New here, would like some assistance with my SMC Rex! :D

[ukno]

Hey all,

New here - looks like a great forum with a lot of experienced folks. Created an account to refresh my memory a bit and learn a thing or two.

My story:

I purchased a SMC "REX" 50cc back in about 08' because I, ahem, had some legal issues and could not drive. I wanted some simple upgrades for some headroom so that I wasn't a safety hazard being capped at 35mph all the time (people around here are total f0cks).

I purchased a few upgrades with the guidance of my local dealer where I purchased my moped from, installed and tuned it myself - of course, quite the crash course, although I learned a lot.

Fast forward, I think about 2000mi / km (I forget what the speedo reads @) later, after filling up at the gas station one day, as I was leaving, it dies.  Pulled the head off and found that the circlip for the piston wristpin somehow dislodged/broke (wtf), wedged itself between the piston and scored it to hell.. that was it, and the scooter sat in my garage for, wow, must be 12 years now!?

I would like to fix it, get it running well again, and I probably would need some help from the experts here .. My local dealership of these has since closed down and i'll have to do my part to get it running again. - I have to find all the parts, stuffed somewhere in my garage, bleh.

Might be a long process but i'll have to get a grip of what I have again so that I can fix it.

Please bear with me as I will try my best to remember what I did to the thing.  If I remember correctly ..

-Polini Corsa 70cc bore

-Dellorto(?) 21mm(?) carb with some different jetting. I want to say the main jet was .. 105?

-Stock airbox, I think I was stupid and drilled a bunch of strategically placed holes in it so that it could breathe better without going to a pod filter.

-Stock Oil Injection System, adjusted for more flow - of course used something decent, like Redline Race or Redline Smokeless - no premix

-Polini Variator Kit (incl. belt) (totally forget what rollers, springs, etc.)

-Polini Clutch Kit + stock clutch bell?

-Gearing.. man.. I forget what it was replaced with, although it was geared a little taller for top end.

-Some kind of aftermarket pipe, "midrange" rev type, to keep the noise down and since it was a mild tune. Totally do not know what brand.  I'm sure if I can snap a pic, I could determine what RPM it's designed for with how the pipe dia. change or trumpet looks like.

-I believe stock spark plug, whatever that's worth.

I don't think there were any other supporting mods, so stock crank, bearings conrod reeds etc.

So I have to begin the long process of fixing it - here we go.

- Gas tank - I was an absolute idiot and left fuel in it for the whole time.  So, check the fuel tank for rust.  If rusted, what should be done?

- Brakes - I don't know if the brakes are all jacked, check the fluid and seals?

- Piston / Head - Since the bore + piston has a deeeep gouge and is scratched, I might as well just buy a new Polini Corsa Bore Kit, easier that way?

- Crank / Rod bearing - I don't know the condition of all of this. After the failure, I never checked anything. I pulled the head off to see wtf happened, then left it sitting open to the atmosphere since. 12 years, jeeez thats a long time.  Should I buy a new crank / upgrade, new bearing and some kind of better wristpin clip that will not break and create this mess again?  I read something about 10mm pins and 12mm wristpins.  I'll have to measure what I have but doubt it would be the bigger wristpin.

Would like to avoid going through the re-jetting process if possible as i'm lazy, ha-ha, but it would seem that if I buy the same bore kit, I should be okay, no?  Since we have E10 here, dangit I think I would need to reseal the whole carburetor anyway after sitting.. lol

Lastly.. I was told back then.. SMC REX = Horizontal Minarelli = "Jog" Style.  I think @ the time, they were sold out of "Rexys" and I needed transportation so I had to opt for the big fat "Rex 50" with bigger wheels / tires.

If anyone can chime in and give me a few tips, that would help a lot!

Thank You!

[geoffh]

Ahem,who cares it,s done and gone take some pictures and start a build thread so we can see what you have,I am pretty sure we can help out,it helps if you tell us what you want to do on the scoot ,drag race or commute both are possible,tips? get a cheap cast iron barrel clean the carb get it running then we,ll begin😈

Geoff

[repherence2]

Are you from Oahu and did you get the REX from Motosource?

As far as i know, a former tuner Motosource told me the SMC Rex is a 90cc and were supposed to be registered here on Oahu as a "scooter" so they were freeway legal.

SMC Rexy was the 49cc version Taiwan clone of the Jog.

Measure your piston to see if its 47mm or 50mm.

[captincvmn]

Since it sat for so long definitely drain gas and soak carb in carb cleaner. Buy a replacement cylinder set and bolt it all back together. I’m preparing to install a Corsa cylinder today on a China clone. I just ruined a Stage6 streetrace cylinder when my wrist pin bearing exploded. Watch for a sale and pick up any sport cylinder and get back out there in traffic.

[shadees]

Welcome to the forum

I just cleaned a few tanks myself.. Drain it from all old fluids,, and insert a mixture of oxalic and hot water in a 1:1 ratio,, and let it works inside the tank for a few hours.. Then remove it,, and use alot of water so none of the acid are left inside.. Works like a charm

- Frederik

[shadees]

I took a few pics of the first tank.. Not thaaaat good,, but atleast you can se the bottom of the tank is totally cleaned on picture 2

Before:



After:


- Frederik

[808ministroke]

Yeah especially worth but exhauste And the set up that you have I'm guessing you definitely got it from Motorsource on Oahu. I have built rexy's rexie's Rex's And I'm very Familiar with every little inch of those bikes. From the sound of it You can probably get away with just a new Bore kit ur old one was probably a polini Contessa and that would be a good choice as a replacement they run $200+. that's a pretty rare pipe you have never ran one myself but they look Hella crazy. As for the rest of your engine I would Take off the cylinder in piston pour a lot of gas in there after taking the engine off the frame in order to make sure you get every bit of metal that may have burst like a broken piece of urine or something so that way your crank won't get damaged The circuit probably didn't break it most likely fell out and I and I went through the crash course you went through many years ago and had probably 3 circlips ruine Cylinders.
As far as the rest of the bike like the transmission I would get a new belt And check the rollers but everything else should be OK As far as the brakes go I've had these stock brakes working after sitting for years and years so you should be able to get them going again. Let me know if you want a so called expert on rexy's to give you a hand Just shoot me a text [phone].

[808ministroke]

oh And the gas tank looks fine

[808ministroke]

Oh and it's definitely a 10 mm Pin as far as the size of kit you need.
And no Rex is not A90CC Rex just Means that they have wider front forksIs to hold wide rims or 12" tiresThey also have taller gears to compensate for the tire size .
I The one you're thinking of bro the 100 CC bikes from Motorsource came in Rex and rexie verisions🛠💣💥

[repherence2]

Jun 29, 2021 8:11:09 GMT -5 808ministroke said:

Oh and it's definitely a 10 mm Pin as far as the size of kit you need.
And no Rex is not A90CC Rex just Means that they have wider front forksIs to hold wide rims or 12" tiresThey also have taller gears to compensate for the tire size .
I The one you're thinking of bro the 100 CC bikes from Motorsource came in Rex and rexie verisions🛠💣💥

The 100cc was the BWS100 stuff. Those those bores dont crossover to the Jog90 platform. I know that Motosource brought in parts for Jog90. That's wherei picked up 2 taida 54mm bore kits and 2 yms v8 large displacement pipes.

[ukno]

Oh wow, my apologies.

There is such a wealth of knowledge on here, firstly Thank You to the Moderator 90GTVert for moving my thread to a more appropriate section!

I've been tied up with crap, but finally got to check back and whoa, you guys are really helpful!

Ok, i'll see if I can take this one step at a time -

repherence2: Yes, on Oahu, but I don't believe I got the 90cc gem.  When I got my Rex, the smaller "Rexy" which was similar in size to the Honda "Dio"? was sold out so it was my only choice because I couldn't wait.  It is basically an uglier (can I say fugly ) looking headlight (do you call it headset?) and a taller suspension / bigger wheels.  IIRC it was still 50cc.

808ministroke: Much Thanks for the info man, yeah I had to get it from MotoSource, they have since closed down, but like 3-5 years ago I was about to get someone to help me get this thing running and just never had the time.  I didn't post pictures of the exhaust pipe have, so not too sure what you are referring to but I was told it was just a mild pipe / mid rpm pipe that would work.  Its currently BURIED in my garage and I have to go dig it out, LOL.  Thanks for your contact info, I may hit you up later, thanks but i'd like to at least try and figure it out before wasting anyone's time.  Time is money, no?

So I had some time to clean the garage a little and get some idea of what i'm working with.  So I do have a Polini Corsa, and I did measure the piston pin, 10MM.

The piston and bore, probably f0cked.  I've heard of an overbore, but of course I have no clue what i'm doing, and the damage is too deep in my opinion.  Might be a waste of time  / cheaper to buy another bore kit.

To make sure, can anyone give me some advice on anything else I should get to get me up and running again? Do I have to disassemble the main crank / rod area and replace the main bearing?  I haven't done that before, but of course don't want to spend a few hundred bucks and a weekend of labor for it to explode again.   For now, i'm thinking or sourcing another Polini Corsa Bore kit (any places you recommend to buy from?) and maybe a main rod bearing?

Also, why the f0ck did the piston retaining pin come off in the first place? Is there a special way to put it in, or some improved design?

After I get this thing running, i'll probably be asking more questions.. but until then, to be continued.

Thanks Guys!

[captincvmn]

The retaining pins can be finicky. Members here say to never ever reuse the retaining pins. Members here also have said not to use the fancy G style only to use the C style

[808ministroke]

Wow I forgot about this build thread until when I came across it right now I can tell you exactly what you should do on every single component in and step also also even willing to personally personally help you assemble it The clip came out out because it was either put in backwards or was slightly lightly not in the groove and the full diameter of it anyways this is happening this is happened to me I think 3 possibly 4 different times so don't feel bad luckily luckily it hasn't happened to me in the past 6 or 7 builds but that's just due to The fact that I know what to look for to assure that it's seeded right.
Please bro just call me I am not after your money I would not charge you anything I just like these mopeds and I am happy to help get another one of them on to the road.
A few of the major things I would tell you about the rebuild or is the rebuild or about what parts is is personally you should go with a polini sport which is exactly the same except it it has cast iron rings and the exhaust port is one mm lower lower which you can easily or I can easily fix with a drill bit in less than 5 minutes.
By all means bro I would love to help you get this if nothis is if nodded into a screamer at least something that you will have A-blast shredding around on and and with the type of build you're doing doing you won't sacrifice reliability at all.
And the carburetor yeah if you let it sit with the E10 gas it is for sure 100% unfixable and you'll have to get a new one I've had a polini carb go for that exact same reason in a matter of months.
However you might be in luck if you wanted to just switch back to another stock carb carb I have a spare mccooney mccooney carburetor that was the original type that came on your bike.
I've had several several rexes and even Iraq's as well so if you want help if you'll take my help I would be glad to help you learn along the way and and maybe I get a riding partner out of it all so you know my number I wrote it earlier Call me dude.

[ukno]

I've had no time to mess with this thing!

Finally had some time to take a look at this thing, about  2 weeks ago.

Bought a new Polini Bore kit, installed.  I noticed that there might be an electrical problem from sitting so long, maybe corrosion or something.  I forgot to check for spark , but the turn signals are weird / headlights don't turn on.

Gas in the gas tank smelled kinda funky, of course just like old gas, but no gunk that I could see. Yay.

I tried cranking a little bit (this is equipped with elec. start) and it looks like I might have to replace this fuel valve that works off of vacuum from the carb.  I thought I found out what it was called but it escapes my mind atm.  It's a fuel valve with a vac diaphragm.

Disconnecting the line to the carb, I gave the line a little suck and the fuel comes out of the outlet portion.  However, while cranking, I do not see any fuel coming out - this probably means the valve needs to be replaced, huh?

Also, I lost the "kicker" pedal to manually kick start the scooter.  How hard would it be to source this? I would have to buy a replacement before I further troubleshoot the poor thing.

If anyone has any insight, it would be appreciated

[gooddog]

if you got gas to come through the petcock when you sucked on the line that means the diaphragm is ok and to me the problem is you're not getting vacuum to the line off the carb. I could be wrong. don't replace the petcock yet. I would take off spark plug at this point and shoot the cylinder with starting fluid, just to see if it fires. kickstarter arm not being there makes it hard to work on it i'm sure. if you use clear fuel line you can see if the fuel is going through the lines. you should def check for spark before firing it up with starter fluid tho.