Installed full motormounts...intermittent knock?
 

Hey all, installed the trio set of motor mounts from Damon MS on my 2010 MS3 with 80k miles.

First, I was ready for / expecting the NVH increase, and love the increase in 'feel' / responsiveness of the clutch / trans. Happened when I went to solid mounts on my RX, happened when I upgraded the 300zx TT motor mounts. Par for the course.

What I wasn't expecting is some sort of intermittent knock / vibration that is indicative of something somewhere hitting something else at lower revs (below 2,000 rpm) due to the engine vibrations now shaking something else.

Sounds like it's halfway between shifter and firewall, doesn't happen at all on WOT or anything above 2,000 rpm, and consistently knocks on startup on turnover, as well as in-gear, off throttle dropping below 2k.

Is there something I should check that could be smacking into a heat shield / the firewall itself at the rear of the engine? Checked torque on all mount bolts etc and they're good to go so I'm thinking the vibrations are now shaking another component that's attached to the block against the body. All those vibrations have to go somewhere.

Searching didn't pull much that seemed relevant to this. Next step is this weekend taking all the mounts off 1 by 1 and reinstalling and tq'ing again, but would love to avoid that.

If you hadn't just put in brand new motor mounts I'd say it was a blown rear motor mount letting the engine buck back and forth. Did you ever figure out what the issue was?

Sort of? I checked the mounts again, and strangely the rear motor mount and trans block look slightly off center now? But the rest of the mounts are in their correct spot. Let the engine off the frame and settle again after 1,000 miles and everything reinstalled in the same position.

Additionally, the noise is louder when its cold, but when the car has been running for 20 minutes, its almost nonexistent. I feel like there's some very mild gap on that bolt that once the trans block heats up / expands it, it diminishes the noise, but again - I tried loosening all the mounts and basically 'settling' the engine where it wanted to go, so I'm not sure what to do. Going to have a shop near me that's done a MS3 build look at it and see what they think but I'm annoyed that I couldn't fix it on my own.

I'm thinking the expanding and contracting of the metal is only slight and it shouldn't lead to that drastic of a knocking. The warm and cold difference could just be placebo, not too write off the entire phenomenon of it being louder when cold and quieter when warm.

Try putting your old RMM back temporarily to see if the problem goes away. It’s easy to do. If the knock is gone, it was something with the new mount. If it stays, then you’re chasing the wrong thing. Look elsewhere, then.

I can definitively say, it is NOT placebo. It's very loud when its cold and makes the sound any time you're not on the throttle or engine braking, and by the time I get to work, it's almost not making the noise at all. Go bcak out after the car has cooled down, noise is back. Warms back up, noise gets quieter / goes away.

I'm going to put the stock RMM back and see if that helps but I'm wondering what I'll do if that's the case..buy a different brand and try again?

If the swap back resolves the problem, contact the manufacturer or vendor and seek their advice. There may be some installation trick you need to follow.

There are only two bolts, as you know. They may offer advice on the order that you tighten them and whether the tightening should be done with a jack in place so that there is no binding or sag while you are torquing the bolts, or move the transmission around a little to line up the bolt holes so that the cross bolt slips through freely with no bind before tightening it up.

Or they may want to give you a shipping label to send it back and have them replace it.

i would check the exhaust, if the new mounts are slightly off with oem and you don't have flex pipe, it may just put the engine at a different angle where the exhaust knock against the body....

This. When swapping my clutch I forgot to hang back up the mid-pipe on the 2 rubber hanger bushing things. Shit banged around quite a bit as I don't have a flex pipe there. PO welded in a 3'' Test Pipe in place. Thought it was my rear mount.