280 SP Drain seal question...

OK, so after killing a lot of time (per other topic) trying to find an up to date P/N for this part, I just drove the 40 mins to the shop I use for parts and asked them to look it up and sell me one. That's when the fun started.

They handed me an O ring, one where the OD of the O ring was about the same as the screw head, but the thickness was about 0.0625". Everytime I've replaced this seal, the dealer sold me one type or another of a washer type seal... the last time ( 09) made of some sort of elastomer with one side smooth and the other side with two distinct ridges. I had him double check the number and that's what its "supposed" to be. I don't like thin O rings that don't sit in a groove to stabilize them when installed.

So... what's it supposed to be... washer style or O-ring?

Bob, to the best of my knowedge, only the old (100/200/250 drives) used the red phenolic washers. The rest have been black O-rings.

Can you post a photo of this seat or groove that you are uncomfortable with?

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Thanx Rick...I should be able to get to the boat and take a pix this afternoon.

My 270 drive had a phenolic washer on the drain plug hole, but that's not say it was right, although as I recall I ordered replacements and they were phenolic. In addition to the washer, I lightly coat the threads of the drain plug and anything else I unscrew from the drive (fill plug and dip stick) with Permatex Blue for some added protection. Never had a problem or leak yet. <knock on wood>

Ok... can't get a decent pix of drain hole... so here goes.
I looked very carefully at the drain hole. It has
1) threaded hole
2) Annular recess above the threaded hole, i.e. a smooth bore diameter larger than the threaded hole
3) Annular recess that is the diameter of the head of the screw.

Now.... the elastomer washer that I took out fit perfectly in #2 above.
The O ring I got as a replacement has an OD exactly the same as the OD of the head of the screw.

If you put the washer on the screw then the new O ring will fit over the washer perfectly and extend to the max OD of the screw head.

While there is a neat seating groove for the original elastomer washer (formed between the shaft of the screw and the recess (#2 above), there is no such support for the quite thin O ring on its ID.

O rings don't like to get compressed without being in a groove, i.e., have no means to prevent the o ring from "squirming" when its tightened down. Also... if you install the washer type seal, the screw bottoms out on its head on metal. If you use the o ring, then the screw when tightened tightens directly on the O ring. It would be easy to see where if one torqued the screw too much when using the o ring, that you could damage ( crush and or split) the o ring... That's why design engineers usually mount O rings in grooves ( mating part can torque on metal, while O ring is compressed in a defined manner, filling groove.)

Pix below... closeup of "old" washer style elastomer seal ( note triangular divot in it that makes replacement necessary)
also... photo showing drain screw, the new o ring that is supposed to be used, and the old seal ( top to bottom)... note cross section sketch of threaded drain hole showing threaded hole and relief (step) for washer seal.

Ok... no helpful hints from the gallery, so I think that I will just source an neoprene O-ring at the hardware store that is the size of the green elastomer washer... (so it will fit and be retained properly and not bottomed out on like the Volvo furnished one).

The change in this part (in my experience) was probably made by a summer intern at Volvo working in the purchasing department tasked with finding a cheap replacement.