The vehicles currently have two problems:
- Small repairs are too hard
- Building deathmobile is too easy
Too hard repairs
So you have a car. The tires are pretty badly damaged (but not broken) and you want to replace the old wheel with this shiny new wheel you found. You could wait until the wheel breaks and you get the option to fix it with new wheel but you of course don’t want to wait for that.
Well it is easy to remove the old wheel: Mechanics 2, bolt turning 2 and some lifting.
Installing the new wheel is a bit harder with requirement of mechanics 3 and same tools.
But is wheel swap really hard enough job to require mechanics 3? Well in the current system you aren’t swapping the wheel. Instead you remove the wheel and then install a new wheel as if there never was any wheel there. So the skill requirement of 3 isn’t for swapping wheel but for rebuilding your car to use one more wheel. Which brings us to the second problem…
Too easy deathmobiles
So installing new wheels on a car requires only mechanics 3. Since wheel swap and wheel install are same job they have same skill requirement. And wheel swap can’t be made too hard so installing new wheels can’t be made too hard either.
Engine installing is another one. Installing inline-4 engine requires only mechanics 2.
The fix
My suggestion is to add new vehicle parts for bulding the chassis of the vehicle:
Wheel axle and engine compartment.
So to install a wheel you would first install wheel axle (high skill/tool requirement) and then you can install the wheel on that same spot (low skill/tool requirement).
Then you can remove the old wheel and install a new wheel one the same spot with low skills. But making a monstorous 8 wheeled deathmobile would require high skills to install new axles.
Same for engine. First install engine compartment (high skill/tool requirement) and then install engine on the engine compartment (low skill/tool requirement).