Technical Service Bulletin Changes made to Distributor 911/Turbo 1978 Models

Subject: Distributor Changes      Models: 911/Turbo 1978

Bulletin Number: 78 – 04

distributor part

Crankshaft drive gear and distributor pinion have been changed for 1978 models to reduce backlash at distributor shaft.

new parts for distributor plus old

Engine numbers when changes were made:

911 SC-628.0907


Drive Gear

New drive gear is identified by “T” on face and is light yellow. Old gear is no longer available as spare part.


New pinion as follows:

Distributor with new pinion

911 SC-No. 920.602.021.02

Turbo-No. 930.602.101.07


New-type distributors cannot be installed in earlier engines without change of distributor pinion.

Repair Instructions

Excessive backlash, correcting

Excessive backlash between distributor shaft pinion and drive gear on earlier 1978 engines can be corrected as follows:

  • Remove distributor
  • Remove distributor pinion (see “Distributor pinion, “changing” below)
  • Install “Special Pinion”, Part No. 930.602.422.90/91


When earlier version 1978 engines are disassembled, new combination of distributor drive gear and pinion should be installed.

To avoid disassembly of earlier engine when installing new-type distributor replace new-type pinion with “special pinion”,

Part No. 930.602.422.90/91


After installing distributor which has “special pinion”, stamp “S” into distributor flange as shown. If engine is disassembled and new drive gear and distributor flange. If “S” was previously stamped on flange, grind this off or X it out.


Retaining rings of different thickness are available to prevent axial play of distributor drive gear.

Retaining rings are available as follows:

Part No.                                               Thickness (mm)                Marking

901.102.148.00                                  2.4                                          0

901.102.148.01                                  2.3                                          1

901.102.148.02                                  2.2                                          2

901.102.148.03                                  2.1                                          3

–              Install timing gear, retaining ring and distributor drive gear onto crankshaft, against shoulder

–              Select and install correct retaining ring to take up play.

warning for distributor img.

Distributor pinion, changing

  • Remove distributor
  • File off or drill one end of pinion retaining pin
  • Tap out retaining pin with drift\
  • Install new pinion together with thrust and fiber washes and selected shim or shims
  • Partially insert new retaining pin (Part No. 930.602.922.00) and check axial play of distributor shaft with feeler gauge
  • Must be 0.2 + 0.1 mm
man working with distributor part


Thrust washer (I) 0.2 mm thick. Fiber washer (II) 0.8 mm thick and at least one steel shim (III) must always be installed.

  • Tap retaining pin in so it protrudes equally on both sides
  • Peen both ends of retaining pin
  • Reinstall distributor
  • Set ignition timing
  • Withdraw pinion from shaft

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