Jon,
One more thing about the handle spring: you will need to use a special tool to get it off. It is part no. SP123. These are the steps to replace it (applies to models 516 to D80):
A. DISASSEMBLY
(1) Remove the housing shell.
(2) If the spring is not broken, it is first necessary to relieve the tension from the handle spring. Remove the spring bushing clip (136356, 136367 or 136373). Engage the pin of the spring tool (SP123) with one of the slots on the outer surface of the spring bushing (137256 or 137273). Hold tension on the spring tool and pry the bushing to the side far enough to allow the spring yoke (137556 or 137579) to be disengaged from the spring bushing; turn the spring tool to relieve the tension.
(3) Remove the screw (137356 or 137373) from the spring bushing and remove the spring clip (1005) from the spring shaft.
(4) Pull the spring bushing, spring yoke, fiber washer (137456), spring shaft (137156 or 137173) and handle spring (137056 or 137067) from the housing shell (135556S, 135562S or 135567S).
(5) Remove the screw (137756) and the spring spreader (137656) from the housing shell. (These two parts may or may not be present on your machine.)
(6) If the bushings (135860 or 135960) are damaged or excessively worn, press them from the housing shell. Be sure that the housing shell is properly supported to prevent cracking or breaking it.
(7) If any of the handle lock parts require replacement, the handle lock should be disassembled at this time.
B. INSPECT THE PARTS FOR CRACKS, DISTORTION, OR EXCESSIVE WEAR. REPLACE ALL NON-SERVICEABLE PARTS.
C. REASSEMBLY
(1) Position the spring spreader (137656) in the housing shell (135556S); secure with the screw (137756). (The spring spreader and its screw may or may not be present on your machine.)
(2) If the bushings (135860 and 135960) were removed, press new bushings into place so that they are flush with the outside edge of the housing shell.
(3) Slide the spring shaft (137156 or 137173) into the spring shaft bushing (137256 or 137273) so that the screw holes are aligned one over the other.
(4) Position the spring yoke (137556 or 137579) and fiber washer (137456) on the assembled spring shaft and bushing.
(5) Position the handle spring (137056 or 137067) in the housing shell so that it is aligned with the spring shaft bore and the straight end is on the side toward the small bushing; insert the spring shaft and assembled parts through the large bushing and through the spring.
(6) Check that the screw holes of bushing and spring shaft are still in alignment; install the shouldered screw (137356 or 137373). Hook the looped end of the handle spring on the shouldered screw.
(7) Engage the pin of the spring tool (SP123) with one of the slots on the outer surface of the bushing. Rotate the bushing until the lip of the spring yoke can be engaged in the second or third slot of the bushing. This is determined by the amount of tension desired. Push the bushing all the way in and lock in place by installing the spring bushing clip (136356, 136367 or 136373) inside the housing shell.
(8) Install the spring clip (1005) on the spring shaft so that the flat side of the clip is in the slot of the spring shaft.
(9) Install the housing shell and foot switch button.
~Ben