The fire was just because it would require a lot of extra work for a mechanic that re-broke the part after X seconds. You are not really fixing it, just holding the parts in place for a bit to get it to work for a short while. There would be shorted wires and fuel and oils spilling out and catching fire.
On the other hand, the tool could be a rebuild only tool that rebuilds faster than the Spanner, and restores 80% or something of a mallet hit HP to a component instantly, but has no repair power. It could only be used after something broke. Give it a cooldown close to the pipe wrench. This option would make it the go-to gunner tool facing disable builds, but still not as valuable as a Pipe Wrench facing Armor/Hull breakers. Pilots would also have a second option for helping fix things in a pinch. Engineers
could take it in place of a Spanner for quick rebuilds and use Mallet for strong repair, but they would have to rely on Mallet for light maintenance. We all know how many times we have reprimanded an engineer for using a mallet on minor repairs. and this tool would be useless for engine maintenance during burns.
I rather like the second option (with testing and tweaks). It makes it a good option for emergency component rebuilds, but risky against progressive damage.
Tool | Rebuild | Repair (HP) | Cooldown (seconds) | Rebuild Instant repair (HP) |
Jimmy Bar | 6 | 0 | 4-6? | 1/3 + 200HP? |
Spanner | 5 | 40 | 2 | 1/3 |
Pipe Wrench | 4 | 120 | 5 | 1/3 |
Mallet | 2 | 250 | 9 | 1/3 |