72 GMC - Engine hitting firewall...need advice - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ducmons · 12-24-2006, 02:50 PM

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 · 12-24-2006, 02:54 PM

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

el curioso · 12-24-2006, 05:27 PM

Quote:

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.

Sweet72 · 12-24-2006, 02:55 PM

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

brak · 12-24-2006, 03:49 PM

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 · 12-24-2006, 04:30 PM

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

desertrat · 12-24-2006, 04:48 PM

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 · 12-24-2006, 04:53 PM

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 · 12-24-2006, 05:02 PM

Quote:

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.

Longhorn Man · 12-24-2006, 05:46 PM

Quote:

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 · 12-25-2006, 03:11 AM

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.

desertrat · 12-26-2006, 12:31 AM

Quote:

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.

1969k10stepside · 12-24-2006, 05:11 PM

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 · 12-24-2006, 05:16 PM

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 · 12-24-2006, 05:22 PM

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.

1969k10stepside · 12-24-2006, 05:34 PM

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?

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**Palf70Step** · 12-25-2006, 08:53 AM

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 · 12-25-2006, 09:36 AM

massage the firewall would be the best

454_72_4X4 · 12-26-2006, 12:00 AM

Quote:

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...

)

69CvyPickup4x · 12-26-2006, 12:32 AM

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.

ducmons · 12-25-2006, 12:24 PM

Quote:

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** · 12-25-2006, 12:39 PM

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 · 12-25-2006, 01:12 PM

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

piecesparts · 12-25-2006, 01:31 PM

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 · 12-25-2006, 08:04 PM

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.

12-24-2006, 02:50 PM	#1
ducmons Registered User Join Date: Jul 2006 Location: Seattle Posts: 56	72 GMC - Engine hitting firewall...need advice 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.

12-24-2006, 02:54 PM	#2
1969k10stepside Registered User Join Date: Mar 2006 Location: USA Posts: 21,020	Re: 72 GMC - Engine hitting firewall...need advice 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 Last edited by 1969k10stepside; 12-24-2006 at 03:01 PM.

12-24-2006, 02:55 PM	#4
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	Re: 72 GMC - Engine hitting firewall...need advice Where is it contacting the firewall? Is it the "tall" valve covers? I'm sure the 4X4 boys can help you out here... __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction.

12-24-2006, 03:49 PM	#5
brak Registered User Join Date: Apr 2006 Location: MinneSNOWta Posts: 1,381	Re: 72 GMC - Engine hitting firewall...need advice 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. __________________ 2003 GMC Sierra 1500 WT 1995 Nissan Hardbody 2016 Hyundai Veloster Turbo DC2 (SW/AW) Clyde W. Harvey USN "Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery" Winston Churchill

12-24-2006, 04:30 PM	#6
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: 72 GMC - Engine hitting firewall...need advice it's a 4X4... it's supposed to be in the 6 cylinder location.

12-24-2006, 04:48 PM	#7
desertrat Registered User Join Date: Nov 2006 Location: Pahrump, NV Posts: 1,079	Re: 72 GMC - Engine hitting firewall...need advice 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.

12-24-2006, 04:53 PM	#8
red71cheyenne Back in the sticks Join Date: Jan 2001 Location: Fordland, MO Posts: 3,188	Re: 72 GMC - Engine hitting firewall...need advice 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. __________________ 1971 Cheyenne C-10 w/700R4 and Tuned Port Injection 1969 K5 Blazer w/Tuned Port 2010 2SS/RS Flaming Orange Camaro 2011 K1500 Suburban 2014 K1500 Pickup 2008 Nissan Altima? The wifes' hoopty

12-25-2006, 03:11 AM	#11
ducmons Registered User Join Date: Jul 2006 Location: Seattle Posts: 56	Re: 72 GMC - Engine hitting firewall...need advice 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. Last edited by ducmons; 12-25-2006 at 03:12 AM.

12-24-2006, 05:11 PM	#13
1969k10stepside Registered User Join Date: Mar 2006 Location: USA Posts: 21,020	Re: 72 GMC - Engine hitting firewall...need advice 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.

12-24-2006, 05:16 PM	#14
Ben IV Registered User Join Date: Dec 2006 Location: Glenpool OK Posts: 255	Re: 72 GMC - Engine hitting firewall...need advice 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.

12-24-2006, 05:22 PM	#15
red71cheyenne Back in the sticks Join Date: Jan 2001 Location: Fordland, MO Posts: 3,188	Re: 72 GMC - Engine hitting firewall...need advice 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. __________________ 1971 Cheyenne C-10 w/700R4 and Tuned Port Injection 1969 K5 Blazer w/Tuned Port 2010 2SS/RS Flaming Orange Camaro 2011 K1500 Suburban 2014 K1500 Pickup 2008 Nissan Altima? The wifes' hoopty

12-24-2006, 05:34 PM	#16
1969k10stepside Registered User Join Date: Mar 2006 Location: USA Posts: 21,020	Re: 72 GMC - Engine hitting firewall...need advice 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?

12-25-2006, 08:53 AM	#17
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 47,083	Re: 72 GMC - Engine hitting firewall...need advice 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. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

12-25-2006, 09:36 AM	#18
bowtiehotrodder SIX BANGER Join Date: Sep 2005 Location: NC Posts: 169	Re: 72 GMC - Engine hitting firewall...need advice massage the firewall would be the best __________________ http://www.cardomain.com/ride/2597018(NN) 1979 chevy truck swb 454 w turbo400 with buckets 1977 chevy truck swb soon to be 454 1976 chevy dually 454 1969 chevy truck six shooter

12-26-2006, 12:32 AM	#20
69CvyPickup4x Registered User Join Date: Apr 2006 Location: Bellflower Posts: 79	Re: 72 GMC - Engine hitting firewall...need advice 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.



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12-25-2006, 12:39 PM	#22
Yukon Jack Post Whore Join Date: Feb 2000 Location: Rose Hill, KS, USA Posts: 12,684	Re: 72 GMC - Engine hitting firewall...need advice 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. __________________ 1970 Blazer with a 400 sbc and 4" lift 1980 Pontiac Trans Am, 455 Oldsmobile 2012 Kawasaki Concours 14

12-25-2006, 01:12 PM	#23
Green Machine Senior Member Join Date: Jul 2004 Location: Estherville, Iowa Posts: 3,371	Re: 72 GMC - Engine hitting firewall...need advice New cab mounts may help, if they are sagging, you can gain some space that way. __________________ 1968 C10 307 3spd Long Fleet ------ http://67-72chevytrucks.com/vboard/s...d.php?t=201103 1970 C10 305 Super T10 Long Fleet --- http://67-72chevytrucks.com/vboard/s...d.php?t=202285 1971 C20 383 TH350 Dana Posi ----- http://67-72chevytrucks.com/vboard/s...d.php?t=206894 2001 GMC Sierra 1500 C3 6.0

12-25-2006, 01:31 PM	#24
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: 72 GMC - Engine hitting firewall...need advice 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.

12-25-2006, 08:04 PM	#25
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: 72 GMC - Engine hitting firewall...need advice 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.

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