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Shovelhead Flywheel Identification 23923-78 & 23945-78

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  • Shovelhead Flywheel Identification 23923-78 & 23945-78

    So I was always under the understanding that harley flywheels with casting numbers 23923-78 and 23945-78 were 4.25" stroke wheels for 80" motors. After poking around the interwebz, that's what all of the information I saw showed as well. After trying to use a take off left side wheel from one bike on another I've learned that information is completely 100% wrong.

    After assembling and putting the wheels in my truing fixture I stood back and scratched my head about why they were so cock-eyed. So I disassembled and did a side by side comparison. The wheel I was trying to replace is from an 80" 79 FXE. It measures 2 1/8" from crank pin center to sprocket shaft center which gives you a 4 1/4" stroke. The take off is from a late 78 FLH that I was told had previously been set-up as an 80" motor and looking at the casting numbers I had no reason to question that; however, that wheel measures about 2" from crank pin center to sprocket shaft center and since 74" motors have a 3 31/32" stroke, it's clear that it was not an 80".

    The reason I'm writing this is to debunk the theory about the -78 castings all being 4 1/4 stroke. So if you're trying to identify what wheels you have or are looking to buy replacement shovel flywheels, measure instead of just going by the casting numbers...

    I'll be posting side by side pictures soon.

  • #2
    So just to clarify, the wheel on the left is a 3 31/32" stroke 74" wheel and the wheel on the right is the 4 1/4" stroke 80" wheel that I need to replace. In the pictures, you can see the 74" wheel has a number 1 stamped in the outer rim and the 80" has a number 2 stamped in the same location. I had already replaced the flywheel thrust washer in the 80" wheel and balanced it for a a 79 FXE I'm building for a customer. Unfortunately, the crankpin taper is worn in this wheel to the point that I cannot get TIR into spec. Once the variance in shaft run out stacks and the wheels are in the case (checked with left case bearings correctly pre-loaded and the 3 case alignment studs installed and torques), I end up with .00525" run out at the end of the pinion shaft. As stated before, I was going to replace the worn out wheel with this take off unit before I discovered the stroke difference. So now I will see if the customer wants to buy T&O wheels and have me balance and assemble using most of the new parts I ordered to rebuild these wheels. Note: I say "most of" because the factory used an 8 degree sprocket shaft taper until late 1981 when they they introduced the "commonized wheels" with a 6 degree sprocket shaft taper. All T&O wheels for the 72-81 big twins, regardless of stroke, use the 6 degree taper sprocket shaft.

    Any whoooo, I tend to ramble and nobody probably gives a shit about this anyway but I hope it helps clear up any confusion and possibly saves you time/money if you're ever hunting for replacement flywheels for a shovel.

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    Last edited by TheBCB; 12-17-2017, 06:36 PM. Reason: Wards...

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    • #3

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      • #4
        Knowledgeded as fuck

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        • #5
          Big difference!!!

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          • #6
            Gray beard stuff. I think the first 80" was only the 79 fxe, no fls, or fx? Is the over all outer wheel demetions the same? If they are different, do you have to build up the scrapper? A few years back I put together some late pan cases bored to 3 5/8" with 74 wheels. It was under square something like 84" it ran strong, i learned some things. I went with the t, and o's. I think you should recomend that to your guy. This is good chopper knowledge your giving us.

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            • #7
              I'm fairly certain the 80 was available in all the big twin chassis for 79. I might be wrong but...

              Apart from the crank pin location, the two wheels are identical. I already reworked the oil scraper to improve oil scavenging.

              I'm going to give her the option of going the T&O Torque Monster route or a complete S&S rotating assembly. She got taken for a hard ride financially by another shop (long story reserved for beer/campfire conversations) so I've been doing everything in my power to keep the cost to a minimum for her to the point that she's only getting charged for parts but I'm not going to start fucking with unknown flywheels from baskets in basements until I find a useable combination...

              Eventually, I'll put together a full build thread on this bike but I'm back to being a 1 man show in the shop at the moment and I have enough work in here to keep me hopping 80+ hours a week until June if nothing new walks in the door to get on the waiting list. For now, here's some random pictures of the build.

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              • #8
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