All reports seem to indicate that the installation of the idler pulley is one of the more important steps undertaken during the construction of the helicopter. One needs to align the pulley with the secondary and main drive sprocket in order that the main drive belts run smoothly with no tendency to walk up or down.
The order of installation of the drivetrain components would normally be the main mast and main sprocket followed by the secondary. The idler pulley can then be mounted. If the Rotorway supplied main sprocket and chain drive is utilized the idler pulley install proceeds smoothly. I chose to use John Spurling's cog belt drive which comes with a different main sprocket. In image #1 one can see that the outter rim of the main sprocket directly overlies the top of the idler pulley bracket preventing access for drilling the mounting hole from the top. Prior knowledge of this alerted me to drill the upper hole before final install of the main sprocket. Now the thinking prcess started! How do I align the idler pulley weldment with the secondary and then transfer the needed location of the bolt hole to the underside of the lower bracket flange?
Following some thought I sectioned a 5/16" transfer punch into 3 pieces each of which would fit between the underside of the main sprocket and the upper idler pulley bracket. The pullley was aligned and then each section was placed through the top hole in the bracket and through the idler weldment. The first section of the transfer punch placed had the sharp point and the last one protruded above the bracket. I then place a C clamp from beneath the lower flange to the top of the protruding transfer punch. Tightening the clamp then made a mark on the top of the lower flange. In image #1 one can see the machinist marking fluid where I transferred the mark to the underside. Now I could drill the lower bolt hole!
With the idler pulley now installed I checked the alignment with the secondary. Laterally I was within .006" of being parallel between the two. A good da
