grade 8 nuts on ?grade studs

[19_again]

I've checked the archives and there's lots of talk about the subject but I am curious if we know what grade the head and manifold studs are on the engines we work with (my 1800 MG and 1988 Triumph in my case). I am wondering if it makes a difference if torquing a grade 8 nut onto a grade 5 or lesser stud. I presume it's best if they match, but I suspect we're not putting enough torque onto these studs that it really matters, does anyone know the grade of stock studs in these cases?
thanks, Mike

 

[Scott_Hower]

Hi Mike-

Too many factors to consider to give you an accurate answer, I'm afraid. I'll share my opinion...

Most of these cars have passed through so many owners/shops that there's simply no telling what's "stock" anymore in terms of installed components. There's no way to know what you currently have given 30 years of prior maintenance/repair/abuse/whatever.

Head studs stretch when torqued repeatedly. Manifild studs are cheap. If you are wary of your existing hardware, replace the head studs with ARP and the manifold hardware with something grade 5 or above from Aircraft Spruce (or at least with a known manufacturing provenance).

Look at it this way... what would you rather do... spend $100 on quality hardware, or snap a stud off flush with the head while torquing your new grade 8 nuts on unknown quality studs some DPO installed 15 years ago.

Easy decision for me.

--Scott

 

[Stewart]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Look at it this way... what would you rather do... spend $100 on quality hardware, or snap a stud off flush with the head while torquing your new grade 8 nuts on unknown quality studs some DPO installed 15 years ago.
[/QUOTE]

Or head studs put on last weeks by a previous owner. If you are messing with head studs spend the money on the arp bolts. The stock stuff that is out there now is junk.

 

[19_again]

Thanks guys, right answer. As a rule I'm the first one to say spend the pennies and save the dollars, but I didn't want to mess up perfectly good looking studs for no reason. The other rule is don't fix what ain't broke.

 

[Scott_Hower]

I didn't want to mess up perfectly good looking studs for no reason. The other rule is don't fix what ain't broke.

Well, you seem to have somehow fallen into a set of grade 8 nuts that you are curious about using. I would not use grade 8 nuts and (over) torque them on unknown quality studs. The unknown hardware is the weakest link in this equation and you need to respect that.

Once a head stud stretches and loses it's tensile strength, it's trash. Modern TTY (torque to yield) studs/bolts are meant to be used once and then discarded.

 

[PAUL161]

You can use a grade 8 nut on anything with the same threads. The grade on the nut only comes into play when it's used on a grade 8 bolt being torqued to it's max as the threads on a grade 5 or less bolt are not as hard as the nut. By torquing the original bolt to original specs, you can not strip the threads regardless of what nut you use! If it were me and in doubt, I'd replace all the studs! It's worth it just for peace of mind.

 

[Hap Waldrop]

I'm a big believer in ARP hardware, in the 1275 engine I building right now for ray mccaleb, it has the ARP head stud kit, rod bolt kit and flywheel kit. I repalced the factory bolt used to secure the main caps with grade 8 bolts. I use almost all grade bolts in my engine rebuilds, in alot case it more about cosmetics than need, I don't need a grade bolt to hold the timing cover or oil pan on, it just looks better to have all yellow znc hardware on the engine, grade 8 is not alot more expensive than grade 5, which is normally white zinc plated. The only fastners in a engine rebuild i use are the one-off fastner unique to the engine, all common hardware is repalced. If you live in the middle of nowhere, then sourcing ahrware may be difficult, but if you live in or near a populated city, then you probably have several industiral fastner shop around, I have three with 5 miles of my shop, one will sell 1 or 100 bolts of whatever size I need, I keep a fairly good working stock of fastner and have been doing this for 20+ years, I'd probably say I have well over 10,000 new units.

 

[Scott_Hower]

By torquing the original bolt to original specs, you can not strip the threads regardless of what nut you use!

I really dont want to get into a peeing contest, but I respectfully disagree with the statement above.

If the studs have stretched, or bottomed out, or become embrittled due to heat cycling, the "original torque" spec is not accurate. Are you oiling the threads, or torquing dry? Stripping and snapping are both distinct possibilities on the stud and the nut, and I've seen both on original and "new" cheap hardware. The current manifold studs sold by a popular vendor who shall remain nameless are pure junk. Might as well be made from compressed goat manure.

I use only double height brass nuts on manifold studs.

 

[GeeBee1]

Me likes the double head brass nuts on the manifold....

It will make life alot nicer the next time....

 

[Scott_Hower]

Me likes the double head brass nuts on the manifold....

It will make life alot nicer the next time....

I also use them on exhaust manifold downpipes. Add a dab of antisieze paste and your life will be even nicer.

 

[19_again]

Scott, I didn't fall into some nuts, but since I'm doing a complete restoration (or at least touching every single part in the GT) I figured I'd find out once and for all what the "proper" grade is for our type of work. I had a couple of nuts that were tough to get off and I thought that I might replace them, that led to "with what" and here we are. I didn't want to put grade 5 or 8 nuts onto a grade 8 or 5 stud if it made a difference.
Well all that's left to do is order those stud kits from ARP, btw are they a supporting vendor?
Thanks as usual for the advice, the books are great but the experience on the forum is immense.

 

[WA1KWA]

Like Hap said, SAE Grade 8 (sometimes called MIL spec) aren't that much more than SAE Grade 5, which is pretty much commom coin in cars using inch fasteners. My local hardware store keeps a pretty good supply of them, so I tend to replace SAE Grade 5 with SAE grade 8 when on a project on the B. My front end, for example, now has SAE Grade 8 fasteners.

Makes me feel better.

Don't overtighten just because they are SAE Grade 8, though. Stick with spec. Good shop practices still apply.

Colin

 

[Scott_Hower]

Don't overtighten just because they are SAE Grade 8, though. Stick with spec. Good shop practices still apply.

Colin

And don't forget to use the ARP lube.

 

[Hap Waldrop]

I'm a ARP dealer, I mostly just get them for the engines I'm building, I'm not big into part sales, other than wheels, custom piston a few hard to get items, bit I can get them for you, give me a call, I'll be back in the shop Monday, heading out for the track event at CMP.

 

[19_again]

Thanks Hap. I will.