Frequently Asked Questions (FAQs)
1. What bolts are best for exhaust?
For exhaust flanges, the common options are 3-bolt or 2-bolt types. The recommended bolt sizes are M10 for 2-bolt and M8 for 3-bolt flanges. It is important to use bolts with a grade of 8.8 tensile strength or higher to ensure they can be tightened without stretching or breaking.
Header bolts are typically made of either black oxide chrome moly or Stainless 300. Both options have a nominal tensile strength of 170,000 psi, which is significantly stronger than Grade 8 hardware.
For headers with 1/4-inch or 5/16-inch thick flanges, bolts with a 3/4-inch UHL (Under Head Length) are typically used. Flanges that are 3/8-inch thick usually require bolts with a 1-inch UHL.
4. Should you put anything on exhaust manifold bolts?
When reusing exhaust manifold bolts, it is recommended to apply a metal fortified anti-seize to prevent seizing. However, it is best to use fresh OEM bolts for optimal results.
5. Is Grade 8 or 10.9 stronger?
Grade 8 bolts are generally considered to be stronger than 10.9 bolts. The strength of a bolt is determined by its material and mechanical properties, rather than just the grade number.
6. Are higher grade bolts stronger?
Yes, higher grade bolts generally have higher tensile strength and are therefore stronger. The common grades for metric bolts are 5.8, 8.8, 10.9, and 12.9, with each grade having a specific bolt strength.
7. What is the maximum span between bolts?
The maximum spacing between bolts for painted or unpainted members that are not prone to corrosion is 24 times the thickness of the thinner part, up to a maximum of 12 inches.
8. Should I use loctite on my exhaust manifold bolts?
Using a medium-strength thread locking compound, such as the blue Loctite 243, is recommended for exhaust manifold bolts. This helps prevent them from loosening over time.
9. Can you over tighten exhaust manifold bolts?
It is important not to over tighten the bolts where the exhaust mounts up to the engine. Over tightening can lead to damage or other issues.