Bolt Identification Question

[Tom L.]

I bought a 1970 LS-5 in pieces. I have a plastic bucket full of unmarked hardware from the disassembled engine that I'm trying to sort out. The bolts shown below are all 3/8" by approximately 1 1/2". I was certian that the bolt in the middle with the "E" head mark was for the fuel pump, but I found four of them. Does something else use the same bolt?

Regarding the other two, one has a standard 16 thread, but the one with the "c" headmark has a non-conventional looking thread that won't thread into a 3/8 16 hole.

Any thoughts on where these go would be greatly appreciated.

Thanks.

[Tom L.]

Re: Bolt Identification Question

Here's another picture with the odd thread on the right.

[Terry M.]

Re: Bolt Identification Question

I would call the E mark a fuel pump bolt also. I think it is what is on one of the fuel pump bolts on my 1970 LT1. The other fuel pump bolt has the same smaller hex head, but a different headmark -- and I don't recall now what that one is. I just remember they are different. Fuel pumps were installed at St.. Louis but of course they might have been different lengths for the different engines, although I doubt it -- I just don't know about the length.

Joe Lucia will chime in, but my guess is that C head mark bolt is one of his late favorite 1969 and newer exhaust manifold fasteners -- but I might be wrong. If I were home I could look at the example I have -- but I'm not home for more than a week.

[Joe L.]

Re: Bolt Identification Question

Tom------

The bolt in the center with the "E" headmark and captured lockwasher is the fuel pump bolt. I can't think of another engine bolt position that uses this bolt. So, if you have 4 of them, 2 are likely "extras" from more than one engine. These bolts are likely of GM #3874876 which are "officially" of 1-1/8" length, but, as I recall, the actual measurement is a bit longer.

The bolt with 6 lines and the "C" headmark is a special locking bolt of GM #3909821. For LS-5, it was used ONLY for the exhaust manifold end runner positions (i.e. 2 bolts for each end runner; 8 bolts total per engine without C-60 and/or N-40). Special locking studs were used for most end bolt positions requiring studs for peripherals attachment.

I'm not 100% sure what the other 3 line, flanged head bolt is for. However, I expect it's either an intake manifold bolt or a bellhousing bolt. If it's an intake manifold bolt, it's likely GM #1231418; if it's a bellhousing bolt, it's likely GM #3828782.

[Tom L.]

Thanks Joe. Let me ask one more question

I think that I've properly identified the bell housing and intake bolts. As I recall, the intake bolts have a very thin flange and an "M" headmark and the bell housing bolts had no flange and used a lock washer. Is it possible that the three line flanged bolt in the picture is for the inside locations on the exhaust manifolds? I was thinking that because the level of rust on them matches the manifolds.

Thanks for the info on that special locking bolt. I assume that's what they used in 1970 and early 1971 before they changed to french locks on the ends of the manifolds?

Thanks again.

[Joe L.]

Re: Thanks Joe. Let me ask one more question

Tom-----

Yes, the flange on these bolts looks thicker than what I would expect. However, some of the bolts might have had thicker flanges than others. The ones typically seen have thinner flanges.

Is it possible that the non-locking, flanged head bolts were used for the non-end positions on the exhaust manifolds? Yes, it's possible. However, they're not the bolts that GM says were used for those positions. Plus, there are 2 other factors that make me wonder about such use. First, they are GM 280-M material grade; exhaust manifold bolts are usually GM-300M. Second, I think I can see just a trace of engine orange paint on the one you have pictured. I cannot see where any engine orange paint would survive very long on an exhaust manifold bolt.

I have not seen bellhousing bolts on C3s with a standard hex head and lockwasher. All that I have seen were flanged head with no lockwasher (lockwashers are rarely used with flanged head bolts). However, I suppose it's possible that standard hex head with lockwashers were used in some cases.

GM says that the locking bolts for big block end positions were used from 1968 through 1974. However, it's possible that their use ended prior to 1974 and there was a return to french locks as has been reported sometime in 1971.

I cannot see any reason why there would have been a reversion to french locks since the locking bolts are far superior as far as a bolt locking mechanism is concerned. However, perhaps there was some sort of assembly difficulty caused by the locking bolts, so they decided to go back to the standard bolts with french locks.

[tom444634]

Re: Bolt Identification Question

Tom,

Just looked at my 71 LS5, the bolt on the left is an intake manifold bolt. I looked at the bell housing bolts also and they have a thinner flange on the head then the intake ones do.

Tom

PS, I'm always looking for an excuse to go out to the garage pull the cover off of the car in the winter. If you want some pictures, let me know...