The fabrication was one of the most involved aspects of the build: the firewall and chassis frame rails required many significant modifications, a custom steering shaft with center U-joint was installed, front subframe was modified, I had to relocate the ABS module which required running new custom brake lines, the engine and transmission mounts were custom fabricated, the driveshaft had to be shortened and shifter carrier and selector rod were modified and countless other small changes and alterations were made.
The most significant chassis modification was the frame rail on the driver's side. The alternator was way too big to fit between the frame rails, so a huge hole was cut in the frame rail, it was then reinforced internally for strength while also being cognizant of the fact that this is a designed crumple zone.
This opening was also cut out a little larger than 2x the depth of the alternator. The reason for this was so I could remove and replace the alternator with the engine installed in the future if needed.
A new section was welded in after some internal reinforcement was added.
This shows the alternator sitting in place.
I used some body filler to smooth things out a little bit and even carried part of the body line into the pocket. This is the area in primer
The opposite side frame rail had a similar modification for a small little clearance pocket for the timing chain tensioner.
This is that area finished in primer.
This was not necessary for the swap but I also reinforced the shock towers at multiple locations, adding sections of weld where they were previously just attached with epoxy from the factory.
Shock towers on the top, bottom and sides and then the sway bar mount brackets, some firewall sections and a lot of the frame was reinforced with additional welds.
Internal frame coating was also sprayed into both framerails right before painting (which happened much later). This was to protect the backside, providing rust proofing of the welds on the inside of the frame.
The below modifications were not at all necessary for the swap, but I wanted to install the 750i dual intake system so I modified the radiator core support to fit it. This is about mid-way through fabrication of that part.
And this is how it looks painted with the intake installed.
The front subframe had to be modified, here is a stock subframe compared to the finished custom subframe.
I reinforced it internally with an extra piece on the front edge, the pieces on the side extend all the way to that front piece and then there is a piece at the rear spanning the width between the two side pieces.
I probably could have gotten away with cutting a little bit less off, but I was still deciding how far forward the engine was going to be when I was doing this step. Next time I'll cut a bit less out.
Later on, I also modified the front subframe again by modifying the steering rack mounts. I angled the steering rack down a few degrees, to place the
input splines further down.
With clearance all the way around the focus then became the engine and transmission mounts. I started at the transmission side, as I had a rough idea what that would look like because mixing and matching some other factory BMW components got me pretty close, but it did need to be custom in the end. I used a euro E36 M3 mount for reference and built the first iteration of the mount.
I then had a custom 3d printed piece that mounted to the transmission in place of the giubo.
This was designed with a laser measuring device mounted into the middle and then I used this to determine when the transmission was pointing straight rearwards. The engine was raised/lowered and the transmission mount had washers added to it to adjust up and down as required.
Once I got that about where I wanted, I then used a magnetic digital angle gauge to verify that the transmission output and differential input were exactly parallel, 180 degrees offset from eachother.
Once that was aligned, I then had to use the laser to again verify the driveshaft was centered. This process (using laser alignment for straightness, then angle gauge for parallel input/outputs) was repeated quite a few times, narrowing down on the correct angle until I got it perfect.
While doing all of that I was also verifying the engine was flat and straight using the digital angle gauge. This whole process took a few days on it's own as well as countless times crawling under then back out of the car to make minute adjustments.
I then welded the final iteration of the transmission mount together and the next step was engine mounts. The engine height and fore/aft location was already set at this point; being determined by the angle of the transmission.
The exhaust manifolds were installed and the stock engine mounts were used as a rough template for these. I had help on welding these as I was new to welding back then and these are probably the ugliest part of the swap.
I will be sending these out to be 3D scanned and a CAD drawing made from them so I can fabricate nicer versions in the near future.
Clearance was tight, but sufficient.
Finalizing the steering shaft was the next major task now that the engine was in it's final place.
I used just about anything and everything I had on hand to roughly mock things up. Here I am using an extension to indicate the path of the steering shaft.
With the engine out this is what it looked like.
I then cut the DD shaft to size and started to finalize the shaft.
The shaft sat so low that I ended up needing to cut an additional pocket into the frame rail.
The initial version used a heim joint to hold it in place.
However the heim joint later developed a little play and was replaced with a bolt-in bearing assembly on a custom bracket I made.
Other modifications had to be made as well, including modifying (shortening) the steering rack input splines. This was required because the joints have maximum permissible working angles and I was exceeding them by just a few degrees. Clearancing the input splines here allowed me to get the joint down further on the shaft, which slackened the angle just enough to get it within it's operating range.
The bracket for the ABS was properly relocated at this point, as previously the ABS was just resting out of the way.
An additional pocket for fuel and rear brake lines was made to keep them out of the way of the engine.
Custom lines were made - first in a copper line, then eventually the final versions were made in a stainless steel line.
Then I got to the paint prep stage.
Seam sealer was then applied
Multiple light coats of primer were applied.
Then it was painted.
Reinstalled.
There were numerous other small things done, but this covers the major tasks. Back to the main page
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