Left side Crankcase Cover and the mystery O-ring

[skinny-j]

I replaced my left side crankcase cover on my 2007 WR450F this weekend with a brand new one after my shifter got pushed through my old one and broke it. After putting everything back together and cleaning up, I found a small O-ring in the bottom of the oil drain pan that I believe to be #10 as shown on the attached parts diagram as supplied by Partzilla. This Partzilla diagram shows the o-ring on the outside of the gasket on the cover side. However, when I look in the service manual it shows the o-ring on the inside of the gasket on the engine side. So I have 2 questions:

1. Which side of the gasket should the O-ring be placed?

2. Is it even necessary? I know the dowel-pin is in its place and with the new gasket nothing is leaking (it’s a dry sump anyway). When I look at the old cover it does not seem to have a recess where the o-ring would fit into around the dowel; and I recall the dowel-pin fitting snuggly into the engine side. So I am kinda confused about the use of a gasket and an o-ring at the same time; can anyone help?

Thanks!

[grayracer513]

The O-ring belongs there. I believe the recess for it is cut into the crankcase, however, and not the cover, so it belongs under the gasket. And yes, it's necessary, especially so because the recess is cut for it, and would not seal well in the absence of that ring.

The use of redundant sealing devices here and there is why, for the most part, Japanese stuff doesn't leak very much.

[skinny-j]

The O-ring belongs there. I believe the recess for it is cut into the crankcase, however, and not the cover, so it belongs under the gasket. And yes, it's necessary, especially so because the recess is cut for it, and would not seal well in the absence of that ring.

The use of redundant sealing devices here and there is why, for the most part, Japanese stuff doesn't leak very much.

Grayracer,

Thanks for the input; and making me get off my ass and tear it apart again last night. Sure enough there was a recess on the engine side under the gasket (so the manual is correct). All is good and I will feel a lot better knowing its right when we get to Colorado next week!