Locking nuts, stud insertion and other dilemmas

[Guest]

In the process of laying in my triple intake and stainless headers. I have placed all new studs on the head for these parts and have a few questions. First, I feel that the studs should be screwed into the head with a reasonable amount of torque, not finger tight. More than a few times when removing manifolds the stud will back out with the nuts. Correct assumption? Next, because the Falcon headers can be a real challenge to bolt up because of the curvature of some of the pipes ( three areas ) getting a standard nut and lock washer onto the stud is impossible so I want to resort to all metal locking nuts with slightly thinner flat washers because the locking nuts are tapered and don't require those thick split lock washers. ( these will most certainly back the studs out if and when I take it all down again no matter how tight the studs are placed ) Again, does this make sense? Next, I will be using a standard stock-style metallic-looking gasket ( the aftermarket paper-looking "header" gaskets won't last a year ) and my machinist suggested using an extremely fine bead of copper-silicon high heat sealer around the exhaust ports. To help stop exhaust leakage, which I have had a problem with in the past. I had the header flange faced to flatten it but these beasts never seal up like the stock cast exhaust manifold. Little things that cause big problems unless they are addressed properly. Changing anything from stock on these engines often requires innovation. Surely some of you out there that race have had these problems. Pardon the wordy post. I am beginning to sound like Alan, but without the correct answers......

Bill

 

[Camping57]

Your idea of putting the studs in with a reasonable torque is a good one. First make sure the tapped holes have been chased with the proper sized tap to get all the vintage rust and grunge out of the threads. Then I would double nut the studs (using standard free spinning nuts and torque them in snug tight. Your idea of using the all metal lock nuts is excellent. They will actually work much better than the helical lock washers will at preventing loosening. I would put a little high temp anti-sieze onto the stud threads to prevent them from all rusting into a nice solid mass after running for a while. The copper coating you see on exhaust flange nuts is an attempt to prevent them from siezing onto the studs after seeing high temps that will burn off regular zinc plating.

I don't know about the high heat sealer. I didn't know that they made stuff that will live at those temps.

Dick

 

[Guest]

Thanks, Dick...
You are a welcome addition to the forum! Your technical expertise is invaluable.

Bill

 

[Camping57]

Don't pump me up.
You didn't see my interior when I forgot to attach the oil line to back of the gage and started the car up. Or the time when I didn't pull the jack stand out far enough from under the front apron when I lowered the car. Or when I didn't latch the hood Dzus.....the list goes on and on.

 

[Guest]

Don't tell me that, I'll think that you made up all you said about bolt technology!

Bill

 

[Dave Russell]

Re: Locking nuts, stud insertion and other dilemma

Hi Bill,
Remove any burrs/pulled up threads around the stud holes. Screw the studs in securely. Make sure that the stud does not bottom out in the hole before the top thread is tight & that it doesn't raise any threads.

I mentioned once before the need to have adjacent flanges, on a stud, be the same thickness or to shim the thinner ones. Otherwise, the washer being at an angle to the stud & nut will have to "try" to bend the stud slightly to get equal pressure on both flanges. The stud won't bend, so unequal pressures. It makes a big difference in sealing. With correctly fit flanges, I really don't see any need for locking nuts, lockwashers, or sealer. Hardened flat washers should be all that is needed. I can't imagine a correctly torqued nut unscrewing by itself.
D

 

[Bugeye58]

Re: Locking nuts, stud insertion and other dilemma

Dave, the Triumph uses a double ended clamping piece, much like a double ended machinist's clamp, to secure the intake/exhaust manifold to the head. This alleviates somewhat the unequal clamping forces caused by differences in thicknesses of the separate flanges. However, in my experience, header flanges are traditionally somewhat thinner than their stock, cast iron counterparts, so shimming may be required.
Bill,
As to stud torque, I install all of mine at 50 lb. in. Slightly more than finger tight. Provided the stud is not bottoming in the hole, the shoulder of the stud will be resting on the upper thread of the hole. Excessive torque on installation only serves to deform the top thread, and gall the shoulder of the stud. I usually relieve the top threads by countersinking, or counterboring, a minimum of 1.5 threads to eliminate the possibility of a raised thread interfering with the sealing surface.
While locking nuts won't hurt, Dave is correct in saying that a properly torqued nut shouldn't back off. One advantage to using a "Jetnut" is that they have a reduced head diameter as compared to a standard nut, making it easier to get a socket on them, given the confined space on a Trimph manifold. So what if the stud comes out of the head when you remove it. On my race 1500, I have to remove the studs completely to remove or install the header. No big deal.
As to the "High Temp Copper Sealant", well I guess it's a personal choice. I've never found any need for it, but if it makes you feel more comfortable, use it.
Sorry for being so wordy.
Jeff

 

[Camping57]

Re: Locking nuts, stud insertion and other dilemma

Bugeye,
Good stuff. I'll agree 100% with everything except the part about a properly tightened nut not backing off. That is the case when you have a long enough fastener length and a stiff enough joint to get the stud to stetch and act like a spring under load. This is what is done on rod and big end bolts and they stay tight no problem. When you get parts that have a small length to diameter ratio (< 4:1) and or a gasket in the joint, they don't get enough stretch to prevent vibration loosening. Hence the need to add a bandaid in the form of a locknut. Locknuts aren't bad; the next time you get onto an airplane look at the nuts on the hardware by the door...all locknuts. The 'modern' car companies use locknuts on almost every chassis part because of bad L ratios and soft compressible joints.
As an aside, if you look at an older model GE or Pratt jet engine you'll see rings of bolts holding the different sections of the engine together. The flanges used are as thin as possible to save weight, but they put a .500 to.750 long sleeve under the head of each bolt to increase the stretched length of the bolt so that they didn't loosen in service (for some reason peole got realy excited when the engines came apart in flight!). This added weight to the engine, but getting a better L ratio and more stretch far exceeded the weight penalty.

Dick

 

[Bugeye58]

Re: Locking nuts, stud insertion and other dilemma

Dick, I use jetnuts everywhere. Along with locking nutplates in a blind installation. Where I can use it, I use my bolt stretch gauge in lieu of a torque wrench.
When I mentioned a properly torqued nut not backing off, I was assuming proper stretch and clamping forces. I generally still retorque header nuts after a run in period.
I've still got a bunch of hot section bolts from a TF39 engine lying around here somewhere.
And, yes, having a compressor section come apart in flight will definitely get your attention!
Jeff

 

[Camping57]

Re: Locking nuts, stud insertion and other dilemma

Bugeye,
Wow!
There are only a handfull of folks around that know what a bolt stretch gage is, let alone knowing how to properly apply bolted joint theory. I better watch myself now that I know there is someone else that will be able to double check my aimless ramblings.
What is interesting (and what keeps me in pay checks) is that something that seems as simple as a bolt and nut (or even a screw) can be so complicated to get to function that way that you want it to. I have plenty of horror stories about different parts over the years.

Dick

 

[TRMark]

Re: Locking nuts, stud insertion and other dilemma

I saw this in Dec. issue of Rod & Custom; rodders have all kinds of cool stuff. Really don't know if it fits our applications or not. https://www.go-breslin.com/text.html

 

[Bugeye58]

Re: Locking nuts, stud insertion and other dilemma

Dick, you're way ahead of me in this department. I'm an old aircraft guy, and had a bunch of this stuff in college.
For some applications where I can't use the stretch gauge, I've made fixtures to correlate proper stretch with applied torque.
And yes, I take proper pre-installation length values for critical fasteners, and keep record of them, so if I find one down the road that has exceeded its elastic limit, I can replace it before it fails.
How's that for being anal?
Jeff