Inliners International Forums General Discussion Engines Burned Manifold Gasket

My last manifold gasket burned out on a '68 292 L6 w/Clifford headers and Offy intake. Manifolds got loose after 600 miles of break in. I forgot to tighten the headers regularly and an air leak occurred, the Holley backfired -- the power valve got blasted and then I had to limp home. Tearing down the carb and manifolds today, I found the gasket was burned (charred) at the #4 + 5 exhaust ports, and the bottom of the gasket was blasted away.
I have a new Clifford header gasket but I am wondering if I should coat it with Permatex Copper Spray-A-Gasket or leave it dry like the guy at the speed shop said. Last time a different guy at the same speed shop told me to dab a small bead of Ultra Copper RTV around all the holes. That didn't work too well. I like the idea of reinforcing a basically cardboard (composition?) gasket with something metallic.
Also I tried to recycle the same 28-year-old header bolts. Having now re-inspected the threads, I will definately replace them with Grade 8 fasteners, at least.
What do you guys think?

Sounds like a good idea. I coat all my header & intake gaskets with the Copper RTV Never lost one as of Yet. and In Most cases I have been able to reuse them. Next Time do not wait 600 miles to check that intake & exhaust gasket Once motor has heated up and Cooled Always Recheck Bolts I do mine Twice. and In your case Recheck after The fisrt Tank Full. You shold be fine their after. Hope this helps }[oooooo]

Larry:
What do you recommend for header/intake fasteners?

I gave up on the paper type. Napa sell a alum. looking thick type,Thats all I use.I cant depend on the others.

46 -- I'll check in at NAPA for that. Thanks.

i would use studs and nuts instead of bolts. i have better luck with them staying tight.

I have Studs on all my heads With stock clamps/Hold downs. Hope this helps.}[oooooo]

I have gone "modified" from the stock set-up. While the stock intake and exhaust use pegs on the ends, I removed the pegs and use 1" 3/8-16 header bolts with 7/16 cap heads in position # 1 and #8. Positions #2, 3, 5, 6 & 7 use 1-3/8" L. 3/8-16 bolts, w/ 9/16 heads. [I bought new stainless steel bolts today. They're 1-1/2" long -- I'll have to shave them down with a grinder.] On position #4 I use a lock nut 3/8-24, (9/16 dia.) These fasteners are used with the factory "clamps" (except the long ones) to hold onto both pieces at the same time.
I'll look into the stud set up, since I have one on #4 already. Is it a 3/8-16 x 1-1/4" changing to 3/4" of 3/8-24?
46Wheezy: I asked at my local NAPA for the aluminum L6 gasket, but the kid couldn't find one on his computer. Do you have a part number?

I'll try to put it back up with what I've got now. But the studs look like an evolutionary trend.
Thanks everybody.

A good parts person is hard to find,make sure to send them A Christmas card. The NAPA gasket# you are looking for is MS16033X Good Luck Bob B

I'm with twisted6, I run a very thin line of high temp rtv around my gaskets 1/32" ~1/16" wide and it works great.

Thanks Bobby -- I'll run those numbers at NAPA and see if I can get one.
Well, I bolted it all back together after coating both sides of the Clifford gasket liberally with Permatex Spray-a-Gasket copper stuff. Intake and headers went on (grudgingly -- next time I'm going to studs!), then I bolted on the Holley 390. It started up and purred. RPM was low at 600, and manifold pressure was 14"Hg -- should be +17"Hg-- but that's all fine tuning.
I got it down the block and around the corner and the power valve went out (silently). Lucky my neighbor came along so he could steer the pickup when we later towed it behind the GMC.
Now I'm thinking about an Edelbrock 1404 AFB 500 CFM.

Bob, thanks for the #'s.. 68, the power valve issue? I have a 46 chevy truck/54'235, 4 sp sag. ford 9' rear. i'm having head work done as we speak and have an "offy" 4bbl intake. This 390 seems to be choice and this power valve stuff comes up alot. Is this a common problem? Thanks for your info.

46Wheezy: The newer Holleys have power valve blow out protection built in. Mine was new in 1978 -- ran 25 years on my last engine and got a quick rebuild for this next mill. We added a 50cc accelerator pump on it before the last engine went down in 2002, and that solved a lot of bog problems off the line. The older Holleys are more susceptible to backfire knocking out a $7.00 power valve. [Not to mention the gaskets, O-rings and spilled gas used up everytime you R&R a Holley]. There is a gizmo that involves a drill bit and a micro-sized
"power valve restrictor" but I don't want to mess with that. The carb had been set up with an 8.5" Hg power valve. I was out of replacement 8.5s, so we tried a 6.5" Hg power valve and reassembled the carb. Theory being that a later opening power valve would be a step toward better fuel economy. It started up OK, ran at a lower RPM and a few inches of mercury lower than optimum, but seemed ready otherwise, so I tried a test hop. As stated in my last post, it flunked. One symptom of the problem is that I'm getting 120 miles to the 20 gallon tank. 6 MPG is 454 territory, a 292 should get at least twice that even with a lead foot. One possibility for the manifold vacuum instability could be a warped carb base plate. (Factor the siamesed exhaust/intake configuration with Tucson summer heat x 25 years + 250,000 miles-- much of it off-road). For whatever reason operation has not yet stabilized. A new throttle base plate costs about $130. A whole new 4160/8007 Holley 390 CFM carb costs about $289. My friend who usually helps me tuning Holleys, is incommunicado. Well, that and the used car dealer he bought his '98 Dodge Dakota pickup from used some non-Mopar approved anti-freeze and it thrashed the entire heating & cooling system: heater core, radiator, thermostat, under dash leaks, etc. So whatever -- he's busy.
That leads me to consider carb alternatives:
The Barry Grant _Road Demon Jr._ at 525 CFM is a 'cute' billet 4160 clone, for only $260. But I hear they're sensitive to atmospheric changes and have to be tweaked continually. Maybe too much like a Holley.
Jegs' also lists a 450 CFM Holley 9766 4Bbl for only $188, but it's chokeless (and still a Holley).
I have run Carter AFBs on my V8s with good results. A 750 CFM on the 454 in my former ride, a '67 K/10 Suburban, and a 600 CFM on the 350 in my current daily driver, a '71 GMC K/5 Jimmy. I like the AFB design for its robust simplicity and field -servicable nature.
Unfortunately Edelbrock bought Carter out. Edelbrock chose not to continue making a 400 CFM AFB. Closest to it is the 500 CFM Performer EDL-1404 for about $225. Checker Auto did not have one in stock today, so I didn't get one yet. I may mail order. Depends on bottom line. They are supposed to be drivable right out of the box -- unlike any Holley I've ever had -- if a little rich at first. Also the Idle mixture screws would be sited on the left, facing the drivers side fender, a very handy place for tune ups. A carburetion site had a program to crunch numbers of RPM x CI and it spit out that my ideal flow rate would be 408 CFM. I'm hoping 500 will not be too much. A few other bored-out 292 4Bbl users have stated their satisfaction with the AFB, so I'm optomistic.
Sorry for the novel. HTH