3.4 V-6/T-5 Engine/Tranny swap Phase II - Building the subframes

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ENGINE SUBFRAME LAYOUT

Caution: READ THIS IN ITS ENTIRETY, I MADE A MAJOR MISTAKE IN MEASURING, IT HAS COST A LOT MORE TIME AND MODIFICATION!!!

This is what I did to build the engine subframe, this is the general layout using 1” X 2” square tubing with a medium wall thickness. Choosing to utilize the original frame mounting holes, I noted the original subframe being stamped steel, has multiple compound curves that necessitated using 5 pieces of square tubing. The outer pieces are approximately 6 inches long and the center section is 24 inches long with the left intermediate piece being about 6 inches long and the right intermediate piece right at 5 inches long. After consideration of the finished pieces, I will say that square cuts are a necessity and will assist in building the intermediate pieces. Also, the outer pieces and the center section are not on the same plane, either horizontally or vertically, the enclosed pictures will make that evident, the finished piece looks almost like a set of square tube motorcycle handlebars.


Here’s what I did to build it: The outer sections were carefully measured and cut at exactly 6 inches. I purposefully had an inch of overhang going to the center section to insure a good welding platform for the intermediate pieces, the same with the center section going outward beyond the frame. I measured for the centerline on all three pieces and center punched the exact center for each hole, drilled pilot holes, then drilled all holes out to ½ inch diameter. The bottom of the pieces was then drilled out to 1 1/8th inch to accommodate the large washers on the mounting bolts. All three pieces were then installed using the mounting holes. Now comes the fun part. After agonizing how to make one piece out of five, and noticing all the angles involved, I took some 1/16th plastic sheet I have and cut out the four sides of each piece by laying the plastic pieces against the installed pieces and using a very fine point “Sharpie” marked the plastic pieces where the edges of the steel pieces ended. This gave me top, bottom, front and rear plastic templates for each piece. I used rubber bands to hold all four templates in place on the intermediate steel stock and traced the outlines with the “Sharpie”. After cutting the square tubing and the initial trial fit, I found I needed a lot of filing to make the pieces fit properly. During the cutting with a hacksaw, I was careful to cut on each line with the blade at the same angle as the intersecting lines, this is critical. On the right piece, I noted that either the body was twisted, or the original frame was made that way, but I could not get all the edges of the intermediate piece to mate up with center or outside pieces. So a compromise was made to get the piece force fit into the gap with as many edges lined up as possible. On a side note, both intermediate pieces were force fit into their respective gaps. Not that a hammer was needed, but just enough hand force so they could be pushed in place and tack welded.

In order to simplify anyone considering the V-6 conversion, I measured each edge of the intermediate pieces using a reference datum line and measuring each side of the line to the edge of the piece. This will give you approximate lengths of the pieces, but are not exact and some machining/hand filing may be required to make them fit.

I know that more cutting and welding will be required to make this piece mate up to the engine mounting holes and I will have to fabricate the engine mount plates.

On a side note, I decided to build a pair of dollies to be able to move the engine/tranny assemblies around the garage. The plan was to build the dollies that would emulate the mounting bolt holes on the car. To this end I made a plate for the transmission support that picked up both the automatic and manual tranny bolt holes, the plate was welded to a 2 X 2 square tube 4 inches long that would slide inside a 2½ X 2½ square tube. For the engine support, I cut 2 pieces of 2 X 2 square tube 2 inches long, turned it so they would be a platform for the center bolt holes on the engine support. They were welded onto 2 X 2 square tubes 4 inches long that would also slide into 2½ square tubes. All the supports were bolted in place on the car, the 2½ tubes were c-clamped in place and 2 x 2 square tube cross members were cut to fit between the supports. Casters were welded to the bottom of the 2½ square tubes. Care is needed when moving the dollies with the assemblies on them, they turned out to be extremely front heavy and they can tilt forward easily.

Now, on to the subframe mounts. After bolting the subframes to the dollies and careful measuring the centerlines of each assembly, I found that I had to modify both the engine and tranny subframes. The tranny mount was the easiest, all I had to do was drop the crossmember ¾ of an inch. This was done by cutting the crossmember subframe just inside the frame rail on both sides and trimming an additional ¼ inch from each side of the new center section. Two pieces of ¼ X 2 inch steel strap were cut 1¾ inches long and the three pieces welded so the outside pieces were flush with the top of the straps and the center section was flush with the bottom of the straps, effectively lowering the transmission mount ¾ of an inch.

The engine subframe was trickier, I had to move the center section forward 2 ½ inches to clear the oil pan, have a platform for the vertical posts and still maintain the structural integrity to hold up the engine. The cure was to cut out the center section just inside the frame rails, weld in a section of 1 X 2 square tubing 6 ½ inches long and re-attach the center section after trimming the length 4 inches. To add rigidity I opted to weld 1 X 4 inch strap to the open ends of the modified cross-member.

The engine mounts were harder to build for a couple of reasons: First, I had to build the engine plates to clear the sensor and accessory mounts on the right side and the oil filter housing on the left. Then match the angle of the engine centerline to the angle of the subframe and still have hood clearance Secondly, I had to make provisions for the rubber mount bolts. I decided to use 2 x 2 square tubing for the vertical risers from the subframe to mimic the original mounts with a rotated 2 X 2 x 2 section to use as a platform for the rubber mounts and for access to the attaching hardware.

Two things here, an adjustable angle bubble level was used to determine the angles and the plastic sheeting was used to locate the holes on the engine block and transferred to the engine plates at the correct angle.

The original plan was to have the engine plates welded with a top plate sitting on the rubber mounts, but because I had decided to use the original accessory mounting brackets and all sensors to the computer, I had to change the configuration.

The right mount had to have the horizontal plate welded to the bottom of the engine attaching plate and supporting plates welded in to make an open side box with the open side on top. This is because the engine knock sensor dictated the change, it was in the way for my original idea to work.

The left plate was a little harder because the plate mounting bolts are not on the same plane. The two top bolts were OK, but the bottom bolt boss was extended above the plane of the two top bolts. The cure was to make two plates, the top one of ½ plate and the bottom plate of ¼ plate, then weld the two into one piece, crude, but functional.

In order to have the crankshaft and transmission shafts longitudinal angle the same as original Opel configuration, both assemblies were carefully measured on the dollies as stated previously. The V-6 assembly was supported on the dolly with the tranny mount, floorjack and hoist, centered on the dolly and again, carefully measured to determine the angles and provide a hood clearance point.

The tranny mount was decided to be the pivot point for the longitudinal angle because of the smaller change of the u-joint yoke angle that would come from raising and lowering the engine to the required height for the correct angle.

After the engine was determined to be in the correct position, the longitudinal angle of the subframe was determined and engine plates drilled to match that angle. After the holes were drilled in the engine plates, minor trimming was required to clear the sensors and oil filter housing.

The horizontal plates were then tack welded to the engine plates after the angles were checked and rechecked. The vertical posts were cut and welded to the right height, with the rubber mounts installed and then mounted to the engine with the lower end of the post sitting on the subframe. Everything mated up perfectly.

The bottom of the posts were marked on the subframe, then the subframe was removed and bolted in the car. The right post was almost perfect, just a ¼ inch had to be trimmed from the horizontal plate for clearance.

The left post was a different story. The steering shaft was in the way. Back to the drawing board!

After agonizing how to mate up everything on the left side, I decided to make a mounting plate similar to the left side. Differing slightly because of the bolt holes being too close to the bottom mounting plate.

The cure here was to add a 2 x 2 x ½ square piece at the bottom of the engine plate at 90 degrees, then pick up the horizontal plane of the vertical post with another 2 x 4 x ¼ plate. The angles were again, checked and rechecked then tack welded in place. The whole assembly was removed, then welded into one piece.

Angle pieces were cut for each mounting plate using the outline of the engine brackets and welded in place for structural integrity. On the right mounting plate and elongated hole was cut in the bottom for access to the bottom rear bolt, other than that all bolts were easy access for a socket to torque the bolts on final installation.

I decided to use hanger straps like the original Opel frame to stabilize the framework and prevent tilting. This was accomplished by using 1/8 x 2 steel strap. I drilled 3/8” hole in the center end of each strap piece after determining the length needed to weld the strap to the vertical posts. The subframe was installed, the straps bolted in place, then welded to the posts.

In summary, if I had to make another subframe, I would move the vertical posts inboard about a ½ inch and make them ½ inch taller for more clearance to the oil pan and cross member and to gain clearance for the rubber mounts, I had to trim them a little. As it is I have to add a ½ inch shim plate to the right vertical mount and a ¼ inch shim plate to the left vertical mount.

I would also use different rubber mounts of the same style. The ones I purchase had a shorter threaded bolt on one end. This caused me to use the thinner wall 2 x 2 square tubing verses the 2 ½ square tubing I had planned to use for the rubber mounts. This would have given me a stronger support base for the rubber mounts.

Also, because I had to change my original configuration thoughts on the engine mounts, I ended up with lower posts and engine mounts, they will not be subject to excessive engine torque action that taller posts would be as they are just above the oil pan mating surface.

All in all, the mounts were not too hard to build, just time consuming because of the double checking all angles before tack welding in place and having to change the original configuration.

One other thing, after the cross member was welded, some of the mounting holes had to be opened up a little because of the minor flex and warping that occurred during final welding. Nothing critical, just a little trimming with a rotary file. The subframe mounts to the engine perfectly and bolts into the car with ease. So hopefully, after putting the engine in position, the subframe will bolt right up to the engine and car.

Here’s what actually happened: The engine/tranny was put in the car for an initial check, the tranny shifter was up against the forward edge of the shifter hole in the car, I screwed up.

The subframe measurements were taken using the original bolt holes. What I did was forget the Opel tranny uses the front holes and the T-5 uses the rear ones. My measurements for the tranny shifter were taken from the bolt holes with the assemblies on the dollies. I had to move both mounts back 2 ½”.

I didn’t need to cut the engine cross member and move it forward, although I did have to cut it and drop it to clear the pan.

The cure I used, although really crude, but structurally sound was to cut the engine mount crossmember and remove the section I had modified originally. I welded a short piece of 1 X 2” square tubing to the shortened center section. Then used the 2½” square tubing that slid over the ends new short sections and slid another 1” X 2” square tube crossmember in with it, running under the oil pan and welded them all together. Doing it this way allowed me to move the vertical posts inboard where I wanted them. For the tranny mount, I welded a 5” X 6” X ½” plate to the rear of the frame, and drilled a hole in the center of the plate. Because I moved the tranny back on the mount, I had to notch the front of the mount to accommodate the angled piece of the case to the tailshaft. Easily done by cutting the front side, about an inch back, out of the 1” X 2” square tubing, turn it around and weld it back in place.

The rubber engine mounts I purchased for the engine have already compressed about ½ to an inch with the engine weight on them, so future builders may want to take that into consideration.

Again, everything bolts up out of the car, the subframes bolt up to both the engine/tranny and car. With the assembly installed for a trial fit, the shifter is now centered in the console hole, but the engine is about 3” off center to the passenger side of the car. I have to cut the footwell and wiper motor well to center the engine in the engine bay………All in Phase III.