Cam lobe to crank throw clearance & cam lobe to rod

Discussion in 'Small Block Tech' started by Mart, Oct 5, 2018.

  1. Mart

    Mart '71 350 GS, almost stock

    What's acceptable using roller cam? Checking things out with the new build. Crank hits cam lobe big time!
    IIRC Mike at TA recommended at least .020.
     
    Last edited: Nov 7, 2018
  2. alec296

    alec296 i need another buick

    You have the Molnar rods?
     
  3. Mart

    Mart '71 350 GS, almost stock

    No on the molnars, not to that point yet. Degreeing cam, & crank throw hits lobe. Did the same only with different throw on last build too. Crank needs to clear roller cam lobes.
    This is a blue motor crank with a 68 block.

    What is, or is there a standard clearance spec?

    It clears after some surgical grinding, but only have .020 and think I should go with at least .035
     
  4. alec296

    alec296 i need another buick

    I would think you would want to go. 035 also. Maybe give Derek a call. He might have some thoughts there
     
  5. Mart

    Mart '71 350 GS, almost stock

    He likes .05
    Maybe JW or one of our top notch 455 builders here will have a desired spec.....
     
  6. Jim Nichols

    Jim Nichols Well-Known Member

    Mart, I have heard the later capscrew rod crank has larger counter weights. If your cam has super high lift and is advanced or retarded you may be even closer. I hope your timing chain never breaks.
     
  7. Mart

    Mart '71 350 GS, almost stock

    Lol, :Ddon't want timing chain to let loose, :eek: that's for certain. Yes, that's the whole purpose using the blue crank. Internal balance should use no or minimum mallory metal.
    And yup, it's all in the degreeing. Trying to have 4* retarded to 6* advance range with plenty of clearance.

    This is not my numbers matching motor, so I'm pushing some limits.

    Rod clearance is up next!:rolleyes:
     
  8. Mart

    Mart '71 350 GS, almost stock

    Here's 71, & blue motor cranks side by side....yellow area's are missing on the 71 crank, and other spots, So yes, the blue cranks have heavier throws. 20180417_143329.jpg 20180417_145620.jpg
     

    Attached Files:

    Last edited: Oct 6, 2018
  9. Mark Demko

    Mark Demko Well-Known Member

    Gee wizz, NEVER considered any differences in cranks:eek:
    My other crank ( the one with #3 rod journal ground down) was a ‘78 crank.
    The crank I’m running now I bought from TA many years ago, don’t know what year it is.
    Didn’t have any issues tho with the crank itself hitting the cam......... interesting :cool:
     
  10. Mart

    Mart '71 350 GS, almost stock

    Well rods hit too,:rolleyes: I'll take care of that.
    Meanwhile, crank/cam clearance is now .050 :) Front throw and second to last throw were hitting/tight/ marginal, at best.
     
  11. Jim Nichols

    Jim Nichols Well-Known Member

    Mart, Are you just going to angle the area where rod bolts stick through on cam side? What lift is your cam and what stroke is your motor? You are pushing the limits! On Chris's 300 Stroker (Late 350 crank and 350 capscrew rods) had no clearance issues in those areas. Just had to use washers under the windage tray and a little ball peen work on the bottom front shallow area of the oil pan.
     
  12. Mart

    Mart '71 350 GS, almost stock

    Yes Jim, rods will get chamfered/angle ground to clear. Lift is .584, stroke is slightly over 3.990, maybe 3.992
    Roller cam running solids. Advertised duration is 306/ 318, 107 lsa, 35 * overlap. Should wind up nicely.....

    Got the iron heads in for additional porting, trying to max out this N/A iron head build.
     
  13. Extended Power

    Extended Power Well-Known Member

    Marty, did you get my email?
     
  14. Mart

    Mart '71 350 GS, almost stock

    Yes Ivan, thanks. Great pics.
    Looks like a lot of "meat " needs to be removed to get .060 clearance. If that's what it takes, that's going to get done......

    You only advanced Haydn's cam +2?
    Did you still have additional room if degreed -4* and up to +6*?
     
    Last edited: Oct 10, 2018
  15. Jim Nichols

    Jim Nichols Well-Known Member

    Mart, Piston to valve clearance gets closer too. Advancing, the intake valve gets closer. Retarding, the exhaust valve gets closer. +4 degrees is usually safe, +6 is probably pushing your luck with high compression.
     
  16. Mart

    Mart '71 350 GS, almost stock

    20181011_072610.jpg Jim,
    Degreed cam at +5-1/2* last time it was together. Had .100 piston to valve clearance on both Int & Exh. Don't worry, I model clay all the potential tight spots.
    So far, this blue crank and my gearset line up perfectly square to this 68 block, go figure.....
     
  17. Extended Power

    Extended Power Well-Known Member

    Yes, we only went +2.
    Straight up, the cam was hitting the rods.
    We clearanced the #1 rod until we had about 0.070", and clearanced them all the same, checking all the while.
    I don't even wanna think about how many times we installed, and pulled each piston/rod.
    But, without doing that....it isn't gonna run at all before destroying itself.

    Way too much money into it to just call it "good enough", or "close enough".
     
  18. sean Buick 76

    sean Buick 76 Buick Nut Staff Member

    And people wonder why I’m not super eager to encourage others to stroke a 350... we pretty much see all the challenges here in this thread and I know full well the car would run super hard with a few less cubes... especially once boost is added.
     
  19. gsjohnny1

    gsjohnny1 Well-Known Member

    not a fan of stroking a 350 buick. too many compact areas for hitting each other.
    couple of things to consider stroking the 350.
    didn't some people worry about the bottom end and want to add a plate for block strength.
    has anybody taken in the issues of thermal expansion.
    has anybody taken in the issues of centrifugal forces by high rpm's. look at how the block was made.

    lastly, will it do 7500rpm all the time with a s/charger on it.....
     
    Mark Demko likes this.
  20. Mart

    Mart '71 350 GS, almost stock

    Yes, but same issues with Molnar rods using roller cam, same crank closeness also. TA even advocates checking crank clearances, so roller cams without a small base circle seem to be the factor.
    I don't know about your Hersch rods, but I would think if the strength/ size is configured like Molnars or Carrillos, you may have the same issues.

    You can't have strong rods that are dinky.:D
     
    300sbb_overkill and Mark Demko like this.

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