Inliners International Forums General Discussion Engines 250 Intake Driving Me Nuts

I have had one heck of a time getting my intake on my '67 250 to keep a seal. I have had the manifolds milled (intake/exhaust together), used Felpro gaskets, and Permatex Copper Spray-A-Gasket. I torqued all of the bolts/nuts to the proper settings and retorqued after one thermal cycle. Everything runs fine, idles great, good smooth power; then after about 100 miles of driving, it begins to miss at idle and generally runs rougher as the RPM increases. I'm on my third go around with the same poor results. I really love the engine when it runs correctly, but I'm at the end of my rope. Any suggestions?

Thanks,

Dan

are the bolts just comming lose or what?? Sometimes it does take more then one retork to get things to seal. there have been times i have done mine 2-3 times before not having to go back.

I found changing to studs on some key boltholes helped. [Esp. the ones the intake hangs on.] Also replaced all my 25+ Y.O. hardware with new grade 8. I used a thick Clifford gasket and sprayed both sides with Permatex Copper-Spray-A-Gasket. After that dried I ran up a bead of Ultra Copper RTV on all the openings. I let it dry 24 hours before firing up. Good luck.

The middle bolts/nuts don't seem to come loose, but the two outers I do have to retighten a couple of times. Orange, what is the difference between the Fel-pro gasket and the Clifford gasket?

Dan

I always use KW 'Copper Coat' for exhaust, vs spray. THis stuff is thicker and may seal better, had same problems until I found this stuff.

There are, or used to be gaskets that had a soft gasket material that sealed both sides of the intake(no metal material).The exhaust part was still metal & composition material combo.
I would think they are still around???
Can't remember the brand name, but I always used the Felpro intake/exhaust gasket w/minimal problems

Is it possible there is a flaw on the cylinder head causing it to leak?????

Hank

Dan have you replaced the the 2 end pins with studs? They just unscrew with a vise grip. Replace them with studs long enough to allow you to add a lock washer and a nut. They are on the exhaust manifold ends and shouldn't be causing a vacuum leak but still a good thing to do. Are the bridges that span between the intake and exhaust flanges bearing down on both? It is possible for them to bear more on one flange than another either due to different flange thicknesses or deteriorated bridge pieces.

My engine machinist warned me that he had this same problem in the past with Chevy L6's. He said it was from the assembly being so long, that the thermal expansion and then contraction upon cooling just literally "scrubs" the gasket apart. His advice was to use silicone lubricant (not sealer) on the gasket. Actually, I didn't use his advice: for 3500 miles before the rebuild, I had assembled the intake (aluminum) and exhaust (tubular) to the engine using NO sealer. And for 2000 miles since the rebuild, NO leaks yet.

The Clifford gasket is thicker and wider than the stock gasket.
Clifford p/n: 62-0096.
I have found two types of gasket from Clifford under this same p/n.-- one is black and 1/16" thick, the other [preferred] is white and 1/8" thick. Both are a composition gasket. The Clifford header gasket is wider than a stock gasket [~2-1/2"] and runs this width thru the length of the gasket except for some cutouts for water temp sender, etc. The Stock gasket is designed for cast-iron manifolds and is trimmed flush to barely cover the inlets/outlets. headers need a wider gasket. The stock gasket is metal (mine was a Victor Reinz, but they're all the same). Nothing wrong with a metallic gasket, but you need the wider gasket for a header application.
Are you tightening your manifold bolts from the center (#4) out? I have found this sequence helps.

I have been useing the Mrgasket (155) for well Over 17yrs. Offey intake & headers, Clifford intake & headers, My Intake(3x4) Headers Then even with my own Headers. And Never had a issue.If i know I maybe taking things back apart and back together Soon I'll use the Copper RTV.
Everything is always PORT Matched to this gasket. I tighten things down from the center and work my way OUT which is the way it should be done ,EVEN with a STOCK set-up. And with any after market set-up(headers or Intake) studs are better to be used. And eventhing is retorked after 2-3 heat cycles.I have also Nkown guys to Not even use a gasket But only the copper RTV. and Not had issue. Personaly I think you need to take a Close look at you head (intake/exhaust side) to be sure that it is TRUE/FLAT.

Also I have lockwashers On each stud.