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Thread: FL or FLH pistons for 1976 Harley with sidecar

  1. #1

    Default 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. #2

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    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.

  3. #3
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    Quote 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 at 01:24 PM.

  4. #4
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    Quote 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 at 05:44 PM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  5. #5

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    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.

  6. #6

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    The #1 may make it worse.

  7. #7
    Join Date
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    Quote 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!

  8. #8
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    Quote 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?

  9. #9
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    Mar 2017
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    Quote 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.

  10. #10
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    Quote 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 at 08:13 PM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

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