[C1] The torque head gaskets
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Melting Slicks
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From: Scottsdale AZ
Re torque head gaskets
Is this required any longer?. I have a fresh rebuild 327 from a local outfit (five star engines) with about 500 to 700 miles on it.
Last edited by John S 1961; Mar 27, 2024 at 01:17 PM.
Thread Starter
Melting Slicks
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From: Scottsdale AZ
Drifting
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From: Sierra Vista, AZ
Pull a valve cover, torque a few bolts to spec, if they don't move, then quit. If they do move, then you might want to torque all of them in order. I think you have to remove the exhaust manifolds to get the bottom row?
I've never retorqued them on a Chevy since the 1970s, but have on a few off brand cars, they needed it.
I've never retorqued them on a Chevy since the 1970s, but have on a few off brand cars, they needed it.
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No matter what the gasket it always proves better (though not necessarily always required) to re-torque after the initial heat cycle if possible; and if noted, most always one will realize some gain in rotation on the fastener from the previous setting.
As for "re-torquing" a threaded fastener, that which is not of the "stretch to yield" or "turn to angle" types, or some which might posses hard setting locking compounds, or unique friction reduction coatings intended for one pull only, it is generally considered proper to back the fastener off, say 90 degrees plus or minus, and then re-pull to the intended torque value in a single and continual movement.
Though here (particularly with the GM product that exhibit having the threaded portion breaching the cooling jacket), a mitigating circumstance might be for those fasteners which incorporate a fluid sealing compound (vs. a lubricant) and whether this possesses the ability to tolerate this movement and still provide for it's function.
But, just pulling on an already torqued to "specification" fastener proves to be only a test for those which may have become "loose", not a good procedure for establishing that the fastener is still torqued to spec.
Scott.
As for "re-torquing" a threaded fastener, that which is not of the "stretch to yield" or "turn to angle" types, or some which might posses hard setting locking compounds, or unique friction reduction coatings intended for one pull only, it is generally considered proper to back the fastener off, say 90 degrees plus or minus, and then re-pull to the intended torque value in a single and continual movement.
Though here (particularly with the GM product that exhibit having the threaded portion breaching the cooling jacket), a mitigating circumstance might be for those fasteners which incorporate a fluid sealing compound (vs. a lubricant) and whether this possesses the ability to tolerate this movement and still provide for it's function.
But, just pulling on an already torqued to "specification" fastener proves to be only a test for those which may have become "loose", not a good procedure for establishing that the fastener is still torqued to spec.
Scott.
Last edited by PBF777; Apr 5, 2024 at 12:47 PM.
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Cylinder head re-torquing is generally not needed if the correct procedure and components are used initially. The only time I re-torque would be on a copper head gasket in an extreme cylinder load situation. (supercharged pulling truck for example). I do not re-use factory head bolts though. I do often re-use ARP or A-1 bolts/studs if they are in good shape. When re-torquing, the proper procedure would be after the initial heat cycle or dyno load, back to room temperature, back off each nut or bolt about an 1/8th of a turn, and pull to final torque in 1 sweep. This is done in proper sequence. The reason to back off is to overcome the initial friction to get the fastener turning. you do not want to "relax" or completely unload the nut/bolt as this could break the seal it has.
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I would also consider whether this rebuilt engine used iron heads or aluminum heads, what head gaskets were used and what were the block deck and head surfaces spec'd to before assembly, and whether torque to yield bolts/studs are the hold down fasteners in question. Additionally, if the engine is not a super high performance engine and with or without power adders might also make a difference, as well as what kind of duty it is being used for (e.g., tractor pulls). So way more information would be needed to provide an informed answer. But if it's just a warmed over SBC and was assembled with reasonable care - in short I wouldn't bother. But if I did I would just check a few cold and if any moved I would circle pattern recheck them all. But I would also be careful not to over torque them by pulling past the torque spec to 'see' where they broke free. Also keep in mind that the head bolts that penetrate the water jacket may wind up having their sealant disturbed and could possibly leak after being disturbed.
