C5 Corvette/LS1 Manifold to downpipe bolts?

So I am swapping the starter on my C5 and I snapped off 5 of the 6 manifold to downpipe/x pipe bolts. Good news, got them all out easy peasy. I hammered an 18mm 12 point socket onto the flange of the studs, and they spun right out of the manifold. I am going to get some new bolts from the stealership tomorrow.

My question involves the nuts. Word on the street is these nuts are self locking, and the studs are made of bubble gum. On DSMs, I had spectacular luck using stainless nuts, lock washers, and antiseize in place of standard manifold stud bolts, as they liked to do the same thing, seize to the stud, and then snap the stud on disassembly. With stainless nuts and lock washers, it always came apart easy.

Any reason I should use the OEM nuts on the exhaust studs, or should I do my stainless nut/lock washer method? Are these soft studs common on all Gen III engines?

Keep in mind the car will be coming apart soon (less than a year) for long tubes and a ZO6 trans swap.

Another solution would be copper alloy nuts, some come "squeezed" (slightly out of round) so they function as a lock nut, but are removeable

Personally I don't find any use in locking mechanisms except Nordlocks and wiring the heads, but neither technique is of any use here. I think even a regular plain steel nut and washer (spring for hardened washers (washeres are not really graded like bolts et al, so hardened ones are much better) - it matters a lot) with a goof coating of anti-sieze will hold up just fine. Antisieze is a great rust deterrent and it doesn't come with the huge strength loss of stainless nuts and washer, not to mention the cost.

Plain steel + antisieze for me. Stainless would work (please don't use lockwashers), but beware that it's a lot weaker, don't strip it.

Here is just a list of POSSIBLE (meaning some have gotten along just fine without seeing these) failure modes for different locking mechanisms:

Nylock: only single use, low temperature.

Loctite: Much better than above, but require primer to be consistent and can be temperature related depending on formulation used

Lockwashers: Utterly useless except in machine screws or very low grade steels or very low torque applications

Squished nuts: Single use as the compromise the male thread

Wired heads: Difficult to install correctly, and very operator dependent. Doesn't hold torque, just prevents total backing out.

Your mileage may vary. Just one engineers opinions. For locking, use loctite, proper torque and good washers. For rust prevention, use grease, paint or anti-sieze.

Tuna, have you seen issues with stainless in this sort of application? In the DSM world, it was common to replace stock head-to-manifold studs and nuts with stainless and antiseize them. I have 6x M10 studs holding up half the weight of my X pipe. My DSM used 9x M8 studs to hold up a manifold, turbo, and so on. Probably similar weight, 20-30ish lbs.

My plan for right now is to order 6 M10 x 1.5 stainless studs and 12 M10 nuts from McMaster, TIG one nut onto the stud to give me a hex to turn it into the manifold, and run the other nut on to hold the downpipe to the manifolds.

Please talk me down from this plan if its a bad idea.

In reply to 93gsxturbo:

I've not seen issues at all, I've never even worked on one. I'm just saying that stainless gives up a lot of strength to plain steel and assuming both are coated in anti-sieze, stainless doesn't really buy you anything.

Also, I'd never ever ever weld on a fastener in an application like that. You're just asking for trouble. Any time you heat up a fastener like that you're killing whatever heat treat it has, making it even weaker. It may not rust, but it may snap off.

Just get good plain steel pieces and coat them accordingly.

^ Unless you're in the rust belt, where stainless offers other long term benefits...

njansenv wrote: ^ Unless you're in the rust belt, where stainless offers other long term benefits...

If he's coating them in antisieze, it will prevent rust there too - I used to live in central New York - I know all about it and all of the bolts I touched had the stuff. I've literally pulled lugnuts off of cars that I routinely worked on only to find that the wheel won't come off. I've then dropped the car back on the ground in frustration, started the engine and turned the wheels lock to lock and they remained stuck fast. At that point, the BFH finally got them loose (with the truck in the air again).

I do live in the rust belt, but this is my summer fun car. My Dodge is my Daily Driver Rust Sponge.

You're looking at somewhere between 1/2 to 2/3 the strength depending on what fastener you get:

http://www.boltdepot.com/fastener-information/materials-and-grades/bolt-grade-chart.aspx

Plain grade 8 (or metric equivalent) for me, thanks. Like I said, though, just one guys opinion.