Very Early 1966 427 blocks

[Patrick B.]

Re: Very Early 1966 427 blocks

Patrick: Will make some comments under your comments above.

Larry- Since that block was a late VIN car, you must be right. Tonawanda must have cast both 942 blocks and 351 blocks in early June 66. The beginning and ends of model years seem to produce interesting anomalies.

Note: see comment #16, a correction that the early 351 block cited was cast F 17 6 not F 1 6.

[Larry E.]

Re: Very Early 1966 427 blocks

Patrick: Would also like to hear your theory on how late in the 66 year was the 942 cast? Also was there a time
frame where GM/Chevrolet cast both 942's and 351's. Thanks>Larry

[Patrick B.]

Re: Very Early 1966 427 blocks

Patrick: Would also like to hear your theory on how late in the 66 year was the 942 cast? Also was there a time
frame where GM/Chevrolet cast both 942's and 351's. Thanks>Larry

Larry- I shouldn't have relied on my memory when I said 942 blocks ended in May since I had a F 1 6 351 block at one time. I went back and checked my records, and my early 351 block was F 17 6 not F 1 6. I still think GM did not cast a block and its replacement at the same time. However, your F 6 6 942 block is no longer an anomaly in regard to a F 17 6 351 block. I can only conclude that the last 942 block was cast some time before June 17, 1966

[Larry E.]

Re: Very Early 1966 427 blocks

Patrick>Thank you so much for your insight on this subject. I enjoy your input on the Chevy Engines.
Thanks; Larry

[Robert B.]

IMG_6643.jpgIMG_8195.jpg 1966 car 351 block July date code

[Larry E.]

FWIW: Looks to me that all June 66 BB Corvettes used the "942" Casting
and the July Corvettes where made with both the "942" and "351" castings.
Comments Please>Thanks>Larry

[Mark F.]

Just curious - does anybody know what changes were made in the castings going from 952 to 351 ?

Joe Lucia has indicated C2 brake caliper castings changed in terms of casting iron composition (nodular vs grey iron)...could that have also applied to these castings ?

Were they interchangeable from an engine build perspective ?

[Patrick B.]

Mark—The oiling system around the rear cam bearing was changed from the 65-66 to the 67 and later arrangement requiring a different rear cam bearing and doing away with the groove in the 65-66 cam.

To make things even less orderly, while there are legit 66’s with 351 blocks there are also legit 67’s with 942 blocks on which the factory ground off the 942 casting number and hand stamped the 351 casting number with distinctive stamps. I assumed my F 17 6 block had the 67 style rear cam bearing but I should have checked it. I don’t know if GM did any alteration of the oiling system of the 67 942 blocks they stamped 351 on. They created ambiguity about what cam and cam bearing would be required for future rebuilds.

[Robert B.]

IMG_4030.jpgoriginal 66 351

[Mark F.]

Mark—The oiling system around the rear cam bearing was changed from the 65-66 to the 67 and later arrangement requiring a different rear cam bearing and doing away with the groove in the 65-66 cam.....To make things even less orderly, while there are legit 66’s with 351 blocks there are also legit 67’s with 942 blocks on which the factory ground off the 942 casting number and hand stamped the 351 casting number with distinctive stamps. I assumed my F 17 6 block had the 67 style rear cam bearing but I should have checked it. I don’t know if GM did any alteration of the oiling system of the 67 942 blocks they stamped 351 on. They created ambiguity about what cam and cam bearing would be required for future rebuilds.

Wow. Unless they really did the internal modifications as you mention above, I really don't see the point in changing the casting number. But there must have been a reason - they didn't just do it for fun...

And as you say, if not re-done internally it could also be a QA warranty problem...

if I recall correctly, when there were only a few "leftover castings" many times they were simply busted up and remelted in the cupola. That's the same thing that would happen w/ defective castings (they weren't "thrown away"). So, I'm guessing they must have had a fair number of the 942 blocks left to warrant making the internal mods (hopefully ); grinding off; and renumbering - rather than scraping them and sending over to remelt...we'll probably never really know...

[Patrick B.]

I doubt they would melt perfectly good expensive parts when they could sell them as service parts. Since it was just warrantee work that was of concern, maybe they just depended on dealer mechanics to replace cams and rear cam bearings with whatever style they encountered when they disassembled the engine. It is only restorers 60 years later encountering bare blocks rather than assembled engines that would be fooled by a bare 351 casting requiring a grooved cam and early bearing. A factory remarked 942 casting is pretty rare, and hopefully would be rebuilt by someone who investigated what parts were required or at least tested the oil flow before starting the engine. The most reasonable explanation for Tonawanda using 942 castings in 67 would be some supply problem with 351 castings.

[Mark F.]

I doubt they would melt perfectly good expensive parts when they could sell them as service parts...

Hi Patrick,

Thank you for your knowledge on these issues

I would agree if the "overruns" of 942s came at the end of the model year (think sometime in summer moving into the next model year), they may have been considered SERVICE replacement blocks - rather than PRODUCTION blocks.

Also, in that inter-model-year timeframe, service replacement runs of XXX? could have been run at each of the foundries...see below...

As you know, shutting down foundry lines is a VERY expensive process - so, for the literally thousands of castings needed (Corvette and all the other GM product lines), forecasting for future demand is a guessing game at best...

As for salvaging the cost of several (or many) engine blocks, keep in mind Foundries were not warehouses for parts that "might be used" sometime down the road. IOW No room at the foundry for "banking" blocks for future use or "potential sale".

My recollection back then was that auto manufacturers were required to have 10% extra parts (AKA service replacements) for each model year they produced after the last one rolled off the line...I could be wrong on that and have no documented source to verify it.

Many of those "excess" parts were in the domain of the outside suppliers auto manufacturers used.
Translation: force the inventory costs back on the suppliers as their cost of doing business.

As for castings (Corvette or not)...we know they were all GM-produced parts.

My experience at another BIG 3 auto manufacturer was that those "after-run-parts" were done as as separate runs and shipped directly to a warehouse - rather than over to the engine plant adjacent to the foundry...

My memory and recollections could certainly be incorrect, but I think the concept is justified...maybe even today ?

just my thoughts based on my work experiences...

[Larry E.]

FWIW>A picture of a ground off 942 casting number with a 351 stamp can be seen
on page 93 in the Alan Colvin "Corvette By The Numbers" book. It claims this block
was used and varified on a 67(435 HP) with serial #7115073. Larry

[Mark F.]

Hi Patrick, Thank you for your knowledge on these issues ...My recollection back then was that auto manufacturers were required to have 10% extra parts (AKA service replacements) for each model year they produced after the last one rolled off the line...I could be wrong on that and have no documented source to verify it.

As this Hemmings article points out, my assumptions and recollections noted above are apparently wrong...

https://www.hemmings.com/stories/ask-a-hemmings-editor-how-long-do-carmakers-have-to-provide-replacement-parts-for-older-cars/

[Larry E.]

FWIW>A picture of a ground off 942 casting number with a 351 stamp can be seen
on page 93 in the Alan Colvin "Corvette By The Numbers" book. It claims this block
was used and varified on a 67(435 HP) with serial #7115073. Larry

Hay Patrick: What surprised me here was the 67 VIN; which is well into the production
year. Sounds like they had an abundance of 942 blocks left at the end of the 66 run.
Comments Please>Larry