C2 Oil Pan Drain Plug -- what's correct ?

[Wayne M.]

The '65 Tech Manual says (for SB's) "thin flat head 3/4 inch"; (for BB) "bolt head is 3/4 inch across the flats with a thin head approximately 1/8 inch thick"
Are these two descriptions of the same drain plug ?

OK, now what do I have ? -- two different plugs, one has magnetic tip and I got if from a May '65 961 2-bolt 396 big block. It takes a 7/8" wrench (not 3/4") and it's head is a few thou. shy of 1/4" thick. For head marking there's a capital "A" filling a circle of 1/4" dia. at the center of the head. There's also 3 punch marks in a triangle (0.46" to a side) enclosing the center markings. The second drain plug was given to me by a friend who says it came off a '66 L72. It is identical to the first plug except no magnet and absence of the 3 punch dots.

The GM parts catalogs aren't of much help -- the Rev. July 1/65 lists 3779764 for all Corvettes and Passenger (exc. 396 Sp. H/Per.), and 3866916 Magnetic, for Passenger and Corvette w/Sp. H/Per (396). Then, the '67 GM Parts catalog (Oct 1, 1966) calls for 3779764 for ALL Chev's, incl Corvettes, yet goes on to indicate 3866916 (magnetic) for '65-'66 Corvette w/Sp/ H/Per., F.I. (396,327); '65-'66 Passenger w/Sp. H/Per. (396, 427) and '66 Corvette (427).

So... what's right (head size / magnetic / markings) for C2's ?

[Gary B.]

C2 Oil Pan Drain Plug on my 66 L79 is 7/8"

Wayne,

The oil pan drain plug, which I beleive to be original, on my '66 L79 (327/350HP) is 7/8" across the flats, is more or less 1/4" thick and has the capital A inside a circle headmark. I don't see any evidence of the punch marks you mention.

This is another case when I believe the 3rd edition of the '66 TIM&JG is incorrect when it says the small block drain plus is 3/4" across the flats. I can't say if 3/4" is correct for BB.

Gary

[Eugene B.]

Re: C2 Oil Pan Drain Plug on my 65 is 7/8"

Wayne,
Another data point for your information. The drain plug on my '65 SB (250 HP) is 7/8" across the flats. It appear to be approx. 5/16" thick and has a recess in the center of the head approx. 1/4" diameter and is head stamped TR.

Hope this helps.

Gene

[Gary B.]

Wayne: PS to my 1st message

Wayne,

Regarding the 3 punch marks you noted. I didn't see any on my drain plug, but my engine is on an engine stand and the supporting column of the stand is about 2-3" from the drain plug, so I can't really see the plug close up. Pluse 1/2 of my plug has orange paint on it, so that makes it hard to see head details as well. In any case, if I were to remove the plug and clean it, I would be better able to tell you if it has the dimples or not, but I may not be able to get around to this soon.

Gary

[Wayne M.]

Thanks, Gary --- my hunch is...

... that the 3 "punch" dots (about the size of a fine point pen) might be an external indicator that it has a magnet on the stem, based weakly on my sample of only 2 plugs.

By the way; were motors shipped from Flint / Tonawanda with proper oil level in the pan ? Were the oil drain plugs and nylon washers on the pan when the engine was painted ?

[Gary B.]

Wayne: I don't know; many John Hinckley knows. *NM*

[Terry M.]

Re: Thanks, Gary --- my hunch is... *TL*

Wayne,
All V8 engines built at Flint (through Gen II) and Tonawanda (through at least Mark IV) were "hot tested." That is they were run on natural gas. Initial timing was set, and balance weights added at this station. Among the parameters verified at that station was engine oil pressure. To the best of my knowledge that oil remained in the engine when it was shipped to the assembly plant.

[John H.]

Re: Thanks, Gary --- my hunch is...

The oil that was added at the engine plants was drained immediately after the hot-test, filtered, and re-used many times over; the "initial fill" of oil (and the oil filter) were installed at St. Louis. The addition of 1.25 gallons of engine oil is shown in the A.I.M. in UPC 6, and in the UPC 0 "Lubrication" section.

[Mike M.]

Re: Thanks, Gary --- my hunch is...

john: what kind of carb was used with the natural gas fuel used during initial startup? thanks, mike

[Terry M.]

Re: Thanks, John for the correction *TL*

I must have missed the oil drain at both plants. I saw the coolant go through the grates, but that was only H2O.

[Terry M.]

Re: Thanks, Gary --- my hunch is... *TL*

What I saw didn't look like a carburetor, just a flexible pipe with a flange on the end. Since natural gas is already a vapor, and there is no liquid to turn into a vapor, no carb is need. There was an accelerator lever on the side of the pipe that looked like it might control a butterfly inside the pipe.

[Loren L.]

In loking back thru my parts books, it

appears that the magnetic drain plug appears for the first time in 1965 and its application is for the 396; interestingly, there is a differenct # for the pasgr 396; then in 1966 it is expaned to in its application to high performance 327's - a way of encouraging owners to buy a magnetic plug?