Intake Manifold WTH
Thread Starter
Instructor
Joined: Aug 2010
Posts: 101
Likes: 1
From: Moriches NY
Intake Manifold WTH
So i have taken the intake manifold on my 1991 L98. And started cleaning off the head so i can install new gaskets, Noticed that where the 4 corner bolts go there is some type of metal ring/gasket pressed into the top of the threads. I popped them out because it was a pita to clean the area.
My question is do i need to put them back? (They look like crap). What are they called? And if i need to replace they where can i order?
My question is do i need to put them back? (They look like crap). What are they called? And if i need to replace they where can i order?
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Those are probably thread replacements, (Heli-coils) which are a common sight in aluminum heads. Leave them alone. Pics would settle what they are, I'm just guessing.
I re-read your post, if you popped them out then they can't be Heli-coils, post a pic
I re-read your post, if you popped them out then they can't be Heli-coils, post a pic
Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
GM counterbored your heads for intake gaskets that have retainers (at the front and rear) that maintains alignment and stops the persistent intake leaks that plague the earlier years. Per GM's bulletin, these leaks set up galvanic corrosion which was then eating up the head gaskets. You need special gaskets which for your Vette (Only the '91 got this, though current production has this feature), can be hard to find. Carb and the F-Body intake gaskets are a little easier to come by, but they don't have the coolant restrictors at the rear. A competent Dealer should be able to look them up or poke around www.acdelco.com or call the guys at Street & Performance - www.hotrodlane.cc - be sure to tell them it's for a Vette or they will send you the F-Body/carb intake gaskets. If the old intake gaskets left the retainers in the Head, you obviously need to remove them first.
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
Gee - I don't know - about 50% of the aluminum headed Vettes around here seem to have had blown head gaskets (it's how I found this Site 10 years ago) and considering the litigation that took place because Dealers were denying warranty claims for blown head gaskets, maybe that's why GM came up with this solution. I'm not so sure it's the right one, but at least the intakes seemed to have stopped leaking (of leak less). GM finally gave up and stopped running coolant through the intakes on everything they make; but I'd take advantage of it if you can find them; sure makes stabbing the intake a lot easier as the gaskets aren't going to slip into the valley. Whether or not #7 starts to suck coolant on this Vette isn't known, but a lot of head gaskets were leaking well before the warranty ran which makes a low mileage example of a late L98 a risky bet; particularly if the intake gasket has been leaking. Oh - the longer intake bolts go where the retainers are and they're needed to provide sufficient clamping given the retainers, so you might want to make note of them.
Thread Starter
Instructor
Joined: Aug 2010
Posts: 101
Likes: 1
From: Moriches NY
The longer intake bolts are another story. I stripped the torx head on one of the longer one's during the removal process. I have found many replacement sets but all the bolts look to be the same size. If any one knows where to get the retainers (haven't had much luck) or the longer bolts, Please chime in
Race Director
Joined: Nov 2003
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
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Gee - I don't know - about 50% of the aluminum headed Vettes around here seem to have had blown head gaskets...GM finally gave up and stopped running coolant through the intakes on everything they make; but I'd take advantage of it if you can find them; sure makes stabbing the intake a lot easier as the gaskets aren't going to slip into the valley.
I went the Cometic (brand head-gasket) route. They're pricey though. ProComp makes a remarkable-looking knock-off. I was very tempted to go that route. They don't come with (and I didn't worry about) the rear coolant block-off passages being present. Too many people are successfully running w/o them.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
If you run without intake gasket coolant restrictors, the coolant bypass from the core is no longer needed. The original design was to provide additional coolant at the rear of the heads and to keep it there longer to prevent hot spots. My theory is that once galvanic corrosion set in, the coolant that was sitting there simply ate up the head gasket; almost always at cylinder #7. The F-body and ZZ4 crate motors (which use current production 113 heads) don't have this feature and are seemingly fine, if not better, without it. GM's Service Bulletin, issued in November '89, addressed all of the aluminum headed motors though, so I'd guess that intake coolant leaks were prevalent across all lines. None of the production changes addressed in the Bulletin were adapted until '91 and after that, a new strategy was implemented to get coolant out of the intake altogether.
