The only difference in the engines is the lack of an oil filter on the 16G and the stickers on it.
As for the the throttle slot, that was a running change in the design of the dash board and throttle cable. If you have the right throttle cable for the right dash panel, you will get full throttle operation with no problem. Older G tractors used a plastic "T" handle throttle, with a smaller dash slot, newer ones (after about 1994?) used a metal "L" handle with a rubber cover and a longer dash slot. The early cable could be serviced piece for piece, the later one must be replaced as an assembly. Obviously they changed vendors and had to adjust the dash slot for the new throttle handle design.
Now for the important part, 16G or 18G, GRAVELY decided to set the governors on these engines at 3300 RPM, so actually as delivered both were only about 16 HP. But Kohler designed the engine to run at 3600 RPM, with a very flat torque curve, so to get max power, reset the governor to 3600 RPM - you will not hurt the engine and you will really have 18 HP. Kohler designed the engine to run generators and welders, constant wide open throttle at 3600 RPM.
None of the internal engine parts that would effect HP production are different between the spec numbers of the Kohler M18 engines delivered to GRAVELY. 16G or 18G, they have the same cam, heads, pistons and governor. The original carbs have different part numbers, but they all crossover to the same replacement carb. And carburetors do not by themselves change HP. They can only limit max RPM, but we are talking two carbs that are the same bore, take the same rebuild kit, on engines that never see the max air flow the carb can deliver.
All G tractors got wider front rims about 1994, but 14G and 16G still had the smaller 16 x 6.50-8 tires. 18G and 20G had 16 x 7.50-8 tires.
Rear tires - early G's all had 7" wide rear rims, again, about 1994, 18G and 20G tractors got an upgrade to wider rear rims, I think 10". This is a known fact but not documented by GRAVELY. And again, 14G and 16G had 23 x 8/50-12 tires, 18G and 20G had 23 x 10.50-12 tires.
Steering - 14G and 16G tractors had lighter duty tie rods and shorter/lighter steering arms. 18G and 20G have very heavy duty steering parts - this is well covered later in my improvement thread.
Early 16G tractors did not have low oil pressure lights or hour meters, by 1994 both were standard.
These minor differences are subject to exact year/model, but the major differences are as Yamato pointed out:
Steering linkage
Wheel/tire size
Availability of the manual lift only on 14G and 16G
The shorter/taller steering wheel shaft is also an early/late issue with all G tractors, early = short, late = tall.
Important thing to understand - GRAVELY never went by any kind of "model year". Model numbers stayed the same until a change was made to the tractor, which could be mid year, or not for many years....so knowing your actual model number, like 987061, tells a lot about your specific tractor, and can make a big difference when buying some parts.
I know, I have likely bored you to death by now.
Feel free to ask any specific questions you may have.
Sheldon
