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What part is missing from this 5AR and what movements have it?

Submitted by xyzzy on January 14, 2021 - 9:20pm

What part, other than the stem, is missing from the 5AR movement?  And what other movements have an interchangable part?  The 5AR appears to be too new to be in any of the parts lists.

I know what part is missing and the manner in which it became so.  I thought it might be more fun to ask this way.

5AR disassembled

JimDon5822
Posted January 14, 2021 - 11:26pm

It looks to be missing the keyless lever spring or click spring. 

Reverend Rob
Posted January 15, 2021 - 5:58pm

The yoke spring looks to be next to the click, so I'm guessing the click spring is missing. A lot of these movements of this size have similar click springs.

This is an in-house Bulova movement, so has no interchange with other Swiss ebauches. 

The family includes the 5AN, 5AH, 5AD, 5AT, 5BA, 5BC, and 5BT, and it is very likely they share the click spring. 

Reverend Rob
Posted January 15, 2021 - 6:01pm

I haven't got any pics to confirm, but I think the click spring is similar in appearance to the one shown, only has no crook. It should be an uneven 'U', with one long arm, if memory serves. I thought I had one handy, but it looks like I don't. 

xyzzy
Posted January 16, 2021 - 4:29am

Look like we have one vote for yoke/clutch spring and one for click spring.  One more day to guess before the answer will be revealed.  I have some photos of the part, both from this movement and some others.

mybulova_admin
Posted January 16, 2021 - 5:56am

I think both Jim and Rev are talking about the same spring, just different names.

I believe the proper name is a 'clutch lever spring' as listed on page 26 (https://mybulova.com/sites/default/files/1952-Bulova-parts-interchange-…)

That's the only part I see missing.

A trick I use after spending many hours on my hands and knees.....a good size piece of glad (cling) wrap, doubled over and placed over the movement, then use a small pin or screwdriver to remove the tension from the spring. Has worked 100% since using this trick and have not been on my hands and knees since :-)

xyzzy
Posted January 16, 2021 - 6:37pm

I counted Rev as having guessed click spring, part #31, as well.

I guess this was too easy.  Everyone is right, it's the clutch/yoke/set spring.  Even Bulova doesn't use consistent names, the parts catalog is "clutch lever spring", but the part packet is "set spring".set spring

It didn't fly away during removal or installation.  I was taking it out of a jar of solvent and it wouldn't come off the tweezers due to the liquid, and then as I reached for another pair to pull it off, the tweezers slipped and bumped against the mat, sending the spring into another dimension.  Being magnetic, I thought I'd be able to find it, but no luck.  I did find an escapement that I don't remember when I lost.

This is what spring and the rest of the keyless works looks like in a 5AR.  The clutch spring wraps around the clutch lever and has a concave curve on the longer end.  The right screw post on the main plate for the yoke bridge, just above, is raised all the way to edge of the plate.  A shorter screw is used here vs the hole on the left side.

5AR keyless

This is what the 5BA looks like.  The right side screw post has an cutout around it, which is where the clutch spring rests.  Both yoke bridge screws are the same, matching the longer screw used on the left side of the 5AR.  I think the main plate is thinner around this location on the 5AR for something on the other side, thus a shorter screw and no space for the spring.  While the spring looks similar, the longer side has a convex curve.  The rest of the parts, clutch lever, etc., look like they are exact matches.  The yoke bridge, not pictured, is a little different but it looks like they would both fit.  The 5AR has an extension on the bottom right to cover more of the clutch lever spring.

5BA keyless

If I understand the way Bulova did their parts, the presence of a part labeled "5AR set spring" means it's either unique to the 5AR, or the 5AR was the first of the group it interchanges with.  If it was the same as the 5BA, then the part would only be labeled "5AD", since that was the first of that group.

mybulova_admin
Posted January 17, 2021 - 5:58am

Ah yes that lost screw that you gave up searching for two years ago and NOW decides to turn up...been there :-)

xyzzy
Posted January 22, 2021 - 4:45am

I found a newer Bulova parts catalog that the ones available here.  No date, but uses 1964 in reference to Accutron stems.  It has the 5AR and the set spring is unique to that movement.

I was able to get another 5AR cheaply from ebay and get the spring from it.  Interestingly, it's not quite the same as the one I lost.  I suspect that this was not the first time the spring from this movement had gone missing.  The lost one looks a lot like someone took the common 5AD spring and the bent the long end to be convex.  The one in the replacement 5AR spring does not have a "S" shape on the short end and the long end is straight with a single convex bend midway down, rather than the gradual curve along the entire length.

Or maybe the replacement is a click spring that's been bent?

Also the 2nd 5AR movement has two identical normal screws to hold the yoke plate on.  The 1st has a smaller oval head (counter-sunk with a rounded top) screw.  I thought it was because the main plate is thinner here, but normal screw is not too long.  The parts list just says "44 Set Bridge : 5AH" for this screw.  It doesn't saw how many, but no other screws for the set bridge are listed, so I assume they are the same.  Leading me to believe the 1st movement is the one with the incorrect screw.

parts list