Fuel Filter Bleed Screw Failure

Here's a lesson I learned that might save you some trouble:

For bleeding the fuel system, my Yanmar manual says to open the smaller of the two screws located on the top of the fuel filter casing (the filter mounted on the starboard side of the engine block). The smaller screw is the one closer to the block, and the less accessible of the two. I always wondered about what the larger easier-to-get-to screw was for.

Recently, the threads stripped in the filter unit casting on my engine, resulting in fuel leakage. I replaced the filter unit- not too expensive at about $43 for the part. Now that I've had the filter unit off and could examine it thoroughly, here's what I learned:

1) The threads stripped because for some reason the threads, by design, have vertical slots cut in them such that they do not go around the entire I.D. of the opening. This makes them vulnerable to stripping. So don't put too much torque on that screw!

2) The larger, more accessible screw opens to the same cavity and looks like it was designed to be a bleeder. The screw is hollow, with horizontal openings at the top, probably specifically for bleeding. So don't mess with the smaller screw. Use the larger one. After replacing the filter, I used this screw and the bleeding process worked fine.

I expect that many of you have used the larger of the two screws all along, since it's much easier to get to. I was just trying to do what the owner's manual says to do. That's what I get for looking at the instructions!!! I think they are wrong.

Fred

Amante #392