Results 1 to 8 of 8

Thread: Differences between BN2 and BN4 speedometer gears??

Forum to discuss Austin Healey Sports Cars

  1. #1
    Jedi Warrior
    Join Date
    Oct 2014
    Location
    Western Canada
    Posts
    452
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Differences between BN2 and BN4 speedometer gears??

    The speedometer on the 1956 100-4 BN2 had issues. It looked fine but was disconnected when I bought the car. On hooking it up, I found that the needle bounced and floated all the way up to 120 mph, when the car was going about half that speed. Also, both odometers did not work. I took it apart and found both small phenolic? odometer gears chewed off, and that part of the mechanism appeared jammed.

    So, I looked in the box of Healey gauge parts and found a number of speedometers from 100-6 and 3000 cars. Picking what looked to be the oldest one (almost certainly from a 100-6), with the best chance of matching the workings of the one from the 100-4, I took that one apart. The parts inside looked identical in design to the one from the 100-4 (Smith's made three different types over the years), and both of the little odometer gears were good. So I put that together with the face and case from the 100-4 and hooked it up. For those that don't know, the 100-4 uses a black face for the speedometer, while the 100-6 cars have white faces for the speedos, which is why I couldn't just install the newer speedometer and have it look correct.

    It's much better now than before, but a couple of issues remain. I played around with calibrating the "new" speedometer, using the GPS speedometer on my phone as a reference point. After another disassembly of the speedo, I got the needle in the right spot for accuracy at 20 mph. But as the speed rises after that, the speedometer reads high. By 60 actual mph, it reads about 75 mph. Also, while both odometers now work, they turn the miles over every 8/10 or so of a mile.

    The only thing I can think of is that the speedo from the 100-6 is geared differently internally than the speedo from the 100-4. I could disassemble it again and count the number of teeth on the gears, but prefer not to do that without the correct parts to put in there.

    Does anyone here know the difference in gearing in these two speedos? I could send it off somewhere, but where's the fun in that?

  2. #2
    Senior Member Jake's Avatar
    Join Date
    Nov 2005
    Location
    Manassas, VA
    Posts
    103
    Thanks Thanks Given 
    1
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Re: Differences between BN2 and BN4 speedometer gears??

    What are the two part numbers on the faces? Should be SNXXXX/XX.

  3. #3
    Jedi Warrior
    Join Date
    Oct 2014
    Location
    Western Canada
    Posts
    452
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Re: Differences between BN2 and BN4 speedometer gears??

    Part numbers from faces:

    Black face dial from 100-4 - SN 6305/00 1325.
    White face dial from 100-6? -SN6155/21 980.

  4. #4
    Yoda John Turney's Avatar
    Join Date
    May 2002
    Location
    Concord, CA
    Posts
    3,540
    Thanks Thanks Given 
    41
    Thanks Thanks Received 
    28
    Thanked in
    27 Posts

    Re: Differences between BN2 and BN4 speedometer gears??

    That 1325 and 980 should be the turns per mile for the speedometer cable.
    John, BN4

  5. #5
    Senior Member Jake's Avatar
    Join Date
    Nov 2005
    Location
    Manassas, VA
    Posts
    103
    Thanks Thanks Given 
    1
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Re: Differences between BN2 and BN4 speedometer gears??

    These two gauges are calibrated for different rear end ratios. The numbers 1325 and 980 are their TPM numbers (turns per mile). If looking to just swap the face over, you'll want to look for a 1325 TPM gauge.
    Or send it to a shop that can re-calibrate it correctly.

    http://thegaugeshop.com/epages/77fe2.../Products/1289

    http://thegaugeshop.com/epages/77fe2.../Products/1287

  6. #6
    Yoda John Turney's Avatar
    Join Date
    May 2002
    Location
    Concord, CA
    Posts
    3,540
    Thanks Thanks Given 
    41
    Thanks Thanks Received 
    28
    Thanked in
    27 Posts

    Re: Differences between BN2 and BN4 speedometer gears??

    Steve Day, British Car Ranch, recommended these guys earlier this year: https://www.westvalleyinstruments.com/.
    John, BN4

  7. #7
    Senior Member Jake's Avatar
    Join Date
    Nov 2005
    Location
    Manassas, VA
    Posts
    103
    Thanks Thanks Given 
    1
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Re: Differences between BN2 and BN4 speedometer gears??

    ^ Seconded. Have heard nothing but good about West Valley, my brother-in-law uses them for his business.

  8. #8
    Yoda
    Join Date
    Feb 2007
    Location
    California USA
    Posts
    3,888
    Thanks Thanks Given 
    4
    Thanks Thanks Received 
    44
    Thanked in
    41 Posts

    Re: Differences between BN2 and BN4 speedometer gears??

    WVI restored and calibrated my safety gauge for my BJ8. I'm happy with the work.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •