A common performance upgrade to 944 and 951 model Porsches is the installation of a Crank Scraper. It is a cheap way, especially when included during other procedures, to increase power and improve oiling. It works by reducing the amount of air the crankshaft carries with it as it rotates. This air will saturate with oil at high rpm's reducing the level of oil in the pan and causing aeration and foaming of the oil, while at the same time increasing drag resistance to the crankshaft. There are two styles available from Ishihara-Johnson (Crank-Scapers.com). The most common and cheapest is the all metal style, which will require grinding and fitting to clear the crankshaft and oil pan. A Teflon self fitting style is also made and the principal behind the Teflon crank scraper is that the crankshaft will create its own clearances as it spins, rubbing off any material that touches the crankshaft, allowing closer clearances. The all metal style requires careful fitting to ensure proper clearances to the crankshaft. Both styles will most likely require modification by grinding the backside to allow oil pan clearance. Which one you decide on will be a matter of choice based on cost and personal preferences. Do your research first to help you make this decision. As the install is a very lengthy process, most people will do it as part of a larger overhaul on the engine. Regardless, the oil pan will have to be removed first and the obvious other procedure is the checking and possible replacement of the rod bearings. It is also important that the thrust bearing is in good condition. If it is worn, a new set of main bearings should be considered. The crankshaft must not contact the metal scraper. Care must be taken not to introduce dirt or filings to the engine. A poor install, at the very least, will require removal of the oil pan to correct, with the possibility of damage to the crankshaft.
This install was conducted using an all metal I-J crank scraper on a 1987 951. Instructions included with the crank scraper recommended that material should be removed from the oil pan, rather than from the back of the crank scraper, to allow clearancing of the back of the crank scraper. This was not done as it would have required more complex grinding of the inside of the cast aluminum oil pan and modification or removal of one of the oil pan baffle bolts. It is also noted that 1986 and older 944/951 engines used a shallower oil pan with less internal baffling; the author does not have experience with crank-scraper installs on early engines.
The only special tools you will need, will be a high speed air or electric die style grinder or Dremel-style tool to clearance the fingers and a grinder to help profile the back side. After final fitting, a hot soapy wash is required to remove cuttings.
A Teflon or all-metal style crank scraper with proper washers. O-Ring for oil pickup.
The oil pan must be removed to install a crank scraper. This may be done in the car or while the engine is out of the car and on a stand. See: LUBE-06 or ENG-01.
This is written for an all metal scraper. If installing a Teflon style scraper, follow the instructions included with it. Many procedures will be the same.
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 crank shaft end play may cause contact between the connecting rod caps and the installed crank scraper, and is indicative of a worn thrust bearing (part of the crankshaft #3 main bearing.)
Remove the five 19 mm (M12) main bearing nuts on the left side of the motor. The washers from these nuts may be discarded and replaced with the thinner ones included with the scraper.
Test fit the scraper by installing it using three nuts on the front, center and rear studs. Lightly tighten to position scraper properly. Check the crankshaft-to-scraper clearance. Critical locations are the connecting rod caps and the crankshaft counterweights. A tight fit is desired, however proper clearance is necessary. Be aware that the crankshaft can move forward and rearward. Rotate the crankshaft by hand to check all clearances. DO NOT USE THE STARTER MOTOR! Check the instructions supplied with the scraper. This will give the recommended minimum clearance for the scraper (1 mm in this case.) While a tight fit is desired, be aware that if the crankshaft touches the scraper, now or in the future, damage will occur. Some people prefer to increase the crank clearances to ensure no possibility of touching, ever. By carefully forcing the crank forward and back, you can see how much the clearance changes. Do not pry against the bearings. Use a marker to mark all spots on the scraper where the clearance is too little. Remove the scraper and use a high speed die type grinder to remove the necessary material. Clean completely. Reinstall the scraper and check the clearances. Repeat until the clearances are proper. This may take several trial fittings and grinding.
The second part of the fitting process is to ensure that the oil pan does not touch the scraper. It is normal to have to remove material from the back side of the scraper (or from the inside surface of the oil pan) to clear the oil pan. To do this, install the scraper and then smear contrasting coloured grease on the outside edge of the scraper. Take the old oil pan gasket and cut a ten inch section from each side and temporarily glue to each side of the oil pan gasket surface using a silicon base gasket maker. These will allow proper positioning of the oil pan while fitting.
Attempt to position the oil pan. It will most likely interfere with the scraper before the gaskets meets the engine gasket surfaces, and the grease will transfer to the inside of the oil pan allowing you to see where it touches. Remove the scraper and mark the areas of interference with felt pen. Grind the extra material off using a bench grinder and then follow up with a file or the die grinder. Clean. Reinstall the scraper and repeat the fitting procedure. You might have to do this several times until you can fit the oil pan so it does not touch the scraper. An area of conflict to be aware of is if you have a new style pan with internal baffle tray. The scraper could interfere with the plastic at the back edge and with a tray mounting bolt. Shorten and round off the scraper at this location and remove plastic from the edge of the tray along the back of the oil pan. A tray mounting bolt may also touch. The tray mounting bolt top could be shortened, or if necessary the scraper might have to be ground until it clears around this bolt. Do not short cut the fitting procedure as oil leaks from a poor fitting pan could result. This picture shows a modified scraper ready for install. Note how much material has been removed from the back side of the scraper. The gaps where the crank weights go and the gaps where the connecting rods go have also been widened.
Once you are happy with the fit, do a final cleaning and then install the oil pickup using a new O ring. Install the scraper using the proper washers and torque the 19 mm (M12) main bearing nuts to spec: 1st stage 30 N-m (22 ft-lbs); 2nd stage 60 degrees. A 19mm crowfoot wrench is required for the 19 mm nut behind the oil pick-up tube Install oil pan using LUBE 06. Check for leaks.