My 4C has done higher mileage and during shifts it jerks, I tried a normal launch it didn't feel nice at all.
In my opinion the factory engine mounts in the 4C are way too soft. I remember seeing a video footage of the engine compartment during acceleration, it looked like the engine was trying to jump out of there.
I considered replacing all the mounts to see how they perform brand new but figured it would still be too soft for my liking. The engine side mount is also liquid filled and seems to prematurely fail even on low km vehicles as per Upper Engine Mount Deterioration at 17k miles | Alfa Romeo 4C Forums (4c-forums.com)
There are some aftermarket options for lower engine mount but nothing for the other two mounts.
I got the Powerflex Lower Engine Mount Bushing Insert
however this still felt too soft. Time to try making these mounts solid and casting my own from liquid polyurethane.
• Forsch Polymer 1LB Liquid Urethane Kit 80A High Performance
• Rubber Primer - Forsch Polymer PRI-1050 or DevCon FL-20
• Oven for curing at 65C/150F (optional unless short on time)
Note please read all the safety datasheets if working with these materials as if mishandled aren't good for your health.
I sourced from a local supplier but here these guys stock it DIY Liquid Urethane Engine and Motor Mount Inserts (suspension.com)
I had just completed some maintenance on the car so I already had it up in the air on 4 axle stands with all the rear panels and underbody off the car. I use the ESCO 10498 Jack Stand
, it has flat rubber mounts and suitable height to get 4C up in the air to work under and around it.
If you have access to engine crane you can lift up the engine/trans from lifting points. I don't have access to crane here so we have a couple more steps.
Remove all 3 engine mounts:
- Remove the lower engine mount first there are lots of guides on how to do this already.
- Jack under sump just enough to take the load off the mount.
- Remove the engine mount then raise the jack a bit more to make room between engine/trans and subframe. Note you don't want to lift it too far since everything is still connected just enough for shims. I used wood to make up some shims to go between the sump and the subframe and transmission to subframe.
- Lower the jack the engine should now be sitting on shims on subframe.
- Reposition the jack to under the transmission and use it to take the load off the transmission mount.
- Used an additional axle stand on the end of the transmission. Remove the transmission mount and slowly lower the jack so trans sits on axle stand.
As I'm writing this, I really should have taken photos of these steps.
If your engine mount looks like mine it would have perished already and dropped the liquid so clean up subframe and bolt.
Tear off the rubber on the bottom as circled in red. Using needle nose pliers and screwdriver remove the rubber baffle as circled in yellow.
Now that mounts are out we need to degrease and clean them. I just used hot soapy water brush and then water blasted them.
I was in a time crunch so I had to accelerate the cure using an oven which brings 7 days down to 18 hours.
The vapors from polyurethane aren't greatest so using your kitchen oven isn't wise. I purchased the cheapest benchtop oven I could find on Amazon that would fit all the mounts in it Galanz GRH1209RDRM151
I used it to dry the mounts off after washing but you can use the power of the sun if you have time.
Once everything is dry, we need to prime the rubber for good adhesion of the polyurethane.
I used Devcon FL20 in a well ventilated area brush it around all the rubber where the polyurethane is going to adhere then put it back in oven at low heat or in the sun to dry.
The rubber in the cavity should look nice and clean like this. If you have time you can peel/cut that top layer of perished rubber.
Next step is sealing off the mounts so the liquid polyurethane won't run everywhere when we pour:
- Transmission mount is the easiest to seal I used some contact adhesive and duct tape to seal off the small hole on the back.
- Lower mount I cleaned surface used contact adhesive around the outer shell of rubber mount then wrapped in duct tape. I also recommend putting a piece of duct tape on the hole on the other side in case some drips inside the bolt hole during pouring.
- Engine mount is the hardest to seal off use contact adhesive to seal the seam then use duct tape layers to seal off the cavity.
Let the contact adhesive cure for a while then we are ready for the fun part pouring! Since the engine mount has 2 cavities on opposite faces we are going to need to mix/pour in 2 batches.
Note the ratios of base to activator are very important! Use some scales that you know are accurate to measure out. Once you start mixing you don't have much time to pour so make sure you are ready.
This product is 10:1 on the first batch I used 100 grams of base to 10 grams activator. I was a little short during the initial pour so use 150g of base and 15g activator next time.
First batch we are going to pour the liquid cavity on the engine mount and the lower mount.
Start slowly pouring into the engine mount cavity once it reaches the top of the opening before the perished rubber. Now the lower mount pour until it is level.
We need to leave the mounts level and alone to cure. Ideally you could leave them overnight but I was trying to complete this quickly so I moved them to the oven at 150F for an hour.
The toaster oven doesn't have markings down to 150F. Use a thermometer to dial in settings to hold at 150F
Once the first part has cured enough reposition the engine and transmission mount to be level and fill remaining cavities.
Mix up the remaining polyurethane and fill the remaining engine mount and the transmission mount.
Let it rest for an hour or so then arrange all mounts in the oven to cure. After 18 hours at 150F the mounts are now cured and ready for action.
You can now remove the duct tape and glue that was used during the sealing process. I forgot to take photos of the other mounts cleaned up after tape removed.
I made a quick video of the process Alfa Romeo 4C Engine Mounts
Fix the mounts back into car in reverse order that we removed them.
I didn't do a great job of providing scientific evidence here I should have:
• Logged in-cab vibrations before and after.
• Video engine movement from launch to 60 for before and after.
At idle I really cant tell the difference in NVH. What I can tell you is night and day difference on launch feels planted, shifts feel solid very happy on that front.
I ran out of time to take it for a good drive to see if there are any speed/rpm that causes excessive vibration but so far so good.
Next time I have decklid off I will mount a GoPro and take video on a 0-60 to document engine movement.
I will put some miles on these and let you know how it goes.