I've had a gas and a couple of diesel bucket trucks. All three were underpowered on the road.
Of course I like the diesels the best but one problem was that if the diesel motor is run slow is that it can 'wet stack'. Meaning fuel condensates on the cylinder walls and gets into the motor oil. I was told by several people that rpm's of 1,100 would keep the cylinder walls warm enough so that condensation did not occur. I'd also run radaitor blockers in the winter time to keep diesel motor temperatures up. Running at 1,100 resulted in faster than I liked boom movement but you learn to work with it.
On the gas unit, which was a 1982 Asplundh AR50 I believe, it had an 18hp two cylinder cast iron Wisconsin engine as a pony motor. It drove the boom hydraulics and also an air compressor for the bucket pneumatic system. We didn't use it so we took the air compressor off of the truck and put a little larger pulley on the Wisconsin so it would rev slower at working rpm's. That Wisconsin was the perfect driver for the hydraulic system. It ran just a little over half speed and put out a nice deep sounding sound and you could tell from the bucket as the load changed on the motor. It also charged the main truck battery system.
One problem I do see with a single diesel motor in a bucket truck is that when the motor is driving the hydraulics only that the diesel is way large for the task and is often run in rpm ranges that are not the best for the large motor.
The Wisconsin motor was air cooled but I've often though if it was water cooled and shared the cooling system of the main motor just how nice it would be to have heat in the cab and an already warmed main motor when it came time to move around. I've seen small Kubota diesel pony motors but they always had separate cooling systems from the main diesel.
My last of the four bucket trucks that I've owned was an 1985 International with a 65ft. High Ranger non over the center boom. DT466 motor, 5 speed, dual speed rear. It didn't have good ground speed either especially in hilly areas but ran like a top.
Just a little remising from a 62 year old tree guy. Today I climb everything but am doing much less work by choice. Kind of sliding in to home plate. I do have a Raptor gas powered ascender which was largely responsible for me selling my last bucket truck. Don't miss that truck a bit.
