RR, the upper (non-magnetic) screw looks like it requires the conventional screw seal/gasket. I can't tell from your pic if the lower (magnetic) screw takes the screw seal gasket or the newer O-ring. If the underside of the lower drain screw head has a relief channel machined into it, it requires an o-ring. If the underside is flat use the standard gasket. Normally both screws are the same, but you could have mismatched hardware. The procedure you described is correct. Mike
The Sierra # for the screw seal gasket mentioned above is 47-2945. You can get them from a local NAPA store but their marine # is 18-2945. I'm not positive, but I think that the most current part # Mercury Marine has for this item is 12-20260. Mike
If you have the older style screws that are flat, just use the screw seal gaskets. Mercury Marine started using the drain screws that require an o-ring about 1999 or so. I have seen even newer Mercury Marine stern drives & outboards that still use the earlier design. I personally don't like to reuse the gaskets when servicing gearcases that come through my shop, but some of my customers keep their boat docked all season & won't check the oil level at all. The only drawback to the screw seals made with a waxed gasket material is that they will come out in multiple pieces after being compressed for a long period of time. Annual replacement generally avoids that minor inconvenience. Additionally, I'll always check the drain screws a second time to ensure that they are good & secure. OMC uses a nylon washer that holds up really well but the slightly larger O.D. rarely fits into the recess on a MCM product. Mike
Thanks, Mike. Upon revisiting this issue I'm leaning toward the necessary part(s) being the following shown in Design I. They are describing it as a "seal" as opposed to an o-ring. However, the old ones look fine. Leaning toward reusing them to avoid the hassle, then again at $1 a piece plus shipping I guess I can wait and get new ones.
Which ever you decide on, you can get them locally if you have a good NAPA store or business that sells hydraulic seals, packing, fittings etc. Just take your old one in for them to match it up. I got mine at Hersch Packing close to Carrol Ohio. But our NAPA store in Lancaster can match them as well.
i have an 86 90hp merc that uses the flat gaskets on the screws and every spring i head to my local boat shop and for a couple bucks replace them and carry a couple for just in case ...
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