Frog/Blackfoot gearing questions

[Saito2]

I'm in the midst of trying to put together a Frog from my large stock of Blackfoot spares. I don't have the 2-piece Frog spur/counter gear in my collection but rather the 1-piece Blackfoot version. The BF 1-piece gear features a 52 tooth large gear section and 17 tooth smaller gear section. If I'm reading my Frog manual correctly (which offered 50 tooth, 49 tooth and 52 tooth spur sections of the counter gear which could be paired with various pinions to achieve different gear ratios), I should use a 16 tooth pinion (without the BF motor spacer) to get the correct mesh. Am I correct?

One thing I did find somewhat strange however. The 1-piece BF gear is a 52 tooth large section/17 tooth small section gear, while the Frog versions (regardless of which number tooth spur gear section you choose) all use an 18 tooth small gear section (brass in the original, aluminum in the re-re). Considering how both the Frog and the BF share the same gearbox components/side plates (and thus gear spacing) as well as the same 47 tooth diff gears, how is the mesh between the counter gear and spur gear correct for both models if one is running a 17 tooth gear on the 47 tooth diff gear and the other is a 17 tooth gear? 

 

[Frog Jumper]

Based on my notes that I took when I was into Thorp stuff, the BF has an 48t diff gear while the Frog has a 47t diff gear.

 

[[[Blackfoot Counter: 52T outer, 17T inner

Blackfoot Diff: 48T

Frog Counter 01: 49T outer, 18T inner (high speed)
Frog Counter 02: 50T outer, 18T inner (standard)
Frog Counter 03: 52T outer, 18T inner (Torque)

Frog Diff: 47T

Thorp Counter (standard): 52T outer, 18T inner (Thorp #4520)
Thorp Counter (overdrive):  48T outer, 18T inner  (Thorp #4530)

Thorp Diff: 47T (Throp #4506)

The Blackfoot Counter, the Frog Counter 03, and the Thorp Counter (standard) are all 52T and are the same diameter.  The Frog 50T is slightly smaller, with the 49T being smaller still...

The 18T Frog and the Thorp Counter inner gears are the same diameter. The 17T BF inner is slightly smaller...

The 47T Frog and the Thorp Diff are the same diameter, and the 48T BF is slightly larger.

The Frog and BF gears are the same thickness, and the Thorp are slightly thicker.

IMO, the Thorp system is a clone of the Frog stuff... and that the 17T is slightly smaller to accommodate the slightly larger 48T Diff on the BF... It solves the riddle of why each set of gears is marked with the car! You wouldn't want to put a BF Counter on a Frog Diff!

That said, the Thorp stuff should plug-and-play with the Frog stuff...]]]

[Saito2]

Ok, the plot thickens...I got out my re-re Frog and Blackfoot manuals and counted the diff gear teeth on the illustrations in the back pages. Both the re-re Frog and Blackfoot feature 47 tooth diff gears. Now here's the kicker. Looking in the original Blackfoot manual, the original issue Blackfoot did indeed have a 48 tooth diff gear. I dug into my original Blackfoot spares and found all the diff gears (all 48 tooth) imprinted with "Blackfoot" as  @Frog Jumper noted.   

So, what I'm gathering is Tamiya reproduced the 52T/17T 1-piece counter gear for the re-re Blackfoot but not the correct 48T diff gear to mate with it. Instead it appears they felt the already reproduced 47T Frog diff gear was "close enough" and threw that in the re-re Blackfoot (and Monster Beetle) kit. Incidentally, the re-re Wild One and Hotshot series cars use the 47T diff gear as well. 

Great, now it looks like I may have to pull apart my "blueprinted Blackfoot" to install the correct tooth-count vintage diff gear.

[Saito2]

Further research indicates the illustrations in the back of the Blackfoot and Monster Beetle re-re manuals are incorrect. The replacement diff gear set for the BF/MB is part number 9335026 as recommended by MIP when using their 48 tooth BF/MB ball diff in the Frog, Brat or Lancia. All actual photos of the 9335026 diff gear set show the proper 48 tooth diff gear not the 47 tooth one pictured/drawn in the re-re BF/MB manual (yay, I don't have to pull apart my Blackfoot). 

[Toolmaker72]

Also if you use a monster beetle motor adapter fitted to the frog 50 tooth gear set a 13 tooth motor pinion can be used.