Late Model SBC and Vortec Head Bolts

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L31MaxExpress

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I just want to point out the mis-information that is floating around regarding the 1/2" head late model SBC head bolts used in the later TBI, Vortec and LT1 engines as well as the GM crate engines. I keep seeing people posting claims they are torque to angle but are not torque to yeild. That information is FALSE. Always replace the head bolts if they have 1/2" heads. I compared a new set of GMPP head bolts as well as a once used set that came out of a Vortec 350 engine. Every last bolt had streteched about the same. I keep seeing this false information and hope this saves someone a real headache.

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454cid

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Are these smaller diameter than past head bolts, or just a smaller head?

Nowdays GM loves TAY bolts, since they can be smaller/lighter.
 

L31MaxExpress

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Are these smaller diameter than past head bolts, or just a smaller head?

Nowdays GM loves TAY bolts, since they can be smaller/lighter.
Same thread size, smaller hex. They are a 7/16-14 with a 1/2" hex vs the older 5/8" hex.

GM literally loves to break things by improving them too. Lifters for one thing.

Actually something that just clicked. Going off memory I think just about every blown head gasket I have seen on a factory engine had this style of bolts and factory MLS gaskets. I think the hot spot created at the center siamesed exhaust ports stretches the bolts there if the engine is even remotely close to overheated. Then the head gasket blows between 3&5 or 4&6 or sometimes both places. I have seen this exact head gasket failure a dozen times over on the later TBIs, Vortecs and LT1s. I have seen heads and blocks ruined because of this too. No coolant leaks, but misfiring. The combustion gases erode the area between the cylinders if it is run very long after the gasket fails.
 

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Are these smaller diameter than past head bolts, or just a smaller head?

Nowdays GM loves TAY bolts, since they can be smaller/lighter.
Never measured but the shank section of the older style bolts doesn't taper down like these newer ones as L31max has pictured.

Not all head bolts on a vortec head get torqued to the same value either. I mention that because because there a lot of misinformation out there as well telling people to torque them to a specific ft. lbs. value. Torque to a minimal value then following with a measurement of an angle is pretty much the textbook definition of a TTY fastener.

The outer row under the exhaust ports call for less torque.
 
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PlayingWithTBI

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I think the hot spot created at the center siamesed exhaust ports stretches the bolts there if the engine is even remotely close to overheated. Then the head gasket blows between 3&5 or 4&6 or sometimes both places.
That's exactly what happened to my Mr Goodwrench TBI engine made somewhere ~2000. I was losing ~a quart of coolant a week and it started running warmer than normal. I threw a jug of Bars Leak blown head sealant (or whatever it was called) in it. And started ordering parts for it.
 

tayto

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it seems all the new aftermarket head bolts available for SBC are this design. looking on RA a lot of them (felpro, victor reinz) they say TTY. felpro instructions say to "Consult latest OEM torque specifications." I used a set of these 1/2" hex head bolts supplied by an engine shop on a marine 350. i found mercrusier literature we torqued them to the TTY specs. I mentioned this to the engine shop and got a "why would you do that?"

see: http://www.rockauto.com/genImages/6/CI1909.pdf
 

tayto

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here are the instructions from mercrusier..note they offer an "optional method" which is close to the traditional torquing specs. either way. like stated above i would NOT be reusing this new style of head bolts....
 

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Schurkey

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1997 C/K service manual, page 6A-182.

15. Clean cylinder head bolt threads, and threads in the block.

Why would they tell you to clean the bolt threads but NOT tell you to replace the bolts?

On the next page--6A-183, item 3 tells you to apply a certain GM part number sealer to the bolt threads. Since new bolts come with sealer already applied, what is the logic of that?
 

L31MaxExpress

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Never measured but the shank section of the older style bolts doesn't taper down like these newer ones as L31max has pictured.

Not all head bolts on a vortec head get torqued to the same value either. I mention that because because there a lot of misinformation out there as well telling people to torque them to a specific ft. lbs. value. Torque to a minimal value then following with a measurement of an angle is pretty much the textbook definition of a TTY fastener.

The outer row under the exhaust ports call for less torque.
The main cap bolts in the newer Vortecs are also TTY. The shank is undercut above the thread and it has a centering dowl under the head. Look like a LS main cap fastner. Talking 2004+ production engines. I have a later Mercruiser manual that shows to remove and throw them away as well as the head bolts.
 
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