big-block exhaust manifold gaskets

rustyold66 · September 25th, 2008, 09:14 PM

Got the Thornton LH manifold for my '66 88. They (Thornton) said I don't need a gasket. HUH???

Is this really so??? I could swear there is a gasket on the current manifold.

Danny Wiseley · September 25th, 2008, 09:27 PM

Factory didn't use 'em.

rustyold66 · September 26th, 2008, 12:05 AM

Wow...and this seals OK? I find that hard to believe. But you guys are experts. Was this common among other manufacturers?

Danny Wiseley · September 26th, 2008, 04:07 AM

Yes, it seals fine if both surfaces are straight and clean. Olds generally maintained closer tolerances on machined surfaces, I've been told, than some other mfrs, but Olds wasn't the only one without exhaust manifold gaskets. One thing that is very important, but overlooked by many, is not to overtighten the bolts. Oldsmobile put the aggravating locking tabs on the exhaust manifold bolts for a reason. The torque spec is only 25 ft/lbs and the tabs are necessary to keep the bolts from backing out. But, that accommodates the different rates of expansion/contraction between the hot manifold and the cooler cylinder head.
If your manifolds are warped slightly, gaskets are available if you don't want to have them machined to fit properly.

Olds64 · September 26th, 2008, 05:29 AM

I suggest using gaskets. I just installed my manifold gaskets and I used gaskets because eventhough I cleaned the mating surfaces with a razor and sandpaper they weren't true enough to seal without gaskets. Once the manifolds and heads get 30+ years old they need machining to be true enough to seal without a gasket.

rustyold66 · September 27th, 2008, 08:09 PM

What kind/brand of gaskets? Copper? Cork? Paper? Wrigley's? Just kidding. Is there a different torque setting when using gaskets or is it still 25 ft/lbs? Thanks for your help as always!!!!!

hamm36 · September 27th, 2008, 08:25 PM

Fel-pro MS 90021, manifold set # 47089 that is if you need the big ones. Don't get stuck with the wrong ones. There are two sizes: small and large. 25ft lbs is what I used, or 300in lbs.

Joe, I went to a place that only sales gaskets. American Gasket here in Dallas, 10 yrs ago when I knew I had an exhaust leak that I only got to recently and last week. Both times they gave me the small ones when I asked for the 455. Even before I went this last time I called to make sure they were open. And I told them the big ones. I took one of my old manifolds and they gave me the small ones, they said, "You were right. You need the bigger ones." Both sizes come in the 455 rebuild kits. I was just trying to save him a trip.

joe_padavano · September 28th, 2008, 08:13 AM

Quote:

Originally Posted by hamm36

Fel-pro MS 90021, manifold set # 47089 that is if you need the big ones. Don't get stuck with the wrong ones. There are two sizes: small and large. 25ft lbs is what I used, or 300in lbs.

Actually, the "small" gaskets are for 307s with 7A heads. Every other Olds motor uses the "large" gaskets.

Olds64 · September 28th, 2008, 08:45 AM

I used 25 ft. lbs. as well. I also coated the bolts with anti-sieze before I installed them. I will recheck the torque in a week or so.

September 25th, 2008, 09:14 PM	#1 (permalink)
rustyold66 Registered User Join Date: Aug 2008 Location: Minneapolis, MN Posts: 72	big-block exhaust manifold gaskets Got the Thornton LH manifold for my '66 88. They (Thornton) said I don't need a gasket. HUH??? Is this really so??? I could swear there is a gasket on the current manifold. __________________ 1966 Delta 88 425 HC 2bbl working clock "rust IS a metal"

September 26th, 2008, 12:05 AM	#3 (permalink)
rustyold66 Registered User Join Date: Aug 2008 Location: Minneapolis, MN Posts: 72	Wow...and this seals OK? I find that hard to believe. But you guys are experts. Was this common among other manufacturers? __________________ 1966 Delta 88 425 HC 2bbl working clock "rust IS a metal"

September 26th, 2008, 05:29 AM	#5 (permalink)
Olds64 Landyacht Club President Join Date: Jul 2007 Location: Lawton, OK Posts: 4,286	I suggest using gaskets. I just installed my manifold gaskets and I used gaskets because eventhough I cleaned the mating surfaces with a razor and sandpaper they weren't true enough to seal without gaskets. Once the manifolds and heads get 30+ years old they need machining to be true enough to seal without a gasket. __________________ Ferris, my father loves this car more than life itself... Apparently, you don't understand! Ferris, he never drives it! He just rubs it with a diaper! Cameron Frye Ferris Bueller's Day Off 1986

September 27th, 2008, 08:09 PM	#6 (permalink)
rustyold66 Registered User Join Date: Aug 2008 Location: Minneapolis, MN Posts: 72	What kind/brand of gaskets? Copper? Cork? Paper? Wrigley's? Just kidding. Is there a different torque setting when using gaskets or is it still 25 ft/lbs? Thanks for your help as always!!!!! __________________ 1966 Delta 88 425 HC 2bbl working clock "rust IS a metal"

September 27th, 2008, 08:25 PM	#7 (permalink)
hamm36 Registered User Join Date: May 2008 Location: Dallas Posts: 338	Fel-pro MS 90021, manifold set # 47089 that is if you need the big ones. Don't get stuck with the wrong ones. There are two sizes: small and large. 25ft lbs is what I used, or 300in lbs. Joe, I went to a place that only sales gaskets. American Gasket here in Dallas, 10 yrs ago when I knew I had an exhaust leak that I only got to recently and last week. Both times they gave me the small ones when I asked for the 455. Even before I went this last time I called to make sure they were open. And I told them the big ones. I took one of my old manifolds and they gave me the small ones, they said, "You were right. You need the bigger ones." Both sizes come in the 455 rebuild kits. I was just trying to save him a trip. Last edited by hamm36; September 28th, 2008 at 09:32 PM.. Reason: respond to Joe.

September 25th, 2008, 09:27 PM	#2 (permalink)
Danny Wiseley Registered User Join Date: Mar 2007 Location: West of Lubbock, TX Posts: 160	Factory didn't use 'em.

September 26th, 2008, 04:07 AM	#4 (permalink)
Danny Wiseley Registered User Join Date: Mar 2007 Location: West of Lubbock, TX Posts: 160	Yes, it seals fine if both surfaces are straight and clean. Olds generally maintained closer tolerances on machined surfaces, I've been told, than some other mfrs, but Olds wasn't the only one without exhaust manifold gaskets. One thing that is very important, but overlooked by many, is not to overtighten the bolts. Oldsmobile put the aggravating locking tabs on the exhaust manifold bolts for a reason. The torque spec is only 25 ft/lbs and the tabs are necessary to keep the bolts from backing out. But, that accommodates the different rates of expansion/contraction between the hot manifold and the cooler cylinder head. If your manifolds are warped slightly, gaskets are available if you don't want to have them machined to fit properly.

September 28th, 2008, 08:45 AM	#9 (permalink)
Olds64 Landyacht Club President Join Date: Jul 2007 Location: Lawton, OK Posts: 4,286	I used 25 ft. lbs. as well. I also coated the bolts with anti-sieze before I installed them. I will recheck the torque in a week or so. __________________ Ferris, my father loves this car more than life itself... Apparently, you don't understand! Ferris, he never drives it! He just rubs it with a diaper! Cameron Frye Ferris Bueller's Day Off 1986

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