The following slipper drive article is an illustrated and ...



The following slipper drive article is an illustrated and enhanced method of it’s removal described in the “Rolls – Royce Small Horsepower Engines” book by R. Haynes and M. A. Grigsby. It is demonstrated on my 1929 20 HP (GEN 36) “N” series during ground up restoration. (With the engine in place and the fan, fan belt, and radiator removed).

By John B. Carey NCRROC life member

Removal of the Crankshaft Vibration Damper

1) “Commence by removing the dynamo drive brake housing,” (pg. 53). “It is first necessary to take down the dynamo and magneto by uncoupling immediately behind the timing case. Remove the two covers on the dynamo drive brake housing, and withdraw the brakes and springs. Take off the four nuts securing the housing to the timing cover, and extract the cover by screwing a pair of ¼” B.S.F. bolts into the threaded holes in the housing flange. (pg. 71). (See picture #1). This description is straightforward. The small covers come off the top and bottom and spring pressure on the covers will be released that let the brake blocks come out. The only difference here is that my threaded holes in the main cover are 3/16” B.S.F. and they are in brass inserts. With age and crud, you will need to be careful not to damage these during the extraction, which is meant to apply pressure through the holes to the case. Be sure the threads are clean all the way through. The assist holes are a convenience, but damage would be unsightly and render them useless.

2) “Undo the securing nuts and withdraw the timing cover.” (pg. 71). On 20 HP Chassis 501 to 20/25 HP Chassis GKT21 remove the fan pulley securing nuts and take off the lock plate. (pg. 53). (See picture #2). There are 5 nuts securing these to the damper mechanism. Carefully loosen the lock plate first, then remove the fan pulley. The serrated nut, threaded left hand, is next to be removed. (See picture #3). Then the starting dog nut (where one engages the hand crank) can be removed, threaded right hand, with great force using a “slogger spanner” or proper large socket. This will require blocking the flywheel. I made a flywheel-blocking tool, which may be installed in place of the starting motor with or without the oil sump installed. (See picture #4). “With the crankshaft spragged, a smart blow with a two pound hide faced mallet on the spanner will loosen the nut. Use of a ring spanner or a socket and strong-arm bar does not impart the necessary shock (pg. 54). I loosened my starting dog nut with a large socket using a large breaker bar with a cheater extension. The slooger spanner recommended by the book is long, thick metal with a hexagon cut out that may be given the “smart blow”. “Take off the timing cover noting the position of the four ream fitted 5/16” bolts.” (pg. 54).

3) “Mark the Cam Timing.” (Pg. 54). “At this stage bring the engine up to the flywheel TDC mark, and mark the meshing teeth of the cam wheel, the idler gear, and the water pump pinion with a scriber. (pg. 54). The Top Dead Center mark is seen behind the flywheel cover on top of the bell housing below the front seat floorboards. It is necessary to mark the position of the cam gear when at TDC. This is done by relating the cam gear to a timing cover stud as well as to other gears. One must also realize that when the damper comes off, the cam gear rotates clockwise at least two teeth, so it is good to mark that relationship about two teeth to the counterclockwise of the TDC mark you made opposite the stud. When replacing the crank gear, this mark can be used as the start point for engaging it so that the cam gear spin will result in the original cam timing. (See picture #5). It is best to test and practice replacing this alignment while it is fresh in your mind since it is easy to get the cam gear off by one tooth or more which will alter the timing of the car. Always check the flywheel TDC mark against the cam mark to be sure you are dead on.

4) “Removal of the Damper.” (pg. 54). While the book says that the above car parts may be used as a simple damper puller, I found that much more force was required. With instructions written by John Flockart (Australia) and provided by Gil Fuqua (RROC), I was able to make a stout puller adapted to my application. (See picture #6). It is bolted to the 5 studs that held the fan pulley to the damper and applies force via the end of the crankshaft through 5 studs which are drawn up slowly and equally. The crankshaft is tapered and has two woodruff keys so it is quite a tight fit. I was prepared to use heat as well as a machined drift bar to apply some shock to the center of the shaft, but none of this was needed. When the damper releases, however, one is un-nerved by a sharp crack not unlike a rifle report. Remove the puller and then take the damper off while observing how the cam gear rotates in the process.

5) Making the Puller. The ring that attaches to the damper by its studs is the most critical part and most likely will require a lathe to make it accurately. It is mild steel 11/32” thick and can be no more otherwise too few threads on the damper studs will be utilized. The damper stud holes are 17/64” diameter and are 2 - 15/16” on center. The outside diameter of the ring is at least 3 – ½”, and the inside diameter is 2 – 3/16”. (See diagram #1). I used hardened ¼” x 28 thread studs 3” long that are threaded into the ring holes between the damper stud holes. These were brazed up for strength. The outer slug is the same outside diameter and is mild steel at least ¾” thick. The 5 stud holes in this piece are also on 2 – 15/16” centers. Use hardened nuts and washers to distribute the force to the damper.

I would be happy to answer any detailed questions from anyone preparing to get involved with this procedure. John Carey (E-mail: JCarey4NGs@)

(Photo Captions)

Pic 1: The dynamo drive brake mechanism must be removed before the timing cover. There are two sets of the parts shown that come out of the top and bottom of the drive cover. Shown is one of two 3/16” B.S.F. bolts that may be used to force the cover loose.

Pic 2: The five damper stud nuts are removed in preparation for taking off the lock plate.

Pic 3: The serrated nut (left hand threads), and finally the fan pulley may be removed. To remove the starting dog nut (right hand threads), the flywheel must be blocked.

Pic 4: This blocking tool may be used in place of the starting motor to keep the flywheel from spinning when removing the starting dog nut. It is designed to be used with the long starter bolts if the oil sump is fitted. When the oil sump is off, shorter bolts are used (shown).

Pic 5: Very accurate and carefully tested (TDC) marks on the timing gear, idler gear, and the relationship of the cover stud help to assure correct re-assembly.

Pic 6: The tool shown in position on the front of the crankshaft and ready to apply pull on the damper towards the front. One of the damper stud nuts is off to show the amount of threads that are used.

Drawing 1: The ring part of the two-piece damper removal tool is shown dimensioned. Also described is the steel slug that completes the tool. (Drawings is not to scale).

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