Achilles Heel: Porsche 996 motors

Internet doom mongers will tell you 996 Porsches are guaranteed to implode. Is the risk really that high?

3y ago

It’s fair to say the water-cooled flat-six family fitted to Porsche’s 996 and early Boxsters has a bad rep. We’ve all heard horror stories about them grenading, but have the blow ups been blown out of proportion? Just how likely are they to go wrong and how much does it cost to fix?

Porsche M96 engine. Yours for £12k

Porsche M96 engine. Yours for £12k

The Rumour

All Porsche 996 engines suffer catastrophic engine woes – from IMS failure, cracked cylinder liners and nasty bore scoring. It all results in one thing: an engine that grenades itself and hands you a five-figure repair bill.

The truth

There are several problems with the M96 engine in the 996, but according to Josh Sadler of Autofarm (, forget about cracked cylinder block stories - his company hasn't seen a failure in years. Most of the cars that had poorly cast blocks have detonated and been replaced more than a decade ago.

Broken cylinder liner. Big bill on the way

Broken cylinder liner. Big bill on the way

What is an issue is the infamous Intermediate Shaft (IMS) that drives the camshafts indirectly off the crankshaft. Porsche has used one on every flat six-cylinder engine since the 911 was born back in 1965.

It's wear and lack of lubrication that kill the little bearings. If it fails the consequences are devastating – think intimate liaison with the valves and pistons in the fiery furnaces of hell.

Piston, meet valve

Piston, meet valve

Ignoring the reported crack cylinder head problems (caused on early cars by overheating after damage to the front rads) the next issue that can seriously take the edge off the experience is bore-scoring cause by 'hotspots' damaging the Lockasil cylinder lining.


Sadler's Autofarm became an expert for all three issues back in 2005 when engines started to fail and the Bicester-based 911 specialist has done more than 100 996 engine rebuilds, demand dropping after 2010 when values of the water-cooled 911 fell through the floor. Common consensus is that just 5% of cars have suffered an IMS failure.

The problems don't only affect 996s, but early Boxsters and Caymans fitted with the M96 engine. The M97 engine introduced with the 997 (only on the Carrera S; the Carrera stuck with the M96) still wasn't trouble free but later 997s got an upgraded IMS – worth knowing if you're in the market for a car.

When does it happen?

One day the IMS will fail due simply to wear and tear, but some cars were failing at just 20,000 miles and some last more than ten times that. According to Sadler, in his experience, low-revs are more punishing on the bearing.

Like a roulette wheel, there's more force transmitted at low speeds. At higher speeds the dynamic tension smooths out the load forces.

Weirdly, early cars with 'dual-row' bearing are more robust than later cars. That's right, Porsche made the problem worse. Later single-row IMS-equipped cars that were introduced in early 2001 were subject to more failures.

Sadler thinks the bore scoring was caused by Porsche's move to a drive-by-wire throttle that is less accurate than the mechanical system at low revs causing the driver to rev too hard when the engine is warming up, causing the damage.

How can I tell if my engine is about to die?

Finding out if your IMS bearings are failing is easy – if there's any evidence of gold shrapnel in the oil filter housing you're in big trouble.

How do you spot a bore score failure? The nearside tailpipes will be darker than the offside as cylinders five and six begin to burn oil.

What's the solution and how much does it cost?

To repair bore scoring or an IMS failure a respected specialist like Autofarm charges at least £10,000 (plus VAT) – but it doesn't stop there. With the engine stripped, most 911 specialists will charge £1000 to overhaul the hydraulic tappets (more for a latter car with Varioram Plus) and refurbish the oil pump. Go for a bigger bore engine for more power and you'll pay the thick end of £15,000.

Now that 996 values are rising it could well be worth changing the IMS bearings as part of an insurance policy to save you needing that rebuild. Autofarm charges £1850 (plus VAT) and it'd be sensible to throw in a new clutch (£450 plus VAT) at the same time. If your car needs a clutch anyway, it'd be a no brainer to get the mod done.

So a case of 'they don't make 'em like the used to'?

'That's what makes me laugh', says Sadler.

'The 911s of the 1960s and '70s were renowned for camshaft tensioner failures that caused horrendous damage - but they happened in the days before social media…'

Tags: #Porsche #911 #Porsche-911 #996 Porsche#996

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Comments (14)

  • Not all 996's, the Turbo is almost bullet proof.

      3 years ago
  • I heard, that in 996s which were often pushed hard on track days, the problem is not common, because IMS bearing is lubricated thanks to the G forces. The right solution of this failure is installing Direct Oil Feed, which sprays oil all the time directly on the baring by using factory oil port in the engine (Thank you so much Porsche).

      3 years ago
  • Inherited my fathers 2002 C4S with 110k miles. Dealer told us to redline it everyday once it is warm and it will run like a swiss watch, sure enough, still working perfect. I REALLY think this is a blown out of porportion issue.

      3 years ago
    • Maybe but most of the problem engines have been replaced or modified by now. Nevertheless, it's something to keep in mind since repair costs are huge.

        3 years ago
  • Thanks Chris for this great feature and the Autofarm references. If you're reading this article and have concerns about your Porsche 996, Boxster or Cayman M96 engine, then give our specialists a call on 01865 331234. We're happy to chat through any issues you may be experiencing. #Autofarm #PurelyPorsche

      3 years ago
  • I have a 1999 3.4L 996.1 car with the M96 engine and I had an IMS failure, thankfully it didn't completely collapse and it was replaced before it caused any damage to the engine, so the repair bill was around £1700 which isn't the end of the world! I'd advise anyone considering this car to get it replaced, the class action law suit data is now so old it's irrelevant.

    The dual row cars are failing just as often as the single rows now they've got more years on them, just have it replaced and sleep better and enjoy the car, the other failures are quite rare! Just be glad you don't have a 997.1 which bore score far more often than 996 engines fail due to IMS.

      9 months ago