Stud/Nut vs. bolt

[vrinner]

For the turbo to exhaust manifold, is there any reason why I cant use a bolt instead of studs and nuts?

[MikeFleming]

1. You will forever have thread locking issues. if you use a locking thread bolt, then the threads in the manifold will wear after each removal/installation.

2. Bolts that will work at that temp are very expensive, relatively rare, and hard to get.

3. Some SVO owners will laugh at you (well, at the turbo mounting on your car)

4. If you go that path, be sure to use a high-temp material with a washered head. DO NOT use lock washers.

[vrinner]

OK...studs it is.

I also found the following from Thomasnet.com

Torque Efficiency

During engine assembly or maintenance, a bolt must be installed by torqueing it into place. Due to the head bolt’s design, it has to be rotated into its slot in order to engage the threads and secure it into place. This process creates both twisting force and a vertical clamping force, which means that when the cylinders within the engine’s combustion chamber begin accumulating load, the bolt will both stretch and twist. Because the bolt has to react to two different forces simultaneously, its capacity to secure the head is slightly reduced and it forms a less reliable seal in high-powered engines.

By contrast, a head stud can be tightened into place without any direct clamping force applied through the tightening. A stud can be threaded into a slot up to “finger tightness,” or the degree to which it would be tightened by hand. Afterward, the cylinder head is installed and a nut is torqued into place against the stud. The nut torque provides the clamping force, rather than the torque of the fastener itself, and the rotational force is avoided entirely. Because the stud is torqued from a relaxed state, the pressure from the nut will make it stretch only along the vertical axis without a concurrent twisting load. The result is a more evenly distributed and accurate torque load compared to that of the head bolt. This ultimately translates into higher reliability and a lower chance of head gasket failure.

[MikeFleming]

1. Those are flat washers, yes? If lock washers (spring type), loose them.

2. There is no difference in how a stud and bolt twist and stretch and no difference between the two as far as clamping forces goes. As long as they are made of the same material. as a general rule studs are a much stronger material (which does not change their load/stretch ratio though).

When the nut is tightened, the stud is still twisted - just the same as with a bolt. The ONLY difference is there is reduced wear on the block threads due to *less* rotational movement of the stud. Note that using thread locking compounds on the stud/block side does not eliminate this movement, although it may reduce it a few percent.

Lastly note that most studs for automotive use (going into cast blocks) use coarse thread into the block and a fine thread on the nut end. This only changes the "rotation angle versus stretch" ratio so TTA (torque-to-angle) rotation changes severely. The nuts must be rotated more for the same stretch.

3. I'd also recommend to use a deformed locknut on the studs. Can't tell from the pic what nut type is used.

[vrinner]

They are lock nuts. What is a deformed locknut?

[MikeFleming]

What is a deformed locknut? Wikipedia:
Distorted thread locknut

Elliptical offset nuts, also known as oval locknuts[1] or non-slotted hex locknuts,[3] is a nut that has been deformed at one end so that the threads are no longer perfectly circular. The deformed end is usually shaped into an ellipse or obround triangle. The nut is easily started on the male fastener as the bottom portion is not deformed. As the male fastener reaches the deformed section it deforms the threads of the nut elastically back into a circle. This action increases the friction between the nut and the fastener greatly and creates the locking action. Due to the elastic nature of the deformation the nuts can be reused indefinitely.[2]

[vrinner]

Drilled studs, double nutted then really torqued them down, then self locking nuts, the safety wire. That sucka better not come off now!

[MikeFleming]

Looking good!

For future reference: Those nuts should go in the 35-40 Ft-Lbs range. It's only a 10mm thread. And torque (double-nutted) the studs in to manifold in the 5-10 Ft-Lb range. They will get tighter as the nut is installed.

Note that your wiring will only keep the nuts from falling off, not from loosening. That's a much more complex job.

[vrinner]

The nuts are those distorted thread type you talked about before so hopefully those wont back out. The wiring is to keep the studs from backing out which was the last issue that I had at the track.

[MikeFleming]

When's the next track session? The real test!

[Bob Holmes]

I stake the studs at the manifold. Its one of the few things that seems to work.

Of course that technique makes it hell to get the studs out later, if you need to.

[MikeFleming]

I stake the studs at the manifold. Its one of the few things that seems to work.

Of course that technique makes it hell to get the studs out later, if you need to. And has a tendency to damage the female threads in the precious manifold holes.

[Bob Holmes]

Well, I should disclose that I do that on a Bob's log.

[vrinner]

OK...back on topic if you can stay there.

Here it the DP attached and safety wired. Seriosly if this doesn't work I'm going to put the header and external waste gate on. I cant imagine this coming loose though.

[Bob Holmes]

So how many bloody finger pokes from the safety wire?

[MikeFleming]

No support brace?

[Bob Holmes]

Damn, your eyesight is a lot better than mine.

[vrinner]

I often wondered that...is it absolutly necessary? I bet thats a big part of my issue eh?

[Bob Holmes]

That's a gotta have part, Vince.

[MikeFleming]

Helps alot with the vibrations and weight load. That and some sort of flex hose/pipe section between the engine and the rest of the exhaust system.