1970 Oil Pan Bolt (aka plug) marking

Discussion in 'Original Drivetrain Topic' started by DCL70, Apr 29, 2012.

  1. DCL70

    DCL70 Veteran Member

    1,209
    1
    May 5, 2007
    Merrimack, NH
    I would like to know the correct marking (or markings) on the oil pan bolt (aka plug) from original 1970 Camaro engines made in Tonowanda. According to my 1970 Chevrolet parts catalogs the GM part number is 3923420 in Gr. 1.456 and is described as "1/2"-20 X 13/16" - non-magnetic". The gasket is listed as GM # 3921989 ("nylon 1/2" I.D. X 29/32" O.D.).

    I have a bolt from a 1970-1974 oil pan with the letter "A" inside 2 concentric circles with 9/16" hex head (actually a washer-head) as shown in the link below. The threads are 1/2"-20 by about 0.50" long. The end of the bolt does not have any threads and measures 0.41" in dia. and 0.34" long. The net length of the bolt measures about 0.84" (13/16" = 0.81"). The "smushed" nylon washer measures about 0.92" in dia. (29/32" = 0.91").

    BTW, the main bolt that holds my 1970 factory Hurst shifter onto the transmission has the letter "A".

    I assume the oil pan plugs installed on 1970 Z28 engines from Flint had different markings.

    I would appreciate any comments after the next oil change from those with original engines.

    I also have a oil pan bolt from a 1969 oil pan that is almost identical. The marking is in the shape of a "dog bone" of "bow tie" with rounded corners.

    Dave

    http://imgur.com/a/syoJz#0
     
    Last edited: Apr 29, 2012
  2. spons

    spons Veteran Member Lifetime Gold Member

    427
    0
    Mar 21, 2010
    Indy
    Did an oil change yesterday on my 70 LA-built SS350. Looks like I need to get a new nylon washer for next time.
    [​IMG]
     
  3. DCL70

    DCL70 Veteran Member

    1,209
    1
    May 5, 2007
    Merrimack, NH
    Andy,

    You oil plug looks exactly like the one that I have on a 1969 oil pan. I assume your engine was built in Tonowanda.

    According to my 1970 Chev. parts catalog the nylon washer should measure 1/2" I.D. and 29/32" O.D. (0.91")
    My original washer measures about 0.94" O.D., 0.50" I.D. and about 0.065" thick.

    I found a suitable replacement nylon washer made by Dorman (part # 65270, M12-1/2"). It actually measures about 0.99" O.D. . 0.55" I.D., and about 0.065" thick.

    Thanks for your reply.

    Dave
     

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