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Thread: Selecting the correct valve springs?

  1. #1
    Speedin' Ian
    I want to replace the valve springs on the motor I just purchased and I have a good idea of what I need, but I wanted to confirm with a few of the experts on here first. They're Dart aluminum heads and the cam is a solid roller with about .725 lift. I was thinking something with about 265-300lbs on the seat and about 750lbs when open. What do you guys think?
    Also one of the oil seals failed (I pulled off the valve cover and there was teflon and pieces of metal sitting in the valley of the head). I pulled the manifold and oil pan and it looks like everything stayed in the head, so we got lucky there. Can I replace this without removing the head? What do you think would cause one of those to break?

  2. #2
    Senior Member
    Join Date
    Mar 2010
    Posts
    883
    SI,
    What are doing with this thing?
    Race boat?
    Pleasure boat?
    What?

  3. #3
    Speedin' Ian
    It's basically a race boat... it's in a flatbottom and we only run it for a few minutes at a time. The motor is a blown injected 523, here's a few specs
    Bowtie block
    Dart Pro 1 heads
    intercooled
    1271 25% over
    Enderle injection
    TM shaft mounted rocker arms
    I'm going to pull one spring tonight so that I can measure the installed height and inner diameter, but the outer diameter is 1.625 and it looks like the seat presure is about 275 right now

  4. #4
    Speedin' Ian
    Near as I can tell the installed height is 2.1 Does that sound right?

  5. #5
    Fiat48
    2.100 is the tall spring and best way to go. At 275 on the seat...sounds to me like it is good to go. I run 250 to 260. I consider 220 lbs time to change.

  6. #6
    Speedin' Ian
    Well maybe these springs are fine... but I still need to replace the valve seal. Can this be done without removing the head? Do you know what would cause a valve seal to fail?

  7. #7
    Moneypitt
    Ian, you can use an air hold to keep the valve closed and remove the keepers and spring while the head is on the engine. OR my favorite, a ski rope stuck in the plug hole, about 18" worth, and rotate the engine by hand until it locks up, then the same operation. Just remember to turn the motor backwards when removing the rope...........Ray
    PS: see your PMs about the block.........

  8. #8
    Fiat48
    Well maybe these springs are fine... but I still need to replace the valve seal. Can this be done without removing the head? Do you know what would cause a valve seal to fail?
    Possibly the retainer hit it or if a triple spring is used maybe the inner spring got it. If just the one seal then maybe it worked loose off the guide or was not pushed completly onto the guide.
    Check retainer to seal clearance.

  9. #9
    Speedin' Ian
    Thanks for the advice guys!
    I'm pretty sure it is a double spring, but I will check all the things you mentioned. I kind of think it just worked it self loose.
    Can I press a new one on with out removing the head?

  10. #10
    Senior Member
    Join Date
    Mar 2010
    Posts
    883
    I agree with Fiat, around 260 to 275# on the seat.
    You'll have to air the cylinder and yes you can replace it without removing the head.

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