Third motor mount
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I’ve been using some stock Volvo 544 mounts to keep my engine in place in my 71 volvo 1800. I’ve been using these particular mounts because they have an approximate 1″ thickness vs. the stock mounts 1 3/8″ thickness and give me hood clearance needed by the supercharger. Over time, the amount of torque and traction produced by the car is a bit much for this design. Autocross starts are 4500 rpm clutch drops on race tires and a sloppy downshift on a road course can transmit a lot of energy to these mounts. Recently one of the mounts let go and sent the forward edge of my compressor into the sheet metal of the hood. This sucked, time to fix it.
I tried working with polyurethane universal mounts to stiffen things up but the level of vibration transmitted into the passenger compartment was unacceptable for a full race car much less a vehicle used on the street. I decided instead to create a 3rd anchoring point for the engine. I read a bit and looked around at OEM arrangements and the designs sold by aftermarket companies for tuner cars for inspiration.
The poor availability of potential anchoring points and my lack of fabrication skills made it a little bit of a puzzle but I eventually settled on a support spanning the driver’s side fender sheetmetal and the front of the cylinder head. You want to make sure the anchoring point is up high on the block or on the cylinder head itself. If you picture the range of motion of the engine under load the top of the engine will move side to side far more in relation to the base of the block where the standard mounts are. I considered several scenarios where I could make a vertically aligned mount anchored to sections of the frame or crossmember but none of these seemed like they would do as good of a job dampening movement as a higher, horizontal mount.
I reckoned that the Swedish steel of the 1800’s fender was thick enough to dampen movement as long as I spread the load well. I don’t think this would work on many cars built after ’75. There needed to be some give in the system and it also needed to be soft enough to not transmit too much engine vibration to the chassis. After looking at a few options including motorcycle shock absorbers and plain old ratchet straps as dampener/isolator I found a used Volvo 164 Transmission mount I had laying around in my parts bin. This is just a rubber puck with two threaded studs protruding from either end like the existing motor mounts. I drilled a hole in the fender with some consideration of the resulting line from the head to the fender and how that would affect the mount once I torqued everything. I slid the stud through the fender and anchored it on the back side with a large washer to spread the load.
Next I went to speedway.com and ordered a swedged aluminum tube with female threads on either end of the rod. I also ordered a heim joint rod end to attach the arm to the engine. This heim joint would allow the mount to move in many directions without adding any give to the system.
- 910351-8 8″ Aluminum Swedged Rod, 3/4″ x 3/8″ 1 $9.99 $9.99
- 1170806L Aluminum LH Male Heim, 3/8″ Shank/Hole 1 $11.99 $11.99
- 91001153 Stainless Jam Nut, 3/8″ LH 1 $2.99 $2.99
I used a piece of scrap aluminum from Home Depot and drilled it to span the front AC mounting holes on the cylinder head. Two bolts locate it vertically on the head and a hole drilled in the middle is used to attach the heim joint rod end. The rod end threads neatly into my swedged rod. The other end of the rod needed to be tapped to accept the rough threads of the 164 mount. This was the hardest part of the whole project, trying to clamp onto the swedged rod hard enough to drive a large tap into it.
I eyeballed a correct length and tightened the mounting bolts. I then set a very slight preload on the stabilizer by adjusting the rod end out. Started the engine, no rocking, no vibration, better control of engine movement. I’ve done 25 autocross runs and done 2 track days with this setup and I can detect no fatigue on the fender sheet metal. Along with my polyurethane transmission mount the drivetrain is firmly set and a pleasure to shift. This was about $35 in stuff after shipping. I was slightly concerned about the aluminum I used for my engine side mount point and routinely inspect it but it appears to be fine. YMMV.