72 GMC - Engine hitting firewall...need advice

[ducmons]

So I took the 350 out and I'm installing a 383 stroker. (We're talking about a 72 GMC 3/4T 4x4.) We finally got the engine built and installed, but it's barely touching the firewall. What should I do? It's the first time I've done this, and I'm not sure what the best option is. Should I move the firewall back? notch it out? move the engine forward and the tranny too? .... advice and pics of what to do would be very much appreciated. Hope you guys have a great x-mas.

[1969k10stepside]

All 4x4's motors were close to hitting the firewall stock.Thats why big blocks in 4x4s have clearance problems.You could
(A) move engine crossmember/tranny/t case forward but that would mean you would have to get new driveshafts made
(B) add a body lift
(C) make some changes to the firewall to allow room.
(D) If its the valve covers get different ones

Hope this helps.Someone else might think of something to add that I forgot.Nice motor btw

Merry Christmas

Dustin

[Sweet72]

Where is it contacting the firewall? Is it the "tall" valve covers? I'm sure the 4X4 boys can help you out here...

[brak]

it looks to me, like the motor is mounted in the 6 cyl location.

I base this assumption on the location of the fuel pump versus the section of the frame that is bent up.

this is exactly how my motor looks, and it is mounted in the 6cyl location.

[Longhorn Man]

it's a 4X4... it's supposed to be in the 6 cylinder location.

[desertrat]

It looks like you are doing a super clean build and I think pulling the motor/tranny forward would be the cleanest move and best in the long run.

[red71cheyenne]

Why does it being a 4X4 mean its in the 6cyl location? Just trying to learn here, not disputing...Were all of them mounted that way? I know my engine in the Blazer is close, but its the dizzy thats super close, not the valve covers.

[desertrat]

Originally Posted by red71cheyenne

Why does it being a 4X4 mean its in the 6cyl location? Just trying to learn here, not disputing...Were all of them mounted that way? I know my engine in the Blazer is close, but its the dizzy thats super close, not the valve covers.

count me in as someone that wants to know which way and why chevy mounted the differant motors.

I had a 2 wheel drive small block mounted close to the firewall and a co-worker had the same truck but big block mounted closer to the radiator. So I always thought the big block made the differance in mounting but I'm sure I will be corrected.

[1969k10stepside]

On my 69 4x4 the distributor cap was almost hitting the firewall on the 350.The 71 C/10 I had with a 350 had no clearance issues.

[Ben IV]

I was going to say the same thing about the 6-cyl location< dident know all the 4wd truck were like that. My msd distributor barely clears after a little hammer work on the top of the fire wall. I want to move the whole thing forward so I can run tall valve covers when I do some more engine work.

[red71cheyenne]

Mine are the same 1969k10stepside. My 71 has no clearance issues with the motor in the original location, just had to move the crossmember for the 700R4. The Blazer I thought I put the motor in the same spot, but the original engine was disassembled when I bought it too. Also changed out the tranny on it as well. I didn't have to hammer the firewall, but the dizzy is touching. At least on of the plug wires is anyway.

[el curioso]

Originally Posted by 1969k10stepside

(B) add a body lift


Dustin

Just like 1969K10stepside said body lift you now have an official excuse to up grade.

[1969k10stepside]

Pic time..
The pics are off my 71 K10 swb.It had a 292/sm465/np205 in it.I took pics of the holes the motor crossmember bolts too.There is several different holes.BTW,like the paint job?

[Longhorn Man]

Originally Posted by desertrat

I had a 2 wheel drive small block mounted close to the firewall and a co-worker had the same truck but big block mounted closer to the radiator. So I always thought the big block made the differance in mounting ...

all the 4X4 trucks had the engine, regardless of WHAT engine, mounted in the same location as the one in the first photo.
2 wheel drives had the inline mounted back there, but the small blocks and big blocks were pushed considerably forward.
desertrat, your old 2 wheel drive you mention was assembled wrong. There should be something like 6 inches to the firewall from the back of the intake to the firewall on a 2 wheel drive.

[ducmons]

thanks for all the suggestions and advice. I have another quetion for you. If we were to move the T-sec & tran forward say 3-4", how much would that affect the drive line in terms of balance when under extreme pressure such as towing a heavy trailer, or say getting unstuck (which is unlikely since I have another rig for playing in the mud)?

Also, what all is involved in moving everything forward? That does sound much easier than messing with the firewall, which I'd hate to do anyways.

[Palf70Step]

I would massage the firewal, rather than move the engine forward. You may not be able to move the engine forward because of the front driveline. I belive that is why all the 4x4s were mounted in the rear position was to allow clearance fro the front drive train.

[bowtiehotrodder]

massage the firewall would be the best

[ducmons]

Originally Posted by Palf70Step

I would massage the firewal, rather than move the engine forward. You may not be able to move the engine forward because of the front driveline. I belive that is why all the 4x4s were mounted in the rear position was to allow clearance fro the front drive train.

Good point. I had forgotten about the front driveline. So what is the best approach for "massaging" the firewall. I need advice as I've never done metal work on body's. Should i just notch out where it's hitting, or move the entire engine area curved portion of the firewall back?

[Yukon Jack]

I'm a little confused on where you engine is touching the firewall. Your prior 350 and the 383 are the same physical side so that is what has me confused. I'm assuming it is touching at the valve covers as that is all that could really be different. Did you change to a different style motor mount?

Lots of people move the engine forward a bit when swapping to a bbc so you can go that route. You will increase the front driveshaft angle a bit and it might have to be shortened. You will also maybe need to have your rear driveshaft lengthened.

Give specific info on where the contact is.

[Green Machine]

New cab mounts may help, if they are sagging, you can gain some space that way.

[piecesparts]

Take the motor out (after you have marked the rubbing spots) and then rework the fire wall. There are ways to do it right and then there are ways that will just crap it up, so be careful of what you do and how you do it. Repainting the firewall is easier than rebuilding the qwwhole drive train. Make it as smooth as your engine and it will look great.

[Longhorn Man]

sagging cab mounts could hinder the issue
tall valve covers could be the curlprit
you could try loosening all the mounts, the motor mount to towers, towers to frame, tranny mounts... and slide the whole engine forward about a 1/2 an inch...maybe just a quarter inch. There's that much slop in everything.
IIRC, the clam style later motor mounts jackl it up a hair
maybe you could shim the tranny mounts and tilt it forward (or level it out a tad more acuratly)
A combo of all this would probably do the truck.
As for firewall mods, i would mark the offending area, jerk the engine out, cut that outlined area out, flip it around so it is inside out, and weld it in place. The shoe box guys call this bubleing the firewall, I plan on doing this in the one problem spot on my caddy swap.

[454_72_4X4]

Originally Posted by bowtiehotrodder

massage the firewall would be the best

I'm in agreement with bowtie.

I did mine with a ball peen hammer and another hammer to tap the ball peen with. (Sometimes it takes more than a tap... )

[desertrat]

Originally Posted by Longhorn Man

desertrat, your old 2 wheel drive you mention was assembled wrong. There should be something like 6 inches to the firewall from the back of the intake to the firewall on a 2 wheel drive.

It's possible the previous owner moved the motor back on my old 2x. I know the motor was not original.

[69CvyPickup4x]

When i installed my new big block, the valve covers were lightly touching the firewall. I just used a ball peen hammer and started lightly tapping the area and just worked it in a little bit into a circle, it came out great. No heat, just tap it and work it until its smooth. I got mine back a good 1/2". Ill see if i cant get pics if i remember. If its lightly touching, i dont think its necessary to move the motor and trans forward. But thats up to you.