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Old 09-16-2025, 08:13 AM
JEC3039 JEC3039 is offline
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Default Exh Manifold Bolt Locking Tabs

How many locking tabs did the factory use - all 12 positions or just the front and back on each head or ?? Working on a 1968 F'bird 400 restoration.

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Old 09-16-2025, 11:50 AM
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From a previous thread on this subject...
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Old 09-16-2025, 01:27 PM
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Perfect, thanks. I have that manual and missed that detail.

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Old 09-16-2025, 06:41 PM
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Are not the end holes a larger diameter as well ?.... My belief is larger holes for manifold expansion then locks to keep bolts tight from large holes and expansion cycles

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Old 09-18-2025, 07:59 AM
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Formulas - I secured the manifolds before seeing your note so too late to check the hole diameters for now. Next time manifolds are off the car I'll try to remember to report back...

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Old 09-18-2025, 09:21 AM
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I know the locking tabs where done away with by 75 and washers where exchanged.

This could have even had taken place back earlier as in when the low comp fully set in by 1971, but I have no definitive proof of that due to the circa of manual’s I have.

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Old 09-18-2025, 10:07 AM
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Originally Posted by JEC3039 View Post
Formulas - I secured the manifolds before seeing your note so too late to check the hole diameters for now. Next time manifolds are off the car I'll try to remember to report back...
On cast iron manifolds the outer holes are larger to account for expansion and contraction (thermal cycling). I researched this when I noticed the larger outer holes on my ram air manifolds. There is a thread or two about this subject on this forum.
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Old 09-18-2025, 10:37 AM
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And the above is a darn good reason when running exh manifolds to use the factory steel gasket only and with a coat of antiseize on both its sides .

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
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