C4 Frame Project

[Custer55]

After the first time putting the body down on the frame I was able to see where I need to cut holes for dog bone mount clearance. I could tell pretty much where and how big to cut the holes by the gray primer sprayed around the mounts and the slight crease the mounts left in the body.

With the body back up on the lift I cut out the holes and lowered the body back down to recheck clearance. The holes were just big enough to clear so it was easy to see just how much bigger to make them. Next step is to make the mini tubs to fill the holes. These will be made from 3 pieces. (2 sides and a middle)

To give the sides the same shape as the floor pan I cut a 2 x 4 in half to that shape then clamped the side piece in and hammered it over the 2 x 4.

The sides bent to a 90 with the curve to the floor pan. I know you could just do this with a shrinker but I don't have one so this is what I came up with.

the 3 pieces tack welded together. I bent a slight radius on all 3 where they meet to give them a rounded corner. The middle piece is just a rectangle bent to the curve of the side pieces to clear the dog bone mounts.

Finished mini tub with the welds sanded out and the flange on the wheel well side trimmed for clearance.

Finished tub held in place with sheet metal screws. Now I will need to do the other side of the car and lower the body to double check the fit. If everything looks good they can be permanently installed. The plan is to use metal epoxy and rivets. I don't want to weld them in because the back side of the floor pan is covered with hushmat (I melts really fast from just using the cut off wheel to cut the holes) and the interior is still in the car.
Brian

[NickP]

I love progress.

[Custer55]

Since the last update I built the mini tub/pocket for the dog bone mount for the driver side and got that screwed in place. Before lowering the body back on the frame to check clearance I removed the gas tank mounts since I knew the tank would have to be moved back a few inches.


These are the 3 pieces for the pockets before tacking them together. With this one welded up and screwed in place I lowered the body back down to check clearances before permanently installing them. (The body lift was sure worth the effort to build at this point!!)


It's hard to tell in the pictures but everything looked good for clearance. My cross member clears the tunnel very well with 1/4" to 1/2" all the way around. While the body was still sitting on the frame I looked at everything to see where I will have room to run the brake lines, fuel lines, & emergency brake cables.


The mini tubs installed with metal weld epoxy and a dozen pop rivets in each one. You have to work fast with the epoxy as it sets up in 4 to 5 minutes.
The notch in the inner wheel well pinch weld is for the upper dog bone mount bolt removal. Next project is the gas tank relocation.


I decided to move the tank back 3" from the stock location so I made up a couple of strips of 18 gauge to weld the stock mounts to which will them be spot welded to the trunk floor.


For the rear mount bolts I just had to drill a new hole behind the original, but so the carriage bolt would sit below the floor I used a hole saw to cut out the upper trunk brace and then used a piece of 1" heavy wall tubing and a washer the same size as the hole saw to reform the trunk pan as best as I could. I then made a reinforcement plate from 16 gauge and filed the holes square for the carriage bolts and tacked them in place.


Strips with the relocated tank mounts welded to the trunk floor. I drilled to strips with 1/4 holes every 4" on each side to plug weld them in place. I used a
2 x 2 to wedge them tight to the trunk as I welded them in which worked pretty well.


The tank strapped in to check the fit. It looks like I may need to use a rubber spacer or weather stripping to lower the tank a hair as the filler neck is now just behind the trunk indent for it. I will also need to clearance the pinch weld where the filler neck goes. Also I will probably angle the filler neck back to the fuel door in the quarter panel. I'll most likely have to make a spacer for the mount at the top of the neck also, probably just an inch or so you can still reach the fuel cap.
Next up will be to repaint the areas with the mini tubs and the tank mounts.
It's probably a good thing I have till spring to get this thing back on the road.
Brian

[chevynut]

Nice job Brian. Since you don't have a swaybar back there, I assume you had to move the tank to clear the differential? I have been recommending a different, reasonably priced 16 or 18 gallon EFI-equipped tank for this application, especially if a guy needs a new tank anyhow. We mount the tank to the frame instead of the body.

[rockytopper R.I.P 5-13-2017]

Very nice fab work!!!!

[Custer55]

Thanks guys, I am learning a lot as I go on this project. Also getting lots of ideas from the site.
Yep, I had to move the tank back to clear the C4 rear end, mostly the toe rods, and to have enough room to get to the fuel lines, sender wire and the rear end itself with out having to remove the tank. I am just using my stock tank for now as it is in very good condition and I will be using my present engine with a carb. If I ever upgrade to EFI, TANKS has a reasonably priced tank that fits the stock location set up for EFI.
I did get the filler neck set up so it will work with minimal mods. Basically just a 1" spacer where it mounts to the inner trunk (I had to rebend and put a little twist in the mounting tab on the filler neck) and grind about a 1/4" or so off the pinch weld at the trunk pan for clearance.


I just need to get a shorter screw hers, The one I had is a little long!! The spacer is just 5/8" tubing, I may make one out of Aluminum later.


The filler neck just contacts the pinch weld so I will need to grind it out slightly,
Brian

[Custer55]

I have been working on setting up the motor mounts for the last week or so. After being on the fence about moving the engine up and forward to go over the steering rack, vs recessing the firewall to move the engine down and behind the rack I decided to go the first route and leave the firewall alone. That way I can see how this works out and still have the option to recess the fire wall down the road.


The first step was to grind away the rest of the original Corvette motor mounts.


With the body back on the frame I positioned the engine high to clear the steering rack. My engine is a 283 from a 62 Chevy (I bought the whole car for the engine for $35. back in 1977) so it doesn't have a harmonic balancer, just a pressed on pulley hub. I raised the engine enough to clear a 6 3/4" balancer however. The engine is about a 1/2" to 3/4" forward also so I can get the distributor in and out without pulling the engine. I made some L shaped brackets with 1/2" threaded rod adjusters that bolt to the front motor mount holes to adjust the height and level out the engine.


The motor mounts I am using are the aluminum ones from Speedway Motors. I reversed the arms (they bolt to the block plates) so they will point in a more downward direction. The arm ended up right in line with the steering shaft the other way so that would not have worked. I am setting the mounts up so they will bolt to the Corvette suspension cradle. I have the mount base plates cut and bent to fit the cradle with holes drilled where they will bolt in and a bigger hole drilled to access one of the bolts that holds the Corvette spring in place. I will tack weld them in place to fab the rest of the mounts. Once every thing is tacked up I will pull the engine back out, drill the holes in the base plates through into the Corvette cradle so it should all bolt back in and line up correctly. Since most of the bolt holes will be blind holes I am using 3/8" threaded inserts.


One mount arm fitted to the base plate ready to tack in place. I will also have a spacer on each side of the aluminum mount arm. The one in front of the arm is 5/8" to clear the spring bolt head, and I am putting a 1/2" spacer behind the arm also. This will allow me to move the engine slightly forward or backward if needed. I will put a slotted hole in the trans mount also to allow for this.
At this rate I should be on the road again by Spring!!
Brian

[chevynut]

Brian, to move the engine behind the rack is a big deal, especially when you look at your crank pulley as well as your damper. If you use a serpentine pulley or a 2-track v-belt, your engine would probably have to go back around 3-4" to clear them. I went through this with a BBC for a customer and we ended up moving the damper behind the rack and the pulley sat over the top of it. The pulley was smaller where it bolted to the damper, and larger further forward so it worked ok. It still required us to move the engine back about 4-5", but that was a BBC that we normally put 1.5" forward. The problem is he won't be able to use a different pulley if he changes out his accessories for some reason. This is how he wanted to install the engine.

[Custer55]

Brian, to move the engine behind the rack is a big deal, especially when you look at your crank pulley as well as your damper. If you use a serpentine pulley or a 2-track v-belt, your engine would probably have to go back around 3-4" to clear them. I went through this with a BBC for a customer and we ended up moving the damper behind the rack and the pulley sat over the top of it. The pulley was smaller where it bolted to the damper, and larger further forward so it worked ok. It still required us to move the engine back about 4-5", but that was a BBC that we normally put 1.5" forward. The problem is he won't be able to use a different pulley if he changes out his accessories for some reason. This is how he wanted to install the engine.

That's why I decided to just raise the engine up and leave the fire wall alone. I have it set up to clear with a 6 3/4" balancer also. I could have set it lower with the small pulley hub on my 283 but I would have had to redo everything if I put different sbc in at a later date with the 6 3/4" balancer. At least with the small pulley hub I shouldn't have to reclock the steering rack. Maybe just reroute the lines.
Brian

[Custer55]

My next project was to make the transmission mount. This will just be a short piece to bridge the gap in the frame center section, but it turned out to be more work than I expected.
I first made a flat piece to go across the flanges I added to the center section. Then I made a curved piece to match up to the height of the trans rubber mount.


After getting the top piece bent to shape I trimmed the ends to fit between the mount flanges, drilled holes and spot welded it to the bottom piece. I had intended the whole thing to sit on top of the center section flanges but It quickly became obvious that it would be a major pain to get it in and out so had to go to plan B. It will bolt to the bottom side of the flanges with a plate on top of the cross member sandwiching the center section flanges.


Here is the cross member with the sides welded in and the welds ground out. The 2nd picture shows the plates that will sit on top of the flanges with nuts welded in place. With 4 bolts on each end 2 will go thru the cross member into the top plate and 2 will go thru the cross member and the flange into the top plate. The slotted hole in the cross member is to allow the same forward or backward placement of the engine and trans as the motor mounts.


Here is the trans cross member bolted in place.


This picture shows the spacers in the motor mounts to allow forward or backward placement.
My son made me the spacers out of aluminum so I will be able to polish them to match the motor mounts (covered in tape right now to protect them from welding sparks). My son just completed his third semester in Machine Tool at the local Technical College, so I'll probably have some more projects for him if he has time.


This picture is my original 55 Chevy Steering (red) column next to the 78 Chevy van tilt column I plan to use. I bought the van column at the Iola swap meet many years ago for 30 or 40 bucks. The overall housing lengths are almost the same and both have a 2" diameter tube. The adapter from my Grant GT Steering wheel should also work on the van column with a minor mod to the horn connection in the column.


This shows the van column bolted in place. I was able to use all the stock mounts to bolt it in place. The steering shaft will need to be shortened so the intermediate shaft will clear the upper a-arm for sure. I might have to shorten the lower end of the column housing a bit also, but it should all work without to much trouble. The steering shaft is 3/4" dia. so I should be able to just cut it to length and machine or file some flats in the end to make it into a double D shaft.

Next up will be to pull the engine back out and finish the motor mounts.
Hope everyone has a Very Merry Christmas!!!
Brian