Kymco SC10AS 100cc and beyond:

[oldgeek]

Some of the following is taken from another thread Naked Kymco I decided to start this thread to have the motor build info in one place.

I want to build a 100cc (or bigger) SC10AS engine. I have been doing some work on a set of SC10 cases, seeing what it will take to build a 100cc+ motor. The process is very much the same as modifying a set of 50cc minarelli cases to be 100cc. As a matter of fact the jig/tool I made to cut the crank area of the minarelli ended up working perfectly on the SC10 cases too. I just had to modify the side edge of a Kymco bearing to allow the tool to cut a little lower.


To grind down the side of the bearing I installed a grinding cylinder in the minarelli jig and slid the bearing to be modified on the shaft of the jig. I held it against the grinder and allowed to rotate slowly until it was ground down to where i needed it to be.

After getting the Kymco bearing modified, I slid it on the minarelli jig and turned it into a Kymco SC10 jig. I had chips flying in no time. I cut a little too much on the pass in the video, the cutter works faster and better if you take smaller bites.





In the last picture, I noticed the rod was rubbing on the cases just a bit. Turns out the rod is kinda cheap and was actually bigger on that side than on the other side. I just reset the cutting tool and made another pass with the cutter. I also spent some time making slip bearings that would slip into the cases AND onto the crank to make test fitting cranks easier. I spent quite a bit of time making the two bearings, I gotta find an easier way to make them. I also had to trim some material from the webbing above the crank wheels in order for the rod to clear as it rotates.

This is the Taida 50mm cylinder and Taida crank with a stroke that is listed to be 49.6mm (I have not verified the stroke yet) they are designed to be used together, and come out to 97cc. They were very inexpensive, total price shipped was about $224 Later, I also ordered a Taida crank listed as having a 51.6mm stroke. I test fit both the 49.6 and the 51.6 cranks to the 50mm cylinder and the durations were nearly identical More on that later.

Jun 3, 2018 0:06:20 GMT -5 oldgeek said:

So I measured the stroke of both cranks. They both have a stroke of 49.8mm. One of them was advertised as a 49.6mm and the other one as a 51.6mm. The stroke on a stock crank is 41.4mm. They also have a 52.6mm stroke crank, but I wonder what it really is. I sent a message to the seller to see if they can shed any light on the situation.

Jun 3, 2018 3:43:13 GMT -5 190mech said:

ARRGGG!!!Gotta love having a project stalled by mispacking/false advertising...I check a crank stroke and rod length as soon as its unpacked as Ive been bit by skewed dimensions also...

So I am am getting the runaround from the place I purchased the cylinder and cranks from. No real help or answers from them, they just question my methods to measure the stroke. No worries, there are other places that sell dio stuff and I ordered a 52.6 crank elsewhere to see what I get this time.

[oldgeek]

The 52.6 stroke crank came in and it is a whopper. I have spent considerable time geting to where I am currently at


There are also some problems with this crank.


Something very corrosive was left on the conrod and has pitted the small end of the rod. I cleaned it up as best as I could but I doubt it will last long if I were to use it. The seller offered to replace it if I would send it back to him. It was not really expensive so for now I have just been using it to test fit the case and the cylinders I have. I ordered another 52.6 crank from the same seller, hoping for a discount, but only got a "I will check this one out personally before shipping it to you" from them. So I have another one of these cranks and at least the second one is not rusted on the con rod.

The crank wheels measure 79.35mm on this 52.6mm stroke crank. The crank wheels on the 49.6mm stroke are 77.8mm in diameter, So I had to open the cases up even further in order to get the 52.6 stroke crank installed.


As you can see from the pictures that caused some different problems to appear. As the cases were cut 3 of the 6 bolt holes that hold the cases together were cut into. I decided to drill through the cases and tapp the resulting holes to M6 so I could install studs in them. The studs are M6 cylinder studs that have been cut down, threaded, and flattened on one side to clear the crank.





Since I finally have the 52.6mm stroke crank installed in the cases, I test fit the 50mm cylinder that is supposed to be made for the 49.6mm stroke crank.

As I suspected in my earlier posts, the 52.6mm stroke crank makes the 50mm cylinder setup nearly perfect! At BDC the piston top is just barely below the transfers, and flush with the exhaust port. At TDC the piston is very close to being flush with the cylinder deck. Durations look very good for what I think I want to achieve, about 184 for the exhaust and 130 for the transfers. This stroke and bore combination should = 103.28cc

I also have a 54mm cylinder to eventually test fit but I have not opened up the throat of the cases yet so it will not bolt up until I get that done. This bore should = 120.46cc with a 52.6mm stroke crank.

I also wanna add that this set of cases is the one with a bad gearbox. I am just using these cases to see what needs to be done to make them 100cc+

[Lucass2T]

Nice work OG!

[ryan_ott]

Those guys running corsa’s wont even see you coming!

Nice solution to the bolt clearance issue.

[oldgeek]

I am open to suggestions on what size carb I may need to use with each cylinder. I think a 21mm dellorto PHBG should work with the 50 x 52.6 (103cc) I believe Brent has used the 21mm for his mina 103's before. I have no clue what size I may need to use for anything bigger such as a 54 x 52.6 (120cc)

I also need ideas for a pipe for these builds. The ones I have seen are not cheap! The only reasonable pipe I have seen for the larger bores is the V8 for up to 120cc. I have the smaller V8 pipe I am using on the 75cc cylinder, it seems to be pretty good so I guess I will go that route unless someone has another idea.

[gsx600racer]

I run a 21mm PWK with Polini Corsa/Tecngas exhaust. Runs low 300's temps

My other Kymco was 28mm PWK with Polini Corsa/PG short exhaust. Runs low 300's temps. Plan on using same carb/exhaust combo on L/C build

My understanding with running larger carbs helps with keeping the engine temps down.

[Jwhood]

Geek did you try Brandon over at scooter swap shop he should be able to get you something exhaust wise for it

[90GTVert]

I've used a 21mm up to 110cc (54mm bore x 48mm stroke) on the Minarelli AC. Worked fine. Ran strong just past 9,000RPM. Have been using 21mm on my current 103cc that peaks around 10,000RPM. 24mm didn't give me anything but more headaches, though it prob would cool more. Way back during Project 90, I used up to a 28mm carb and indeed got better cooling with bigger carbs (Link to data). I think most of this info is relevant, because you don't have huge transfers either so probably a similar ballpark for output. When you go bigger, you can always give the 21mm some test runs and see what happens. If you're using the same CHT setup, you should be able to tell if it's running much hotter.

[oldgeek]

Aug 15, 2018 6:35:18 GMT -5 Jwhood said:

Geek did you try Brandon over at scooter swap shop he should be able to get you something exhaust wise for it

Yeah, my pockets are not that deep. I will give him a try though, Thanks.

Aug 15, 2018 7:22:22 GMT -5 90GTVert said:

I've used a 21mm up to 110cc (54mm bore x 48mm stroke) on the Minarelli AC. Worked fine. Ran strong just past 9,000RPM. Have been using 21mm on my current 103cc that peaks around 10,000RPM. 24mm didn't give me anything but more headaches, though it prob would cool more. Way back during Project 90, I used up to a 28mm carb and indeed got better cooling with bigger carbs (Link to data). I think most of this info is relevant, because you don't have huge transfers either so probably a similar ballpark for output. When you go bigger, you can always give the 21mm some test runs and see what happens. If you're using the same CHT setup, you should be able to tell if it's running much hotter.

Thanks for the link, thats the info I was searching for. I will definitely try the 21mm Dells I have, since I sorta made friends with them LoL! I also saw the CHT data you have, Is there a maximum temp to stay below for these AC cylinders? I guess the higher you go, the faster the motor is worn out.

[190mech]

Perhaps modding an existing pipe for the bigger CC and lower revs would be a good home boy fix instead of seeing your banker for a second mortgage??

[90GTVert]

Aug 15, 2018 16:57:52 GMT -5 oldgeek said:

I also saw the CHT data you have, Is there a maximum temp to stay below for these AC cylinders?

Not really sure what it is accurately, because mine have varied by sensor setup. With the Trail Tech and under plug sender I was running below 300F all of the time. I think with my open frame and the area above the plug open, maybe it cooled it. With my old Auto Meter and sender tapped into the fins I'd run in the 320-340 range regularly and that was more shielded by the shrouds. I've primarily used observation going through a tuning process and seeing what temps do. If it seized, then it was too hot. If I started hearing detonation after holding it WOT for a bit it was too hot. Sorry that's not numerical data. Many seem to want to stay below 350F though. You can find others saying 450F is the absolute max. I've only ever seen 450+ on my four strokes, but those both have sort of pockets around the plug which goes back to my idea about airflow changing results because I really wouldn't think my 139QMB or GY6 150 should have ran way hotter than my 2Ts.

[gsx600racer]

I guess the higher you go, the faster the motor is worn out.

I am happy being in the 9-10k range. I don't ever see building something any faster.

I would think if you could build a torque-y(new word)engine, keeping revs down, you could make up the difference with taller gears. Sadly my experience was a trade off, lost takeoff acceleration for a little more speed. I think I could of fixed some the take off issues with higher end cvt parts, but playing with cvt's is not one of my favorite things to do. lol

[PIG]

SSS has this on sale right now. Should do what you want

scooterswapshop.com/collections/94-honda-elite/products/vastro-big-stroker-pipe

[90GTVert]

Aug 15, 2018 18:33:49 GMT -5 gsx600racer said:

I am happy being in the 9-10k range. I don't ever see building something any faster.

I would think if you could build a torque-y(new word)engine, keeping revs down, you could make up the difference with taller gears. Sadly my experience was a trade off, lost takeoff acceleration for a little more speed. I think I could of fixed some the take off issues with higher end cvt parts, but playing with cvt's is not one of my favorite things to do. lol

I don't know how it is with the Honda style engines, but I'm guessing you'll end up in the same boat as those of use with 100cc+ Minarellis. There's only so much RPM you can get out of them that really produces power. 190mech has said many times that he believes it's largely due to poor transfer area and design. After looking at MX jugs beside scoot jugs, it's a ridiculous difference. Not just the area of the ports, but they also use tea cup handle design ports that are good for flow vs our straight up bore-hugger ports.

For the big Minarelli clones, the best power I've seen has always been between 9K to 10.5K, and really I'd lean to more like 9-10K. I have had one 103cc that pulled to 70MPH at around 12,000RPM, but I had really high overkill port durations and it was more like it could over rev that much just to keep going but it didn't make any more power than it did around 10.5K. That became even more clear when I got my first OR CVT and suddenly it didn't like to pull over 10.5K. It was just running out of CVT ratios before it ran out of power with the smaller pulleys, so it pushed up RPM till cylinder filling just couldn't keep up with power demands I guess. Once the CVT could shift a little more, it never wanted to over rev.

There are high end 90+cc kits out there like the Big Evo, Stage 6 R/T, and 2FAST that rev though. The S6 R/T 95cc used an adapter plate that made large transfers possible.

[oldgeek]

Aug 15, 2018 18:54:53 GMT -5 PIG said:

SSS has this on sale right now. Should do what you want

scooterswapshop.com/collections/94-honda-elite/products/vastro-big-stroker-pipe

Nice, it was $399 when I looked at it not long ago. I just gotta decide which kidney to sell now!