997 Questions

[Mike T.]

3740997 dated K 14 6 has large valve guide bosses and does not have a passage in the center of the intake side to warm up the carburetor.

3740997 dated H 15 7 has small valve guide bosses and does have a passage in the center of the intake side to warm up the carburetor. This one also has "X58" cast into the spark plug side.

I know that they do running changes on parts. I checked Colvin's book and wasn't able to see any sketches or work orders documenting the changes.

Questions:

1. When did the running change take place concerning the size of the valve guide bosses?

2. When and why did the running change take place concerning the passage in the center of the intake side to warm up the carburetor?

3. Have we finally reached a conclusion on what the "X58" casting means.

Thanks for your help!!

[Joe L.]

Re: 997 Questions

3740997 dated K 14 6 has large valve guide bosses and does not have a passage in the center of the intake side to warm up the carburetor.

3740997 dated H 15 7 has small valve guide bosses and does have a passage in the center of the intake side to warm up the carburetor. This one also has "X58" cast into the spark plug side.

I know that they do running changes on parts. I checked Colvin's book and wasn't able to see any sketches or work orders documenting the changes.

Questions:

1. When did the running change take place concerning the size of the valve guide bosses?

2. When and why did the running change take place concerning the passage in the center of the intake side to warm up the carburetor?

3. Have we finally reached a conclusion on what the "X58" casting means.

Thanks for your help!!

Mike------


First off, let me say I know next to nothing about the 3740997 cylinder head. However, I could see the valve guide boss change being a running change without change of part number. It would be unusual but not impossible. But, the fact that some of these heads apparently have an exhaust cross-over and some do not really surprises me. That would be a major functional difference and it would surprise me that such a difference would occur within a given casting number.

[Mike T.]

Re: 997 Questions

Thanks for input Joe.

I'm thinking the answer may be in the "X58" casting in the side of the H 15 7 head.
One of the theories of the "X58" is that the foundry did this when they made an initial casting run for the new model year.
H 15 7 was made August 15th, so maybe it was intended for the 1958 model year.
Possibly the Flint foundry did not get word that the 1958 Vettes were not going to use 3740997 heads. I even heard someone say that a few undocumented 1958 Vettes had 3740997 heads.
Who knows? Hopefully we can figure it out.

[Cecil L.]

Re: 997 Questions

I've seen late 57 539 heads with X58 cast on them. The size of the valve guide bosses typically indicates dual vs single valve springs.
The casting number is the basic casting, it's the finished part number that matters.

[Mike T.]