Project ROKTOY - Drivetrain Mounting
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By: Jay Kopycinski - 3/2002

I wanted a sturdy and reliable power plant for this project so I decided to go with a stock Chevy TBI engine. The TBI is a fairly simple system and has a good track record of reliability. It is easy enough to get custom ECM chips and aftermarket parts as well.

Here's the 1994 donor TBI 350 V8.

I bought a salvage TBI 350 V8 from a 1994 Chevy truck. It was purchased with 61k on the odometer. I bought the engine complete with all accesories, exhaust manifolds and y-pipe, and original harness. It has a serpentine belt system.

Behind the engine will be a GM TH350 auto tranny with 4WD output shaft in basically stock form. A Downey 1.5" adapter will be used to mate this tranny to my current Toyota dual case setup with stock 2.28:1 gears in each case.

Engine & drivetrain trial fit into frame Mock-up of dual cases and starting planning

To start the layout, I temporarily mated the drivetrain components. I had a spare transfer case and used some pieces of tube to mock-up the transfer case setup to determine length and location of the output flanges. I hoisted all the parts over the frame and started trying to decide exactly where I wanted it all mounted.

I decided to raise the engine a few inches higher than it would normally be in a typical Toyota engine swap. This will offer added ground clearance at the tranny pan and transfer case. The engine has also been moved rearward a few inches to allow for better weight distribution. The transfer case was raised as well, as compared to stock height.

Fabricated motor mounts & poly bushings

I fabricated motor mounts using some 2" x 1/4" square tube stock and 1.5" schedule 80 pipe (1.9" od x 1.5" id). Jeep poly spring bushings and steel sleeves were added to mate to Moroso #62500 stamped steel motor mounts.

Solid steel-on-steel motors mounts could have been used, but I feel that adding poly bushings allows just a little flex and will prevent frame cracks in the long run. When I did my original 4.3l V6 swap I used the stock Chevy rubber motor mounts and found them to be too soft and allow too much motor movement when combined with large tires and lots of traction.

Motor mounts on frame Crossbar spans mounts

With the mounts mated to the engine and the engine position finalized, I was able to do the final cutting of the mounts and weld them to the frame. I also added a small cross-brace that connects to both motor mounts and runs under the oil pan of the engine. This should provide just a little more support to prevent any frame spreading at the motor mount area, plus provide a mounting point should I ever want to add an oil pan skidplate in the future.

New version of transfer case mount Another view showing tab mounting

I was looking for a way to improve on the stock rubber transfer case mount. While it is a pretty decent piece, I think it is a bit on the soft side for tougher wheeling use. I also don't like the metal head on the bottom that must protrude through the crossmember.

I took a stock mount and cut it apart. I kept only the top piece that bolts to the bottom of the transfer case. To that, I added two pieces of steel tube and some stock rubber spring bushings and sleeves off a Jeep Wrangler. This setup then mates to four steel tabs welded to my high clearance crossmember. No biggie, but is a 1/4" to 1/2" shorter in height.

Start of the new transfer case crossmember Frame mount for transfer case crossmember

I made the main structure of the transfer case crossmember from a piece of 3/8" x 4" flat stock. I wanted something thin to allow me to easily route my exhaust up high above the bottom of the frame rails. This crossmember will not mount to the stock frame flanges. Those have been removed and new mounts fabricated up higher on the inside of the frame rails. The new crossmember will mount with two 5/8" bolts on each side.

Completed transfer case crossmeber Skidplate protects both transfer cases

Once the crossmember was complete, I added a 3/16" skidplate to protect the transfer case. This skidplate also connects to the rear case using a stock rubber mount (with lower bolt head removed). Extra bracing was added between the crossmember and skidplate using some 3/4" steel rod. The only thing left to do to the crossmember is to remove a little material at the front edge to clearance for the front driveshaft.

With the drivetrain laid out and mounted, the construction of the rest of the chassis can begin.

Will be using 1 3/4" .120" wall mild steel tubing to build the majority of the tubular cage.

More to follow........

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