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Headbolt torque

imageHeadbolts is 44 lbs plus 90deg. Any guess as to that final torque value? I say no more 60lb total. Yes I have torque angle gauge.

I’ll guess less than 60.

That seems to be reasonable @George_San_Jose1. And I consider the “torque to yield” specification an effort to make engine assembly appear to be rocket science.

Torque is a pretty useful spec. When I worked in the technology sector we’d sometimes spec the torque of a fastener connecting sub-assemblies needed to achieve a good electrical connection for high frequencies.

About 75-80 lb/ft, that 1/4 of a turn can take some effort.

A good summary-

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The bolts came off easy. i even wondered if they were loose. but they all felt the same. 1st torque is 44lbs and than 90 deg.

Don’t forget torque sequence.

What problem is TTY supposed to cure?What was the failure rate of head bolts prior to TTY compared to the failure rate now using TTY?

That article I cited mentions it somewhat. Blocks and heads are now aluminum which has a much different thermal coefficient of expansion than older design steel blocks (Remember when they were mixing the two? Yikes!). Across the thermal range, the aluminum will expand and contract more and so keeping the proper clamping force on the head gasket is more critical than in the past. The TTY bolt provides a more consistent clamping force regardless of lubrication and breakaway torque values. They can also be made smaller and so fit into tighter spaces and provide higher and more consistent torque settings. Contrary to suggestions, it is not to obfuscate, complicate or stop people from DIY, it serves a technical purpose and is an actual improvement in performance. The only downside I know is they are one time use and have to be replaced if torqued and then loosened.

my v6 vue/opel motor had iron block/alum heads and the sequence was torque/angle/angle/angle while the chevy 3.4 is iron/alum and it is torque/angle. same basic physical size of block/heads but the vue bolts are for sure longer. i think the vue had m12 thread while the chevy is bigger, maybe m14?

ready to torque them down

The problem with using torque only, especially at higher torque values is that some bolts may have more drag than others. The torque consists of two parts, friction of the threads sliding past each other and clamping force. The goal for the gasket is consistent clamping force.

If the gasket isn’t clamped evenly, then as it goes through many heat cycles, it will tend to get weak in some areas and maybe even contribute to warping the head (aluminum). Stopping at a specific low torque value, before thread friction becomes significant yield and even clamping force across the head. Using the torque angle gauge after than maintains the even clamping force.

Not all aluminum engines use torque angle for the head bolts though. The Nissan 2.5 has a very complex torque procedure that involves torquing to a certain value, loosening and then torquing to another value, loosening and torquing again to another value. They also have a procedure to insure the bolt threads are clean.