Currently I'm working on upgrading the belts on Goliath from 20 mm to 30 mm wide. Most of the hardware arrived a couple of weeks ago and I've been working on getting things installed. Below are the new and old prop pulleys with the ball bearing bushing. Both pulleys take SH Quick Disconnect (QD) Bushings, so I can reuse the same bushing.

HTD 8mm pitch pulleys come in standard widths of 20, 30, 50 and 85 mm. Since the center pulley needs to accommodate two belts, the center pulley needed to be 85 mm wide. Below is the old and new center pulley with bushings. The new pulley required a bigger SD size bushing so a new bushing was needed.

A critical difference between the two pulleys is that for the the new pulley, the bushing is recessed and the top of the pulley sits above the top of the bushing. This means that the upper belt is closer to the engine. This was an issue since there was barely enough room previously between the upper belt and the center beams that the engine sits on top off. To make room, the engine had to be removed and the wide slotted angle replaced with narrow slotted angle.

I was concerned that the narrow slotted angle wouldn't be stiff enough so I bolted a second narrow slotted angle to it to form a c-channel. To save some weight, the second piece only covers the primary span and none of the all thread runs through it. This means I can remove it easily if it proves to be unnecessary.

Next, the top of the center pulley had to be aligned with the rotor pulleys for the upper belt. The center beams already sat 1" below the top of the frame, but it had to be lowered another 3/4" so that the the pulleys were lined up. This part was a lot easier to do with the all thread construction. However the the cross beam that sits underneath the cylinder covers was in the way. It was a wide slotted angle piece, but after lowering the engine, there wasn't clearance for a narrow slotted angle. The solution was to flip the narrow angle over so that it pointed downwards.

With the upper portion of the frame completed, the remaining modification was to make the whole frame taller to fit the center pulley between the cross members. This meant increasing the space between the decks about 1". While I had left some excess length in the all-thread to allow the frame to be expanded like this, it was somewhat fortuitous that I chose the length I did because it was just barely enough.

As you can see, there isn't much excess room. Here's another shot to give you an idea of how Goliath as a whole looks now with one of the belts installed.I think the changes to the frame are complete. The next steps are adjusting the pulley layout to account for the larger diameter pulleys and placing the tensioner on the slack side of the belt.