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Boring out a small gas engine

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  • Boring out a small gas engine

    Any thoughts on boring out a student's small gas engine .010 to clean it up for a new piston? We have a milling machine and a traditional adjustable boring bar. I know engine boring bars are available but a school budget does not quite cover that.
    We are ready to try our boring bar but I am worried about accuracy because the cylinder is so deep.

  • #2
    For what it's worth, I've done a few small Briggs cylinders and some smaller motorcycle cylinders on my Bridgeport and have had good results.


    • #3
      On automobile engines we used to use what is called a ridge-reamer (a hand tool)in the cylinders prior to installing new rings. Would that apply to your small engine?


      • #4
        I seen this in Third Hand first. I attatched linked the post from my asking a similar question.
        Paying Attention Is Not That Expensive.


        • #5
          I have done a few Briggs, verticles and horizontals. There is just enough stroke on a B/P spindle to acoomplish this. Keep your speed low to reduce chatter. Leave .002" or .003" for honing.

          Paul G.
          Paul G.


          • #6
            Do you need torque plates when boring a small gas engine? I know that it is a standard practice on blocks that you take to a engine machinist.
            Civil engineers build targets, Mechanical engineers build weapons.


            • #7
              If the cylinder doesn't have deep scores, I wouldn't bore it at all. Use a good hone! Ten thousandths will go in a hurry. Use a REAL cylinder hone with 180 stones then switch to 260. Use a light weight oil like WD-40 or similar.

              Start at the bottom of the cylinder then work up a few strokes. That will tell you if the cylinder is barreled. It can be done on a drill press. Or even a drill, if you have or make the guide mount.


              • #8
                Going on past experience, I wouldn't recommend boring out an aluminum cylinder. Briggs & Stratton anodizes there cylinder walls to make them hard and resistive to wear. If you bore it out you remove the hardening and thus increase the likelyhood of oil consumption. When I had a small engine shop we would check to make sure that the cylinder bore wasn't too out of round. if it was we would run what we called a "dingle berry" hone to break up any glaze. We would also use a ridge reamer to remove any ridge at the top of the cylinder. With carefull measurement, you should be able to use .010", .020", or in worst case senarios .030" oversize CHROME rings. We had best results using chrome to reduce seating run time.

                Just my 2آ¢ worth.

                Hal C. ,
                No matter where you go, there you are!

                Hal C.


                • #9
                  Thanks for all the input. We are going to try several different methods on junk engines and see what happens.

                  I'll let you know.



                  • #10
                    A shop I worked in had a standing contract to bore small single cylinder engines .010 ( I can't remember what brand they were, but they were cast iron). We did them on a Sunnen hone, the kind used for connecting rods and piston pins. It was a time consuming pain in the a**, and the profit had to be next to nothing. But for a one off it would work well.

                    [This message has been edited by Carl (edited 04-12-2005).]
                    THAT OLD GANG 'O MINE