The battletech manual doesnt say so, it just describes VTOL's and their function, primarily as a support vechicle since the rotors cant be armoured.
I also recall seeing quad rotor mech lifters back in the day, and mechcommader used quad rotor Vtols as feild repair units IIRC
If you look at the picture bottom left on this sheet you will see a mech lifter in action
Edit: Looking a little deeper i see the max tonnage for Vtols is 30.
So if we are talking US measurements There are 2,000 pounds in a US ton, a Chinook weighs in with a chassis of 23,400 lb, so about 11.7 tons