As specified in Technical Bulletin TB 78-03, a change occurred in 1979 when an o-ring groove was removed from the camshaft and added to the camshaft sleeve bearing. A larger o-ring was required.
Specified in TB 78-03:
- Early o-ring P/N 99970145240, size 18.4 X 2.4mm
- Late o-ring P/N 99970159240, size 23 X 2mm
NOT specified, an additional change occurred to the cam carrier housings when an o-ring groove size increased. A larger o-ring was required, however this was not documented.
- Early o-ring P/N 99970142540, size 52 X 4mm
- Late o-ring P/N 99970160240, size 50 X 5mm
The TB reads from following engine numbers: 8280082 (manual) and 8289026 (auto). Physically check your 928 before ordering parts. While performing this service, I recommend that you replace the following parts as well:
- Camshaft seal P/N 99911328240
- Oil galley seal P/N 92810518400
- Distributor seal P/N 92860210300
Quantity 2 each Use assembly lube on all o-ring seals
Important: Set engine timing to TDC before removing the distributor.