CAT D7 7M compared to D6 9U (Dimensions)

What is this thing?....

I just bought a 1/87 scale resin kit of a WW2 era D7, civil version. It is wonderfully detailed, but sizewise rather a D6. Since I bought it at our antique equipment club and we own a D6 9U based MD6 pipelayer, I thought I can do a quick check. So I simply measured the distance between the centre of sprocket and centre of the front idler, which was 2200mm on a decent adjusted track. In 1/87, that would be 25.3 mm. The D7 model has only 24mm. My first conclusion was, Artitec has realised a D6 9U and mistakenly offers it as a D7 3T.

But I was wrong. Back home, I realized the pony motor is on the left side of the diesel engine, not on top of the flywheel like on our D6 9U. This speaks for a D7. And the track frame has 5 track rollers, not 6 like on a D7 3T or our D6 9U. So it seems to be a D7 7M.

Since the kit is well detailed, I want to figure out, what it really is. Is a D7 7M about the same size as a D6 9U?


I downloaded a US Army technical manual of the D7 (M1 heavy Crawler Tractor), but so far I couldn't find any useful measurements for comparison. https://archive.org/details/caterpillar_TM9-1773/page/n19/mode/2up


To clear this up, I'm looking for some dimensions of a D7 7M, like

Length of track on the ground or distance between the centre of sprocket and centre of front idler
Track gauge
Width of radiator
Length of bare tractor


Maybe some of you are HO scale nuts like I am and are interested in the Artitec kit. Offered in two variants, military with LeTourneau S-blade and headache bar or civil with S-blade and front PCU. The kits are also offered as built and weathered models, just like you see it on the photos. The civil D7 kit is about 14.90 €, the ready-built and weathered model comes along at 40.90€

[attachment=56968]bulldozer-d7-civilian-kit.jpg[/attachment]
[attachment=56967]us-bulldozer-d7-kit.jpg[/attachment]
[url="https://www.artitecshop.com/en/bulldozer-d7-civilian-kit.html"]
https://www.artitecshop.com/en/bulldozer-d7-civilian-kit.html[/url]
https://www.artitecshop.com/en/us-bulldozer-d7-kit.html


Best regards,

Max

I can measure my 7M later today, but they’re really close to a 3T.

BP.

I've idly wondered what the difference between a 7M and 3T is, other than that prefix.

Hi Bruce, thank you for helping. Looks like they modeled a D7 and somehow made it D6 size. We will see.

Neil, so by counting the track rollers, we have a solid way to see the difference between a 7M and a 3T.


Best regards,
Max

From a 1966 Performance Handbook.

A 7M and 3T 4T in standard form all share 5 roller track frames.
From a distance it is difficult or perhaps impossible to tell them apart.
A high serial no 7M is the same as a low serial 3T.
There were many improvements , upgrades made as time went on. How long have you got??
Perhaps the most visible is the change in the radiator and bonnet from copper tanks under the bonnet to cast tanks exposed. This happened early 3T series
Hope this is useful .
A. K.

My 7M298 measures 97” from center of front idler to center of the sprocket. Rails are in good condition. It’s 74” from center to center of the sprockets. The front sheet metal around the radiator is approximately 41” wide.

My 7M is fairy early. It has a water pump on the starting engine and a non enclosed flywheel clutch. The early ones have different steering clutch linkage too, but you can’t tell from the outside. I miss driving my 7M, I need to fix the steering clutch.

BP.

Andrew, thanks for sharing the pages from your Performance Handbook. I have a copy from 1995, which covers only the 3T and this in a rather superficial manner.

Bruce, thanks for taking the measurements. Time to compare it to the scale model:

97" Sprocket CL to idler CL is 2464mm. In 1/87 that's 28.3mm - the model 24mm
74" track gauge is 1880mm. In 1/87 that's 21.6mm - the model has 21mm
41" width of radiator housing is 1041mm. in 1/87 that's 12mm - the model has 11mm
13'6 1/4" length of bare tractor is 4121mm. In 1/87 that's 47mm - the model has 40mm

So, regarding its details, it is a D7 7M or 3T, but rather in 1/100 than 1/87. A pitty. Since it is a 3D printed master model to cast the resin parts and a lot of detailig work went into it, they simply used the wrong scale.

Thanks for your help!

Best regards,
Max