PSA: Make sure your motor mounts are connected

PSA: Make sure your motor mounts are connected

A bit of an embarrassing story to tell -

I've had my E30 (91' 318is) for 3 months now and have been slowly addressing all the deferred maintenance and botched repairs during my spare time on the weekends. Well, this weekend was the weekend to drop the oil pan and make sure the upper oil pan bolts were tight - apparently it is common for them to loosen up on the M42.

Well, when I had the front of the car jacked up, I noticed that the driver side motor mount looked off - in fact, the bolt had torn straight through the subframe bracket! At first I thought it was just the driver side, but I found that the passenger side was the same way! So for the 3 months I've had this car, I've been driving around with the motor just sitting on the subframe, completely unsecured.

Looking back, I had noticed a lot of drivetrain slop but put it down to a worn driveshaft or diff or something (I'm new to this whole working on cars thing). This is my first enthusiast/manual transmission car so I didn't know exactly what to expect.

Well, I reattached the motor mounts this evening with a large flat washer as reinforcement against the torn subframe, and holy hell! The entire car is different. Not just zero slop in the drivetrain anymore, but even the handling is improved. There is much less play in the steering, less body roll, and the engine is way smoother.

I know it probably goes without saying that having the motor mounts attached is pretty critical, but I just had to share. Thread title is a joke, I don't expect anybody else to be driving around with disconnected motor mounts for any length of time.

Yay!

As I learned the hard way, new doesn't always mean great, either. When I rebuilt the Porsche's engine, I replaced the engine mounts. Might as well, right?

While the car was recently in for service, my mechanic located the cause of my shifting issues: Those non-OE mounts were failing, allowing things to shift around. To keep me going, he slipped in some old but genuine Porsche mounts. Problem fixed.

"OE quality" engine mounts for a 911 start at about $20 each. Genuine 911 engine mounts are $110 each. You need four of them.

I mean, seeing as the engine is the largest structural member in the car, i could certainly see the handling improving with it connected :p

Don't feel bad.

At least you put the bolts in before you tried to drive the car, unlike someone I know (me).

Dietcoke wrote: I mean, seeing as the engine is the largest structural member in the car, i could certainly see the handling improving with it connected :p

They are not usually structural.

However, it is a lot of weight moving around in there!

David S. Wallens wrote: As I learned the hard way, new doesn't always mean great, either.

I ordered a new Monza Spyder back in the day. Waited 6 months for it to finally arrive. When I got in to drive away from my uncles dealership I turned the key and got a loud bang. Turned the key off immediately and walked over to the service manager and said "Somethings really wrong, like there's no motor mount bolts or something". They thought I was nuts and were busy so I walked home and got a call later from service manager. Cross bolts for the engine mounts weren't installed at the factory.

I'll add a PS to this PSA: Don't think you can leave out one of the four mount because "the other three will do fine." I got suckered into this once by listening to bad advice and not thinking it through. Doing so ended up forcing one of the weight-supporting mounts to resist engine torque in tension. It eventually failed, spewing stinking hydraulic oil everywhere and allowed the engine to jump upward about 3", breaking a bunch of hoses which took me awhile to figure out.

Dietcoke wrote: I mean, seeing as the engine is the largest structural member in the car, i could certainly see the handling improving with it connected :p

Except engines are not structural.

Mercedes made a big deal over electronic motor mounts improving turn-in on one of their new models. When the various systems would sense a rapid cornering maneuver, the motor mounts would go to full-soft for a moment, allowing the mass of the engine/trans to disconnect from the chassis for that critical first bit of turn-in, making the front of the car act a few hundred pounds lighter.

Gravity will generally keep the engine roughly where it should be...

My cheap motor mount story- I have a 67 Camaro, which I've updated (That might not be exactly the right word...less ancient dated) the front suspension with a front clip from a 77 Nova. The original mounts were pretty typical Chev mounts, old, crusty, covered in oil, but intact. I was ordering a bunch of stuff, so I got some new mounts from Summit and installed. All my fabrication skills were internally questioned when nothing fit as it had when I'd mocked it up with the old mounts. They were soft, and the steel locking plates had bent as well, so the engine sat a full inch lower. I couldn't figure out how I had managed to allow the steering linkage to run into the oil pan.

Reinstall 39 year old mounts, all is fine. Anybody want to buy a brand new set of Chev clamshell motor mounts?

Those 318is engine mounts are the hydraulic type to try to dampen some of the 4 cylinder vibrations. There is no through bolt - it's more like two flanges with threads on them with the isolator part of the mount holding it all together. This is a fairly common design, but my point is that you should also make sure that the mounts are still in one piece. Mine looked like they were until I removed them - one was totally broken in half, and the other was on its way. They were both collapsed about a half inch over stock. New stock mounts made a huge difference.

Also, get some of the weld-in reinforcement plates for that subframe and fix it properly - unless you got some properly good washers in there, the soft steel typically used will eventually pull through as well. At 200k miles, my subframe was wallered out on one side and cracked on the other; pretty common with E30s if they get driven hard.

When I put the new engine in the wagon with roughly double the stock power, I also put in new stock engine and trans mounts, trying to keep NVH down. The break in period alone, babying it, was enough to break the trans mount, probably because it was a crappy mount more than anything else. After 5k miles, the new rubber mounts had basically turned to goo, and every time I opened the hood, the engine would be in a different place. It moved so much that it actually broke every single exhaust mount all the way back to the rear axle, and the engine would hit the firewall at WOT above 3500 rpm. Poly engine and trans mounts actually reduced NVH (but it's body on frame) and shift quality improved an unbelievable amount. It's all in the little things; made it feel almost like a new car.

gearheadE30:

Oh I have every intention of eventually replacing the old mounts and the subframe w/ the Garagistic reinforcements. My subframe appears bent, as the mount on the passenger side is mounted with the bolt nearer to horizontal. The washers appear to be holding up okay for now - I certainly won't be autocrossing or driving the car hard like this though.

This is priority #673 on a car that needs a thousand things. The immediate concern right now is the cooling system and oil pan leak.

Thanks for the E30 info! FWIW, I still don't see how the mount bolts can actually tear through the subframe metal. Would this and the bent subframe indicate a curb incident? My car had a lot of work done to the front suspension before I got it (new steering rack, bushings, etc.) and now I'm a little suspicious.

David S. Wallens wrote: "OE quality" engine mounts for a 911 start at about $20 each. Genuine 911 engine mounts are $110 each. You need four of them.

I've had similar experiences with other cars. The price difference is similar for many cars as well - its not just a Porsche tax. Its easy to copy the design of the engine mount, it isn't easy to copy the chemical composition of the rubber.

I used to work for Goodyear Engineered Products. A LOT of research goes into the right rubber properties for an engine mount (and even more for hydraulic mounts)... how many crappy "OE Quality" manufacturers are going to get that right?