Stainless vs zinc bolts
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Teching In
Joined: Jul 2019
Posts: 18
Likes: 1
Stainless vs zinc bolts Pickup up a 6.0l iron block and 4l80e from auction and was just the block, heads, intake, transmission and convertor. I've got everything else for the rest of the motor to complete from other projects but no hardware to mount it all. Just wondering why they always use the zinc bolts for mounting the externals. Is it best to run the zinc bolts or can I go and pick up stainless from a bolt supply place instead? Would stainless in aluminum heads be an issue? Stainless bellhousing bolts?
TECH Addict
Joined: Oct 2016
Posts: 2,513
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From: PDX-OR-USA
There are coated bolts that really do well to prevent seizing in the holes.. 
(Porsche uses them all over anywhere they are bolting in to Aluminum
Stainless doesn't always play nice threaded in to aluminum without some never seize or similar product. (Adjust torque accordingly)
(Porsche uses them all over anywhere they are bolting in to AluminumStainless doesn't always play nice threaded in to aluminum without some never seize or similar product. (Adjust torque accordingly)
stainless bolts are nowhere near the grade 10.9 used in most every bolt on the engine and other places.....so keep that in mind when choosing to use it....and as said ....alum and SS...... DO NOT PLAY WELL ....anti seize always
Teching In
Joined: Jan 2005
Posts: 22
Likes: 3
From: Snohomish, WA
Be careful here........ What he said, stainless bolts from the hardware store will break just trying to torque them to the same level as the OEM 10.9 grade bolts used in a lot of places on the LS. The are not even as good as grade 8.8. Not to mention the problem with them galling up when using them. The stainless bolts you can use in place of grade 10.9 are exotic and way expensive, you won't find them at the hardware store or even most bolt supply places. Hardware store stainless bolts are for places where corrosion is a concern but you don't need anymore strength than an SAE grade 2 bolt.
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On The Tree
Joined: Oct 2021
Posts: 147
Likes: 56
I'm probably recapping what others have already said here.
The factory uses (mostly) zinc plated bolts because they're fairly inexpensive, and they are somewhat corrosion resistant. Pay attention to the "material class" on the bolts. 8.8 is about the lowest you'll find in most automotive/engine situations. 10.9 is stronger, and is about the strongest you'll find on most LS engines, except possibly flywheel bolt (I don't remember for those), and 12.9 is the strongest material class widely available commercially.
You may also see cad plated bolts (a brassy yellow color to the plating), and black oxide coated bolts. Different coatings all for about the same effect. It's about corrosion resistance.
Avoid stainless steel bolts. They are almost always weak compared to steel or any plated steel bolts. Stainless bolts have an entirely different system for strength rating. You'll see mostly A2-70 in the hardware stores, which is not as strong as SAE grade 2, and similar in strength to metric class 4.6 or 4.8 bolts. Stronger stainless bolts are sometimes found at marine shops, and are marked A4-80 and are almost as strong as class 8.8 metric hardware.
So with stainless, you're generally paying more for weaker hardware. It's not a good idea for most bolts on an engine.
Also, there's galling issues with stainless steel bolts going into female threaded Aluminum parts. Anti-seize is your friend there, or possibly a thread locker that keeps air out and reduces corrosion and galling.
The factory uses (mostly) zinc plated bolts because they're fairly inexpensive, and they are somewhat corrosion resistant. Pay attention to the "material class" on the bolts. 8.8 is about the lowest you'll find in most automotive/engine situations. 10.9 is stronger, and is about the strongest you'll find on most LS engines, except possibly flywheel bolt (I don't remember for those), and 12.9 is the strongest material class widely available commercially.
You may also see cad plated bolts (a brassy yellow color to the plating), and black oxide coated bolts. Different coatings all for about the same effect. It's about corrosion resistance.
Avoid stainless steel bolts. They are almost always weak compared to steel or any plated steel bolts. Stainless bolts have an entirely different system for strength rating. You'll see mostly A2-70 in the hardware stores, which is not as strong as SAE grade 2, and similar in strength to metric class 4.6 or 4.8 bolts. Stronger stainless bolts are sometimes found at marine shops, and are marked A4-80 and are almost as strong as class 8.8 metric hardware.
So with stainless, you're generally paying more for weaker hardware. It's not a good idea for most bolts on an engine.
Also, there's galling issues with stainless steel bolts going into female threaded Aluminum parts. Anti-seize is your friend there, or possibly a thread locker that keeps air out and reduces corrosion and galling.
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