66 Big Block

[John C.]

Gentlemen

I'm restoring a 66 BB (built date Dec. 8, 1965). In the archives some people say that all right side valve covers should have indent for AC bracket even on 425 HP. What's you opinion? I have a regular set of valve covers with no indent. Do you think I should use them? I don't want to lose any points in judging. Thanks,
John

[Michael H.]

Re: 66 Big Block

Gentlemen

I'm restoring a 66 BB (built date Dec. 8, 1965). In the archives some people say that all right side valve covers should have indent for AC bracket even on 425 HP. What's you opinion? I have a regular set of valve covers with no indent. Do you think I should use them? I don't want to lose any points in judging. Thanks,
John

The 425 HP right side valve cover did not have a depression for the A/C compressor that was only available on 390 HP cars for 66. There were two separate part numbers for the right side covers. One for 390 HP and one for 425 HP.

[John C.]

Re: 66 Big Block

Thanks Michael
John

[Steven S.]

Re: 66 Big Block

I was under the impression that all BB cars regardless got the right side indent cover during it's use in production, but after reading Michael's post and re-reading some information I have it sounds like all L36 cars regardless of C60 or not got the indent. Anybody else care to comment?

EDIT: TIMJG is suggesting dimpled valve cover was used on all BB engines regardless, although it sounds as though this is a grey area.

[Michael H.]

Re: 66 Big Block

I was under the impression that all BB cars regardless got the right side indent cover during it's use in production, but after reading Michael's post and re-reading some information I have it sounds like all L36 cars regardless of C60 or not got the indent. Anybody else care to comment?

EDIT: TIMJG is suggesting dimpled valve cover was used on all BB engines regardless, although it sounds as though this is a grey area.

If that's exactly what the JG states, it should be corrected to say "all 66 L36/390 HP engines" instead of all 66 big block engines.

The 1966 printing of the parts book agrees, there are two different covers/numbers shown for the right side of 66 big blocks.

The RH cover for L36/390 HP is part number 3893232. It's shown for all 427 exc. Sp. H/Perf. There's no mention of it being unique to cars with A/C even though it has the depression for the compressor. That means all L36's had the 232.

The RH cover for L72/425 HP is part number 3877632. It's shown for 427 with W/Sp H/Per.

I'm not sure if the 3893232 was used for the entire 66 model year. It's likely that very early production L36 cars did not have the cover with the depression.

[Mike M.]

Re: 66 Big Block

Hi Michael,
is it possible that even though there were two part numbers, that one or the other may have been installed solely for a period of time?

Or, another way of stating the question is; just because there were part numbers assigned for a specific application, yet a potentially interchangeable application, is that a guarantee that one or the other, or, both were actually used.

A good deal of current research and surveys indicate that the right side "Dimples" were used on both engines from sometime in November, '65 through January, '66, then back to the two separate covers.
Perhaps, due to the dimple being unnecesary on the L72.
Could this have been a cost cutting measure to use a single supplier, then abandoned?
Another thought, material shortage, vendor problems?
Were you still on the engine dress line during that time span?
Looking forward to your thoughts.
HaND

[Michael H.]

Re: 66 Big Block

Hi Michael,
is it possible that even though there were two part numbers, that one or the other may have been installed solely for a period of time?

Or, another way of stating the question is; just because there were part numbers assigned for a specific application, yet a potentially interchangeable application, is that a guarantee that one or the other, or, both were actually used.

As always, anything is possible. However, I seriously doubt any standard/non dimpled covers wound up on L36/390 HP engines because that dimple was there for a reason. If it wasn't important, engineering definitely wouldn't have spent the money/time to introduce a specific part if it's unnecessary. GM was/is kinda funny about things like that.
If only some of the L36 engines had the depression in the cover, that would have meant only some of the L36 engines could have been used with A/C and the guy that picked the engines off the rack at St Louis would have had to climb up and look for one with the dimple if the manifest called for L36 w/AC to be next up.

It's entirely possible that the L36/390 HP cover could have wound up on some L72 engines, although I don't think I've ever seen one. It certainly wasn't GM's intention to mix the 632 with the 232. If it was, they would have just dropped the 632 non dimpled cover.

I may be wrong but... wasn't the L36 cover lacking the rocker arm drippers in 66?? If so, that would be a reason why the L36 cover wasn't used on L72.

I have several GM pic's of L72 engines and none that I remember have the dimple.
My 66 is a Nov 65 build and the old warped/bent right side cover sure looked original when I bought the car 25 years ago.

In the mid 60's, I didn't even know what the Corvette plant looked like.