Header Gasket

Russell

Russell

Active member
Jan 2, 2017
357
88
28
Dunedin, Florida
On a recent trip, our GMC ('78 403) developed an exhaust noise. On Saturday I found the exhaust leak at the number 8 cylinder where it looks like a
small piece of the header gasket broke and blew out. I ordered the Mr. Gasket 7170 copper gasket to put in. I have older Thorley headers (date
unknown). My questions are: 1) Do I need to remove the AC bracket to removed the passenger side header? 2) Which RTV gasket sealer should I use, if
any? 3) Should I replace the donut gasket at the same time? 4) Can I replace the gasket with just top and bottom access (jacked up), or do I need to
remove the fender well liner?

Any tips or tricks are greatly appreciated. Thanks.
--
Russell Keith,
1978 Eleganza II "Harry" 403, Danny Dunn Tranny (w/shift kit, 3.50 sprockets, Allison), Thorley, Stock Brakes w/Remote Vacuum Brake Booster, Mico
Electric Actuated brake lock, Dakota Digital Dash, 6.5kW Onan,
Dunedin, Florida
 
>
> On a recent trip, our GMC ('78 403) developed an exhaust noise. On Saturday I found the exhaust leak at the number 8 cylinder where it looks like a
> small piece of the header gasket broke and blew out. I ordered the Mr. Gasket 7170 copper gasket to put in. I have older Thorley headers (date
> unknown). My questions are: 1) Do I need to remove the AC bracket to removed the passenger side header?

1. No it is not necessary to remove the A/C bracket.
> 2) Which RTV gasket sealer should I use, if
> any?

I used a thin coating of Permatex Ultra Copper on both sides of the copper gasket.

> 3) Should I replace the donut gasket at the same time?

Only if it’s leaking.

> 4) Can I replace the gasket with just top and bottom access (jacked up), or do I need to
> remove the fender well liner?
>
No need to jack it up or take out the liner. You can do it all from the top. Only remove the bolts which go through holes in the copper gasket. Where there are slots loosen the bolts but leave the header attacked but hang ing loose. Slip the gasket down behind the header, hanging it on the bolts, and replace the removed bolts and tighten all bolts.
> Any tips or tricks are greatly appreciated. Thanks.

Note— after a few years the copper gaskets burned out and I replaced them with the composite Remflex gaskets the Applied GMC sells. They have lasted fine for the last 10,000 miles.

Emery Stora
> --
> Russell Keith,
> 1978 Eleganza II "Harry" 403, Danny Dunn Tranny (w/shift kit, 3.50 sprockets, Allison), Thorley, Stock Brakes w/Remote Vacuum Brake Booster, Mico
> Electric Actuated brake lock, Dakota Digital Dash, 6.5kW Onan,
> Dunedin, Florida
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Having just done this (twice), here's my advice:

1. Remove the wheel well liners and wheel on each side. This will give you lots of room to work from the side.

2. Tighten the header bolts slightly before trying to back them out.

3. Use the Remflex gaskets and torque the 4 main bolts in stages to 20 ft/lbs without touching the hanger bolt.

4. Don't torque the hanger bolt, just snug it once it's done.

5. I would replace the donuts, but that's just me.

6. Be careful with the tranny dipstick tube. If it pops out, you'll have a mess.

7. Keep the 3/8" wrench in the glovebox. Re-torque every heat cycle for at least 500 miles.

Hope that helps :)

Shaun
--
1977 Palm Beach, 455, mostly stock and original
 
You would pick the A/C compressor side. Don't know if the copper gaskets
are the best choice here, but they are not the worst either. If you already
have them, use them. Dry. No silicone. But, my suggestion would be to also
remove the donut and replace it. If I were doing yours, I would take the
header completely off and inspect all the pipes and flanges for erosion and
cracks, as well as flatness. The A/C mounting bracket is a wrestling match
on the 403, and the 3 studs on the manifold can be problematic if they have
been in place for several years like you mention. Use your favorite brew of
penetrating oil, for several days if you have the time. It will avoid
fighting broken studs out. You really, really, really don't want to have to
do that. One thing that helps here is a low powered pneumatic impact
wrench. The rattling of the wrench turns the rust into powder and
facilitates removal. Resist the urge to CRANK UP THE POWER. You will regret
it if you break off studs getting them out. Yes, it is easier to have the
wheel and tire and inner fender out of the way, especially on the 403
around the oil filter base. Inspect the head where the gasket blew out and
make sure the exhaust gasses have not damaged the head. If they have, then
ideally the head should come off and be resurfaced. If you want to take the
cheap way out here, you could try JB weld. Others swear BY it, I just swear
AT it. Experiences differ greatly, but if you find the surfaces quite
irregular, REMFLEX gaskets work really well for me.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On a recent trip, our GMC ('78 403) developed an exhaust noise. On Saturday
I found the exhaust leak at the number 8 cylinder where it looks like a
small piece of the header gasket broke and blew out. I ordered the Mr.
Gasket 7170 copper gasket to put in. I have older Thorley headers (date
unknown). My questions are: 1) Do I need to remove the AC bracket to
removed the passenger side header? 2) Which RTV gasket sealer should I
use, if
any? 3) Should I replace the donut gasket at the same time? 4) Can I
replace the gasket with just top and bottom access (jacked up), or do I
need to
remove the fender well liner?

Any tips or tricks are greatly appreciated. Thanks.
--
Russell Keith,
1978 Eleganza II "Harry" 403, Danny Dunn Tranny (w/shift kit, 3.50
sprockets, Allison), Thorley, Stock Brakes w/Remote Vacuum Brake Booster,
Mico
Electric Actuated brake lock, Dakota Digital Dash, 6.5kW Onan,
Dunedin, Florida

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Emery, did you use any type of gasket sealer on the Remflex?
--
Bryan Hayes
'76 Eleganza II
Salt Lake City, Utah
 
Thank you Emery and Shaun for the answers and tips.
--
Russell Keith,
1978 Eleganza II "Harry" 403, Danny Dunn Tranny (w/shift kit, 3.50 sprockets, Allison), Thorley, Stock Brakes w/Remote Vacuum Brake Booster, Mico
Electric Actuated brake lock, Dakota Digital Dash, 6.5kW Onan,
Dunedin, Florida
 
Thank you Jim
--
Russell Keith,
1978 Eleganza II "Harry" 403, Danny Dunn Tranny (w/shift kit, 3.50 sprockets, Allison), Thorley, Stock Brakes w/Remote Vacuum Brake Booster, Mico
Electric Actuated brake lock, Dakota Digital Dash, 6.5kW Onan,
Dunedin, Florida
 
Jim K has the best price over all for the Remflex, even with shipping they are less than I could buy them locally.

DO NOT use any silicone or exhaust paste as you can cause them to fail, put them on dry. The package says 14 FT/# of torque. As said tighten only the main bolts and the center just barley snug. Important that you check that all the old gasket material has been removed.

J.R. Wright
GMC GreatLakerTech Editor
78 Buskirk 30' Stretch
75 Avion Under Reconstruction
Michigan

>
> +1 for Reflex.
> No leaks so far
> --
> Justin Brady
> http://www.thegmcrv.com/
> 1976 Palm Beach 455
 
Thank you Justin and J.R.
--
Russell Keith,
1978 Eleganza II "Harry" 403, Danny Dunn Tranny (w/shift kit, 3.50 sprockets, Allison), Thorley, Stock Brakes w/Remote Vacuum Brake Booster, Mico
Electric Actuated brake lock, Dakota Digital Dash, 6.5kW Onan,
Dunedin, Florida
 
Copper gaskets are good, however a header is partially hand crafted so the
ports do not always match up to the gaskets and will end up leaking.
There is also a way to tighten the headers to avoid leaking.

On Mon, Feb 19, 2018 at 12:50 PM, Russell Keith
wrote:

> Thank you Justin and J.R.
> --
> Russell Keith,
> 1978 Eleganza II "Harry" 403, Danny Dunn Tranny (w/shift kit, 3.50
> sprockets, Allison), Thorley, Stock Brakes w/Remote Vacuum Brake Booster,
> Mico
> Electric Actuated brake lock, Dakota Digital Dash, 6.5kW Onan,
> Dunedin, Florida
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
One thing that I ran into is not having the surfaces completely clean when installing the new gaskets. When I replaced my header gaskets the first
time, I had some old gasket material stuck on one of the the header surfaces that eventually caused another leak. The second time around, I was in a
hurry to replace the gaskets before hitting the road, and didn't completely clean the surfaces again. This, of course, led to even more leaks.
Hopefully I learned my lesson the third time around. :)
--
Bryan Hayes
'76 Eleganza II
Salt Lake City, Utah
 
Bryon,
Never tighten the CENTER TOP bolt.
Just tighten the 4 inline ones and after 200 miles retorque it.

> One thing that I ran into is not having the surfaces completely clean when
> installing the new gaskets. When I replaced my header gaskets the first
> time, I had some old gasket material stuck on one of the the header
> surfaces that eventually caused another leak. The second time around, I was
> in a
> hurry to replace the gaskets before hitting the road, and didn't
> completely clean the surfaces again. This, of course, led to even more
> leaks.
> Hopefully I learned my lesson the third time around. :)
> --
> Bryan Hayes
> '76 Eleganza II
> Salt Lake City, Utah
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
These headers are crap IMHO, too big primaries and that stupid 'o-ring' flange. Good headers have thick flat flanges.
But there is no other choice except build your own. I aint got time for that.
________________________________
From: Gmclist on behalf of Jim Kanomata
Sent: Monday, February 19, 2018 7:13 PM
To: gmclist
Subject: Re: [GMCnet] Header Gasket

Bryon,
Never tighten the CENTER TOP bolt.
Just tighten the 4 inline ones and after 200 miles retorque it.

> One thing that I ran into is not having the surfaces completely clean when
> installing the new gaskets. When I replaced my header gaskets the first
> time, I had some old gasket material stuck on one of the the header
> surfaces that eventually caused another leak. The second time around, I was
> in a
> hurry to replace the gaskets before hitting the road, and didn't
> completely clean the surfaces again. This, of course, led to even more
> leaks.
> Hopefully I learned my lesson the third time around. :)
> --
> Bryan Hayes
> '76 Eleganza II
> Salt Lake City, Utah
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
You must log in or register to reply here.
Get your shine on at www.cruzingear.co
GMCMI Spring 2026 Rally

Share this page

Share this page
Top Bottom
Back