Engine Mount - Concave or Convex
 

What's the concensus on the large engine mount washers? Do they go concave up or down? i've seen it both ways. how did they come from the factory?

From memory......
The concave part went towards the mount originally (they used to "cup" the mounts) and were changed by porsche to FACE AWAY from the mounts due to noise harshness vibration concerns. Older vehicles were then reassembled facing away if serviced in that area and new went to the cup facing away as well (CONVEX side toward mount).

If someone would like to confirm, I'm at work and believe thats right...

Harold

I'm curious about this because I just replaced my engine mounts and rear engine bracket. I bought all new fasteners, etc... and my neighbor helped me. He's a pipefitter and semi-professional mechanic and he said the "cup" washers should "cup" the rubber part of the mount, so we put them on that way. The old ones were mounted with the curve facing upward, but it seemed like they were wrong.

It's said that cupping the rubber will be a little firmer. Dunno if true or just a guess.

Did you search for this? I thought there was a thread on it.

Good point Randy -

Seach the board and came up with this one from Warren -

I have replaced my engine/transaxle mounts, and they were 'convex up' from the factory and that is the way I put them back on. The factory engineers seem to have been obssessed with noise and vibration levels in the cockpit for the last 25 years. My best SWAG (scientific wild-ass guess) is that turning those washers over might provide a slight bit more vibration isolation, but I'm not going to turn them over, because I have considered putting on 'sport mounts' or even solid mounts, as I have 100% Poly-Graphite suspension bushings, so you know why I am not too sympathetic to the factory's 'quietness' obsession!

Warren Hall

Also this from Andras Nagy -

1. Either way is no problem. My 1983 911SC was delivered to me at the factory with the concave side up; i.e., you could see the concavity under the bolt. This is the "stock" setting.

2. When I got serious about track and autocross events, the "trick of the day" was to change the washers to convex side up; i.e., just turn over the washers.
3. Warren is right, with the convex side up, there is more compression to the rubber, and therefore, the engine will twist less before it is restrained by the engine mounts/body.
4. Is this worth anything other than just minor, perhaps unmeasurable, vibration? There is no real answer. Only your common sense can dictate which way is best for you.

Ok, who is going to do a double blind test on a statistically valid sample of 911s to answer this question??

I struggled with this when I was re-installing my motor last winter but unfortunately I must have missed Warren's post ... I went concave down.

Now I've got a quick little project before the next track event :)