Engine Strip Down
The oil pump
The pump itself is beautifully simple: two intermeshing gears sit in an aluminum housing, drawing oil from the sump and forcing it under pressure to the filter and throughout the engine. The curved chamber in the housing guides the oil flow as the gears rotate.
I was initially considering replacement - a new pump would have set me back £375 plus VAT. But after disassembly and inspection, the gears showed no significant wear for a 156K engine, the housing was clean, and everything looked serviceable. A thorough clean was all it needed.
The 944's oil pump is a robust design, and unless you're seeing metal particles in your oil, excessive wear on the gears, or major scoring in the housing, there's usually no reason to replace a perfectly good unit.
This is one of those moments where simply putting back what Porsche originally engineered - properly cleaned and inspected is the only requiremnet.
Balance Shafts: The Hidden Complexity
The 944 S2 uses two balance shafts to smooth out the inline-four's inherent vibrations, each running on single-shell bearings in their housings. These shafts are driven by their own belt system, separate from the timing belt.
Simple in theory, but here's where it gets interesting: the bolts holding these bearing housings get extremely hot during operation. On my engine, one had already snapped completely, and the other three required serious heating before they'd budge free.
That snapped bolt? It turned out to be the source of a mysterious belt whine I'd been chasing for ages. I'd thrown everything at diagnosing it - a new balance shaft belt, a new timing belt, multiple re-tensioning sessions, a new water pump, and even a full rebuild of both the alternator and steering rack pump. 😂😂😂😂
All along, it was a broken bolt allowing just enough movement in the bearing housing to create that irritating noise.
To fix it, I had to drill out the broken bolt and install a Helicoil. My engine builder then advised me to Helicoil all four bolt holes - not just the damaged one. His reasoning was sound: with the thread damage and thermal stress these bolts endure, Helicoiling them all ensures I can achieve the correct torque setting across all four bolts consistently, giving equal clamping force and preventing future issues.
Sometimes the simplest failure hides behind the most elaborate troubleshooting. And sometimes the proper fix means going beyond just replacing what broke.
The Sump (Oil Pan)
The sump itself was in good shape - no damage, no warping, just needed a thorough clean. I stripped out the internal baffling (the oil windage tray that stops oil from sloshing about under hard cornering and acceleration) and gave everything a proper degrease as the hardened oil builds up behind the windage.
Most of the sump bolt threads were fine, but the two middle ones had seen better days and needed drilling out for Helicoils. While I was at it, I also Helicoiled the bolt threads at the front and rear of the engine - they were showing signs of wear, and I'd rather address them now than deal with a weeping sump gasket later because a bolt won't torque properly.
