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Forged connecting rod oil hole

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  • Engine: Forged connecting rod oil hole

    I’ve noticed that many of the after market high performance connecting rods do not have the small oil hole in the rod at the big end. The hole is meant to squirt oil on the cylinder wall. All stock rods have the hole and replacement standard rods that are not numbered have the oiling hole on both sides of the rod. My question: I have a set of performance rods that do not have the oiling hole. Should I have this hole added to the rods or is it not really necessary?

  • #2
    Hi I recently overhauled a Ford 347 stroker and found the same thing , So i spoke to a couple of guys who know more about Hipo engines than I do and they said its normal , 1 guy is big on drag racing and the other roundy round racing , Even with the short skirt pistons in my engine there appeared to be No abnormal wear on the cylinder walls , and the reason for my overhaul A bad flat tappet cam ! Ed

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    • #3
      Performance connecting rods have not...had that hole for a LONG time, if ever. I don't think newer engines run that hole either. I know that "many" motorcycle engines run a hole in the rod, but that's to squirt oil into the underside of the piston to help keep it cool..!
      You can probably ask for it if you have custom rods made for the Stude engine if you feel the need.

      There's plenty (!) of windage in most engines to whip the oil around in the crankcase to soak the bottoms of the cylinders and then the piston will carry it up the cylinders.
      Just don't run a "vacuum pump" to evacuate the pressure from the crankcase. Then you may need an oil hole in the rod.

      Question...why do you run oil rings on the pistons ?
      Answer...to help control the...excess...oil, and keep it out of the combustion chambers.

      Mike

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      • #4
        Years ago, Joe Mondello had me machine half inch wide slots, 10 thou deep on the big end in order to ensure adequate oil squirting (and cooling) on the back side of the piston. I trust his wisdom.
        Bill

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        • #5
          Those holes are for lubing/cooling in a 'stock' motor. Stock motors usually don't get into higher RPM ranges, so they need it. 6 cylinder motors (most if not all) have them to help lube the camshaft. 'High performance' motors run at higher RPMs, so there is a lot of oil splashing everywhere. That is why there are holes in the rods, or not. If you are going to run your motor at lower, 'stock' type RPMs, then have the hipo rods drilled, or drill the holes yourself. You might have to drill through the bearing also, if it doesn't have one. Chamfer the bearing just a bit at the crank side if you do drill the bearings. Do you plan on running the motor above ~3000 RPM for extended times? Then you don't need the hole. If below ~ 3000 RPM, then you need the hole. With a 6 cyl motor, the cam lube hole is necessary at any RPM.

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          • #6
            Originally posted by yeroldad View Post
            Those holes are for lubing/cooling in a 'stock' motor. Stock motors usually don't get into higher RPM ranges, so they need it. 6 cylinder motors (most if not all) have them to help lube the camshaft. 'High performance' motors run at higher RPMs, so there is a lot of oil splashing everywhere. That is why there are holes in the rods, or not. If you are going to run your motor at lower, 'stock' type RPMs, then have the hipo rods drilled, or drill the holes yourself. You might have to drill through the bearing also, if it doesn't have one. Chamfer the bearing just a bit at the crank side if you do drill the bearings. Do you plan on running the motor above ~3000 RPM for extended times? Then you don't need the hole. If below ~ 3000 RPM, then you need the hole. With a 6 cyl motor, the cam lube hole is necessary at any RPM.
            Im sure it will see some 6k rpm’s but not often. Most of its life will be driving around like I drive any Avanti powered car. Occasionally it will get a good dose of right foot.

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