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Projects Old school cool 248 Gmc

Discussion in 'The Hokey Ass Message Board' started by Neb Hillbilly, Dec 26, 2019.

  1. Baumi
    Joined: Jan 28, 2003
    Posts: 3,043

    Baumi
    ALLIANCE MEMBER

    Wow , this sixxer sounds great! Maybe this^ may have something to do with the low oil pressure issue at low rpm?
     
    loudbang likes this.
  2. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 339

    Neb Hillbilly
    Member

    possibly, I am going to reduce it to 3/16 and see if it helps.

    Sent from my S48c using The H.A.M.B. mobile app
     
    Baumi and loudbang like this.
  3. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 339

    Neb Hillbilly
    Member

    Happy independence day. I hope everyone enjoys the day with family and friends while remembering the cost many paid to allow me to play with Old junk GMCs and other pursuits of happiness!

    Sent from my S48c using The H.A.M.B. mobile app
     
    Last edited: Jul 5, 2020
    64zim, LAROKE, Gofannon and 6 others like this.
  4. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 339

    Neb Hillbilly
    Member

    Haven't had a chance to do much because of work. Added more rope to tighten the rear main seal and added o-rings to the dist to stop leaks. Reduced the oil to the head to a .095 hole. Started it today, still to much oil at the top, reduced the hole size to .067 (half the area of the .095") and it appears the oil to the rockers are much better. Still lots of oil but doesn't over run the glued on gasket at idle. Hot idle pressure up to 20 psi. Rear main might be leaking again, might have to come up with a new solution.

    Sent from my S48c using The H.A.M.B. mobile app
     
    jimmy six, 6-bangertim, 64zim and 3 others like this.
  5. jimmy six
    Joined: Mar 21, 2006
    Posts: 14,795

    jimmy six
    ALLIANCE MEMBER

    Not heard much about Ned and his build. Been thinking about the rear main and my thought is to add a PCV system. I did on my sons and no leaks with the same rope seal. The rear main cap in front of the seal has a great drain hole.
    Funny as it sounds, I just added a PCV system in my Ford y-block and it’s drip from the rear main is all but gone.
    The 2 photos show our GMC’s system. The valve is a V100 for a 65 Chevelle and screws in behind our center carb but can go anywhere near the center of an intake. By expanding the photos where my son is checking temps you can see the line from the old draft tube that’s now sealed and has a 3/8” pipe boss on it. A proper system will show 1-3” of vacuum on the engine at idle while holding your palm on the oil fill or breather. I take the vacuum off the dip stick hole. These #’ are from reading factory engineering. 6818F0FC-5D57-45FE-AFE0-01EE8C1A7797.jpeg 4CC18949-9707-428E-875F-B1D1B876641E.jpeg
     
  6. Six Ball
    Joined: Oct 8, 2007
    Posts: 5,776

    Six Ball
    Member
    from Nevada

    Ned, Any Progress?
     
  7. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 339

    Neb Hillbilly
    Member

    I haven't got it running. It is in the truck but life and now the summer heat got in the way. After harvest I will get back at it. IMG_20201226_135406.jpeg IMG_20201227_173706.jpeg IMG_20201228_143311.jpeg
     
    Cosmo49, LAROKE, Jet96 and 7 others like this.
  8. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 339

    Neb Hillbilly
    Member

  9. Six Ball
    Joined: Oct 8, 2007
    Posts: 5,776

    Six Ball
    Member
    from Nevada

    Thanks for letting us know. Sounds good.
     
  10. Gofannon
    Joined: Feb 8, 2007
    Posts: 924

    Gofannon
    Member

    I watched that clip of your truck running this morning, then my pistons arrived for my similar build spec GMC 270 with 302 head in the afternoon. I'm looking at similar cam specs so great to hear how it should sound.

    upload_2022-9-20_17-50-9.jpeg
     
    Baumi and nunattax like this.
  11. Six Ball
    Joined: Oct 8, 2007
    Posts: 5,776

    Six Ball
    Member
    from Nevada

    Thise are nice looking pistons. Do you know how the weight compares to stock?
     
    nunattax and SilverJimmy like this.
  12. Gofannon
    Joined: Feb 8, 2007
    Posts: 924

    Gofannon
    Member

    745.8 grams.
     
  13. robert4005
    Joined: Jul 14, 2009
    Posts: 48

    robert4005
    Member

    If you don’t mind telling how much did they set you back? I have a 270 with 819 small chamber head I’d like to rebuild and replacement oem type pistons don’t appear to be available anywhere.
     

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