Head Gasket installation
Thread Starter
Advanced
Joined: Mar 2003
Posts: 98
Likes: 3
From: Oglesby Illinois
Head Gasket installation
I have a 1970 LS5 Vette. The previous owner bored it 30 over and decked the block, not sure how much. In 2011 a piston cracked so we had the engine rebuilt. I put in forged pistons with slightly more compression so the compression is pretty high now since the original was 10.25. I just blew a head gasket and wanted to know what head gasket to replace it with that can handle the compression and how it should be installed. That is with regard to sealant and where or no sealant. Should i follow the original torque specs of something different. Thanks.
Le Mans Master
Joined: Apr 2001
Posts: 5,436
Likes: 1,253
From: Sarver Pa
2021 C1 of the Year Finalist - Modified
Most important question is, why did it blow a head gasket ??? You need to determine that, then take steps to ensure it doesn't happen again. I just put my high dome 468 together with Fel-pro . I used the standard torque pattern and specs.
Last edited by Pop Chevy; Sep 6, 2016 at 09:34 AM.
Burning Brakes
Joined: Apr 2008
Posts: 1,222
Likes: 93
From: shelbyville West Michigan
good blue fel-pro. no sealant. std. torque and sequence. don't oil the bolts. use sealant on the ones that go into the water jacket.
before you do that, make sure you have the head checked for warping. regular quality head gaskets will be just fine, even if you are at 11:1.
before you do that, make sure you have the head checked for warping. regular quality head gaskets will be just fine, even if you are at 11:1.
Instructor
Joined: May 2016
Posts: 178
Likes: 22
From: Vermont
Only my opinion, but replacing the head gasket without identifying "why" it blew will probably result it happening again. Just because the heads or block were decked, doesn't mean they were machined correctly by a shop familiar with high performance big block engines. Overheating can also caused warping. I realize that none of us want to complicate a project, but gungatim & Pop Chevy are right when they say to identify the "real " problem and that is not as simple as " the head gasket blew "
Good luck, Tim
Good luck, Tim
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
If the area between cylinders 4 and 6 blew out, I would suggest that your heat riser valve is stuck closed and the pressure/heat caused it to go. Otherwise, we would have no idea why it would fail...unless the machined surface was not flat.
With C.R. that high, you will need to get 93+ octane fuel and need to go with metal-only head gaskets.
With C.R. that high, you will need to get 93+ octane fuel and need to go with metal-only head gaskets.
Safety Car
Joined: Sep 2007
Posts: 4,458
Likes: 331
From: Indy Indiana
with boring, block decking and higher compression pistons when rebuilt, then you should also consider head gasket thickness. you may want to lower compression by installing a thicker head gasket. you should calculate your compression ratio based on your specs.
depending on how much was decked. you may even require thicker head gaskets. worst case, at least measure the thickness of your old gaskets and replace with equals. all the big name gasket companies should have at least a couple of choices each for thickness.
depending on how much was decked. you may even require thicker head gaskets. worst case, at least measure the thickness of your old gaskets and replace with equals. all the big name gasket companies should have at least a couple of choices each for thickness.
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Thread Starter
Advanced
Joined: Mar 2003
Posts: 98
Likes: 3
From: Oglesby Illinois
I should have mentioned that that block was bored and decked 50K miles ago, before my time. We simply rebuilt the engine 4 years ago when a piston broke. The block and head are flat i have checked that so not sure what else would cause it to blow. I can check the heat riser if that is a possibility but not sure i will know why. I was simply trying to figure out if i needed a better then stock head gasket due to the >11:1 compression and if so what you would recommend. I always use 93 octane fuel or whatever is the highest at the pump. What about octane boost, does that stuff really work or help?
Last edited by bill69; Sep 8, 2016 at 03:31 PM.
Burning Brakes
Joined: Apr 2008
Posts: 1,222
Likes: 93
From: shelbyville West Michigan
I should have mentioned that that block was bored and decked 50K miles ago, before my time. We simply rebuilt the engine 4 years ago when a piston broke. The block and head are flat i have checked that so not sure what else would cause it to blow. I can check the heat riser if that is a possibility but not sure i will know why. I was simply trying to figure out if i needed a better then stock head gasket due to the >11:1 compression and if so what you would recommend. I always use 93 octane fuel or whatever is the highest at the pump. What about octane boost, does that stuff really work or help?
Octane is a measure of how the fuel resists early detonation. high compression, hot spots/carbon build up, improper timing, etc. contribute to detonation and pinging. an octane boost will help if you have that problem, if you run fine on 93 or 91 or even 87, increasing the octane is a waste of money.
lots of things can cause a head gasket to blow. bad gasket, improper torque, stretched head bolts, who knows. detonation can kill a piston, not usually blow a head gasket. sometimes they just go.
out of curiosity, where did the gasket fail? between cylinders? water jacket? was it the same cylinder that had the bad piston replaced?
stock gaskets were pretty poor. just thin aluminum back int he day. modern cometic have a nice coating and they tend to be higher quality. like I said, I like Fel-pro. in the old days with the cheap thin un-coated metal gaskets, it was not uncommon to spray them with copper, or aluminum paint. some still do that on small engines, but you really shouldn't need anything with a decent Fel-pro or other modern quality gasket.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Run a 1003 Fel Pro dry.........buy a new set of quality head bolt (like ARP) and follow instructions. Torque in a pancake pattern, circular, at 45 ft lbs. then go around and do them again....this time at 70 ft/lbs. (Or manufacture rated torque-70 should be close).
If the heads and block are flat....you are done. Improper clamping is almost always caused by torquing head bolts dry.....they need lube of some sort......on a stock block PTFE on the threads and oil or moly under the bolt head.....depending on the manufacture.
Lately I have been having great luck with ARP's kit that has stainless head bolts on the outside......little pricey but worth it in the long run.
Do check that heat riser and make sure it is open......while you are in there go for a set of Fel-Pro 1204 intake gaskets with the heat riser block off.
Good luck and post your findings!
Jebby
If the heads and block are flat....you are done. Improper clamping is almost always caused by torquing head bolts dry.....they need lube of some sort......on a stock block PTFE on the threads and oil or moly under the bolt head.....depending on the manufacture.
Lately I have been having great luck with ARP's kit that has stainless head bolts on the outside......little pricey but worth it in the long run.
Do check that heat riser and make sure it is open......while you are in there go for a set of Fel-Pro 1204 intake gaskets with the heat riser block off.
Good luck and post your findings!
Jebby
Last edited by Jebbysan; Sep 9, 2016 at 06:20 PM.
Le Mans Master
Joined: Oct 2010
Posts: 6,937
Likes: 848
From: melbourne florida
2023 C3 of the Year Finalist - Modified
with jebby. It's possible a bolt wasn't tightened properly or had a false tight. If both surfaces are flat and it didn't overheat put it back together.