1971 LT-1 Intake Manifold Bolts--Markings, Finish, Length, Threads

[Paul C.]

On the 71 LT-1 engine (correct me if wrong):

12 total bolts all grade 5

2 bolts held the lift bracket--they had a shoulder with an A, & black phosphate
1 bolt held the AIR pump-- M & painted orange
9 remaining bolts could have C, M, SB, RSC & black phosphate

Where all the bolts the same length and completely threaded????

Most of my bolts are about 1 1/8 and completely threaded but some are 1 inch and only threaded on the lower half? This puzzles me!!!!

Thanks Paul

[Patrick H.]

Re: 1971 LT-1 Intake Manifold Bolts--Markings, Finish, Length, Threads

Paul,

How many are different?
I have often found that bolts that hold items, especially the two that hold the spark plug supports, differ from the rest. So, typical is one headmark for the lift bracket, one for AIR pump, one for spark plug supports, and the remaining bolts all match each other.
The AIR bolt and spark plug support bolts "might" match if you have 3 that qualify.

Patrick

[Rich P.]

Re: 1971 LT-1 Intake Manifold Bolts--Markings, Finish, Length, Threads

Paul, the bolts you have that are 1 inch long threaded halfway are pressure plate to flywheel bolts.

[Ron G.]

Re: 1971 LT-1 Intake Manifold Bolts--Markings, Finish, Length, Threads

The following is nothing that you have not heard before. All the intake bolts are plated black oxide/black phosphate when they are installed. The 2 bolts that attach the front and rear lifting brackets and distributor bolts received some orange paint. Then most of the bolts were sprayed painted with silver paint because the intent was to cover up whatever engine orange paint got on the lower/outer edges of the intake for cosmetic purposes. Usually the inside portion of the bolts you can still see the black plating. Common logos were "A" and "M". It is not uncommon to see a "TR" or another logo that I like to refer to the GM family of hardware. Bolts are grade 5 with 3 slashes. Also, if your objective is to duplicate assembly line accuracy, then on the inboard of the valve covers received some silver paint as well. The front and rear part of the block will normally have some silver paint over the orange. As Patrick made mention, the bolts attaching the support bracket and the AIR pump may differ in logos.