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72gs455

Exhaust manifold bolt torque

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I'm picking away at my project, mounting exhaust manifolds with new hardened bolts, the manual says 10 to 15 ft/lbs which seems really loose. I am missing 2french locks but will get them. Should I go more than the 10-15 or stick with the manual? Should I be using lock washerrs or no?

thanks for your input!

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I recommend following the manual.  Obviously that's why they incorporate the French locks. Probably looser to allow for inconsistent expansion and contraction during heating and cooling. It's even the same setting up through the 56 year.

 

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Cast iron cylinder head spark plug torque is typically 30 lbs/ft, which is usually snug and a little more to compress the gasket (if they use one).  Getting too much torque on the exhaust manifold bolts, such that no sliding interface between the fastener and the manifold can accelerate cracking tendencies.  French locks are fine, but NO lock washers.

 

Remember that in all fastener situations, there needs to be ONE part which is sacrificial in nature.  Would you desire to helicoil a head bolt hole or drill out a broken bolt's remains (in the hole)?  Be sure that all recommendations of "lubrication" on the threads if followed such that a good torque happens rather than an invalid torque reading from dirty or dry threads and such.

 

You might consider not bending the French locks until a few hot/cold cycles have happened to the manifolds.  This way, if there are any exhaust leaks/ticks, they can be addressed before the locks are deployed.

 

NTX5467

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Be careful on replacement bolts, as well. They need to be exactly the same length, which may not be available from hardware suppliers.

 

I ran into a situation where the exhaust manifold bolts were on the same plane, but at 90 degrees to a headbolt and drilled through. During reassembly of the engine the exhaust manifolds were installed with hardware store stock that was a standard nominal size just a bit longer. When accessories were installed the longer bolt was pressing and deflecting the headbolt. Removal damaged the threads, reinstlalation damaged the block. I had to go in and Helicoil the block, replace the manifold bolts and headbolt, without disturbing the appearance of a show condition engine compartment.

 

No pun, but you really have to consider every angle. I am not so sure I would put hardened bolts in. OEM would be more of a concern than tensile strength to me.

Bernie

 

 

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