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Piston rings and refreshing an engine.

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  • Engine: Piston rings and refreshing an engine.

    I'll try to keep a long story short while retaining all the facts.
    Back in the early 90s, I rebuilt a 1964 259. It ran well, and had good oil pressure. It was installed in a car, driven around 200 miles, then sold.

    The new owner completely disassembled the car, lost interest, and eventually passed away. I bought it in bushel baskets from his estate a couple of years ago.

    I'd like to think I've learned a few things about engines since then, so a teardown, inspection and reseal was in order.

    It is spotless inside, honing marks still present on the cylinder walls with no shiny areas, bearings excellent with clearances in spec, etc.

    But, the rod bolts do not fit tightly. When the cap is removed, most will fall out on their own weight. This is unacceptable for to me, even for use in a sedate 4 door cruiser.

    I have another set of rods, with ARP bolts installed, and resized.

    The question is: Can the pistons be removed, new rods substituted, and everything reassembled in their original places with no ill effect? It has genuine Studebaker chrome piston rings.


  • #2
    Unless they are the exact same weight, they will be off balance and the crankshaft will have to be balanced to the new weight.
    Bez Auto Alchemy

    "Don't believe every internet quote" Abe Lincoln


    • #3
      Bezhawk, Your answer breeds more questions:

      This engine was not balanced during the rebuild. The new rods are stock, only the rod bolts have been changed.

      Were Studebaker engines balanced that closely? I have noticed different die numbers on rods of the same side in the same engine. I would think that different dies would produce different weights. What amount of weight difference is tolerable? Are we talking about big end weight or small end weight?

      There is a whole ugly bag of snakes here, and I am prone to over analyzing things.

      When you replace pistons, bearings, and etc. with other than Studebaker factory parts, everything is going to be of slightly different weight. This is a frightening concept for the OCD
      among us.

      So, the best course would be to take the rods, crank, flywheel and pistons to be balanced?

      Thanks for the help,


      • #4
        Many engines have been rebuilt as you did your 1st. time and left with the slight out of balance that happens when Pistons are replaced, for normal driving it has worked for thousands of all makes of Engines. It will not be much different than with the other Rods.

        However if you want to do some "Higher RPM" for longer distances Driving, perfect balance is best.
        There also should be a Longevity issue possibly as well, as good Balance Should = longer life.
        But the actual Amount of imbalance and Life are both unknowns.

        If you do this, just remember that the Machinist needs ALL Cleaned Rotating Parts
        : Crank, Pistons, Rings, Rods, Bearings, Lock Bolts, Clutch, Flywheel or Flex Plate to Crank Pulleys, and Hardware.
        Second Generation Stude Driver,
        Proud '54 Starliner Owner
        SDC Member Since 1967


        • #5
          "But, the rod bolts do not fit tightly. When the cap is removed, most will fall out on their own weight." Are you saying the cap falls off, or the bolts fall out of the rod if the piston & rod assemble is turned upside down? Since you rebuilt the engine yourself, 30+ years ago, did yo reassemble it correctly? If bearing clearance is OK, I'd think the rod bolts are OK as is, whether it's the bearing caps you are talking about, or the rod bolts. I'd spin the oil pump long enough to build oil pressure on the gauge, then start the motor and run it in. IMHO, you are wasting time trying to 'fix' something that may not be broke. OTOH, if you have serious doubts about your work in 1990, then maybe just e-do everything. Only you know whether that's really needed or not. Good luck.

          As for balancing the rotating components on the motor, I done it both ways, and cannot tell any difference between balanced and unbalanced. Unless a rod is an 'odd ball' among a set, i.e. someone replaced one with NOS yesterdecade, and the balancing pads are untouched, any weight differences will likely be negligible. Be careful of 'mission creep'.


          • #6
            Yes, Studebaker rod bolts are not a tight fit in the rods, so there's nothing inherently wrong there. Change them to those with ARP if you choose, especially since they have resized big ends. (We do this on all builds, even if original bolts are reused.)

            Yes, it's worth the effort to at least weight match the pistons and rods (big and small ends separately)

            Yes, an engine which has the crankshaft spin balanced will run more smoothly.

            jack vines


            • #7
              Joe, the majority of the bolts will fall out of the rod when upside down. I'm guessing they have a couple of thousandths clearance. More than what I've found in other Stude
              engines, which seem to be a light slip fit.

              I'm going to change the rods with the other set I mentioned. Jack, I have a precision scale, and will take your's and Bezhawk's advice and match the weights of the pistons and rods.
              I cannot bear the thought of doing something substandard in one of my beloved Studebakers, and want Stanwood Sparrow's ghost to smile down on me.

              One other thing- will any problems come from removing and replacing the pistons, as far as the rings are concerned? As honing marks are still in evidence on the cylinder walls,
              will the rings continue to seat, and not resent the disturbance?

              Thanks, JT


              • #8
                Pistons and rings should not have a problem with being removed and reinstalled.

                jack vines



                • #9
                  Jack V. - Would it be wise for him to make sure that the same piston and rings go back in the same cylinder? Or would that make a difference. I would be inclined to mark what piston came from what cylinder and put it back together the same way.

                  Just me tho.


                  • #10
                    Yes, marking the piston to the cylinder is good science. Whether it makes a difference depends on how close to the same diameter were your old school pistons and if your machinist made any attempt to finish hone the cylinders to match them.

                    No, it's not going to make a difference with today's pistons. They're CNC machined and almost always exactly the same diameter. We measure anyway; trust, but verify. As to piston rings, they rotate while running and theoretically there's always a film of oil to prevent the piston skirts from touching the cylinder wall.

                    jack vines


                    • #11
                      The rods are numbered. As long as the assembly (rod and piston and rings) are kept together, no need to mark them.
                      78 Avanti RQB 2792
                      64 Avanti R1 R5408
                      63 Avanti R1 R4551
                      63 Avanti R1 R2281
                      62 GT Hawk V15949
                      56 GH 6032504
                      56 GH 6032588
                      55 Speedster 7160047
                      55 Speedster 7165279


                      • #12
                        Originally posted by 64studeavanti View Post
                        The rods are numbered. As long as the assembly (rod and piston and rings) are kept together, no need to mark them.
                        As he mentioned earlier, he's removing the pistons from the rods and replacing the rods with another set, but yes, as long as he does them in order, matching one to the other, he's good. But we all in the enthusiasm of the moment have forgotten what was supposed to go where.

                        jack vines


                        • #13
                          Which brings to mind a story -- I can hijack my own thread, can't I? In my mis-spent youth, I worked in an an automotive machine shop. This happened before my time, but my boss loved to tell the tale. A customer brought in the cylinder head to an old 216 Chevy, the one with the dippers on the rod caps to lube them. The customer was re-ringing the car,
                          and had promised it to his customer by 4:30 that night. The boss reground the valves, and had the head delivered by 10 AM.

                          Around 2:30, the phone rings, and its the customer, and he is frantic, and ugly mad!

                          You ground the valves, and you screwed up! There's no compression on number 3! Not one d**n pound!

                          Well the boss was sure he hadn't made a mistake, and went over to the garage. It was sort of a dirtball place, every bench covered with parts, tools, and rags.
                          He couldn't figure out what was wrong, either, so he moved some stuff out of the way on a bench so he could sit up there and ponder.

                          There he found number 3 piston and rod assembly, all oiled up and ready to be installed.

                          The customer was in such a hurry, he got ahead of himself.

                          My boss went back to the shop, and got another gasket set, and helped him get the car finished on time.

                          I think there may be more than one lesson there of some sort.



                          • #14
                            I've never met a rod bolt that would simply fall out. They should be snug so that they would need to be pushed out with a thumb or even tapped out with a tack hammer. If there is any play at all between the bolt and the bolt hole, I would not use that assembly. Some one might have drilled out that hole and with a perfectly good motor having been completely dismantled, nothing is out of the question. Aggrevatin', ain't it.


                            • #15
                              Jeffry, do enough Studebakers and you'll have handfuls of rod bolts. If they were ever supposed to be snug fit, after fifty-plus years and 100,000 miles, many aren't any longer. No, they weren't drilled out; just the way Studebakers are.

                              jack vines