Torque setting query

[Wrightpayne]

I'm just doing some work on a non seven that has required drilling out some exhaust manifold bolts that have rusted beyond recognition. Originally 13mm and I managed to get some off with a 9mm socket!

The ally face on the head was slightly pitted so I decided to use a composite gasket rather than the single layer OEM shim steel type.

The other change I have made is to use titanium studs and nuts instead of the OEM steel bolts. I know this isn't ideal from a metallurgy perspective but not my problem in 20 years time! 
 

So when refitting the manifold (using studs/nuts rather than bolts) I torqued a bit like a head, middle to outer ends in increments. It felt like the nuts were getting really tight without clicking off at the 24-27 ft lbs setting so I backed off.

I expect the composite gasket was compressing so checked a few old haynes manuals for cars that used traditional gaskets and torque settings were all 15-18 ft lbs across different makes of cars. I used this setting and the torque wrench clicked off OK and didnt feel over-tight.

So my questions....

Do you agree that it was the gasket compressing?

Would the torque setting for a bolt be different to a stud / nut arrangement? The other difference was the addition of a washer with the stud / nut as K nuts were used with quite a small flange. Studs were tightened into the head with a double nut and no lubrication on the nut.

Any thoughts welcome.

cheers

Ian

[ECR]

Hi Ian

if you've replaced steel bolts with titanium studs the torque requirements will undoubtedly be different. The point of torquing a bolt or stud is to stretch them a known amount (like a spring) but not to a point where they permanently stretch. The spring has to be sufficiently strong to prevent movement of the joint which will cause eventual fatigue failure. Your titanium spring will be stronger/weaker than the steel bolt. Can't help with figures... Can't remember how k nuts work, do they have a partially deformed thread? If so, that will also modify torque requirements. I suspect that you'll just have to go with your gut feel and see how it works out...

Good luck ...

[OldAndrewE]

Going back to the original problem of removing rusted nuts and bolts have you ever tried this sort of thing?

Irwin 7pce Screw & Bolt Extractor Set - Machine Mart - Machine Mart

[Wrightpayne]

Andrew,

I tried a similar kit from Irwin that were a bit shorter and was not impressed.

Ian

[OldAndrewE]

OK Ian, sometimes they work and other not.  Not that expensive so possibly having a set just in case.

[Wrightpayne]

Andrew,

Its on a Porsche 996 - its that much of a problem a company in America, Stomski Racing has made a jig!! Also the boxster / cayman and gen1 997 afflicted!

[Wrightpayne]

This was my best effort. After drilling the thread just peeled out! 
 

[OldAndrewE]

OK Ian, interesting.  Very useful to have that jig to allow you to drill in exactly the correct place.

[Wrightpayne]

No way would I attempt it freehand! 
 

17/64 is the optimum size for drilling out m8x1.25 bolts.