Motor Mounts and Steering

Having never attempted a project of this magnitude before I really had no idea what I was getting myself into. I had never built any sort of motor mount before and besides taking a half day welding course my wife got me as a gift I had no experience welding. I just knew that motor mounts, in their most basic form, were pretty simple — connect point A to point B and have something in between to dampen vibrations.

After starting to get the feel for 3D modeling and having some success building the adapter plate I started out with a plan to design an elaborate motor mount solution. My plan was to have a single piece of milled aluminum which would bolt to the block and extend to the existing RX8 motor mounts.

I first needed to determine which bolt holes to use to fasten the motor mount to the block. Since the k-series is a front wheel drive engine the motor mounts are usually on the ends not on the sides. Not really knowing which bolt holes were appropriate to use for motor mounts I scoured the Internet investigating what other RWD k-swaps had used and set off building my first prototypes.

The first step was to get the flanges built. The bolt holes on the left side of the block were all on different planes so it took a fair amount of trial an error to get the flange to sit flush. Thankfully the right side was much simpler and it was just a matter putting the bolt holes in the right spots. Once I had the flanges designed I quickly realized that if I was going to extend these all the way to the existing motor mounts it would be an awfully large piece and excessive for something that was supposed to be simple.

Rather than machining the whole thing I chose to do what a lot of people do and just weld up motor mounts using round tube and flange bushings. I decided to keep the left flange I designed and have it milled from steel instead of aluminum so I would have a solid starting point to weld from. I also had a pair of relocation brackets machined for lowering the power steering rack. They were pretty simple to design and I wanted to move the rack as little as possible to avoid large geometry changes while still giving me enough room for the rack to clear the k24 crank pulley.

I used 3/16th mild steel, 1-3/4″ round tube and Energy Suspension Universal Link Flange Bushings (9.9489R) to make the motor mounts.  Like I said earlier, I’ve never attempted something like this before, but for the most part it was a pretty straight forward process.

The left side was pretty simple. Basically come straight across (more or less) from the engine and connect to an upright that would bolt to the stock RX8 motor mount location. The only thing I had to avoid was the exhaust manifold. I miscalculated a bit and had to notch one of the uprights to allow enough room to fasten the nut to the sub-frame but they seemed plenty strong so I wasn’t concerned.

The right side was a little trickier. Since the k-series sits at such steep angle the right motor mount was much longer and came up at a much steeper angle. It was a bit of a challenge getting everything to line up keeping the angle as shallow as possible to avoid contacting the steering column.

Again, they weren’t perfect but they seem to do the job well. They are probably much stronger than they need to be and easy to unbolt and remove in case I need to pull the engine (which I’ve needed to do a time or two).

A quick spray with some with some self-etching primer and automotive epoxy paint to keep them protected from corrosion and they were ready to hold the K24 in it’s new home.

I knew powder coating was the best option for protecting these but since I wasn’t even sure if these were up to the task I figured I would take my chances. Even after just a few test fits and light bumps the paint started to chip in places. If these prove to be a solid design I’ll have them powder coated in the future.
Since the power steering rack had to be lowered to clear the crank pulley that meant the steering column needed to be extended. There are universal extension options available but it only needed to be extended an inch or so which made me think none of them would work. Rather than going through what would probably be a lot of trial and error, I opted to cut and sleeve the steering column. This was a little trickier than I thought it was going to be.  Even though the inside diameter of the round tube I used was very close to the outside diameter of the steering shaft there was still enough play in it to create a wobble. After a couple tack welds and light adjustments I was able to get the steering shaft to spin true and free of any wobble.