Tube Frame Chassis Rear Engine build from a Buick Riviera donor

Youngfg,

I will check bump-steer on it once I get farther along. For now, I will keep it as.

And now, another update...

Worked on the car this weekend and it is starting to look more like a car now.

I joined the engine sub-frame to the chassis similarly to the Goblin by Adam & Lonnie Doyle. using 4 of the 6 factory sub-frame mounts. I will either use the last two mounting holes for a rear bumper/guard or cut them off and weld some plate in its place.

One thing that is weird on this engine is that it doesn't actually mount to the sub-frame. It has anti-torque mounts on the sub-frame but the only motor mounts attached to the body. I used the factory mounts and just welded a bracket onto them.

Other than a small amount of practicing on some pieces of tubing, this is my first welding project so my welds are pretty ugly... but they will hold.

I need to add some diagonal braces near where the motor mounts are for added support and some braces to the roll bar. Then I will figure out the strut mounting. Right to left will be pretty easy since I know the struts are 48.5in apart center to center and I can just center that on the chassis. Front to back will be more difficult... I am planning to take a measurement from the chassis mount to strut tower on each side of the car and replicate that. I will probably make it adjustable for now just in case I get it wrong initially...

Can you still pull the engine out with the way those mounts are attached?

This looks good so far!

wvumtnbkr wrote: Can you still pull the engine out with the way those mounts are attached? This looks good so far!

Thanks and yes I will be able to pull the engine still. Since there will eventually be bracing above the engine, the way to remove it would be by picking the chassis up off it. I am pretty sure that once I unbolt the sub-frame, sliding the chassis forward ~2in to clear the front mounts, the chassis can be lifted off.

Of course, the engine would have to be suspended for this to happen... so it may not be the easiest thing to remove in the end, but definitely doable.

Also, I was surprised how light the frame is so far. I went to pick it up and move it this weekend and it weighs less than 150lbs so far.

Some free unsolicited feedback that is worth exactly what you are paying:

Turn the heat up on the welder, spend a bit more time grinding the surface clean and steady the cup with your other hand and the welds well be nicer looking. Bevel the edges of the parts where they meet each other for best penetration. The black surface color on the angle iron is mill scale and it pretty much kills weld penetration. Also responsible for a lot of spatter. I use this feature to my advantage when just temporarily tacking pieces together since it can be subsequently separated with a hammer blow.

A few minutes with an angle grinder on the sharp edges of the angle iron brackets will keep more blood in your veins further down the road, and look more like a finished part in the meantime.

Didn't have too much time this weekend to work on the car, but got a bit done.

Put supports from the frame to near the motor mounts for added rigidity.

I made a C Channel bracket to join the two struts. I left the Camber the same as it was on the car, but I left a ~1/2in of adjustment in each tower for future adjustments.

I then squared up the struts, putting much less caster than there was originally.

Then tacked in some supports

Ill add some braces in the Channel for added support where I welded in the tubes.

I wont have much time next weekend either, but I will try to add the braces and weld up the tubing a little more. If I still have time, Ill start working on the front suspension. Hopefully in 2 weekends, Ill be able to put wheels on and roll it around.

I haven't put the rear wheels on yet, but it should have a 7 in ride height currently with a 4.5in ride height after I get my final wheels & tires.

Great progress.

You should have plenty of power! It will be a rocket.

I like how the mass of your donor engine is very well centered from left to right, it is very symmetrical.

Our cobalt donor engine's mass is not as symmetrical, luckily it is heavier on the passenger side.

Thanks Lonny. I guess I forgot to post after last weekend, but I bolted the wheels on the back and it was about a 1/8th in lower on the passenger side, but with me in it, everything is perfectly level.

I didn't get that much done as I was only over there for a few hours.

This week I started working on the front suspension. My uncle gave me some components from a cicle track car to use. He called it a 3-line or strut suspension.

It is at this point that I realized that my current frame design wouldn't work with my needed track width...

So, I had to cut all of the welds on the front half of the car and redo it...

After re-bending all of the main tubes, it was a much better track width.

Checking the track width and turning radius, everything works now.

I had to resize the bottom link, then was able to mount and secure it.

right now, the lower arm has 4-5in of upward travel, so that should be plenty for this car, considering there will only be 5 inches of ground clearance.

I wont be able to mount the upper A-arm until next weekend when my uncle's friend brings back his camber/caster gauge. I am planning to buy some Summit Racing coil-over adjustable shocks with some 110lb/in springs.

I think the 110lb/in shocks should be a good middle-ground between street and strip. I am pretty sure that the front of this car only weighs 500-600lbs. The frame currently weighs ~100lbs with another 50lbs or so to be added; even with the brakes, steering, electrical, & gas tank, it won't be over 600lbs.

So, during the week, my shocks & springs came in. I was surprised just how adjustable the shocks are, with 18 adjustments for compression and rebound. after 6, I cant compress the shock by hand.

My uncle got his caster/camber gauge back. Using that, I was able to get a basic idea of what the brackets will be.

Then I was able to make the brackets, tack them in place, and re-check the geometry. The reason the mounts are not the same on each side is that this suspension was originally from a circle track car with a different ball joint angle on each side.

The steering rack was something my uncle had lying around. His buddy pulled it out of a car to get a quicker steering ratio. It is out of either a Corvette or Camaro, 2010s I think.

I added some supports, reinforced my tacks, then put some wheels I had laying around on it to test.

Ive got to re-drill the bolt pattern next weekend to get my rims to fit the hubs.

Also, forgot to add:

I set it up for 4in bump 2in droop. with Caster of (+)3.5 & Camber of (+)1.5

Pardon me if you have already covered this, but how do the pivots on the rack relate to the inner pivots on the a-arm?

If the rack is not matched to the pivots, you are going to end up with bumpsteer.

NOHOME, I will look at that next weekend. I looked at it briefly yesterday and it didn't look like the steering linkage moved at all when I moved the suspension through it's travel.

Is there any other things I should check to make sure?

You probably know this stuff already...

"...As an independent front suspension (be it A-arms or McPherson strut in design) moves up and down, the wheel moves through an arc, pivoting about the lower control arm's inner mounting point. A farther arc is defined by the outer tie-rod end, pivoting about the ball joint inside the steering rack. Where these arcs differ, the tie rod will cause the wheel to move inward or outward, meaning the car will "self-steer" when traveling over bumps, hence the term bumpsteer.

To eliminate the problem, mount the steering rack so the tie rods are parallel with the lower control arm, and-perhaps the most difficult part, as it may involve searching for a particuar-width rack, though custom-width aftermarket racks are available, as we'll see-ensure that the inner pivot point of the control arm and the ball joint inside the steering rack, at the inner end of the tie rod, are the same distance from the chassis centerline. As you can see, the rack will have to be a specific width between the ball joints and mounted in a specific place to work correctly,

Read more: http://www.hotrod.com/how-to/additional-how-to/0804rc-rack-and-pinion-steering/#ixzz3ZqFY9aD2 Follow us: @HotRodMagazine on Twitter | HotRodMag on Facebook"

more good reading from the locost world:

http://www.super7thheaven.co.uk/glossary/bump-steer/

NOHOME,

I checked again and when I move the suspension through its travel, the steering rack's main shaft doesn't move, so I think I am good for bump steer.

And now for this week's update:

Didn't get too much done, but I got the drivers seat and steering column in place:

I also did about 75% of the welding on the chassis. I will take the engine out, flip the frame, and finish welding next week.

I also got some stuff on order that should be here by the end of next week:

-Fuel pump, regulator, filter -Brake Pedal -Splitting Brake -Gauge

I wont have too much time to work on the car this weekend, but Ill get at least a little bit done.

Bump steer doesn't rotate the main shaft. When you cycle the suspension on a single corner, watch that one wheel for turning.

Keep the updates coming.

Dusterbd13,

Thanks for the info. I didn't get a chance to look at it this weekend, but I'll look at it when I put the suspension back on.

And now for this weekends update:

I got a fair amount done this weekend. Got the steering linkage welded and made a C channel for the between the seats. This channel will hold the wiring harness, brake lines, and power-steering lines.

I will mount the shifter to the top of the C channel.

I will mount a cutting brake to the front passenger seat channel. I'll plumb this into the rear brakes.

I also pulled the frame off the engine and weighed the frame and engine sub-frame individually. The frame weighed in at 350lbs and the engine sub-frame weighed in at 1200lbs. I was surprised how much the sub frame weighed(with all fluids except for radiator & water).

I finished welding 100% of the frame, adding a few more support braces.

I also started on the floor pans. Most of the body panels will be aluminum, but I wanted to make the bottom stronger just in cast I run over something that it doesn't go through the floor.

I will add another steel floor pan in front of the other two also. I had intended to do it today, but there was a tornado warning near where I was working on the car and I didn't want to risk being flooded in...

I was planning to wait to paint the car, but after looking at everything I still need to do, everything from here on out will either mount to a tab I have already welded on, or will be threaded/bolted to the tubing. So I will paint the frame next time I get a chance to work on it.

And now for this weeks update:

I ordered a bunch of parts that all came in this week so I'll have more stuff to work on next.

I got the remaining piece of the floorboard welded in. I also got the mount for the brake and gas pedal in.

Then, I got the frame cleaned, degreased, & painted(my wife was kind enough to help as it is my birthday in 2 weeks). I used Rustoleum High Performance Enamel in Smoke Grey. It should be more than durable for this frame. I brushed it on and it actually worked pretty well. The first coat was full of streaks, but we applied the second coat very thick and it looks pretty good.

Ill start working on the wiring harness next time I am up there.

It looks like your moving right along. It will not be too long before it's rolling.

Keep posting pics I enjoy watching your progress.

Bear with me because I am not a structural engineer, but I feel that you are missing a bar at the rear of the car.

Without something to stop it, the node looks like it will be a pivot point for the rear of the frame.

NOHOME,

I am not quite sure what you mean by "looks like it will be a pivot point". I don't believe I would need need bars as you've drawn, but maybe some more elaboration may help me to understand. Ill try to explain my thinking until you can elaborate:

Right now, the rear C channel that the strut towers mount to is supported with a triangle, as is the roll bar. If you are referring to a potential pivot point of where the motor mounts are(where the strut tower support and roll bar brace meet), that would not be one since the engine subframe is bolted front and rear. any loading taken at that point would be transferred down to the bottom rear of the passenger compartment.

No easy answer without getting into vectors. And vector math always made my head hurt even 35 years ago when I had to learn the stuff.

The way I was taught to do this empirically was to think of each node as if it were a pivot point with no resistance that was free to move in any direction. Our challenge as structural designers is to anticipate where it would move and brace it in that direction. And since we live in a three dimensional world, we must always consider and apportion that bracing in three directions (X,Y and Z planes)

So what would happen if you replaced the node with a universal hinge in your design?

I'd have to agree with NOHOME. build it out of toothpicks/popsicle sticks/whatever and see what it feels like.

NOHOME,

I understand what you are referring to, but even if that node is treated as a hinge, it can't go anywhere without bending the engine subframe as it is rigidly connected at the two points below making those nodes fixed. I know what you mean about vector math not being fun, I didn't like that at all...

I don't think it will be necessary, but I'll think on it some more, discuss it with the structural analyst at work(subsea oil equipment manufacturer).

And now for this weekend's update:

Didn't get to work on the car too much because I had an allergic reaction to the degreaser from last weekend and it is finally starting to go away today...

The paint turned out pretty well, I will touch up a few spots later, but overall I am happy with how it turned out. It is still wet in a few places though...

Got the engine put back on pretty quick this time.

Then I started on the wiring... Everything is in the wrong place, so I tried to connect to the engine harness and go from there.

I starter soldering in ~2 feet of extensions to a connector on the steering column(12 wires down, 25 to go) then Ill lengthen the transmission control wires. Once those are completed, ill see what else is in the wrong place.

I am not doing anything with the headlights or tail lights until everything else is done...

okay, time for this weekend's update:

Finished soldering all the wires that needed to be extended and connected all the plugs and grounds.

The good: Engine spins over with the key

The bad: Electrical gremlins...

When I connected the battery the turn signals all started flashing. after messing with the hazard switch they went from flashing to always on. When you put the right turn signal on, the left bulb turns off and vice versa...

I am thinking it is a grounding issue or electricity back feeding through the turn signal circuit. Next time i am up there ill double check all the 50+ wires I had to extend for continuity and just double check I didn't cross anything...

Have a few questions I could use some help on:

• For the lights & signals, should I continue using the Riviera's or rewire it? If I use the existing wiring, I'll have to extend all the wires to make them fit and Ill have to use this switch on the dash: Here I am thinking the dash will look cleaner overall if I start from scratch.

• Thoughts on flex vs hard lines for brake and fuel systems?

Appreciate any feedback.

Update for the first half of this weekend:

ITS ALIVE!!!

https://drive.google.com/open?id=0B93HqBsSfCQnT3o3OGZ1Rl9KTDQ

Had to turn it off shortly after starting it because the rubber line taking the place of the tranny cooler popped off and spewed several quarts of ATF on the floor... Thats what I get for not using hose clamps for a quick start-up.

After starting it, I confirmed that the only control module I need to keep other than the ECU is the theft deterrent module. I spent last night stripping all the unneeded wires. Before:

After:

got the fuel system finished with a 15.5 gallon tank

After the fuel system got finished, hit the key and it started right up.

https://drive.google.com/open?id=0B93HqBsSfCQndk9WU3lkY2oxZVk

plan to mount the radiator tomorrow and if I get that finished, Ill start on the brakes.