Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Difference Between 2 piece and 1 piece rear main Cranks

Discussion in 'The Garage' started by BigBurban350, Nov 10, 2003.

  1. BigBurban350

    BigBurban350 1/2 ton status

    Joined:
    Jun 9, 2002
    Posts:
    711
    Likes Received:
    0
    Location:
    Michigan
    Whats the difference between 2 piece and 1 piece rear main seal crankshafts?

    /forums/images/graemlins/usaflag.gif /forums/images/graemlins/burb.gif /forums/images/graemlins/usaflag.gif
     
  2. Fubeca

    Fubeca 1/2 ton status

    Joined:
    Dec 18, 2002
    Posts:
    2,100
    Likes Received:
    2
    Location:
    Denver Area
    2 piece seals are just that, 2 pieces the top half goes into a groove in the block and the lower half goes into the last bearing cap. A 1 piece seal is just one piece and it goes right into a retainer over the back of the crank. 1 piece is much easier to replace if you ask me.
     
  3. 84_Chevy_K10

    84_Chevy_K10 Banned

    Joined:
    May 30, 2001
    Posts:
    17,669
    Likes Received:
    0
    Location:
    IL, USA
    1 piece might be easier to change if the engine is out of the vehicle, but if it's in the vehicle, 2 piece is MUCH easier.

    I am not trashing on 1 piece RMS motors though as my trucks all have them.

    The cranks have different patterns to mount flywheels/flexplates in the back. besides that and the rear main seal surface, I don't know of any differences.
     
  4. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

    Joined:
    Dec 14, 2001
    Posts:
    22,060
    Likes Received:
    69
    Location:
    Pleasanton, CA.
    Engines with 1 piece rear main seals are also externally balanced on the back end so you will see a counter weight on the flywheel/flexplate.
     
  5. BigBurban350

    BigBurban350 1/2 ton status

    Joined:
    Jun 9, 2002
    Posts:
    711
    Likes Received:
    0
    Location:
    Michigan
    Let me refraise the question (my bad). I want to know why I cant put a Crankshaft made for a 2-piece rear main on a block designed for a 1-piece rear main. I am trying to find a 383 kit for my Suburbans 90' 350 TBI. The ones I find say for 2-pc rear main seal. /forums/images/graemlins/thumb.gif
     
  6. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

    Joined:
    Dec 14, 2001
    Posts:
    22,060
    Likes Received:
    69
    Location:
    Pleasanton, CA.
    You can install a 2 piece rear main seal crank into a 1 piece rear main seal block but you have to buy a 2 piece rear main oil seal adapter for about $150.00. Scat makes a 3.75" stroker crank for the 1 piece rear main seal block. I bought one about 3 years ago for my stroker build at the time and now I am about to buy another one for my present stroker build-up.
     
  7. 84_Chevy_K10

    84_Chevy_K10 Banned

    Joined:
    May 30, 2001
    Posts:
    17,669
    Likes Received:
    0
    Location:
    IL, USA
    If you use that adapter, which flywheel do you end up using? What do you end up with for a rear main seal when it's over?
     
  8. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

    Joined:
    Dec 14, 2001
    Posts:
    22,060
    Likes Received:
    69
    Location:
    Pleasanton, CA.
    You would use the flexplate/flywheel that fits the 2 piece rear main seal crank along with the old style 2 piece rear seal.
    The bolt circle on the 2 piece rear main seal crank is 3.58" while the 1 piece is 3.00" bolt circle.
     
  9. Triaged

    Triaged 1/2 ton status

    Joined:
    Feb 21, 2001
    Posts:
    3,808
    Likes Received:
    0
    Location:
    CA (LA/OC area)
    They make 1pc cranks and they are only about $20 more than a 2pc seal crank. Most of the places that sell the "kits" will just sell you the kit and just charge you the difference for a 1pc crank. Just give them a call and ask.
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,979
    Likes Received:
    189
    Location:
    Roy WA
    [ QUOTE ]
    Let me refraise the question (my bad). I want to know why I cant put a Crankshaft made for a 2-piece rear main on a block designed for a 1-piece rear main.

    [/ QUOTE ]

    The one piece rear main seal retainer goes on "OVER" the crank. (imagine slipping a rubber band over a paper towel roll) The flange on the crank is turned way down on the 1 piece rear main motors, so the seal and retainer can be bolted down "over" the crank.
     

Share This Page