ThePilgrim nut system used with the shaft and bore surfaces dry and degreased (except for cast steel propellers where wiping of the bore with an oil soaked rag is recommended) achieves the correct push up by a calculation based on the predictable friction of dry surfaces. The calculation gives the hydraulic pressure suitable for the prevailing ambient temperature lo produce the required push up. The operation is of course checked by measuring the push up and the hub movement relative to the increase of jacking pressure is monitored by a dial gauge.
The Pilgrim nut (Figure a ) employed for propeller mounting. has an internal nitrile rubber tube which when inflated hydraulically, forces a steel loading ring against the hub. Outward movement of the ring from the flush position must not exceed one third of the ring width, to avoid rupture of the rubber tube. Temperature of hub and shaft are recorded and also used to find the correct final push up pressure from the table provided in the instruction book.
The propeller, after a check with the blue marker of the mating surfaces, is positioned and initially jacked on to the shaft taper. before the Pilgrim nut is used to apply an initial loading of perhaps 67 bar pressure. A reference mark is made at this point about 25 mm from the forward end of the hub. The nut is then turned until the loading ring is again flush (venting hydraulic flutd) becore full pressure is applied. During this stage, the dial gauge should show the movement. A second mark 25 mm from the forward face of the hub is then made. Push up, registered by the distance between the two reference marks, is measured and noted.
The nut is again vented and turned to bring the loading ring to the flush position and finally nipped up with a tommy bar. The Pilgrim nut can be reversed and used with a withdrawal plate and studs (Figure b) for removal of the propeller. To safeguard against any violent movement at release, wooden blocks are inserted as shown, and a gap of only a little more than the push up distance is left.
The Pilgrim keyless system owes its name to T. W. Bunyan.
Pilgrim Nut Operation
Pilgrim nut is used to ensure a solid frictional drip between the propeller and shaft. The use of pilgrim nut facilitates the transmission of the engine torque without using the key.
Pilgrim nut is basically a hydraulic jack with threads, which is screwed into the slot provided on the tail shaft . The propeller is forced onto the tapered tail shaft region by using a steel ring, which receives the thrust from a hydraulically pressurized nitrile rubber tyre. The same process can be revered, by using an additional withdrawal plate attached to the propeller boss by studs , in order to take the propeller off off the shaft. In simple, when the tyre is pressurized the propeller will come off the tapered region.
The Pilgrim nut Assembly and Removal
Assembly
Propeller bedded to tailshaft and jacked up to usual shop mark. The Pilgrim nut is then screwed on the shaft with the loading ring against the prop boss. With the lever operated, high pressure grease gun, grease is pumped into the inner tube inside the nut at around 600 bar, ( w.p. stamped on nut, not to be exceeded), the prop will be pushed sufficiently up the taper to give the required frictional grip. The pressure is then released and the nut is rotated until it is hard up against the aft face of the prop hub and locked, fair water cone then fitted.
Removal
After removal of fair water cone and the locking plate, the pilgrim nut is removed, reversed and together with a loose shock ring is screwed back onto the shaft. A strong back is fitted and secured with studs to the prop boss. Grease is now inserted to the system expanding the inner tube forcing the loading ring, strongback, withdrawal studs and prop aft.Advantages
- Precise tightening working on a measured applied load
- Adequate interference fit
- no heat used
- Simple and safe to operate
- No shock loads applied
- Considerable saving in man power and time
