Author Topic: Difference between plunger and swingarm gears?  (Read 966 times)

Offline roadrocket

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Hello!

With the possibility to buy a very cheap plunger box, I have studied the parts books, and found that all gears are the same between the plunger and swingarm gearboxes, except for the layshaft top gear and 3rd sliding gear, which for the swingarm are called 42-3020 and 42-3023, whereas the plunger gears are called 67-3196 and 67-3197. They look the same in the drawing, but since they carry different numbers they must be different? What's the story here?

Otto in Denmark
Otto in Denmark

Offline roadrocket

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Re: Difference between plunger and swingarm gears?
« Reply #1 on: 20.03. 2016 21:17 »
Oh, they have the same number of teeth too!
Otto in Denmark

Online beezermacc

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Re: Difference between plunger and swingarm gears?
« Reply #2 on: 20.03. 2016 23:33 »
The issue is the way the gears connect with each other on the side, i.e. the 'dogs'. The plunger gears and swinging arm gears are different and incompatible in this regard.
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Offline Rocket Racer

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Re: Difference between plunger and swingarm gears?
« Reply #3 on: 21.03. 2016 00:05 »
I have a number of NOS dogs that appear almost swing arm, but have a wider selector fork groove, so have always assumed they are earlier plunger type ??
The camplates and change mechanisms of plunger boxes are certainly different.
My assumption  *dunno* is that later plunger boxes may have more commonality to swing arm boxes as I recall reading the swing arm boxes included improvements in selection which presumably included the mating faces of the dogs  *eek* .
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Offline roadrocket

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Re: Difference between plunger and swingarm gears?
« Reply #4 on: 21.03. 2016 06:44 »
Thanks Andrew, it still gives me most of a box for little money. I will make an effort to keep them separate and scrutinize before any assembly.
Otto in Denmark

Offline duTch

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Re: Difference between plunger and swingarm gears?
« Reply #5 on: 21.03. 2016 07:05 »
 I have what I'm fairly sure is an early (pre '50?) Box, and some but not all gears are similar but not the same as the later Plunger box (post '50), and apart from the mainshaft and change mechanism, I think the gears can be interchanged with care.
 There are many variations of gear combinations, and not completely straight-forward...
 There's a chart that shows this, I've been doing some research the last couple of weeks to make a good box from some, and trying to figure out what Beeza-Bill did with his, but have concluded he had a Rigid A10, which I think was originally same as the box I'm currently using.
 I'll post some pics later of different combos

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Offline duTch

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Re: Difference between plunger and swingarm gears?
« Reply #6 on: 20.04. 2016 22:05 »
  Forgot to acknowledge B-Maccs comment last time;
 
Quote
The issue is the way the gears connect with each other on the side, i.e. the 'dogs'. The plunger gears and swinging arm gears are different and incompatible in this regard.

 and then my observations ;
Quote
I have a number of NOS dogs that appear almost swing arm, but have a wider selector fork groove, so have always assumed they are earlier plunger type ??.........

 The box I've been using has these in it and I figure they must be Lonstroke and early A10 pre '50, and also;
Quote
...........My assumption  *dunno* is that later plunger boxes may have more commonality to swing arm boxes as I recall reading the swing arm boxes included improvements in selection which presumably included the mating faces of the dogs  *eek* .


  I think that 'STD' gears may be the same for Plunger & S/A, but as I don't have any S/A ones, but I do have a RRT2 cluster that I grafted into a Plunger box, and apart from different ratios and widths of at least 'B', the dogs are completely different.
 

 My third gear has been jumping out, so yesterday I had a chance to get into it. Being as I suspect an early(pre '50) box, I was going to change the whole box but would need to do bushes as well, so figured best to just change all the gears rather than just third, also due to differences in the dog arrangement.
 
  All was going ok, swapped the constant mesh gears ('B' & 'G') to my shafts as they fit the bushes, and fitted all in the box, but the mainshaft wouldn't go in. *pull hair out* *pull hair out*
  After some dicking around, I discovered that the selector forks are also a bit different, even thought they have the same numbers.
 The early selectors have a 'web', or gusset, which was what was stopping the 'E' gear from meshing to allow the mainshaft to slide in. I guess this is why the early ones have a wider selector groove and narrower gear (but same overall)

 The later forks, in addition to lack of gusset are also slightly truncated on their ends.
 
   These are my observations only and so need to be verified as fact... *eek*

 Now I need to go figure how to reduce the layshaft endfloat from 30+thou and no paper gasket...more *pull hair out*

    Oh and the first gear thrust washer (67-3203) has a smaller OD on the later box  *pull hair out* (~1.088"/~1.173")


 
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline a101960

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Re: Difference between plunger and swingarm gears?
« Reply #7 on: 24.07. 2017 14:32 »
I have just noticed this topic. I intend to carry out some remedial work on my swing arm gear box. Reading this topic I noticed that there are pictures of the two types of gear change selector forks. From the research that I have done the later selector fork should be part p/n 67-3204, and that the earlier type should be p/n 67-3118. However, in this topic there are two different type of selectors shown both with the early p/n. I bought a set of new selector forks from Len Haggis and the p/n is 67-3118 and he assured me that the forks he had supplied are the correct parts for a s/a box. So, was there a change over period where the later s/a selector forks carried the p/n of the early type? Can anyone shed any light on this?
John

Offline JulianS

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Re: Difference between plunger and swingarm gears?
« Reply #8 on: 24.07. 2017 14:45 »
The fork with the web is the early one to 1950 for long stroke A7 and A10 to engine ZA10 1214 only.

 The one with no web is the later one part 67 3024 fitted from A10 from engine ZA10 1215 and all short stroke A7, swinging arm or plunger. . And they do both have the same forging number 67 3118.

Just make sure the forks dont have the web because it will touch the layshaft sliding gear.