139QMB Routine Maintenance  By  volatilepulse (Read 3,729 times)

When you get your new plug in, take it on a quick WOT ride, then pull the plug and check the color of the ceramic around the tip. Coffee brown is what you want. Too white is too lean, too dark is rich, err on the rich side when tuning (lean is dangerous for gy6 engines).

As for gap, follow your scooter manual.

Welcome to the forums, and enjoy the ride!

Is there 30wt or 10w-40 gear oil? I have seen this recommended in some manuals, but it does not say gear oil or engine oil. It just says oil. What are they referring to?

75- gear oil is what i'd be running,,,,,as far as air filters go if it's a paper filter do not use oil,,,if it's a gauze cloth type it should be lightly coated

Yes, it does go to the air filter housing.

The other one is an oil collector, for the bit of oil that doesn't get sucked back in. Check it when you change oils, drain if necessary, shouldn't be more than a sip.

As promised, here is the write up. Any comments or suggestions?

Changing the Gear Oil in Your 50cc Scooter

Things you'll need
Gear Oil - I used SuperTech 75W- Synthetic Blend Gear Oil from Walmart
10mm Wrench - Mine have been lost or stolen over the years so I used a ratchet
Syringe or something similar to fill the gear box - I use the FloTool MixMizer
Oil Pan - I just used a cut up bottle
Used Oil Container - Apple Juice anyone?
Towels - You're bound to make a mess
Gloves - If you like to stay clean
Drain Plug Washers - Only if needed


I did this on my 2008 Wildfire WFH50-S2 139QMB scooter. It only has about 1350km or 850mi. It was easy enough that anyone who could turn a wrench can do.

First, start off by locating the two plugs you'll need. One is the fill plug, the other is the drain plug. The drain plug is located on the bottom of the gear box (noted by my gloved finger)

And the fill plug is located to the right side, in the bottom right corner of the belt cover


Both of these plugs were 10mm on my scooter and we a bit tight. Make sure your scooter is up on the rear kick stand before starting. This not only makes it much easier to work with right bolts, but also allows you to get the right amount of oil into the gear box. I ran my scooter to the gas station and back to warm it up, but it's up to you.

Start by breaking loose the fill hole plug. Mine was a bit tight and the scooter shifted when I broke mine loose. Make sure you have your oil pan ready in case any fluid comes out. I had a small stream come out when I removed the plug.


If your plug falls into the oil pan like mine did, you'll have to fish it out. Make sure you grab the plug AND the washer. Let the fill hole drain until it's to a slow drip and grab your wrench again. The drain plug is straight up and down and makes it hard to have your oil pan ready while trying to break the plug loose. I broke the plug loose with my ratchet and put my oil pan back under. I unthreaded the plug the rest of the way with my fingers.


My plug fell into the oil again as well. Make sure you fish out both the plug AND the washer again. I fished both of my plugs out and cleaned them off. The drain plug, in the top right, had a bit of dirt and debris on it. Check your washers at this point to make sure they're not damaged.


It may take a little while for the gear oil to drain, especially if you didn't warm it up prior to starting. I took the time to open my bottle of gear oil up and loaded up my syringe. My manual says the gear box takes 3.5oz so I filled the syringe to the 2oz line. If your left your tube on there like I did, make sure the plunger stops at 2oz. It will still only suck up 2oz of oil.


By this point, my oil was drained minus a drop or two. I wiped off the excess oil and reattached my plug (don't forget the washer), making sure it was tight. Do not over tighten the plug or you risk crushing the washer and can cause a leak down the round.

I went to stick my syringe in the fill hole and realized that my tube was slightly larger than the hole. This was no good. I took the cap off of the top of the gear oil bottle (the little white thing), and cut the very end of it off.


This fit perfectly in the fill hole and I was able to push the oil in as fast as I wanted.


Once the syringe is mostly empty, minus some in the tube, go back and fill it up again. I filled it back up to 2oz since I missed a little with my first 2oz, but you should only need 1.5oz. Once you're loaded up, go fill the rest of the gear oil. Make sure you put your oil pan back under where you're working.

I had some extra run out, most likely due to using 4oz instead of 3.5oz. If some gear oil runs back out, you're fine. It's just like any other gear box, you fill it until it comes out. Let it drain the excess until it's barely dripping. Wipe up the wet spots and put the plug back in (don't forget the washer). Make sure you make it tight.

Double check your work and that both plugs are tight. Make sure that you have no left over parts, like washers. Pour your old gear oil into your used oil container and recycle at you favorite local shop. Clean up should be pretty easy if you used some paper towels or rags to catch the oil drips.

Thanks to the advice of the people that have helped. My owners manual said to originally use 5W-50 Engine Oil for the gear box but didn't sound right. The general consensus was to use actual gear oil.

I have not. Is this something that can be done with the engine still in the scooter? Do you have a link to a walk through? I did notice my engine was running fairly rich so I leaned it out a bit and it's a tad easier to start now, but still bogs out a bit before warming up. I need to get a video uploaded of it starting cold so you can hear what's going on.

If the valves aren't adjusted immediately, will it cause any damage? I doubt I'll have a chance for at least a week but it still needs rode to work in that time.