Intake valley pan, rubber seals? Yay or nay

Discussion in 'Small Block Tech' started by 70skylarkcusto, Apr 29, 2019.

  1. 70skylarkcusto

    70skylarkcusto God, Country, Cars

    Hey guys, m

    My rebuilt 350 recently started running really rough and no carb adjustments could remedy it. Checked for vacuum leaks and found one in the back of the intake.

    Low and behold there was actually oil pooling on the back of the block from the intake leak. As you can see in the pictures the rubber seal for the intake is not fully seated and sealing, on both sides! I can only imagine this must be the source of the leaks.

    I’ve read many things online, rubber seals, no rubber seals, black rtv/ the right stuff... rubber seals with a touch of rtv to hold them in place, but what is the best solution. I don’t want to have this happen again with the rubber seals getting out of position. Any advice is appreciated.

    Attached Files:

  2. MrSony

    MrSony Well-Known Member

    I've never been fond of using just rtv to seal the end rails, on any engine if the gap is larger than 1/4". I used rubber seals on both of my Buick 350s, no issues. just gotta make sure the dowel pins are still there, and the gasket ends get tucked up UNDER the valley pan gasket. The weight of an iron intake helps them stay put when putting the bolts in, from the looks of it you have aluminum. Just do your best to line it up.
    70skylarkcusto likes this.
  3. alec296

    alec296 i need another buick

    If you have the rail seals , use them. If you don’t have the experience , using just seal will cause leaks , as does types of sealer.
  4. Mark Demko

    Mark Demko Well-Known Member

    Those rubber end seals have no effect on engine vacuum or running condition, you could run without them, but it would make a mess
    1973gs and hwprouty like this.
  5. 70skylarkcusto

    70skylarkcusto God, Country, Cars

    I didnt think about it but I guess you are right. I did see a difference in running conditions with a bottle of ether sprayed in that area tho. When I loosened the intake it barely took any force, i wonder if my engine builder never torqued the thing down right and thats where my vacuum leak came from
  6. Mark Demko

    Mark Demko Well-Known Member

    If idle changed when you sprayed ether in that area you prolly have a leak at one or more of your intake ports, or at the base of the carb
  7. UNDERDOG350

    UNDERDOG350 350 Buick purestock racer

    I never use the rubber seals. Best quality oil resistant RTV with dry/degreased surfaces. Then don't run the engine for 24 hours.

    My stuff is all cut down and the seals would just hold the intake off the heads.
    Mark Demko likes this.
  8. patwhac

    patwhac Well-Known Member

    I've always had the rubber seals want to squish out when installing an intake, even if the dowel pins were there and I RTVed the seals down and let them sit for a day first. However they haven't leaked, just looked bad. I just tried the RTV only thing on my Lincoln and it leaks from the back, probably didn't do a big enough bead :mad:
    Mark Demko likes this.
  9. Mark Demko

    Mark Demko Well-Known Member

    Yeah you gotta build up a nice tall bead for sure
  10. gstewart

    gstewart Well-Known Member

    Rubber seals with some black Permatex added on the ends.
  11. gsgnnut

    gsgnnut Well-Known Member

    I Always used the seals and black permatex on the corners. Gotta set the intake super close to perfect or you chance pushing the seals out. If you don't slide the intake and set it on the pins cleanly it won't leak. Done it lots of times. Gotta torque the intake with the 3 step torque method., use the center out to the ends criss cross pattern.
  12. 70skylarkcusto

    70skylarkcusto God, Country, Cars

    Got her back together, let her sit for a day then fired up. No leaks yet. thanks guys
  13. knucklebusted

    knucklebusted Well-Known Member

    The secret to using only RTV, especially on a set of heads or block that have a fair bit of milling, is to drop the intake straight down. You cannot slide it into the place. You need to get it as close as possible on the first try.
  14. jay3000

    jay3000 Well-Known Member

    Things get complicated when things have been milled over the years. It's easy if it's on the engine stand, but what I did successfully is to cut the ridges off the top of the gasket with a razor. Test fit it dry. Use a layer of RTV under, and then on the top. Then let it cure. Put plenty on the corners.
  15. 70skylarkcusto

    70skylarkcusto God, Country, Cars

    I actually did it in the car with zero issues. My heads have barely been decked, and I had a buddy get on the other side of the engine bay to help me line her up and drop it straight down so nothing would get out of place. Snugged it by hand twice, then torqued it to 30 ft pounds then 40 then to the 5o recommended by TA. went very smooth

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