Fix or replace Qmb 139

[taotaolivin]

Hello,

I recently purchased a 2011 TaoTao ATM50 with 1500 miles on it but it hadn't been used in a few years but the seller out in new oils and it ran fine. I've riden it probably a dozen times with no issues but today I was riding and heard a loud pop and suddenly started leaking oil from the cvt case. I could still drive but only at 8mph and then it sounded horrible. I took the cvt cover off and notice the was oil dripping near the variator but didn't see the exact source because I couldn't get it off.

The engine starts right up and sounds normal until I go over 8mph and it is still leaking oil near the variator.

Does anyone have any idea what might have happened? It is a relatively simple and inexpensive fix or should I just buy a new 139QMB? If I should just buy a new 139QMB for my TaoTao ATM50, where do you suggest I purchase?

Thank you

[GrumpyUnk]

The crankshaft oil seal on the variator end(PTO end) has likely failed or been popped out of place. That allows oil to get into the CVT case. The oil may(will, likely) make the CVT slip so you won't be able to move very well.
The cause may be pressure build up in the crankcase due to the vent being blocked. Most of these little piggies have a tube coming out of the camshaft cover that is routed to the air cleaner. That tube allows any blowby to be fed back to the engine.(and be burned instead of going to atmosphere)
I would remove the variator completely to inspect that end of the crankshaft. You may get by just re-installing the seal. Some use plastic pipe cut to fit as a 'driver' to push the seal back in place(use a hammer gently on the plastic to push on the seal outer edge). It may just work fine if the crankcase can be vented.
If someone modified the vent system, be sure to check that the crankcase can vent somehow.
tom

[taotaolivin]

You were right about the seal behind the variator having popped out. I got that pushed back in and now it runs fine.

I went to add oil back into the engine and when I went to open the fill tube (or whatevrr its called) a bunch of oil came shooting out. So there still must be a lot of pressure in the crankcase. So I will check for that tube by the camshaft you mentioned to see if it is blocked. I also ordered a decompression tube that goes it the oil fill cap to help with the preasure build up.

Anything else I should look for and fix?

[GrumpyUnk]

The oil filler doesn't need a tube to release pressure, and as I remember that was an expensive little gizmo that didn't do much.
You can have oil gush out the filler if the sump(crankcase) is over full. It can be over full if fuel has leaked down from the tank, into the cylinder, and past the rings to the crankcase. Does the oil have any odor of fuel? Oil diluted by gasoline does not offer much lubrication protection, and you will likely ruin the engine if it is run with diluted oil.
The other two reasons for oil to gush out are 1)removing the cap when the bike is tipped back onto the rear wheel while on the center stand, and 2) having too much oil in the sump.
Most take 700-750ml of oil. About 3/4 of a quart. On the center stand, with the front wheel on the ground, remove the dipstick/filler, wipe it clean, and drop it into the filler neck. Do not turn it at all. Pluck it out and look at the hash marks on the dipstick. Oil should be near the top of the hash marks.(best amount) If it is on the hash marks, there is sufficient oil for safe operation. I like to keep it up near the top of the hash to have the maximum amount of oil to dissipate the heat.
Check the tube coming from the top of the engine, top of the cylinder, the rocker arm/camshaft cover. It should be open to air. It should provide sufficient venting for the crankcase to avoid pressure buildup. If the tube is blocked(spider web can do that...) pressure may build in the crankcase. If you find oil is migrating out the tube, you can lead it to a 'catch can', open to ambient air pressure, or add a length of tube routing it higher so gravity will tend to let the oil drain back when the engine is off. If the tube is long enough, there will be no oil coming out unless it is pumping a LOT of oil.
On the underside of the cam cover is a plate held in place by some bolts/screws. Under the plate should be clear of obstruction, with a path for crankcase vapor to travel through and out the vent at the top. If the labyrinth has been filled with 'something' and blocks vapor flow, it should be cleaned of obstruction.
tom

[taotaolivin]

I noticed there was a vent that was capped off at the head cover and an inlet capped off at the air intake just before the carb I believe. Temporarily I removed the cap at the head cover but I believe I should get a line to connect that vent to the air intake.

[GrumpyUnk]

Perhaps someone was doing a 'smog removal' and was ignorant of what they were actually doing.
The machines in my memory have a line from the cam cover to the air tube perhaps 4-5" from the carburetor air intake. An elbow is molded into the air tube, with a barb fitting for the line from the cam cover. The cam cover has a fitting that has a bulge to keep the line attached, perhaps one of those circular clips too.
The crankcase must be vented on all 4-stroke engines, to my knowledge. If it is not, pressure will likely build from any amount of gas that passes the piston rings, and there will be some as the seal is not perfect.
In addition, the pressure in the crankcase goes up and down as the piston moves. You have the 'other end' of the engine 'pump' doing its thing on the crankcase gas, which will definitely cause pressure pulses.
tom

[taotaolivin]

Thank you for all the information. I was able to stop the leaking.