New Exhaust manifold bolts

[Vintage_barry]

I’m changing out the original exhaust manifold bolts on my 57 Special  and was wondering out replacing them with grade 8. Any thoughts and advice?  Barry 

[old-tank]

It's a toss-up.  Grade 8 are less likely to break, but when they do they are harder to cut or drill out.  Use anti-seize, but even that degrades with use and time.

[Vintage_barry]

Thanks for reply. I sheared one bolthead off years ago so when I pulled the motor last month all the others came out ok with some finesse. Even the sheared bolt came out with heat and vise grips.  Thanks again, Barry 

[Larry Schramm]

If you have a blue flame wrench, it helps a lot on stuck bolts.  Used this more than once.

[Matt Harwood]

The bolts holding your exhaust manifold in place don't need to be grade 8, they're not in much tension in that application and a little flexibility is probably beneficial to exhaust manifold fasteners. And as someone pointed out, if they fail, they're going to be that much more difficult to remove in the future. Give the future owner of your car a break and use grade 5, use anti-seize, use high-quality gaskets, and don't over-torque them. This is one place where over-engineering won't help you one bit and might actively cause someone else headaches.

 

If they're stuck, heat them cherry red, then let it cool. Repeat. Add the penetrating oil of your choice. Let it sit. Repeat. Gently try to turn the bolt, then stop. Add more heat and lubricant. Time and patience are your friends when removing stuck hardware without breakage. Don't try to do it all in an afternoon, especially with the engine in the car and where access is limited. I've learned that the hard way; I've been trying to remove 58 head studs from my 1935 Lincoln's V12 for about a month. Still have 10 to go with 13 already broken off at the deck surface. Wish I could go back in time and beat the heck out of the guy who did the work last time...

[NTX5467]

The exhaust manifold bolts, as mentioned, are not "high stress" bolts.  Only about "35" torque is needed.  BUT . . . do not forget to replace ANY and all factory heat washers and such under EACH bolt head -- period.  

 

In EVERY fastener situation, there needs to be one sacrificial component.  Something that will break first, that is easier to deal with when broken, and will not damage other interfaces when it might break.  Using softer bolts is one way to do that, which saving the integrity of the threads that bolt contacts.  By "softer", I mean the normal Grade 5 bolts that are commonly used for everything. 

 

Always use the factory-spec "lube method" for the fasteners, too.  Whether a drop of motor oil, anti-seize, or whatever.

 

Just some thoughts,

NTX5467

Edited May 5, 2019 by NTX5467 (see edit history)

[60FlatTop]

Be careful about sourcing your new bolts. Automotive bolts of that vintage come in lengths of 1/16". Hardware stores don't get that fine in a lot of sizes.

 

I did a job on a freshly restored '59 Cadillac convertible once. The car ran poorly, smoked (white), and since the engine was rebuilt by a very reputable shop, the carburetor was blamed. I got the shiny car in not running. One of my first basic steps on a fresh car to me is to pressurize the cooling system, both cold and warm. Pressurized cold I could here the water running into the front left cylinder. The one accessory brackets were bolted to.

The forensic outcome was a handful of hardware store exhaust manifold bolts. It appeared the engine was dressed out of the car, then installed, and the accessories added. When the head bolt holding the bracket was removed there was tension from the, too long by 1/16" manifold bolt against the headbolt shank and threads. It tore the bolt all up. The work was done in a body shop and I figure the impact wrench drove the bolt home..... and the damaged bolt threads striped the threads in the block. In this case the manifold bolts and head bolt were on the same plane.

I got correct used manifold bolts from Paul Lauracella's Parts of the Past, Helicoiled the block, installed a stud so the Helicoil wouldn't be disturbed, and I think it is still good today. The cost to correct the wrong bolts was about $3500.

Your bolts are not hardened and should use French locks. Even if you get tempted, it is better not to do the engineering respec.

Bernie

 

 

Edited May 6, 2019 by 60FlatTop (see edit history)

[Frank DuVal]

Yes, I always check bolt length of new vs original, as I have seen 1/8" steps in GM bolts myself.  I can always shorten a bolt, lengthening one is more difficult!😁

 

On exhaust studs, manifold to pipe , I use stainless steel studs. I was using anti-seize and brass nuts with lock washers, but I kept loosing the nuts. So now just lockwashers, anti-seize and steel nuts. For those that do not know, I will not use stainless steel nuts on stainless steel studs, as the nuts seize! Even with anti-seize! This was on non-automotive equipment. Bolt people offer special coatings on stainless steel nuts to prevent this seizing. Moly coating is one of the offerings.  Your hands turn black installing them, but they do come off later when needed.

 

Back to original question, stick with grade 5 for the manifold to head (block) bolts.