2006 S60 2.5T AWD - oversize turbo/manifold studs?

[kcodyjr]

I've got the turbo out for inspection and repair of the waste gate and CBV, and a thorough cleaning.

While getting it out, I had two studs come out with the nuts. Of the two remaining, one was in the flange and one in the manifold.

The one in the turbo flange snapped when I tried to remove it. I haven't had the nerve to try with the one in the manifold.

This stud was an absolute bear to drill out. It seemed to be made of kryptonite, kept dulling drill bits, and it seemed the threads were cold-welded into the cast flange even after the rest of the stud was drilled away. It totally ate the standard size tap, so we drilled it out to M8 with a carbide bit and retapped.

I've got four questions:

1. Why did Volvo use such an extremely hard alloy for these studs?

2. What would I be risking to use a lesser metal for the replacements?

3. Where might I get a replacement stud that's M8 on one side and the standard M7 on the other?

4. What say ye about the one still stuck in the manifold? Leave it, chase its outer threads in place?

Thanks in advance, all.

[firstv70volvo]

I've got the turbo out for inspection and repair of the waste gate and CBV, and a thorough cleaning.

While getting it out, I had two studs come out with the nuts. Of the two remaining, one was in the flange and one in the manifold.

The one in the turbo flange snapped when I tried to remove it. I haven't had the nerve to try with the one in the manifold.

This stud was an absolute bear to drill out. It seemed to be made of kryptonite, kept dulling drill bits, and it seemed the threads were cold-welded into the cast flange even after the rest of the stud was drilled away. It totally ate the standard size tap, so we drilled it out to M8 with a carbide bit and retapped.

I've got four questions:

1. Why did Volvo use such an extremely hard alloy for these studs?

2. What would I be risking to use a lesser metal for the replacements?

3. Where might I get a replacement stud that's M8 on one side and the standard M7 on the other?

4. What say ye about the one still stuck in the manifold? Leave it, chase its outer threads in place?

Thanks in advance, all.

Volvo probably used stainless steel bolts for corrosion resistance. Carbide tip multi-material (for metal too) drill bits are needed as you found out. M8 to M7 reduction stud may exist but may be hard to find, how about drilling out the hole to accept M8 stud. Mayhew pneumatic bolt breaker tool is worth considering if you go after the stud stuck in the manifold. Mayhew Tools 37315 Pneumatic Bolt Breaker, 3/8-Inch

[kcodyjr]

Volvo probably used stainless steel bolts for corrosion resistance.

Oh, no, it wasn't stainless, it was something much more exotic.

My Pop helped me work on this, he's done thousands of these over many decades. He got his chops at that famous old Caddy-Olds place. He said he's never seen anything like this metal. Stainless would have been old hat and a cinch by comparison. He said even SAE grade 8 was nothing like this.

Vanadium steel, like most gun barrels, would be a good first guess. That it meets metric 12.9 would be another good guess.

It seems like a silly choice, because the harder a metal is, 1) the harder it is to do this, and 2) the more brittle it is. It really didn't take any great force to twist off the one that broke on me. It was a long 13mm box wrench with the flange clamped in a bench vise.

I wonder if Volvo's all-too-clever engineers were thinking about galvanic cells, or something, between aluminum heads and cast iron manifolds, and then just used the same stuff for the cast-to-cast turbo flange studs as well?

Unless someone can dream up a plausible argument to the contrary, I think I'm looking for aftermarket studs that just happen to fit, and are made of something more conventional in case if I ever have to to go through this again.

This in opposition to my usual stubborn insistence on going with OEM.

[firstv70volvo]

Volvo probably used stainless steel bolts for corrosion resistance.

Oh, no, it wasn't stainless, it was something much more exotic.

My Pop helped me work on this, he's done thousands of these over many decades. He got his chops at that famous old Caddy-Olds place. He said he's never seen anything like this metal. Stainless would have been old hat and a cinch by comparison. He said even SAE grade 8 was nothing like this.

Vanadium steel, like most gun barrels, would be a good first guess. That it meets metric 12.9 would be another good guess.

It seems like a silly choice, because the harder a metal is, 1) the harder it is to do this, and 2) the more brittle it is. It really didn't take any great force to twist off the one that broke on me. It was a long 13mm box wrench with the flange clamped in a bench vise.

I wonder if Volvo's all-too-clever engineers were thinking about galvanic cells, or something, between aluminum heads and cast iron manifolds, and then just used the same stuff for the cast-to-cast turbo flange studs as well?

Unless someone can dream up a plausible argument to the contrary, I think I'm looking for aftermarket studs that just happen to fit, and are made of something more conventional in case if I ever have to to go through this again.

This in opposition to my usual stubborn insistence on going with OEM.

Use a magnet to check if stainless or not. Stainless can become work hardened if heated too much by dull drill bit or wrong drill rate and then it becomes extremely hard to drill, may be something else though. Good quality aftermarket studs with anti-seize should be all you need. For difficult exhaust bolts and studs I've had good success with the Mayhew bolt breaker tool and air hammer.

[scot850]

Volvo engineers are far from smart. Ask why they use steel bolts and aluminum for suspension parts when they sell cars and develop them for cold countries where salt is used...............?!

Neil.

[volvolugnut]

Design engineers have many needs driving their choices - cost, weight, available parts and materials, and assembly ease. I think long term service ease is way down the designers priority for passenger cars.
volvolugnut