torquing down 16v head

[jondee86]

Still a meaningless question. Bolts dont handle torque, they handle stress,
and its a complex relationship with several variables between them.

There's theory and there's the real world. I have never seen a mechanic use
a strain gauge to measure how much load he is putting on a bolt, but I have
seen plenty using a torque wrench.

So I would expect that someone would be able to say... "They were OK at 75 ft-lbs
but I could feel them start to yield at 80 ft-lbs". Or... "I snapped three bolts when
I tried upping the torque to 60 ft-lbs instead of 50 ft-lbs". Empirical data from real
world experience can be good indicator when obtained first hand

Cheers... jondee86

[Grrrrrrr!]

You just don't get it do you.

The reason that they went away from using torque wrenches alone is that its very imprecise at getting good consistent preload values. The preload obtained by mechanic A putting 49ft.lbs on bolt A in head A lubed using oil A could be 30% different from what mechanic B gets putting bolt B, in head B using oil B, even using the same model torque wrench, same type of bolt and same type of head. So going by torque alone you can't use the full potential of the bolt because mechanic A will be 15% below the target preload, and mechanic B just snapped the bolt.

However 90degrees of turn is always 90degs, which with a bolt with a 1.25mm pitch is always going to get pretty damn close to 0.3125mm of extension and a pretty reliably narrow range of preload which can be calculated using material properties of the bolt.

Pro engine builders don't use torque wrenches to do up rod bolts, they use a stretch gauge.. because the right preload is the target, not a torque figure which is a rough approximation. But you cant do that with head bolts or main bolts, so torque wrench and angle gauge are the best real world method for the average mechanic that isn't going to shell out thousands for ultrasonic tension testing devices and obtaining the data and training on how to use them.

I'm done wasting my time.

[jondee86]

You just don't get it do you.

On the contrary, I fully understand the theory and practice off TTY and TTA
and the effect of lubrication on tightening torque. But I like to understand how
things work in the real world... like what is the compression vs load curve for
a MLS gasket ? And how does this compare with a composite gasket ? How
much torque (measured under controlled conditions) does it take to get a bolt
into the plastic region, and can you REALLY/REALLY NOT re-use head bolts ?

It would be nice to be able to discuss these things with a design engineer
from one of the big motor companies, and get some real insight into these
questions. But unfortunately, all the interweb dishes up is advertising BS and
secondhand misinformation. Getting to the truth is not always easy

Cheers... jondee86