Crank Scraper Installation

A crank scraper is a performance upgrade for 944 and 951 models. It reduces oil aeration and crankshaft windage drag at high RPM by limiting the amount of air the crankshaft carries with it as it rotates. At high RPM, this entrained air saturates with oil, reducing the oil level in the pan and causing aeration and foaming while simultaneously increasing drag on the crankshaft.

Two styles are available: an all-metal style (requires grinding and fitting to clear the crankshaft and oil pan) and a Teflon self-fitting style (the crankshaft creates its own clearances as it spins by rubbing off any material that contacts it). Both styles typically require material to be removed from the back side to allow oil pan clearance.

Warning: The crankshaft must not contact the metal scraper. A poor fit will require removal of the oil pan at minimum, with the possibility of crankshaft damage. Take care not to introduce dirt or metal filings to the engine during fitting and installation.

This procedure was written for an all-metal scraper installed on a 1987 951. Instructions included with some scrapers recommend removing material from the oil pan rather than from the back of the scraper — this approach was not used here due to the complexity of grinding inside the cast aluminum pan. Note also that 1986 and earlier 944/951 engines used a shallower oil pan with less internal baffling; experience with crank scraper installation on those early engines may differ.

Tools

• High-speed air or electric die grinder (Dremel-style), for clearancing the scraper fingers
• Bench grinder, for profiling the back side
• Hot soapy water wash, for final cleaning after grinding

Parts

• Teflon or all-metal style crank scraper with proper washers (Ishihara-Johnson style)
• O-ring for oil pickup

Other Procedures

The oil pan must be removed to install a crank scraper. This may be done with the engine in the car (see LUBE-06) or with the engine out on a stand (see ENG-01).

Procedure

This is written for an all-metal scraper. If installing a Teflon-style scraper, follow the instructions included with it — many steps will be the same.

1. With the oil pan off, remove the oil pickup. Check crankshaft end play: new specification is 0.11–0.31 mm; maximum wear limit is 0.40 mm (0.016"). Excessive end play may cause connecting rod caps to contact the installed scraper and indicates a worn thrust bearing (part of the #3 main bearing). If the thrust bearing is worn, a new set of main bearings should be considered.

2. Remove the five 19 mm (M12) main bearing nuts on the left side of the engine. The washers from these nuts may be discarded and replaced with the thinner ones included with the scraper.

3. Test-fit the scraper by installing it using three nuts on the front, center, and rear studs. Lightly tighten to position it properly. Check the clearance between the crankshaft and the scraper at all critical locations — connecting rod caps and crankshaft counterweights. Be aware that the crankshaft can move forward and rearward; rotate the crankshaft by hand (not with the starter motor) to check all clearances. The scraper manufacturer's instructions will specify the minimum clearance required (1 mm in this case). Mark all spots on the scraper where clearance is insufficient with a marker. Remove the scraper and use a die grinder to remove material. Clean completely. Reinstall and recheck. Repeat until clearances are correct.

4. Check that the oil pan does not touch the scraper. Install the scraper and smear contrasting-colored grease on the outside edge. Cut 10-inch sections from each side of an old oil pan gasket and temporarily glue to the oil pan gasket surface with silicone-based gasket maker to allow proper oil pan positioning without a real gasket. Attempt to position the oil pan — interference will cause the grease to transfer to the inside of the pan, showing contact points. Remove the scraper, mark the interference areas, and grind off the excess material on a bench grinder, finishing with a file or die grinder. Clean and reinstall; repeat as necessary.

Note: If your oil pan has an internal baffle tray, the scraper may interfere with the plastic at the back edge and with a tray mounting bolt. Shorten and round off the scraper at these locations. A tray mounting bolt top may also need to be shortened, or the scraper ground further to clear it. Do not shortcut this fitting — a poor-fitting oil pan will leak.

5. Once fit is confirmed, do a final cleaning (hot soapy water to remove all grinding debris), install the oil pickup with a new O-ring, and install the scraper using the proper washers. Torque the 19 mm (M12) main bearing nuts in two stages:

   • Stage 1: 30 Nm (22 ft-lbs)
   • Stage 2: 60 degrees (angle torque)

   A 19 mm crowfoot wrench is required for the nut behind the oil pickup tube. Install the oil pan using LUBE-06. Check for leaks.