

So here is the stock cylinder


Here is the Polini cylinder


and here is the Malossi one everyone seems to use, and that is known to be compatible.



Maybe it's just a US differnce. Since I've never seen a single parts company reference the US models, but use the Euro "eco cat" model line for reference instead. The Euro people 50s in general,  had ceased production by 2005.

Hard to believe they didn't take your advice instead of the fitment information from the company that actually makes the part.

Polini isn't wrong. They're not based in the US. They're based in, and make their parts for, Europe. Which is what they list their parts as compatible for. As far as they are concerned- there is only one model of the People 50 2t (well, two, it's a body differences). That'd be their model.

Try and pull up aftermarket parts for the People 50 2t, with a US model number BA10AD. Then try and do the same with the Europe only model numbers BF10AC or BF10AG.

Nothing will come up matching the US model number, except a few references to OEM Kymco parts. Whatever the difference is between the two- it causes some incompatibility, at a minimum, with cylinder skirts between the two. There's likely some minor port differences too. Cylinder skirt is being modified so that the last 1/8 inch slides in easily, without force, and is being put back in.

Not really. Anytime someone makes pronouncements like the title of this thread, it's obvious they don't know what they are doing. There have been a lot of those Polini kits installed on People 50s over the years that didn't grenade.

Show me? Any US models, or were they all Euro models?

But most of them weren't installed by people who make head gaskets for two strokes out of paper bags.  How many times did you ask yourself, "why would anybody do that?"

It's a US originated thing. If you're not in the US- that's why. Is some interesting motorcycle history. Encourage you read up on it a little.

Is a nice fix for the issue of not having thin enough gasket sheet material with no way to get any, or, in my case, my separately ordered gaskets getting stolen off my porch....cause Polini doesn't include any with this kit. They stole the lye I ordered off my porch for the cylinder too, so, installing a camera and GPS tracked glitter bomb package next.

There's no nikasil in that cylinder.

polished iron looks similar to nikasil to me I guess. WELP GOTA LEARN THE HARD WAY SOMETIMES and read the specs to check what it is I actually have in the future. The actual iron looks okay still though.

Figured out part of the "lean" issue though, and why it took me till a 98 (only larger i had was a 120) to start getting usable power off only the 50 with a derestricted intake. The 98 was too lean though, and the 120 too heavy. Got a kit in yesterday that goes up to 110- so ama try that out. The Carb is certainly not stock after taking measurements, and neither is the needle Ima guess.  The part of the needle pulled out at full throttle, doesn't taper off any. Switched to another needle with a taper, and viola, mountains richer. Which is a good thing considering the temperature just dropped from 90°f days to 55 or below. Texas has no fall....well it did, for, 2 days (literal). Those were a nice 2 days.

Anyway, yeah, some weirdly long barely tapered needle. Can tell it's meant to be used with the restriction only. As with restriction it did geat, but couldn't handle the increased air intake. 

Guy before me buys a larger carb, but air and fuel restricts it to stock carb size. Genius.

[SEANIA]

So. Took the Polini kit. Did a lot of lye baths, rotary work, grinder work, 1200 grit sanding, a cheap replacement piston, and desperate feelings for it being down for two week while a new stock piston comes in ( is at 8k miles-ish, so, time for a new piston).....and my Aprilia's back tire going flat.

It works now! Not sure how long this'll last, but, it works. Will throw the 13 weights on for the break in once they come in. Force the RPM low, since I'm pretty sure the crank is damaged from me pegging the speedo past the "Km/r" mark on stock gearing/tire size, or maybe forcing the cylinder to fit when it shouldn't have, or having used a impact wrench to take the variator off since I couldn't get a good grip anywhere on it with my face wrench.

Ordered the Malossi cylinder kit as well, but I'm not installing it until I buy the Jasil crank, and do a rebuild of the case- or have someone else rebuild the case cause I hate doing it. As, doesn't matter what methods I employ- always loose a screw or other piece if its not done in one sitting. 

I am entirely sure this kit is either only meant for the Dio engines, or I was sent a Dio bore by mistake. Polini uses generic boxes between most their cylinders, and leave no identification markings on the bore to indicate what it's for. It has the same diameter of a 70cc zuma minarelli bore, which, doesn't fit the common People 50 2t, but retains the exhaust for a dio/kymco. Could also have shaved a zuma 50 cylinder skirt to fit, but I don't have the tools to do that accurately.

Back on topic- reviving and modifying it worked. The cylinder I got is obviously not meant for the common US people 50 2t, and until you yourself have tried it, don't assume it does based off a spec sheet. If you do get and try one on a US people 50- let me know how that goes. It'd let me know if I got sent Dio cylinder, or if it doesn't period.

[KymcoRockr]

Maybe it's just a US differnce. Since I've never seen a single parts company reference the US models, but use the Euro "eco cat" model line for reference instead. The Euro people 50s in general,  had ceased production by 2005.

Polini isn't wrong. They're not based in the US.

Try and pull up aftermarket parts for the People 50 2t, with a US model number BA10AD. Then try and do the same with the Europe only model numbers BF10AC or BF10AG.

Lol. Kymco isn't based in the US either. And the engine is the same, no matter where they sell it.  Nothing is internally different between the one someone buys in Milano, Taipei or Omaha.