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New connecting rod question - possible problem

Discussion in 'The Hokey Ass Message Board' started by tjet, Jan 6, 2013.

  1. tjet
    Joined: Mar 16, 2009
    Posts: 1,294

    tjet
    Member
    1. Early Hemi Tech

    I just got a new set of SBC PM connecting rods. It seems like the caps are misaligned at the bevel side (has a ridge) The bearing area & sides are ok though.

    Anybody seen this before?

    Chevy p/n 12495071
     

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  2. J. A. Miller
    Joined: Dec 30, 2010
    Posts: 1,788

    J. A. Miller
    ALLIANCE MEMBER
    from Central NY

    While your drawing is very nice, I think a photo would help us better see what you have.
     
  3. tjet
    Joined: Mar 16, 2009
    Posts: 1,294

    tjet
    Member
    1. Early Hemi Tech

    gotta find the camera.

    The "edge" is on the chamfer side, where the cap contacts the rod.

    Will get a pic
     
  4. Dan Timberlake
    Joined: Apr 28, 2010
    Posts: 1,378

    Dan Timberlake
    Member

    "The bearing area & sides are ok though."

    I'm thinking you >>may<< be describing "cap shift" which is one of the typical bad things that happens when rod or main bearing caps are switched, or rod bolts are replaced.

    The horizontal moveable points of the Sunnen bore gage are measuring a diameter just above this rod's parting face.
    http://image.hotrod.com/f/techartic..._9903_06_+chevy_connecting_rods+new_bolts.jpg
     

  5. 54nomore
    Joined: Nov 5, 2012
    Posts: 137

    54nomore
    Member
    from illinois

    If you're talking about powdered metal rods that are broken instead of machined on the mating faces, I seem to remember that condition being pretty typical and NOT a problem. I've been out of the machine shop biz for a couple of years now, so it's been awhile since I've seen those rods. A picture would refresh my memory, I'm sure;).

    Ron.
     
  6. tjet
    Joined: Mar 16, 2009
    Posts: 1,294

    tjet
    Member
    1. Early Hemi Tech

    Here's a few pics. I tried to illuminate it with a lazer to help show the shadow. My retna's are hurting now...Best I could do
     

    Attached Files:

  7. tjet
    Joined: Mar 16, 2009
    Posts: 1,294

    tjet
    Member
    1. Early Hemi Tech

    step prob measures around .005
     

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  8. 54nomore
    Joined: Nov 5, 2012
    Posts: 137

    54nomore
    Member
    from illinois

    That does seem a little more "off" than I remember seeing, but could still be OK. Have you taken a cap off yet, and are they all this way?
    Are they new from GM?
    Do you know what I mean when I say the rods are "broken"?
    If you seperate the rod and cap, it should be pretty easy to tell if the cap matches the rod as the irregular surfaces kind of interlock.
    The reason I ask if they are new VS. reconditioned is because the reconditioned rods of that type are usually opened up .002" because the mating faces can't be ground on (or at least, they SHOULDN'T be!),
    thus requiring special bearings with a larger OD.
    Anyway, if the thrust faces line up and there is no step in the bore at the parting lines, the mismatched chamfer really doesn't matter since it doesn't make contact with anything.

    Ron.
     
  9. tjet
    Joined: Mar 16, 2009
    Posts: 1,294

    tjet
    Member
    1. Early Hemi Tech

    Yeah, they all have the same issue. I do know what you mean. I worked in a shop that pressed PM parts. Brittle as hell until they go thru the oven. Clever idea on breaking the big end - these are new BTW

    I'm going to talk to a local machinist & get his opinion

    Thanks!
     
  10. kennkat
    Joined: Aug 25, 2011
    Posts: 1,383

    kennkat
    Member

    I don't use Powdered Krap Con Rods, period... and speaking of
    period" what are we speaking of this new type of rod here on the H.A.M.B. for??? I think this belongs on an engine site somewhere... No?? Just my tired ass old as dirt opinion.
     
  11. tjet
    Joined: Mar 16, 2009
    Posts: 1,294

    tjet
    Member
    1. Early Hemi Tech

    did you have previous problems with PM rods?

    Going in a vintage engine, I hope that's period enuff for you :D
     
  12. BOBCRMAN
    Joined: Nov 10, 2005
    Posts: 846

    BOBCRMAN
    Member
    from Holly

    I rebolt/resize a lot of these rods. The left turn racers love them.
    It is common for the chamfers to be mismatched. As long as the big sides are parallel and the hole is round and in spec. They will work fine. A tougher rod than the old "Pink" rod.
     
  13. Deuces
    Joined: Nov 3, 2009
    Posts: 22,024

    Deuces
    Member
    from Michigan

    I'd rather have a set of the old school "pink" rods...
     
  14. moefuzz
    Joined: Jul 16, 2005
    Posts: 4,950

    moefuzz
    Member

    Rods are typical of GM quality. Lotsa late model corvettes and trucks with blown bottom ends due to GM wanting you to buy more engines/parts more often.

    nothing new here...


    .
     
  15. tjet
    Joined: Mar 16, 2009
    Posts: 1,294

    tjet
    Member
    1. Early Hemi Tech

    Ok, that's good. The mis-match is on the non-machined area of the chamfer. Everything else looks A-ok
     
  16. kennkat
    Joined: Aug 25, 2011
    Posts: 1,383

    kennkat
    Member

    You mean besides the built in obsolescence? As in they are not re-buildable? Or the New parts and equipment needs created by them? (if you hope to re-build / reuse them someday) or how about the whole "powdered, molten poured in a mold" concept.... No give me an OEM or aftermarket forging any day.... Again just my tired ass, old as dirt opinion, after 38 years doin this for a living
    and no, its really not about "the engine" it is not even about your choice of rod, it's your $, but it is about this forum being about traditional Hot Rods and supposedly about building them in a traditional way with traditional "stuff" Your issues deserve attention, on an engine builders site...
    again, just my tired ass, old as dirt opinion, after 38 years doin this for a living .
     
  17. tjet
    Joined: Mar 16, 2009
    Posts: 1,294

    tjet
    Member
    1. Early Hemi Tech

    I was looking for original z28 or pink rods, $$
    These were Plan B.

    Thanks for all the info :cool:
     
  18. GeoZ1
    Joined: Jan 4, 2013
    Posts: 74

    GeoZ1
    BANNED
    from Illinois

    You would have been better off with a Eagle rod. But, you own these already. Have you fitted a bearing in the rods yet, or are you just inspcting them before they go in your closet until your ready to use them.
     
  19. tjet
    Joined: Mar 16, 2009
    Posts: 1,294

    tjet
    Member
    1. Early Hemi Tech


    yep - going in the closet for a few months at least

    Wanted to stick with GM.
     
  20. Deuces
    Joined: Nov 3, 2009
    Posts: 22,024

    Deuces
    Member
    from Michigan

    Those are chinese rods....:rolleyes:No thanks!
     
  21. truck
    Joined: Feb 24, 2009
    Posts: 116

    truck
    Member
    from Brisbane

    And you wonder why people either don't ask questions on here, or why you don 't see much fresh blood at shows etc with attitudes like this wanker.
     
  22. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    Sorry Tjet, you sent me this last night, I didnt get off my lazy ass and look at it till today. Does the crank you are going to use these a substantial fillet radius? That would be the only area that i can see that might create a problem. The photos are hellacious hard to see, but that is a pretty big step. Kinda ugly looking, it would bug the hell outta me too.
    And yea, I see what you meant in your pm.:rolleyes:;)
     
  23. tjet
    Joined: Mar 16, 2009
    Posts: 1,294

    tjet
    Member
    1. Early Hemi Tech

    I sent those rods back. I ended up getting a set of Crower Sportsmans with 7/16" capscrews & pressed pins. The crank I'm using is a forged "1182". 4 bolt, forged flat-tops, zero decked. Setting rev limiter at 7000 RPM

    This is the tunnel ram motor that's still at the dyno. Gonna get it next month :D
     
    Last edited: Jan 15, 2014
  24. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    No first-hand experience with pm rods, but I've heard good and bad about those rods. They are supposed to be stronger than "pinks", but kinda like hyperutectic pistons, when they DO fail, they FAIL, like disintegrate. Not pretty. I could see that rod causing fit issues on a crank like a scat 9000 series or similar.
     
  25. Good move. Rods are one of those things that you can't cut corners on. Or have odd mis-matched chamfers on. For years I've bought my rods OTC at my local Chevy dealer. Never an issue and the price was always acceptable.

    Bob
     
  26. under 400hp pm rods are reliable built a dozen or so motors in the last couple years and the rods didn't fail i wouldn't say the same for hyperutectic pistons. which prefer not to use
     
  27. pitman
    Joined: May 14, 2006
    Posts: 5,151

    pitman

    thanks for asking...I learned something here.
    "Hard to tell, not-knowin'!"
     

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