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Porsche 944 Track Car

Porsche Track Car – Part 21 Engine Rebuild, Bottom End

I finally got my components back from the machine shop in late January and engaged upon the engine rebuild.  Since this was my second rebuild I was able to move ahead with a little more confidence.

The first thing I did was clean the block very carefully, first with soapy water, then with aerosol brake clean.  The block had been hot dipped at the machine shop but otherwise it had not required any work.  As part of cleaning the block, I punched out the two plugs at the end of the long oil gallery that runs the length of the block.  I ran water and brake clean through this path and confirmed that fluid exited from all the correct points to oil the crank and the head.  Then I put in new plugs.

After mounting the block upside down in the engine stand, I installed the crank.  The old crank had been damaged when the rod bearing spun.  Rather than turning down the crank journals and installing non standard bearings, I had the machine shop magnaflux, clean, and polish a spare crank that I had.  I mounted this crank with new bearings onto the block and mounted the crank girdle. Before this assembly, I put Plastigage on each bearing journal (except for the one with the one piece circular bearing).  I torqued the crank girdle, then took things back apart to check the squish on the Plastigage.  The bearing to journal gaps were within specs.  I also checked endplay at the center thrust bearing using a dial gauge.  This was also in spec.  For the final mounting of the crank girdle I applied the special orange Locktite as specified in the shop manual.  I was very sensitive to this step, as this was the area that caused a failure in my last rebuild.  I also mounted the rear oil seal on the crank prior to final assembly.

Next it was time to mount the pistons, rings, rods, and rod bearings.  I cleaned the gunk off the piston domes using a mild abrasive wheel and brake clean.  I mounted the new rings in the cylinder bores and checked ring gaps.  As with my previous rebuild, the compression rings came with the correct end gap (you check it by putting a ring in the cylinder bore and checking the gap with feeler gauges) but the oil scraper rings were a little too big and had to be shortened a schosh. (A schosh is more than a tad but less than a wee bit!).  Using a ring compressor, I inserted each piston/ring assembly into a lubricated bore.  At the other end, I mounted one rod bearing half in the end of the rod and carefully guided the rod over the crankshaft journal.  This is much easier if you do the 2 where the crank journal is most accessible and the rotate the crank 180 deg to do the other 2.  I also checked each bearing with Platigage to check clearance.  All were within spec.  I used the new type knurled nuts on the rod ends and tightened per the shop manual.  Every step of the way in this process I checked the crank to make sure it turned easily. No problems there.

At this point you are almost done with the bottom end.  Carefully mount the oil pickup tube and its gasket, as well as the oil return tube, which on my engine does not have a gasket.  Mount the oil pump on the front of the engine.  Reference to the Porsche parts diagram for the engine is vital to determine the correct placement and size of oil seals, spacers, washers, etc on the front of the crankshaft at the oil pump.

Next I found my oil pan and cleaned it really well using the same process I used on the block.  I mounted the oil pan and its gasket and torqued the various fasteners around its perimeter.  At this point, the bottom end is pretty much done.  I mounted the flywheel but deferred on the bell housing and clutch to later, as it interferes with my engine stand.

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