Vortec head bolts.. Torque to yield or old school torque method?

[Schurkey]

I saw an AERA bulletin on exactly this issue, and within the last week. It might have been posted in another thread on this site.

As suggested earler, the bolts are torque-angle, NOT torque-to-yield.

Now I gotta go look for that bulletin...

 

[Schurkey]

^^^

www.gmt400.com/threads/torque-specs-thread.23609/page-2#post-916216

Torque Specs Thread

I'd be interested to see if any of the manuals actually use GM's torque list or if they came up with their own using standard torque values... I got a lot of mine from the instructions with my moog parts and they slightly differ from the Haynes / chiton manuals. I would love actual gm specs.

www.gmt400.com

The AERA Technical Committee offers the following information on cylinder head installation for 1996-99 GM 5.7L VIN R engines. This information is somewhat different than previous engines. GM is now recommending a torque turn method of tightening the cylinder head for this engine. It does not however, use a torque-to-yield bolt to mount the cylinder heads.
The cylinder head mounting bolts may be reused if they are not damaged in the threads or show neck-down or stretch condition. The bolts should be thoroughly cleaned of sealer before inspection and installation. Cleaned bolts should have a coating of GM sealing compound Part #1052080 applied to the threaded area only. The use of an aftermarket equivalent sealing compound is also acceptable to use on threads.
Follow the steps listed below to correctly install head gaskets for this engine being careful not to get any seal on the head gasket mating surfaces or gasket.
1. Place the head gasket over dowels with the bead up.
2. Carefully guide the cylinder head into position over the dowel pins and
gasket.
3. Coat threads of the head bolts with sealing compound and finger tighten all
bolts.
4. Tighten all bolts in sequence to 22 ft. lbs.
5. Tighten all bolts in sequence an additional turn in degrees, using J 36660 tool.
Short Bolts (3,4,7,8,11,12,15,16) Additional 55° Turn
Medium Bolts (14,17) Additional 65° Turn
Long Bolts (1,2,3,5,6,9,10,13 Additional 75° Turn
The AERA Technical Committee

 

[L31MaxExpress]

I saw an AERA bulletin on exactly this issue, and within the last week. It might have been posted in another thread on this site.

As suggested earler, the bolts are torque-angle, NOT torque-to-yield.

Now I gotta go look for that bulletin...

Some are TTY. The later model crate engines and marine engines ABSOLUTELY are TTY. The newer replacemement bolts from GM, Felpro and Mahle are also TTY. AERA might be right on factory 96-2000 engines, but as I understand it engines and bolts made after 2001 MY are TTY. 2001 is when the L31 production moved to Mexico. The factory blocks starting in 2001 have metric bellhousing and engine mount bolts as well and when GM started putting them into the GMT800s the factory casting number went from a 880 to a 417 and gained the 4 bolt LS mounts that sat the L31 on the LS mounts in the same position relative to the transmission bellhousing.

New vs Stretched once from a ~2017 built 6.3L Merc sourced from GM. Basically identical to a HT383E. Bought the engine with only 75 hours on it with a freeze cracked block complete with a marine manifold setup for $500. I put the head back on the block and tried to tighten those old bolts to the old torque spec and the newer TTA spec. Half of them broke trying to get to 65 ft/lbs or started stretching and you could feel the others start feeling plastic before the final TTA degree was met. The 2005 Mexican L31 had the same bolts I turned into the budget L31, stretched and all. The amount of stretch was not consistent either between bolts. I broke one years ago that was in a 2006 era TBI crate engine before I even knew it used TTA as a service replacement engine and never understood why at the time. I used new bolts in the budget L31 and even following the TTA method it had several bolts that started feeling plastic and I stopped like 10-15° short of the full torque value on those. Figured no sense going more if they were just stretching aka failing. So far has not been an issue.

Breaking and stretching the bolts in that junk block trying to tighten them to factory spec told me all I needed to know. New bolts since there is no way to know which style is in the engine currently if the heads have ever been off or possibly a GM replacement engine and TTA paying attention to the way the wrench feels tightening them. I am not betting 5-10 hours of labor plus head gaskets on $70 worth of bolts.

You must be registered for see images attach

 

[L31MaxExpress]

Also consider if they were not TTY the factory would not have changed the angle for the different bolt lengths. If the bolt is not stretching why does it need a different angle for the short bolts, medium length and long bolts? Older non TTY bolts were 65 ft/lbs across the board. As I said a GM Powertrain engineer (VortecIroc) who actually built these things at GM stated they all were TTY not just TTA.

Edit, found his actual post on the subject. VortecIroc was a former GM Powertrain engineer. I will also believe what he stated over most others especially when it comes to the L31 350. He knows them inside and out from a factory engineering stand point and has built some 1,000+ HP SBCs as a hobby as well. The same 1/2" hex TTY bolts were used in the TBIs and LT1s starting in ~94. Find it interesting too that I have seen far more blown head gaskets especially between cylinders 3&5 and 4&6 on engines using the 1/2" hex bolts. Much less common when the SBC had the earlier 5/8" hex bolts. In this case from what I have personally seen and experienced attempting to re-use these head bolts with them failing, I will trust vorteciroc over AERA.

You must be registered for see images attach