Since I have the engine of my ’61 G12 apart, I looked up the “Wet Sumping Fix” for Matchless Twins that involves adding O-Rings to the shafts around the input side of the pump. I decided to video the steps I took to share. The instructions on how to do this are in the Jampot Archives or I updated their copy here.
First, you need to remove the input side of the oil pump. While I’m sure you could do this while the pump is on the engine, I think it’s just easier to pull everything, take it apart, clean it and then put it back on the bike.
You only have to do the input side of the pump. There are “two pumps” on the oil pump, one that puts oil “into” the engine from the external sump, and another that takes oil “out of the engine and returns it to the external sump. We are only concerned with the input side. It is the smaller of the two, and is located on the intake side of the engine. DO NOT MIX THESE UP when reassembling.
This first video, I have disassembled the pump and I’m preparing the plate that will be counterbored:
Once you have the plate all nice and clean and flat, you can get your 9/16 counterbore with 7/16 pilot and prepare your drill press (I guess you can do it hand-held in a pinch, but depth is critical. Make sure the depth is equal to the width of the O-Ring).
Once you get everything together, clamp everything down into a vice, line stuff up, check twice to make sure the pilot goes in and out of the hole smoothly so the cut will be correct. Use the depth gauge on the drill press to make damned sure you don’t go too deep. It’s better to go shallow, then check with a decent set of vernier calipers. I did this. It ended up being 1/128 in short, so I was able to just touch it one more time to make it perfect!
That’s about it. Follow the steps in the instructions, and I hope the videos explain the step-by-step procedures and break it down for you.