The Rock Island G2 15-25 is one of most common of the Rock Island tractors found today, but apparently was produced in far more limited numbers then the 18-35 F. Produced from 1929 until 1932 these were popular tractors and were significant in the Rock Island Line, second only to the F. According to Jon Clingan, Waukesha produced only a little over 1000 CS4 engines of all variants, likely making production about a third of the F/FA line. Despite their popularity, the G2’s never figured prominently in Rock Islands advertising, with most ads featuring an F with only a mention of the G2, or in some cases its predecessor the G 15-25 was featured with text for a G2.
The G2, like the F, was purpose built to take advantage of the more modern 2 speed gear driven transmission arraignment. While it is unknown for sure what role the earlier G had in the lineup, the G2 was without a doubt the tractor Rock Island had been intending. Slightly smaller then the G with the more advanced CS4 series engine, the G2 could be run equally well on gasoline or distillate and in Nebraska Test 157 & 158 was tested with both. What was likely clerical errors on 158 mistakenly reported the listed rating as 18-30 instead of the standard 15-25 however, on gasoline the G2 put out an impressive 25-35 hp. Wendel in “150 Years of JI Case” refers to the 18-30 as a separate model of G2 for gasoline, but this does not seem to be the case as both tests used the same tractor (G2-90001) without listed modification. It is most likely that Rock Island felt that the two tests would clearly indicate that the G2 was highly effective on both fuels as gasoline rose in popularity, although they may have changed carburetors to optimize fuel use.
Unlike the F, the G2 was only sold in one design, although a couple of slight variations have been seen. The standard ball type shifter used on the G and F’s appeared in the 1929 parts guide and on a number of tractors. Later G2’s made use of a sliding shift mechanism that appears more common and was used on the later H models. I have now confirmed from a late parts list that tractors 100001+ made use of the slide shift, this also carried over to some late model F/FA’s.
Another option was a labyrinth style manifold for preheating kerosene as it left the carb or the standard straight style manifold. On at least one early G2 (ours serial 90091) the engine is actually labeled as a CS4, and I have now gotten information of other CS4 variants up to CS4J with D being one fo the more common variants. These variants included changes like mounting for the oil filter, fan mount and oil return.
According to a parts list for the G2 published after the Case buyout around 1938, the following is a break down of significant changes within the line that may impact part swapping. Note rear end differences for 100001+:
Aircleaner listing shows 90340 and below used a top guard sheet on the air intake stack; and 90341+ above added an auxiliary air cleaner.
Clutch Shaft bearing cage is shown as different from 90001 to 10009, from 100010 to 100171, and from 100172+.
Belt pulley bell housing, cap, spline shaft and assembly show as different for 100001+
Differential spider, pin, rear axle nut, felt retaining plate, washer and rear axle bell housing show as different for 100001+.
Double reverse gear, bushing and shaft show as different for 100001+.
Gear shift assembly was entirely changed on the 100001+ from the ball and stick shift to the slide shift. In addition, the transfer case cover, upper transfer case cover and gaskets changed again at 100196+.
On serial numbers 90001- 90418 the gas tank assembly was a one piece tank with two chambers. 90420+ the tanks were made separately and used a wider tank strap to hold both tanks in place.
For a look inside a G2 undergoing restoration, I have posted up a Build log Here
I Have now put a copy of the 1929 G2 Parts List online for download HERE.
Jon has built a dedicated G2 page with more images and information Here including a lot of valuable info from the owners manual. Jon is also producing an excellent copy of the G2 manual for sale.