Factory motor mounts

[fmorelli]

I recently installed Revshift motor mounts. In the process I discovered that my factory mounts had compressed, the passenger side ~3mm shorter than driver side. The Revshift mounts hold the motor ~12mm higher than the old mounts. Revshift mounts are made with the same height as an unloaded factory motor mount.

So now I'm starting to wonder - does anyone know if the factory motor mounts, even when new, compress when taking the weight of the engine/transmission? The reason I ask is that the measurements I've worked out with John @ Revshift definitely tell me my original factory motor mounts are compressed without load. Yet the distance from my strut bar is further than the compression amount we measured. I'm positive the Revshift mounts are identical in height to the factory mount, when unloaded, but I can't account for the additional height of the motor beyond the measurements we've taken. The Revshift mount is designed differently and does not mimic the factory mount's behavior under load.

I'm wondering if anyone has looked at this? It's a PITA to figure it out on the car. If I had a spare brand new factory mount here, I'd load it up in the hydraulic press and see what happens.

Filippo

My original 30k factory mounts shows at least a 1/2" gap to the oil cap:

Replaced with Revshift mounts, which unloaded are the exact same height as an unloaded factory mount, there is 1/8" of clearance to the side of the oil cap:

 

[The Convert]

This isn't rocket science. If they didn't calculate compression under load when they designed the Revshift mounts, then the engine isn't going to sit at the same height as with new factory mounts, given they made them the same unloaded height. Not taking into account compression seems kind of like a rookie mistake and should tell you something. It's one thing to be able to make a quality product, but a totally different one to actually engineer one.

 

[ShocknAwe]

If they don't allow the same compression then the driveline isn't in the same plane. Not necessarily bad, but, better to do it properly. It would be great to have an engine mount that doesn't sag over time. I really do think these will be the ones, just need a tweak!!

 

[Revshift]

We take the loaded height into account when designing mounts. Surprisingly, a brand new oem mount does not compress very much when the engine is placed on it. We are talking maybe 1/16" compression. Our 80A mounts do compress a tiny bit under load as well. The oem mounts compress more and more over a long period of time. Our mounts maintain the original intended ride height of the oem mount. Keep in mind, we have been making polyurethane motor mounts for 12 years now. Everything being discussed here was accounted for when designing these mounts. We took our time designing them and they ended up being the most involved and thought out mounts that we have come up with so far. Our mounts do not raise the engine or lower the engine when comparing to brand new oem mounts. Maintaining proper drivetrain geometry is very important to us.

 

[fmorelli]

Surprisingly, a brand new oem mount does not compress very much when the engine is placed on it.

If that's the case, I am at a loss for explanation. See the two photos above. We know from the measurements we took, with digital micrometers, that the mounts I removed were compressed far less than the engine height difference shown in the photos. I'm miffed! What's causing the 1/2" difference in engine height?

Filippo

 

[Revshift]

Attached are pictures comparing a brand new oem mount to a used mount that I pulled off my 135 with 85,000 miles on it. There is just under a 1/4" difference. Now the worn mount will compress more than the new mount with the weight of the engine because it is weakened and worn out. So with the weight of the engine we are talking maybe a 3/8" difference from the new oem mount with a load.

What I think you might be seeing is that your driver side and passenger side mounts were compressed different amounts. So that would tilt the motor and be apparent at the top since it is already a slant six. If your passenger side mount was compressed more than the driver side and you were to raise the passenger side to match the driver side you would see the gap between your strut bar and the motor close more than the amount that you raised the mount. This is because you are not only lifting the one side of the motor but you are also standing the engine up straighter. I know we are talking small numbers here but if you are looking for where the 1/8"-1/4" height difference is coming from I think that could explain it. I hope that makes sense.