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FL or FLH pistons for 1976 Harley with sidecar

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  • FL or FLH pistons for 1976 Harley with sidecar

    Getting ready to do top end on my stock 1976 Harley FL with stock HD sidecar. I have no ping presently with low compression FL pistons and bike runs good but needs next oversize pistons. Will I have a pinging problem pulling heavy sidecar if I use FLH pistons? My understanding that most Harleys that came with sidecars were FL. Thanks.

  • #2
    I think you're right, the LC will accept heavier load at low speed.
    With either piston, I would try to shorten the cylinders to get something like a quench band. Yes, it affects pushrod adjustment and manifold length.
    What would really help is an ignition with vacuum advance like the later bikes.
    The Linkert Book

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    • #3
      Originally posted by Buster View Post
      Getting ready to do top end on my stock 1976 Harley FL with stock HD sidecar. I have no ping presently with low compression FL pistons and bike runs good but needs next oversize pistons. Will I have a pinging problem pulling heavy sidecar if I use FLH pistons? My understanding that most Harleys that came with sidecars were FL. Thanks.
      Are you running an oil cooler? I am currently having pinging issues on my 69 flh with sidecar. I just cleaned out carbon in combustion chamber, cleaned and lubed timer, added octane boost to 93 octane and I still have pinging. Now I am getting ready to add an oil cooler. I hope this gives you an idea with flh pistons.

      Link to my pinging thread
      https://forum.antiquemotorcycle.org/...-ping-and-ping
      Last edited by ryan; 09-08-2020, 02:24 PM.

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      • #4
        Originally posted by ryan View Post
        Are you running an oil cooler? I am currently having pinging issues on my 69 flh with sidecar. I just cleaned out carbon in combustion chamber, cleaned and lubed timer, added octane boost to 93 octane and I still have pinging. Now I am getting ready to add an oil cooler. I hope this gives you an idea with flh pistons.

        Link to my pinging thread
        https://forum.antiquemotorcycle.org/...-ping-and-ping
        Sorry to intrude where I know I shouldn't,.. Ryan,..

        But I had some direct observations of various cooler assemblies, upon my own stroker hack, even though it was decades ago.

        My first question is the obvious one: What good does it do to cool the oil after it leaves the motor?

        It's an oil tank cooler?

        .....Cotten
        Last edited by T. Cotten; 09-08-2020, 06:44 PM.
        AMCA #776
        Dumpster Diver's Motto: Seek,... and Ye Shall Find!

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        • #5
          No, I do no run a oil cooler. I dont believe you have to when running the lower compression FL pistons (or the higher comression FLH pistons). I run regular gas, however it does fill like it runs better with higher octane. I have bike geared down one tooth from stock motor sprocket and bike will comfortably cruise around 55-57 mph with HD sidecar with fiberglass tub. I have to do top end due to needing rebore and valve job. Speed and torque should pickup with just rebore and valve job since compression is so bad presently. If I change to a very mild Andrews #1 grind cam, would this have any negative effect on pinging? Any advice on a cam for this high torque situation would be appreciated. Engine is completely stock with no other modifications.

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          • #6
            The #1 may make it worse.
            The Linkert Book

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            • #7
              Originally posted by Buster View Post
              Getting ready to do top end on my stock 1976 Harley FL with stock HD sidecar. I have no ping presently with low compression FL pistons and bike runs good but needs next oversize pistons. Will I have a pinging problem pulling heavy sidecar if I use FLH pistons? My understanding that most Harleys that came with sidecars were FL. Thanks.
              I guess I have to agree with Kitabel,...

              What's to fix?

              ....Cotten
              AMCA #776
              Dumpster Diver's Motto: Seek,... and Ye Shall Find!

              Comment


              • #8
                Originally posted by T. Cotten View Post
                Sorry to intrude where I know I shouldn't,.. Ryan,..

                But I had some direct observations of various cooler assemblies, upon my own stroker hack, even though it was decades ago.

                My first question is the obvious one: What good does it do to cool the oil after it leaves the motor?

                It's an oil tank cooler?

                .....Cotten
                Yes, an oil tank is cooler, but maybe not cool enough. Cotten, what happens if you put, cooled oil from the oil cooler, into the tank then into the motor?

                Comment


                • #9
                  Originally posted by Buster View Post
                  No, I do no run a oil cooler. I dont believe you have to when running the lower compression FL pistons (or the higher comression FLH pistons). I run regular gas, however it does fill like it runs better with higher octane. I have bike geared down one tooth from stock motor sprocket and bike will comfortably cruise around 55-57 mph with HD sidecar with fiberglass tub. I have to do top end due to needing rebore and valve job. Speed and torque should pickup with just rebore and valve job since compression is so bad presently. If I change to a very mild Andrews #1 grind cam, would this have any negative effect on pinging? Any advice on a cam for this high torque situation would be appreciated. Engine is completely stock with no other modifications.
                  So you are running a 20 tooth sprocket on the motor and a 23 on the tranny? I am running a 21 motor sprocket and a 24 tranny sprocket I would also like to know about the camshaft, but I am not lacking any power by any means.

                  Comment


                  • #10
                    Originally posted by ryan View Post
                    Yes, an oil tank is cooler, but maybe not cool enough. Cotten, what happens if you put, cooled oil from the oil cooler, into the tank then into the motor?
                    Let's think a bit, Ryan,..

                    Even if its conjuring without any real numbers.

                    The motor needs to warm up to a natural equilibrium to be efficient.
                    It is ~eighty percent air-cooled, and perhaps at best ~twenty-percent oil-cooled, primarily by what oil exits.
                    How cold must the incoming oil be to effectively cool the rest, without being so thick that it doesn't feed anyway?

                    Surely all that restriction upon the exit helps, huh.

                    ....Cotten
                    Last edited by T. Cotten; 09-08-2020, 09:13 PM.
                    AMCA #776
                    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

                    Comment


                    • #11
                      The motor has a stock cam now. Will I be better off to keep the stock cam? Thanks.

                      Comment


                      • #12
                        Originally posted by Buster View Post
                        The motor has a stock cam now. Will I be better off to keep the stock cam? Thanks.
                        I tried to get cam information as well with no luck. I always had good luck with the stock H cam, but I just started running a sidecar. I wish I could tell you what cam my engine has in it, but I do not know, because it pulls strong even with a passenger on the seat and one in the sidecar right on up to 70 mph with a 21 engine sprocket and 23 transmission sprocket.

                        Again, are you running a 20 tooth engine sprocket and 22 transmission sprocket? Stock engine is 21 for sidecar use and 22 transmission.

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                        • #13
                          I have always wondered how long is the oil in the cooler? i would think not long enough to be able to cool that small amount of
                          oil to help much?

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                          • #14
                            Ryan, I have a 23T motor sprocket and stock 22T trans and 51T rear wheel. I was running 24Tmotor sprocket before I installed sidecar and bike would cruise around 60-65mph comfortably. Since I installed sidecar, I removed bike windshield and there is a noticeable 2-3 mph increase. I agree with Cotton on oil cooler, I do not believe there is enough area to effectively cool oil. HD made a lot of sidecar bikes for many years without an oil cooler.

                            Comment


                            • #15
                              Too cold is bad. Easy test (if you don't have a candy thermometer): run the bike hard, place your palm on the oil tank. If you can count past 5 it's cool enough (150-160). Even 180 is safe but less safety margin. If you can't touch it I would run a cooler.
                              How effective is it? Did anyone ask "how big is it, where is it mounted?" Then you don't know.
                              Hint: away from the exhaust port & pipe and the airstream coming off the engine is a good start.

                              Factory? The factory weighed failures due to oil temperature (almost impossible to prove without a lab report) vs. "bike crashed when oil cooler line leaked" and "3% of new bikes serviced under warranty for leaks". Guess what the lawyers told them?
                              The Linkert Book

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