Air-cooled Porsche engines are unlike anything else: horizontally opposed, built from separate case halves joined by through-bolts, and cooled entirely by airflow over cylinder fins rather than liquid coolant. They’re precision instruments that demand specialist knowledge to rebuild correctly. A mechanic who’s rebuilt a thousand inline-fours or V8s still doesn’t know how to properly assemble a Porsche flat-six, and the consequences of getting it wrong are expensive.
Smyth Imports has been working on European performance cars in Cincinnati for over 90 years. We understand the Porsche air-cooled engine’s unique demands: the critical tolerances in magnesium and aluminum case halves, the thermal cycling that deteriorates sealing surfaces over decades, and the specific machining procedures that separate a proper rebuild from one that leaks oil and loses power.
The air-cooled 911 is the car that defined Porsche, and values across all generations have climbed dramatically. From early short-wheelbase cars through the 964 and 993, we handle complete restorations and mechanical rebuilds.
Case halves split, crankshaft inspected and measured, main and rod bearings replaced, cylinders and pistons inspected or replaced, and cylinder heads fully rebuilt with new valve guides, seats, and seals. Every critical measurement is documented. On 3.6-liter engines (964/993), we check for cylinder head stud thread damage and install case savers where needed.
Earlier magnesium cases (particularly the 1974-77 2.7-liter) are vulnerable to warping from decades of thermal stress. We address this with shuffle pinning, line boring, and deck resurfacing. Even aluminum cases benefit from deck resurfacing at this age.
The original single-row tensioners on pre-964 engines can ratchet past their engagement points, losing chain tension and causing catastrophic valve-to-piston contact. We upgrade to dual-row tensioner systems as standard preventive maintenance.
Guides pressed in with interference fit (heads oven-heated, guides frozen in liquid nitrogen for proper installation), valve seats precision-cut with three-angle profiles for optimal flow, and valve spring shimming calculated for correct seat pressure without over-springing.
Air-cooled 911s leak oil. It’s practically in the design specification. But proper case sealing, correct gaskets, and attention to the case half joint, timing chain cover, oil return tubes, and valve covers eliminates most leaks. A proper engine reseal requires splitting the case halves.
The 944 is one of the best-handling front-engine sports cars ever built, and values have finally started reflecting that.
The 356 is where the Porsche legend began, and frame-off restorations on these cars are serious, high-value undertakings. The air-cooled flat-four demands the same precision as the later sixes, with additional challenges from magnesium case corrosion and the age of the components.
We serve Porsche owners across the greater Cincinnati region and beyond:
For Porsche owners outside driving distance, we offer enclosed transport services.
Call us at (513) 793-0434 or contact us online to schedule a consultation.
Smyth Imports has been Cincinnati’s trusted European car specialist since 1932. We also restore BMW, Mercedes-Benz, Ferrari, and other European marques. View all our services →
8773 Remington Rd
Cincinnati, OH 45242
By Appointment Only
Monday – Thursday
Friday
Saturday
Sunday
9 am – 5 pm
11 am – 4 pm
12 pm – 1 pm
Closed
