This Legion Engineering leveling guide will show you the fastest and easiest way how level your Legion Engineering skill up from 1 to 100.
Engineering is the best combined with Mining because you can farm most of the needed materials, and you will save a lot of gold.
Learning Legion Engineering
Legion Engineer is rewarded for completing the 
Aww Scrap! quest. You can get this quest from Hobart Grapplehammer in Dalaran.
Unlocking recipes
Most Engineering recipes are unlocked by doing quests. These quests are given by one of the NPCs around your trainer.
There are 29 Engineering quest in total, they are pretty straight forward, so I will not write down the details of every quest. Some of the quests lead you to dungeons but you can finish every quest easily in a few hours if you start them at 50, otherwise, you will have to wait because later quests have a level requirements.
You don't have to do every Engineering quest to reach 100, but you must complete All Charged Up. (Around 10th quest in the chain)
Recipe ranks
Most Legion recipes now have 3 ranks. Higher rank recipes allow you to craft an item for fewer materials, and give skill points longer.Therefore, you should only use rank 3 recipes when you can.
Rank 3 recipes come from different sources like Vendors, World Quests, Reputation, dungeon drops, and even rated battleground win.
If you hover over the little stars in your spellbook, you can see the source of the next rank for the selected recipe.
Leveling Legion Engineering
You cannot level to 100 with rank 1 or 2 recipes, so you must get the Rank 3 recipe for 
[Gunpowder Charge].
Getting the Rank 3 Gunpowder Charge recipe
Rank 1 recipe
You already have Rank 1 if you completed the Engineering quest chain. It is rewarded from All Charged Up. (You must start the Engineering quests and progress until you reach this quest.)
Rank 2 and 3 recipe
Rank 2 and Rank 3 are sold by The Widow for 250 and 500 
Sightless Eye at the Dalaran Sewers.
You can farm 750 Sightless Eye in around 30 minutes or less. Check out my Sightless Eye farming guide if you are not sure how to get them.
1 - 100
You will need to craft the following recipe roughly 140 times:
140x [Rank 3 - Gunpowder Charge] - 140x Leystone Ore, 2800x Oversized Blasting Cap
[Oversized Blasting Cap] is sold by Hobart Grapplehammer near your Engineering trainer.
2800 x Oversized Blasting Cap costs around 3200 gold, but you may need to craft more because this recipe turns green between 90 and 100 skill. Buy these using shift + left click.
Gnome characters gain +15 Engineering skill from their passive 
[Engineering Specialization]. This extra skill means the recipe stays orange for longer, so you will need to craft fewer items.
I hope you liked this Legion Engineering leveling guide. Congratulations on reaching 100.