BN139QMB piston or crankshaft trouble

[eclipse]

Hey Guy's I have been Re-building scooters from the ground up using old parts and of course sometimes I have to buy new parts to get in good operation, I then turn around and sale them pretty cheap ,, im 60 years old and disabled. I do it as a hobby. But I've came across something that has me bumbuzzled. Well first time I seen this anyway. At first I thought my battery was low. But that wasn't the case. It would turn over and quickly get real slow. And so I tried kick starting it. And now it will lock up after about 2 kicks. So checking around, I pulled the spark plug out, and it kicks over with ease. I put my finger over the plug hole and push the kick start -again and sure enough it will freeze it up again. I pulled off the carb. and I drained the oil. But that wasn't doing it either evidently. I'm praying that someone has seen this happen and knows what it might be. I'm thinking the distance between the piston and the valves might be to close or maybe the chain is stretched.
can anyone give me better things to look at . please

[FrankenMech]

Take the engine apart, check the CVT, check piston travel, rings, wrist pin bore, valves, chain, cam, bearings, etc, -basically anything that moves. Check for bent, broken parts, wear marks.... You will need gaskets, sealants, etc. If you are doing things on the cheap use the scoot parts to fix others or find a donor engine.

[GrumpyUnk]

I have never come across the piston engine that will stop cranking when I put a finger over the spark plug hole.
If it has high compression, I cannot hold it with my finger. The compression will leak past as the starter rotates the crankshaft or the kick start twirls it.
I cannot hold the compression with a finger or thumb, period.

If the electric starter spins quickly when first used, but slows and will not continue to spin the crankshaft, the first suspect to me would be the battery, second the starter, third wiring and starter relay.
Not the engine.
Same thing when cranking using the kick start. If you can kick it over at first but it starts to bind, the only thing I can think of that would oppose crankshaft rotation and piston movement that would increase after a few rotations would be the oil pressure. I do not know it is has enough back force if the passage is plugged to prevent rotation.
The only way to find out if the passage is clogged, well 2 ways, is to observe the cam and rocker arms when cranking with the spark plug removed. Quickly while cranking you should see oil start to drool from the rocker arms. If not, the pump is not working or the passage plugged. The second way would be to check the passage across the block on the bottom of the cylinder, but you have to remove the cylinder to see if the gasket or ?? is blocking oil flow.
I can think of nothing else that would allow free rotation and then start to oppose with greater force.
tom

[eclipse]

Thanks guys, up date, I took it back apart to find a crack or say pin hole!! Above the crank shaft where the bearing sits in , it goes from the top inside of the bearing case to the top or above the timing chain, so it is leaking oil i guess to the timing chain camber, if that is even a problem? And the other thing I found was a problem! The woodruff key has been mashed over to the left a hair. And examining the flywheels position at TDC it is late getting to where it needs to be for the pick up to signal the CDI box. So guys have I found the problem here, or someone please fill me in on it what I can do from here,
on the cheap

[snaker]

Gotta say, for someone who tears this stuff down and rebuilds from the ground up, seems like you should have some expertise and knowhow about some of what your asking about.

I might be wrong here, and I hope your not just cobbling together junk to sell to some unsuspecting poor sucker.

[eclipse]

No I sale them for almost nothing to mostly homeless people for what they can afford and so far they have been over joyed, and besides that they are upgraded from the cheap crap they come out with . I put a relay box with fuses on them with new wiring. And they last them a while if they can keep them from getting stolen. And they can come back for any problems they may have. Unless it's something they didn't take care of . Like oil changes and such

[FrankenMech]

There are a lot of 'old duffers' on here that seem to help like that as we are able.

[eclipse]

I really appreciate y'all's input and help. My memory and mind isn't what it use to be. I find that I will come across things I've done before like in some homes in the electrical area, or plumbing (dad was a plumber). Things I thought I learned as I was growing up. But now sometime having to read up on them or just to be faster and (less aggravating) asking someone ..guess that's old age. It will happen to most all of us someday. Damn it's already happening to me. Well again thank you for pointing me in the right direction. And I see y'all do that lot on here. God bless all of you. I'll look forward to reading some of y'all's builds on here.

[GrumpyUnk]

I think a new woodruff key might help correct the CDI firing/timing. You can also enlarge the pickup holes to ovalize them and then position the pickup rearward as much as the oval allows if you want to advance the timing a bit. Said pickup is near the top of the block, on the edge of the flywheel case area.
Old duffer? Old, yes, but the duffer part I though referred to golf, and have not done that in ... since about 1968-69. My daily goal is: Vertical and above ground. So far, so good.
My advice, worth exactly what you pay for it, is based on fiddling with small engines for years. The first was in the early 1960's when I got a neighbor's power reel mower when they were tossing it. Got it running and that started me on the road. Things got worse from there, as I took apart and PBT a lot of engines.
Locally scoots were offered on C-list and FB, so started poking around with them. No title worries and no registration, and no insurance required. Found the site, and here I am.
tom

[FrankenMech]

Maybe I should have said old FARTS...