Resizing Connecting Rods

Discussion in 'Rotating Assemblies' started by Grumpy, Dec 15, 2020.

  1. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    I stopped over at a buddys shop where hes assembling a 383 SBC
    I notice the used connecting rods he was about to use,
    had obvious marks from the previously used ,bearing shells
    I asked him if the rod bolts were NEW ARP rod bolts or if the rods had been reconditioned
    (obviously, they were not) keep in mind ... connecting rods can stretch or the larger end can expand.
    and if the larger end expands, or is re-used without being resized,
    the bearings can get loose and for darn sure the bearing clearance can loosen,
    causing a loss in oil pressure, as the bearing clearance to crank journal ,
    oil flow clearance expanded.
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    use
    plastic gauge to check clearances at a minimum
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    I suggested we measure the rods so I went home and got a few tools
    every connecting rod from that engines was both out of spec and at least .002-.003 over size
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    Fowler Full Warranty Extender Dial Bore Gage Set, 52-646-400, 1.4-6" Measuring Range, 0.0005" Graduation Interval: Bore Measurement Gauges: Amazon.com: Industrial & Scientific
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    Fowler Full Warranty Extender Dial Bore Gage Set, 52-646-400, 1.4-6" Measuring Range, 0.0005" Graduation Interval: Bore Measurement Gauges: Amazon.com: Industrial & Scientific
    www.amazon.com

    6 Pcs Professional Premium Outside Micrometer Precision Machinist Tool Set 0-1"/1-2"/2-3"/3-4"/4-5"/5-6" Measuring Range Included 0.0001" Graduation: Amazon.com: Industrial & Scientific
    6 Pcs Professional Premium Outside Micrometer Precision Machinist Tool Set 0-1"/1-2"/2-3"/3-4"/4-5"/5-6" Measuring Range Included 0.0001" Graduation: Amazon.com: Industrial & Scientific
    www.amazon.com


    IT rarely makes any financial sense to resize OEM connecting rods
    (especially SMALL BLOCK RODS)
    as the cost is generally higher to recondition used connecting rods and add ARP rod bolts to old rods and the new SCAT rods with 7/16" rod bolts are easily twice as strong as reconditioned connecting rods.

    yes you may need to rebalance the rotating assembly


    https://www.summitracing.com/parts/sca-25700716


    HIS COMMENT WAS RATHER COMMON.
    " you know something, Paul, I watch you work, and bring over the precision measuring tools,
    I don,t know if you're saving me from having the engine fail,
    or saving me from making a great many mistakes
    or just costing me a great deal of extra cash at times"













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    if you skim over or ignore reading
    the RELATED info/links
    you are cheating and potentially hurting only yourself

    http://garage.grumpysperformance.co...ols-than-some-guys-may-want.16414/#post-99621

    http://garage.grumpysperformance.com/index.php?threads/rod-bolts-rpm-vs-stress.341/#post-30778


    http://garage.grumpysperformance.co...ng-and-basic-piston-ring-info-youll-need.509/

    http://garage.grumpysperformance.co...g-and-installing-connecting-rods-pistons.247/

    http://garage.grumpysperformance.com/index.php?threads/bearing-clearances.2726/#post-43385

    http://garage.grumpysperformance.co...market-4340-connecting-rods.13321/#post-72047

    http://garage.grumpysperformance.co...n-wrist-pins-one-really-over-looked-part.978/

    http://garage.grumpysperformance.com/index.php?threads/can-i-get-it-polished.9214/

    http://garage.grumpysperformance.com/index.php?threads/engine-balancing.3900/
     
    Last edited: Dec 26, 2020
  2. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    Last edited: Dec 27, 2020
  3. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member


    well, Id start out by saying that there are very few SBC connecting rods worth rebuilding, especially Id trash any of the newer cracked powdered metal rods
    simply due to the fact that even after being rebuilt,
    they will not be even 60% as strong as most of the better SCAT aftermarket connecting rods,
    that cost less than rebuilding the OEM rods cost.
    ask your local machine shop what they charge to install new ARP rod bolts
    \,in your existing connecting rods

    (remember the OEM bolts and connecting rods have been through MILLIONS of compression/tension stress cycles)
    then resize and mag check all the existing connecting rods for micro-cracks
    you'll rather rapidly find the aftermarket SCAT rods are a BARGAIN, even after the cost to rebalance the rotating assembly if thats required.

    there are some very good quality BBC connecting rods that are worth rebuilding,
    but even there, the aftermarket rods still have a measurable strength and lower cost advantage.
    connecting rods and the rod bolts that hold them together are some of the higher stressed components in any performance engine, and knowing that it really tends to require the engine builder to look into his options, and do the required research.
    I generally look at SBC connecting rods a bit like fan belts and clutch discs , they are simply a component that's reasonably inexpensive in most cases and since they take a great deal of excessive stress they are best replaced when any engine is rebuilt, especially considering the fact that the cost incurred for a skilled machine shop to resize, mag check the rods for stress cracks, and replace the rod bolts easily exceeds the cost of the better aftermarket connecting rods with in most cases much stronger rod bolts and a easily demonstrable, increase of at least 50% or up to 200% in strength, in the better designed name brand rods.
    there are a few OEM BIG BLOCK CONNECTING RODS that are worth rebuilding, but even there, the better aftermarket rods hold some significant advantages in strength, and clearance.
    considering the extensive damage that can and usually does result if a rod bends or a rod bolt fails, its well worth the builders time and the required effort to buy, inspect and install stronger connecting rods, rather than just reinstall OEM rods with millions of compression & stretch stress cycles already endured.



    http://www.callies.com/connecting-rods/

    https://www.summitracing.com/search...necting+Rods&utm_campaign=General+Terms+A+-+C

    http://www.wiseco.com/Automotive/CrankshaftsConnectingRods.aspx

    https://www.crower.com/rod-inventory

    https://www.cnc-motorsports.com/eng...MI7_fg_d347gIVr__jBx2MDQYnEAAYAyACEgJhwfD_BwE

    Last edited: A moment ago




    as usual...watch the videos and read the links :D











    https://www.motor.com/magazine-summary/performance-perspectives-connecting-rod-inspection/#:~:text=Always inspect any connecting rod,plane with the small end.

    http://garage.grumpysperformance.com/index.php?threads/rod-bolts-rpm-vs-stress.341/
     
    Last edited: Feb 20, 2021
  4. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

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