Mower Engine Oil Drain Fitting

The Briggs & Stratton 140cc engine on our mower needs a drain plug to use with plastic tubing for draining engine oil when it needs to be changed, if a mess is to be avoided. The photo shows the drain plug I made from a 5/8 x 11 bolt two inches long.

Materials

• 5/8 x 11 bolt two inches long
• 1/2 inch ID plastic tubing (14 to 18 inches long)

Tools

• Angle grinder with cutting disc
• Drill and bit
• Bench grinder
• Caliper
• Metal cutting disc 1/8 inch thick
• Miniature file

I used an angle head grinder with a cutting wheel to remove the head from the bolt.

Masking tape can be a good guide for grinding where you intend and only there. The outer diameter of the 5/8 inch bolt is just a tiny bit too large to fit the opening for the threads in the oil inlet. Mark off three to four threads. This bolt can be ground by hand. Hold the bolt to the grinder with a very light touch. Roll the bolt against the spinning grinder wheel. Then pull away. Repeat to grind more of the bolt’s circumference. Continue working your way around the bolt as many times as needed until the bolt will fit the threads inside the engine fill crankcase opening. Use a miniature file to touch up any irregularities or tool marks .

I removed the tape from the previous step and applied two bands of tape to define the indented area for the “O” ring. See the second photo for how this mimics the factory dip plug. I used a caliper to determine what the width and depth of the opening for the “O” ring should be. I used a metal cutting wheel like the one shown in the third photo. The fourth photo shows the “O” ring I purchased at the hardware store.

Use some care while starting the recess for the “O” ring because the recess must cross over threads on the bolt and the cutting wheel will want to follow the threads on the bolt.

I drilled a hole through the center of the bolt. This needs to be done with care. Do not make the hole so large that it breaks through the lowest part of the groove for the “O” ring. Keep the center hole as close to the center as possible. The hot oil flowed through the hole more easily than I expected. You can safely use a smaller hole than you might imagine. That will make it less likely that your hole might wander too close to the groove for the “O” ring.

I moved the tape again. This time it marks the area to be ground to fit the internal diameter of the plastic drain hose. Take your time. Grind the outer diameter of the end fitting until it slides into the end of the drain hose without difficulty, but not so easily that the hose can slip off of the fitting while oil is draining from the engine.

The fill/drain hole in the engine crankcase is tucked inward under the top engine cowl. It is difficult to screw in the fitting with the plastic drain hose attached. Screw in the fitting without the hose. Then push the hose onto the fitting as shown in the photo. Place the end of the plastic hose over a waste oil vessel. Only about 15 ounces is inside the crankcase. I use an old fry pan to catch the oil. Gently tip the mower toward the side with the drain plug until the mower is on its side. (See the second photo.) Watch the end of the hose so it remains over the catch vessel. When I changed oil recently, not a drop was spilled, and that is remarkable for changing oil. (I know the oil can be vacuumed out of the crankcase or pumped out. I feel I get a more complete draining by letting it flow out with gravity when the engine is hot.)

In the photo the “O” ring is visible. If a pair of pliers is used to seat the drain plug fitting the “O” ring will recede down into the opening on the engine. As shown, it is only finger tight.