Technical Service Bulletin New Chain Adjuster

Subject: Chain adjuster – new version with modified intermediate piece for piston Models: 911 T/911 E/911 S 1970

Bulletin Number: 70 – 12

Effective date:   June 1, 1970

Vehicle type:      911 T, 911, 911 S

Model year:        1970

Engine type:       911/01 620 2190 911 E Manual transmission

                                911/02 630 2192 911 S Manual transmission

                                911/04 620 8403 911 E Sportomatic

                                911/07 610 9267 911 T Manual transmission

                                911/08 610 8353 911 T Sportomatic

Beginning with the above engine numbers, chain adjusters with modified intermediate piece for the piston are installed.

An O-ring has been added to the intermediate piece to improve oil sealing between the intermediate piece and the chain adjuster piston.

When replacing a defective chain adjuster or when overhauling the engine, install the new intermediate piece with O-ring. It is not necessary to replace the complete chain adjuster.

Effective immediately only the modified chain adjuster with the improved intermediate piece will be supplied as a spare part (Part number 901.105.49.02).

Previous chain adjusters, Part number 901.105.049.01 can be changed with the following parts:

Intermediate piece Part number:              901.105.585.01

O-ring Part number:                                       999.701.298.40

Disassembling, assembling, and testing the chain adjuster is described in the attachment.


For this sequence refer to the drawing on the last page.

  1. Clamp chain adjuster into vice. Remove circlip (17) with a small screwdriver. Caution: Spring seat (16) is under spring pressure.
  2. Remove spring seat (16) and spring (15).
  3. Remove aluminum piston (12) with suitable pliers.
  4. Remove circlip (11) above position (10) with a small screwdriver. Caution:  Piston is under spring pressure.
  5. Remove chain adjuster piston (10), intermediate piece with O-ring (8+9), 5 mm ball (7), ball cage (6), spring (5) and spring guide (4).

Note: It is possible that the intermediate piece sticks in the piston. To free it, tap piston on a piece of wood.


  1. Carefully clean all parts and check for wear. Replace worn parts.
  2. Insert chain adjuster piston together with the aluminum piston without the O-ring into the chain adjuster housing. Both pistons must move freely. Make sure that the adjuster position moves freely at its lowest position. Remove any tight spots with emery cloth.
  3. Install spring guide, spring cage, ball valve, intermediate piece and adjuster piston. Install circlip.
  4. Fill chain adjuster with engine oil 9SAE 30) and bleed. (For all 911 models, see 911 workshop manual page M (E) 106; for 914/6 model see 914 – 914/6 workshop manual, Group 1, page 14.1 – 2/3.
  5. For further assembly, clamp the chain adjuster into a vice with the outer air vent screw for the oil chamber titled up by about 20 degrees. In this position fill the oil chamber until the oil overflows.
  6. Clean the inner and outer groves on the aluminum piston. Lubricate it with oil and install 2 new O-rings (be careful not to damage them). Install aluminum piston. When in position, place adjusting ring (special tool P 215 b) on the piston. At the same time open air vent screws on housing and press down on the piston with the adjuster sprocket. At this point immediately close the air vent screw.
  7. Install the compression ring, spring seat, and circlip.


The chain adjuster is tested as described in the workshop manual. (991 manual, page M € 106 a; 914 – 914/6 manual, Group 1, page 14.1-2/3.)

Installing a new chain adjuster:

If the chain adjuster to be installed is new, make sure that it is pushed onto the pivot pin of the chain sprocket carrier only until the piston seat is half concealed by the chain adjuster arm. Then turn the spring ring above the spring bar until the bar can be removed. Push the chain adjuster fully onto the sprocket carrier pin and fasten into position. After installing the chain adjuster, check valve timing as usual and adjust if necessary.

Installing a chain adjuster after overhaul

Before an overhauled chain adjuster is installed, the adjuster piston must be moved to bottom dead center. Clamp the chain adjuster into a vice so that the jaws are slowly closed the piston is pressed down to the lower limit of its travel. If the piston is moved too fast, the rubber seal rings will be damaged and the oil in the oil chamber will escape. In this position, preload the piston with special tool P 214 and install the chain adjuster. After installing, check valve timing as usual and adjust if necessary.


Engines with the new chain adjusters can be turned over during repairs without risk that the oil will escape from the adjuster as on the previous version.

  1. Chain adjuster housing
  2. Seal ring
  3. Air-vent screw
  4. Spring guide
  5. Compression spring for chain adjuster
  6. Cage for ball valve
  7. Ball
  8. Intermediate piece
  9. O-ring
  10. Piston for chain adjuster
  11. Circlip
  12. Piston
  13. O-ring
  14. O-ring
  15. Compression spring
  16. Spring seat
  17. Circlip
  18. Bar

home page:

Want More?

Get the coolest tips and tricks today

Subscribe to our email list and get regular notifications of new videos and blog articles on how to repair your own car.