Grade 7 bolt

[Gary B.]

Did GM ever use Grade 7 bolts with 5 lines on the head like the one below on a C2 or C3?

Gary

IMG_1315.jpg

[Mike B.]

Re: Grade 7 bolt

Yes, on my '66 427 the harmonic balancer was attached by a grade 7 "FC" head mark bolt and both my '66 BB and '65 SB had grade 7 "P" outer rear spring long bolts originally installed from the factory.

Mike

[Gary B.]

[Mike B.]

Re: Grade 7 bolt

Gary,

A good buddy of mine recently purchased a set of the "P" grade 7 outer rear spring bolts. I'll post a shot of them when I get home. I've never seen a set as pristine as the ones he just found. Very jealous.

[Mike B.]

Re: Grade 7 bolt

Pretty hard to find a set of these P-bolts in this shape. I'm green with envy. Still hunting a nice pair for my '66.

C2 Rear Spring Outer P grade 7 Bolts.jpg

[James W.]

Re: Grade 7 bolt

I have those original bolts on my '65 rear spring.

Pretty hard to find a set of these P-bolts in this shape. I'm green with envy. Still hunting a nice pair for my '66.

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[Gary B.]

IMG_1325.jpeg

[Richard M.]

Re: Grade 7 bolt

Do we know the GM Part number and application/"where used" for any of these bolts?

I'm wondering if suppliers ran out of Grade 5 stock and shipped these instead.

Rich

[James W.]

Re: Grade 7 bolt

The grade 7 bolts I have installed on my late '65 trailing arm to rear spring were p/n 3831585 in the 1965 AIM.

James

[David B.]

Re: Grade 7 bolt

Do we know the GM Part number and application/"where used" for any of these bolts?

I'm wondering if suppliers ran out of Grade 5 stock and shipped these instead.

Rich

Rich,
GM grade 7 bolts & screws 1/4' thru 1 1/2" are designated GM-290-M roll threaded after heat treat, as noted they are ID by 5 lines. GM grade 5 bolts, screws & studs #6 thru 1", 1" to 1 1/2" are designated GM-280-M as you know have 3 lines. It is highly unlikely allowed to be substituted in assembly process unless Engineering approved.

[Gary B.]

[Michael G.]

Re: Grade 7 bolt

Normally, an engineering change would have been necessary, but candidly, plants tended to substitute parts first and then ask for permission later, so you might see a substitute in instances where the design parts were in short supply or had a quality problem.

[Mike B.]

Re: Grade 7 bolt

Gary,

Here's the grade 7 "F-C" big block harmonic balancer mount bolt & hardware. These are parts from a '66 427 with a build date of December 7th, '65. My December 1st built car's exact same bolt was mashed a bit by bubbuh using a mallet there. This one's a better example. Other folks on the TDB have previously reported this same head mark on this bolt for '65 396 cars.

Mike

'65-'67 Harmonic Balancer Bolt & Washer (2).jpg'65-'67 Harmonic Balancer Bolt & Washer (3).jpg'65-'67 Harmonic Balancer Bolt & Washer (4).jpg

[Gary B.]

[Richard M.]

Re: Grade 7 bolt

Rich,
GM grade 7 bolts & screws 1/4' thru 1 1/2" are designated GM-290-M roll threaded after heat treat, as noted they are ID by 5 lines. GM grade 5 bolts, screws & studs #6 thru 1", 1" to 1 1/2" are designated GM-280-M as you know have 3 lines. It is highly unlikely allowed to be substituted in assembly process unless Engineering approved.

Thanks David, I understand. But on the line I think it's possible they did whatever was needed to make the cars and not stop the line. Maybe not in this case, true. But I still need to find a detail specifically showing the part# James posted is spec'd as a Grade 7(GM-290-M), not Grade 5(GM-280-M).

The grade 7 bolts I have installed on my late '65 trailing arm to rear spring were p/n 3831585 in the 1965 AIM.

James

Thanks James. Now on the hunt..... gmpartswiki was no help but I have some other big books in the shop I'll check when time.

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If there are any other part numbers relating to this issue please post them and I'll look those up too.

Rich