I think there is bug related to unequiping engines and installing new ones.

I was able to eventually install replacement engines in two mechs after stripin mech and doing default loadout. However this 3rd one is a pain.

Its JVN-10N, destroyed engine is a engine core 180. I bought 2 engine cores, 170 and 175. I back out of the loadout menu. I go back into the loadout menu.

The destroyed EC180 is installed and most parts need repair or replaced. Weight is 33/30 tons. It was 30 tons before it destroyed.

The EC180 weighs 7 tons. When I unequip the EC180 the weight drops to 24 tons, not 26 tons.

Idk what the heck is going but maybe this will help the Dev or other modders ID the issue.

I'm going to try turning off all the other mods.

Bug still present after turning off all other mods and restarting the game

Turns out I had too many jump jets installed. Still doesn't explain why it was overweight but wutever

When stuff is broken it can do seemingly weird things to the overall weight.

Mechs require a minimum of 10 heatsinks to be a valid build. The engine will include an internal one for each complete 25 engine core rating (listed on the tooltip as Internal Heatsinks). As such, any engine that is smaller than a 250 rating will require additional external heatsinks to bring it up to this required 10. The little bit that causes that supposed oddity you noticed is the implementation of the tabletop rules of the first 10 heatsinks on a mech don't cost weight (so there's some invisible negative tonnage being applied to balance it), so with the engine broken, that counterweight is missing - and with the 180 only having 7 internal heatsinks, it needs an extra 3 external (which would weigh 3 tons, 1 each) to make up the difference.

Also, with jumpjets, you can only have a maximum of whatever the engine rating is divided by the mechs max weight (eg the Javelin with a 180 can have 180/30, aka 6. going with the 175 drops this to 5)

Ty for the info! Are there any docs or guides you'd recommend on YAML?