Sunl SL50QT-16 : Resto-Mod

[2strokd]

I did the same as you did Brent. I took the vari i had filed on and cut the ramp stops out.
The walls and the center stops. I was afraid it might have too much slop in it and rattle like a mofo when idling...NOPE! Sounds great and my customer (test guy) is reporting 2-4MPH gains over stock.
I didnt have an engine ready for a small (13mm crank) vari so i let him use it. I did reduce his roller weight a little, went from 6g to a of 5.5,s. But that should have slowed him on the top-end.
I think this mod is A ok and might just last! Great idea Brent, one for the books!

[90GTVert]

Wish I could claim this idea, but I saw it elsewhere a couple of years ago. Never had much reason to try it till now, when I modded elsewhere till I limited travel on the vari (see saying under 2strokd's avatar lol). I've been able to stretch the belt to the limit of the vari face without this before. I don't think it would have any benefit if you are already covering the face of the vari.

[2strokd]

True....Seems to work tho, and thats all that matters.
I need to check the rollers out in the one i did.

[90GTVert]

Well, it's been an interesting night on the SunL. I had swapped to 4.5g sliders a couple days ago, but haven't got to ride to see if I could do better than the previos 49.01MPH. I went for a 55 mile ride tonight. On 4 occasions I had deer either getting ready to cross the road or cross in front of me. A skunk ran out and I managed to miss him by roughly 2 feet. Had a car come real close to me when I was cruising on the shoulder at about 40MPH. I got to the edge the best I could, but he still got way too close to me for comfort. After he passed by he swerved just slightly farther over and then abruptly back into his lane. Drunk? Tired? Dunno.

I was heading toward home and the SunL started acting like there was a really heavy load on it. 1/2 mile or so later it dies out. I pulled over and tried to start it, but it acted like a heavy load on the starter and barely cranked. I called for a ride home at about 12:45. Really didn't wanna wake anyone up, but I wasn't walking the scooter 10 miles either. By the time I got home, all I did was peep into the CVT cover. Looks like the belt is still there. I have had it bog when a belt snaps before if it gets caught up. No such luck.

Also, I just barely passed 2,000 miles with the 50mm big bore kit and replacement crankshaft. Assuming nothing related to the crank failed, not bad... considering some have estimated the bigger big bore kits to last as little as 1,000 miles before bearing failure.



Now, the real news. I got to just barely over 50MPH!!! It was 50.3X (forgot the last number). Barely made it, but I did. The lighter sliders did seem to get it into it's powerband just a tiny bit better. Rather than stop there, I figured I might as well find a hill now. Unfortunately, this is not hilly land. Our hills are pretty much nothing... not steep and not long. Didn't go much faster, but still faster. Oddly enough, the same speed my friend topped out at, 51.46MPH.



I think the SunL was mad 'cause I made it go 50 and quit on me.

[190mech]

HEY,You made over 50mph!!My hats off to you !Now we must know why it crapped out on you...

[90GTVert]

I get the feeling I'll be pulling the engine. I'll pull the CVT cover first just to be sure it isn't soemthing simple, but I'm not optimistic there. No need for the typical troubleshooting at this point. Something was definitely making the engine struggle, and really struggle when it died. Even once it was home and cooled down, it barely wanted to crank. This was way after I went top speed BTW, so it was not some sort of immediate failure after high revs or anyhting. I did my top speeds right when I went out then I was just cruising around 40 most of the time. It really wasn't revving that hard at 50. Not the crazy 10-12K RPM lots of smaller folks seem to get at least. No tach on at the time, but I'd guess 9,000RPM or so. As I had said earlier, at my weight I really have to keep it close to the peak powerband at it's max speed.

[2strokd]

:rockon: :checkered: :clap:
Congrats on the 50MPH goal :riding:

[stepthrutuner]

Ditto. Hope you find something minor but it doesn't sound good.

[90GTVert]

Thanks guys.

[90GTVert]

I noticed the starter bendix sitting out of position a little, so I checked it over and even tried replacing it. No dice. Still cranked slow. While I was in there...

The sliders are showing a little wear where they meet the ramp plate now. Wear on the section where they meet the variator's cutout seems minimal still.



I think rounding off the endges of the ramp plate may help.



I've got the motor out and more updates to come.

[90GTVert]

The crankshaft was hard to turn over, and I could hear a sort of flat grinding noise from the engine when I turned it over. I began pulling it apart.

I checked the vavle lash, and that was still at .0015". The first things I noticed upon removing the cylinder head were markings showing very light contact between the valves and piston.





I removed the cylinder and piston and immediately noticed glitter in the oil residue when I looked at the crank.



Here's a little video to show you the excellent shape the rod bearing is in. I recorded with my digital cam since it was handy, and it didn't seem to pick up the grinding type noise when I move the crank.



2,003 miles and the bearing is obviously shot. Guess they were right, but I got what I wanted... documented proof that the 50mm+ kits are hard on cranks. The crazy thing, everyone talks about repalcing the crankshaft bearings with better ones. I haven't got the crank out yet, but I have no play in the crank bearings that I can tell so far. It's "just" the rod bearing from what I can see now.

[lshigham]

I killed a crank in just over 2000K with a 52mm BBK, so it's not just you.

[lshigham]

Oh, and congrats on the 50MPH.

[90GTVert]

Thanks, and I know it's not just me. There has been a lot of discussion about the crank bearings and 50mm+ kits, just not many people actaully documenting anything and leaving a lot to debate. I took out most of the stuff they debated to my knowledge, and even installed a fresh crank to be sure of the mileage. All here for anyone to see.

It's a good thing I got to 50MPH when I did, huh? lol For once, I had good timing.



It's all apart. I don't see any issues with the crank bearings, just the rod bearing. So, don't go out and buy expensive bearings with a stock crank and expect long engine life.

Now I just gotta figure out what's next...

Replacement crank, 70cc kit?

Taiwan crank, stick with the current kit?

I guess I gotta figure out who sells the Taiwan cranks and how much. I could try to see what the 70cc kit lasted with the same crank though. Could just go with the 70cc, Taiwan crank, deeper gears, swap back to a 3.50x10 rear tire. That should be fairly reliable and still not disappointing on power and reliable cruise speeds. Hmmmm.

[190mech]

Hate to just walk away from it..What is different here than a Honda that screams for years and never gets an oil change??Perhaps an oil pressure/oil flow issue?Maybe it IS crappy metalurgy in cheap parts?Does a high volume oil pump help?Maybe the bottom end is carefully engineered to provide good service in stock form and additional stress kills it.I remember the big Ford motors needed a ton of extra oil plumbing work to get them to live when put into racing form..No answers here,just questions...