Got to thinking last night that I have a distributor assembly from a '96 4.0 laying around in the hangar. Stopped by after work and pulled the gear. Inspected this used gear from a 60,000 mile engine that died from running with no oil for an extended period of time and it had virtually no wear. Took used gear home and removed my CPS assembly again. Removed the worn gear and compared the two gears using some dial calipers, they are exactly the same! While I had the CPS assembly apart I removed the shaft and found that the shaft had some light scoring in the area of the bottom bushing and moderate scoring on the shaft in the area of the upper bushing. Using some 600 grit silicon carbide paper I quickly removed the scoring from the soft shaft assembly. I inspected the STEEL busings and found no wear. I also noted that there is an oil seal BELOW the upper bushing, which means that the upper bushing DOES NOT get any lubrication during operation, this was evidenced by some burn assembly grease residue in the upper bushing. I then tried to reassemble the CPS using my old gear. The roll pin holes in the old gear did not line up perfectly with the holes in the shaft (maybe off .010 on one side) I tried to seat the roll pin and the old gear cracked. No choice but to reassemble the unit with the old gear and put her back in. I am not 100% convinced that the root cause is an improperly hardened gear and here is why.. #1 the shaft busings are hardened steel not bronze like every other distributor bushing in the world. #2 the shaft is very soft steel as evidencied by the deformaton of the oil pump drive tab. The distributor from the '96 4.0 that I took apart tonight had no wear on the oil pump drive tab and appeared to be made of MUCH harder steel. If you run a soft steel shaft in hardened bushings you WILL have problems like we are seeing. #3 The upper bushing is designed to basically run dry....just the little bit of assembly grease that was applied at time of assembly will never be enough to sufficiently lube the upper busing. #4 Excessive drag/binding/galling of the CPS shaft would cause the gear wear we are all experiancing. I think we are in BIG trouble in the long run unless an aftermarketer or some machine shop like HESCO starts overhauling or making replacement CPS assemblies without the design/manufacturing issues of the factory assemblies. I wish I had a worn gear to take to work with me so I could perform a Rockwell hardness test on the '96 gear and the '06 gear and get some real data.
FOG it is a PA-28-180D
FOG it is a PA-28-180D