Overpowers big mech

From the wreckage emerged a giant, a glittering machine of ridged and segmented battleplate, greater in stature than a Leviathan Dreadnought but with the proportions of a Scarabine Guardians.
...
	The leviathan swung back, finally landing a blow and smacking the chainsword out of contact. Russ held on to the blade, but no longer needed it. With his other hand, he grabbed the leviathan's wrist, and began to turn the siege-drill back against it. The leviathan pushed hard, straining against the Primarch's grip, but even with its machine-augmented motor was not enough, and secondary power units shattered across its spine. Russ twisted the leviathan's arm further, bending the drills until they faced directly into the armour-suit's face.

Leman Russ: The Great Wolf pg. 89