62-65 2 1/2" exh. manifolds

[E S.]

Hi- I'm an oldy but a nubie-I apologize if I am barging in or changing the subject-but I have a question about the casting numbers on these manifolds.
I have seen many varieties of these manifolds over the years,from originals to service replacement to over the parts counter to GM re-issue to poor reprouction to "correct" reproduction.(by the way-to me the "correct"repro's aren't) but that is another discussion.
By originals I refer to manifolds that were actually installed on cars at the factory. I have several of these manifolds in the garage;aguy wanted to buy a set and asked me a question that I could'nt answer.
What does the number under the casting number and to the left of the GM logo mean???
I have seen 1's, 2's, and even 3's here.(My 62,which is an orig.car,has 1"s on both sides)
I thought that if the molds were changed due to wear or damage that maybe they were given a higher number????

[William C.]

Re: 62-65 2 1/2" exh. manifolds

I believe that is the number of the core mold that made the basis for the casting, and you are correct, the "correct reproductions" aren't.

[E S.]

Re: 62-65 2 1/2" exh. manifolds

William-Thank you for your reply,I appreciate your time!
I'm still not sure I understand fully-Why would a 901 have multiple core #'s,a 902 have multiple core #'s,a 942 have multiple core #'s,or a 563 have multiple core #'s when they appear identical otherwise?
Like I stated,my 62 has a 901-1,and a 902-1,and I'm sending a pic of a 901-2.
I'm also sure that I have or have seen a 902-2,and I think The 563 I have is a 2.
It seems I read somewhere that Corvette manifolds were made at Flint foundry,pass. cars at tonawanda??

[Terry M.]

Re: 62-65 2 1/2" exh. manifolds

The casting machines for these parts were like merry-go-rounds with a dozen, or more, core molds on them. Each core mold was formed from a number of separate parts. Each of those parts came from a master mold die. Each master mold die had a different number so that as the master mold die wore they could track it and know which one to repair.

All that said, I am sure I didn't use the correct terms of all those parts, but I get all confused when the foundry guys talk about cope and drag (no it doesn't mean what you think) and core shift, and all that foundry talk.

[E S.]

Re: 62-65 2 1/2" exh. manifolds

Terry-Thank you for your help-
Very interesting-So the core #s relate to mold useage,wear,or damage issues?
Seems older cars would have lower core #'s then?
Could a 65 have a 902-1,and a 62 have a 902-2?
I guess my question is:Is there a correllation between core #'s and ser.# and or year of car?
Thanks-E.J.

[Terry M.]

Re: 62-65 2 1/2" exh. manifolds

The core numbers relate more to the number of molds on the carousel that forms them, and the volume of units they are casting. There will be a number 1 and 2 and so on for each casting number. I can't ever recall seeing a number beyond two digits though, and never out of the teens, although on high volume units like the 3970010 cylinder case I suppose the numbers would be high.

No, there is no correlation between the mold numbers and the date or sequence of the castings. For the most part the mold numbers don't tell us much from this perspective so long later.

One of the occasional posters here, Mark Gorney (sp?), is or was employed (I think he may have recently retired) at Saginaw Metal Casting. He is the resident expert on these kinds of things. Or look him up in the members list and send him a message.

[William C.]

Re: 62-65 2 1/2" exh. manifolds

Essentially the core numbers were there so that if a quality issue appeared, it could be tracked back to the cause easily. The manifolds were used on chevy pass car as well as corvette, so the volume is rather larger than one might surmise looking at the corvette only volume.

[Wayne M.]

Re: 62-65 2 1/2" exh. manifolds

....I'm sending a pic of a 901-2.
I'm also sure that I have or have seen a 902-2,and I think The 563 I have is a 2.....

EJ, Terry, Bill --- here's another example; an early '65 LH manifold on a L76/C60 car, which I have little doubt to be original, as I got the manifolds in boxes along with the the compressor and A/C brackets, back in 1980.

This '563' has the LH_2 mold; note the repeat of '563' for the forward part where the alternator mounts. Note also the fine seam line for the # 1 cyl part. Same line at rear (2nd pic; note what seems to be '901' over '942'. Leads me to speculate that there were 3 mold parts to pour a complete manifold; front and rear sections could be selected according to the options (any thoughts ?)

The '65 TIM&JG shows a casting date table, but goes on to say that small blocks have "no visible casting dates". It's been over 20 years since these manifolds have been off, but I recall some cast #'s on the inside, facing the block. Please refresh my memory as to what they are.

Sorry, but the passenger side manifold yields no easy photos, what with the compressor and all the firewall and evaporator plumbing .

[William C.]

Re: 62-65 2 1/2" exh. manifolds

I guess the only comment I'd make is the manifolds were described by finished part numbers, and the proper finished part was then built into an engine which was coded for the options required by the car build. Yes, some parts of the manifolds for the 902 and 942 were identical and likely used common cores. so far, this all looks pretty normal. There was a pretty in depth description of the casting process a while back, should be in the archives.

[Terry M.]

Re: 62-65 2 1/2" exh. manifolds

<snip>
This '563' has the LH_2 mold; note the repeat of '563' for the forward part where the alternator mounts. Note also the fine seam line for the # 1 cyl part. Same line at rear (2nd pic; note what seems to be '901' over '942'. Leads me to speculate that there were 3 mold parts to pour a complete manifold; front and rear sections could be selected according to the options (any thoughts ?)
<snip>

That is exactly what I would expect them to do. That would give them the maximum flexibility in producing a variety of castings with a minimum of resources. I'll see if I can draw Mark Gorney's attention to this thread because I am getting in way over my head. I'm sure he can give us chapter and verse on these sorts of questions.

[E S.]

Re: 62-65 2 1/2&quot; exh. manifolds

William,Terry,Wayne,Mark-Thanks for your help and time,and I'm sure Mark Gorny could also answer many other questions.
For example-Has anyone ever bought a manifold over the counter that really looked the same as one that actually came on a car? Where did the molds for replacement parts come from?
I'm sure there was a surplus of of 2 1/2" manifolds at the end of 1965-were they sold through parts?
One Corvette parts supplier advertises that they "bought the original GM molds",of which I've only seen a few of,but certainly don't look like the ones that came on cars(don't recall if or what core #s they had)Which GM molds were those?

[Tom P.]

Re: 62-65 2 1/2&quot; exh. manifolds

In addition to all of the above comments (which I pretty much agree with), it appears to me (after examining various 2.5in manifolds) that they ALL used the same INNER mold. Both the 901 and 902 versions have a hole drilled/tapped for gen/alt/accessory mounts on the forward side, thus a boss is required on the INSIDE of these manifolds for this hole.
Well, if you stick your finger inside the the end hole, of each end of each of the 4 manifolds (901, 902, 942, 563), you can feel a boss on BOTH ends of the inside of all 4 manifolds. Thus, that leads me to believe all 4 versions shared a common INNER mold.

Also, it would appear the OUTER main mold is the same for all 4 versions, and only the molds for the end caps and end accessory brackets are different. MOST of the 2.5in manifolds that I've seen have a somewhat distinguishable parting line where the end cap/accessory bracket mold is positioned. This parting line is particularly noticeable on the 563 manifolds that I've seen.

[William C.]

Re: 62-65 2 1/2&quot; exh. manifolds

The manifolds were available in Service for many years, and there were discrepencies, first, as the original run sold out, the dates for service manifolds carried the casting date they were actually were cast. Secondly, wear on the cores over time caused excess flashing on the parting line areas, which was then ground off, leaving a parting line area with a much different appearance than the parts actually used on the cars.

[Tom P.]

Re: 62-65 2 1/2&quot; exh. manifolds

The manifolds were available in Service for many years, and there were discrepencies, first, as the original run sold out, the dates for service manifolds carried the casting date they were actually were cast. Secondly, wear on the cores over time caused excess flashing on the parting line areas, which was then ground off, leaving a parting line area with a much different appearance than the parts actually used on the cars.

The last service 2.5in manifold (563) that I bought from my Chevy dealer parts dept was 2-3yrs ago. I wish I had bought several!!!!!
The 563 is excellent for making a 942 style version.

[William C.]

Re: 62-65 2 1/2&quot; exh. manifolds

Tom, was that a GM Manufactured service part or from the "approved reproduction" parts line? How was it boxed and dated?