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Thread: belly numbers/VIN numbers

  1. #1

    belly numbers/VIN numbers

    I know this subject has been addressed before, but I can't seem to find anything on it when I search. Is there a relationship between the span of numbers in regard to the belly numbers and the numbers stamped on the left case boss? I vaguely remember reading somewhere, some time ago, about the case stamping being within 200-300 numbers of the belly stamping. Also, are the belly numbers traditionally lower than the case number? I'm only asking because I presently have a '52 FL on my stand with matching belly numbers that are in the neighborhood of 5000 below the VIN number on the case. I have scrutinized the VIN boss and the surrounding area and can find no marks that would indicate alteration. The boss looks to be correct for thickness, I can see no mill marks that would indicate that a previous number has been removed. The casting radius below the numbers has no flat on it that would lead anyone to believe that the boss had been machined. No file marks anywhere. For somebody to duplicate that radius, they'd either have had to put the case up on a turntable, or machined it on a CNC machine.

  2. #2

    Re: belly numbers/VIN numbers

    Most belly numbers are within 200-300 before or after the vin, however there are exceptions that are factory stamped.

  3. #3
    Join Date
    Mar 2008
    Beautiful Northern NM

    Re: belly numbers/VIN numbers

    On occasion a set of cases was set aside for a rework of some sort and then put back in the line after the repair was made, totally out of any sequence. Only the factory ever had that info and it was/is inaccessible to the public. Also note that on '60 up Odd/Even rule cases the belly numbers get progressively further to the extent that high VIN #s have belly numbers only about half as high. The VINs skip, the bellys do not.
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  4. #4

    Re: belly numbers/VIN numbers

    It also could have been a replacement case with the number stamped at the MoCo. Pictures?
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  5. #5
    Join Date
    Jun 2009
    Western Australia

    Re: belly numbers/VIN numbers

    omar, as noted above there can be more than one reason why BNs are way different to the SN.

    Are BNs traditionally lower than the SN? For Panheads sometimes the BNs are lower, sometimes they are higher and on occasion the BNs match the SN.

    As for the SN being within 200-300 numbers of the BN, Iíve heard the same thing. Sometimes it is true and sometimes it is wrong. On occasion it appears to be incorrect in the extreme and one such occasion apparently concerns most (?) 1952 model Panheads. My photo collection includes fourteen examples of Pan cases with authentic-looking 1952 BNs and authentic-looking 1952 SNs. All fourteen have BNs lower than the SN, with thirteen having a difference ranging from 1887-2194. The other one has a difference of 3007.

    Why did this happen? My collection also seems to indicate a lot of Pans with 1951 BNs had 1952 SNs. At this stage it appears that cases with 1951 BNs werenít depleted until 1952 SNs reached somewhere around 3000. (For 1952 Pans, SNs began at 1000.)

  6. #6

    Re: belly numbers/VIN numbers

    Interesting info on '52 Panheads, Speeding Big Twin. I posted 2 pics on the AMCA forum, one left case belly number and the VIN from the same. As you can see if you view them, the difference is 4533. I considered that pretty extreme.

  7. #7
    Join Date
    Jun 2009
    Western Australia

    Re: belly numbers/VIN numbers

    It may have seemed extreme at first but the difference drops considerably when my previous post is taken into account.
    For Panheads I have two examples of differences higher than 3000. One is for 1948 (BN higher than SN) and the other is for 1949 (SN higher than BN).

    There were at least two left cases for 52 Pans and the one you posted on AMCA appears to be the second type which is what Iíd expect if the numbers are authentic.

    I canít yet see anything wrong with the SN but could you post a better photo please, partly because Iíd like to see the 5 and 1 more clearly.

    The BN looks normal. First 1 appears to have a short top serif at about forty-five degrees. I canít see a serif across the base and I wouldnít expect to.
    I canít see anything wrong with the 5.
    The 2 appears to be sans serif as Iíd expect.
    Sequence 1 appears normal for 52 with top serif at about forty-five degrees and a serif across the base.
    Round-back 6 looks the usual type for 52. (H-D used more than one style of R-B 6/9 in BNs over the years.)
    Flat-top 3 looks okay, having a vertical serif at top left. (In the sequence portion it changed to sans serif either very late in 52 or very early in 53.)
    I canít see anything wrong with the 5.

    Are 7s stamped on top of the cases near the rear engine mounting bolts? Photos? H-D used at least two types of 7 for Panheads and for a 52 model Iíd expect the second style.

    Does the R-H case have an oil screen for the tappets?

  8. #8

    Re: belly numbers/VIN numbers

    I have 3 pics. One shows the 5 clearly, but not the 1. the 2nd pic shows the tappet screen. The 3rd shows the 7 stamp on the case halves. The 7's are different from knuckle case ones, but the same as the ones on my '55 FL. Unfortunately, even after subscribing to Photobucket as recommended, I still can't figure out how to load the pics from Photobucket to a reply, so I'm going to post them on the continuing thread I have on the AMCA site. FYI, I wish I'd taken a pic when I had the tappet blocks off. As you can see, there is a tappet block screen assembly present, and I know that oil travels under pressure up the cylinder to the top end from that screen, but the oiling diagram also shows that oil traveling to oil holes under the blocks to the tappet assemblies. This case has no oil holes under the tappet blocks. Didn't read the legend about the tappet screen in the manual or in Palmer's book (if there is an explanation). My estimate is that the holes to the tappet assemblies were added with the introduction of updated hydraulic lifter assemblies, correct?

  9. #9
    Join Date
    Jun 2009
    Western Australia

    Re: belly numbers/VIN numbers

    Thanks for the extra photos. I also posted this on AMCA. I canít see anything wrong with the 5 and for comparison hereís another example. BTW, in the past I too used Photobucket but now I use Imgur (

    Notice the 2 is seriffed.
    Notice the lower horizontal stroke of the F is almost as long as the upper stroke and this is normal for later-52. (For early-52 thru about mid-52 the lower stroke is shorter than this.)
    Notice the top serif of the 1 has a slight curve. As expected, the serif across the base is fairly wide/long.

    The 7s on top of the cases both look sans serif which is what Iíd expect for 52. On Pan cases at least two types were used: seriffed; and sans serif. The seriffed 7 is the only style Iíve seen so far on 48 Pans. Iíve seen both types for 1949 and also for 1950 but at some point during the 1950 model year the sans serif 7 seems to have taken over completely. (A seriffed 7 was used for 1941Ė47 F/FL Knuckles.)

    According to Shop Dope 330 the tappet screen started with SN about 52FL3529. But Iím not surprised to see the screen on cases with matching BNs 152-1635, given the range of differences I mentioned earlier between 52 SNs and 52 BNs.

    Re the feed oil holes, youíre right about them being added with the intro of new hydraulic lifter assemblies (1953).

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