139qmb engine test by rotating cooling fan?  By  gift (Read 5,254 times)

Nothing is jumping out at me yet. Are there any deep scratches or anything like that in the cylinder? It looked like there was some scoring on the side of the piston. I'm on my phone, maybe the pics will be bigger on my laptop.

Have you looked in the transmission area (cvt) where the belt, clutch, and variator are?

It's a bit challenging here because A) we don't know what the symptoms were beforehand B)The mechanic thinks the engine is bad (still in the back of my head-- not convinced either way) C) The top end is off, so were kind of working backwards a bit

Usually its check the fuel/carb, air, spark and stuff like the valves/compression.... first.

The crank also has two other bearings that can fail-- and can be checked if you take the variator off for one side, and the flywheel off on the other, both by wiggling the shaft on each side checking for play.

The cylinder looks fine to me as well, a bit of cleaning up and re-honing, then re-install with a new set of rings properly gapped and offset and you should be good to go.

While it may not have been necessary to do a complete tear down, by the time you are finished, you will be on your way to being a decent scooter mechanic, and can brag to your friends that you rebuilt your engine yourself!

For less than $70 bucks, you can buy a honing tool and a drill, $45 depending on the type and complexity. If you can't find a shop that will do it cheap, watch videos on youtube to see how it's done, and you might be tempted to do it yourself. Here's one that shows how easy it is:

Thanks for the video Jerry. I think I am going to buy a hone and borrow my friend drill for this. What do you guys think about this hone? www.ebay.com/itm/2-STONE-MASTER-CYLINDER-BRAKE-HONE-13-16-TO-2-1-2-F-S-/270792644617?pt=LH_DefaultDomain_0&hash=item3f0c7fd809 Would it be enough for my need?


Also this scootdawg.proboards.com/thread/49037 looks like he had the same look of piston and cylinder with mine but my piston rings are still intact. (He found out that half of one of the ring was gone)

I talked to the previous owner and he could not tell me anything more beside his son said it was not running right   


onewheeldrive I already ordered the BBK and new carb. I was rush to order those parts so I can have it by this weekend... I should have waited a bit...Uhhhh!!!! The gasket did fall off and I kept it with the exhaust parts so it was not in the pictures. I put it back in the port now but I will have to clean it up a bit. 

I took off the CVT plastic case today but could not pull the pulley off to see inside but I think they look fine, just lots of black dust. Anything in particular that I should inspect while I have the case off?

did you order a new carb? if not then spend some time unsealing the stock carb while you're waiting on new parts. without access to the jets and air/fuel ratio screw you will have the same problems as the previous owner.

Not to beat a dead horse, but it's more of a push/pull motion with the crank rod---- that's how I should have described it when checking for play. I'm not sure I saw that in the video after re-watching it--it's dark down in the case at times. Push/pull, with a bit of force for extra measure, should do the trick.

For the CVT, unless you can get the variator/clutch off, just check the belt and/or for oil leaks---they usually pool at the bottom of the case over time. The belt is probably fine and they usually are until they wear down to around 15mm or so for the width, but note the brand of belt--- usually the stock belts are rather generic and don't have the greatest reputation. Gates Powerlink seems to be the most popular good quality brand around the scoot forums. Bando gets mentioned a lot, too. I'd also note the size marked on the belt, it's most likely 669-18-30.