Torque to spec

When you say "torque to specification", in case of torque-to-yield specifications, does that include the yield/angle rotation or just the torque? For example, if the factory spec is 40Nm + 90 degrees + 90 degrees, should I be torquing to 40Nm or should I go through the angles as well? Just wondering if that'd require different bolts to be used for measuring clearance and actual/final assembly? Maybe I'm getting something wrong

You torque to the figure given, then through the angles given - this permanently stretches the fastener and you MUST use new ones each time!

If you're doing a simple valve to piston clearance check, etc, there's no need to go through the full process, just take the old fasteners down to, say, the spec'd torque. if you don't have the old ones, take the new down to, say, half the torque figure and DON'T use the angles, so you don't stretch them and they can be used in the final build..

this permanently stretches the fastener and you MUST use new ones each time

Yeah, this is the main question. Even if I use new bolts for clearance measurements, when I torque to spec, I would be using new ones after, for the actual build.

Yes, which is why I'd suggest using a lower than spec' torque. Once it's yielded - stretched beyound it's elestic limit, it is no further use.

Other work-arounds are using old bolts just taken to torque - especially if an otherwise good, used gasket is available.

The differences will normally be in the 2-3 thou' range.

There ARE some exceptions to this, so if you can post exactly whaere you're concerned then we might be able to help further - especially if one of the chaps, or chapesses, is familiar with your application.

This also where, if an engine, or whatever, is expected to be bebuilt more than once, aftermarket studs and fasteners that are simply torqued can be a significant saving, as they are, except for very special applications, re-useable many, many times.

There is plenty of information on-line on fasteners, and how they react under tension, whether 'standard' or TTY, which you should find informative.

To avoid confusing used and good bolts, used ones are normally a little longer with visible thread deformation on close inspection, but if you're keeping the old ones for dummy/test builds it's a good idea to mark them so there's no confusion - taking a grinder to the flat of the head and removing the markings gives a very clear warning they're the 'bad' ones, as it's very easily seen whether on the bench on in place.

IF THERE'S ANY DOUBT, SWALLOW THE PAIN TO THE CC/WALLET AND MAKE SURE YOU BUY NEW ONES! It helps if you don't take them out of their packaging until you KNOW it's the final assembly.

Hi,

What are these bolts for? Only head bolts and crank pulley bolts are stretch (torque-to-yield) bolts. Anything else can be re-used.

Daniel Powell explains torque-to-angle brilliantly in this video:

https://www.youtube.com/watch?v=mRsQqjhmGQY

Regards,

Henrik Morsing