HOW TO: 964 ENGINE MOUNTS

Unusually, the air-cooled 911, from the very first ‘901’ all the way through to the last-of-the-line 993, has its engine suspended from the two rearmost mounting points on the chassis, rather than bearing down on them as in, say, the 944. This makes them

Engine mounts wear out. Here’s how to replace them on a 964

It is famously difficult to discern the gradual changes in the behaviour of any car that you drive regularly, unless perhaps you have another against which to compare it. Which is a compelling argument for an annual roadworthiness test – no longer a requirement here in the UK for cars over 40 years old, although you can still have it carried out if you wish – or at the very least for occasionally having your prized Porsche carefully examined by an objective and dispassionate expert.

This 964 Carrera 2 – itself now approaching 30 years old – was a case in point. Even as he briefly drove the car before servicing it, BS Motorsport’s Rob Nugent could tell from the harshness through the chassis that its two rear powertrain mountings were past their best. If he had had the opportunity of a few circuit laps he would almost certainly have felt the dynamic effects of the slight but none the less unwanted movement of the engine’s considerable mass through faster corners. And the service procedure itself clinched it.

‘Unusually, the air-cooled 911s’ rear engine mounts are in tension rather than compression,’ he says. ‘So effectively the weight of the motor is suspended from them, rather than bearing down on them. As soon as I put the car on the wheel-free lift and raised it clear of the ground I could see that the rubber centres of the two mounts were extending too far. And then, when I took the weight of the car under the engine, so that I could swing the lift arm out of the way for access to the oil tank, the mounts simply compressed again, and the body failed to rise as quickly as it should have done.’

Where to source replacements, then? Predictably, a web search throws up dozens of possibly tempting and certainly confusing alternatives, from suspiciously cheap after-market parts to expensive solid jobs designed purely for competition use. It is also said to be possible to fit the equivalent standard 993 components for a small cost saving. No less predictably, Rob chose to fit the standard 964 items, specific to this

vehicle, direct from Porsche in Reading. ‘It’s a standard road car,’ he argued, ‘and our customer wants to keep it that way. We could have used after-market mountings, and I can appreciate why a DIY owner might do so, but here that could be false economy. We need to do any job like this just the once, and to be sure there will be no comebacks.’

Removing and replacing the mountings could hardly be easier. (All you 944 owners, read it and weep…) With the car safely supported clear of the ground, remove the undertray – missing on this vehicle, and so not shown, but an easy enough task – and then take the weight of the engine with a trolley jack beneath the centre of the crankcase, such that the mounts are more or less fully compressed again. A piece of thick cloth or an old towel, folded over several times, makes a good locating pad for the saddle of the jack.

Remove the plastic plug in the engine tinware, beneath the centre of each mount, for access to the M12 nut screwed on to the stud projecting down through the engine bearer. The plugs have to be pushed up from beneath, and retrieved from inside the engine compartment. Buy new ones from Porsche if they are missing or damaged. Unscrew the two M12 nuts and put them somewhere safe. Up top, undo and remove the two M8 screws securing the body of each mounting to the structure of the car. On the left-hand side one of the screws is accessed through the hole in the enginecover slam panel. Note the triangular ‘washers’ beneath each screw head. It’s probably best to remove and replace just one mount at a time, though, to minimise any movement of the engine.

Unsurprisingly, the new mountings go on in a direct reversal of this sequence. They are handed, as denoted by their different part numbers, but here had also been scribed ‘L’ and ‘R’ for Links and Recht, ie Left and Right, with a marker pen. And the fact is that that they are – or should be,

anyway – impossible to transpose. Each mount has a small tab that locates in a matching hole in the body shell, and this will correctly orientate the device such that the square-section shoulder beneath it locates smoothly in the matching recess in the transverse engine bearer.

That said, you might need to ‘wiggle’ the mount slightly in order to align the two M8 screw holes, perhaps with the help of a tapered bar – or just a screwdriver – pushed down into the hole(s) in the body, but obviously taking great care not to damage the threads. And for the same reason don’t tighten the M8 screws until you have fitted and almost fully tightened the M12 nut on the stud beneath the mount.

And that’s about it. The last job on this particular car – no undertray, remember – was to realign the exhaust tailpipe which, since it had previously been adjusted to compensate for the sagging engine mounts, was now too close to the rear apron. And then to take the vehicle for a quick and rather more satisfying test-drive, with the immediately obvious benefit of a dramatic reduction in NVH, or Noise, Vibration and Harshness. PW

A garage lift is useful for raising the car for access to the mounts’ main securing nuts, but the work is just as easily done ‘on the floor’. You will still need to raise the car, though, and support it on stands – and then to support the engine with a jack. Inset photo shows how the two original mounts (middle and right) had ‘stretched’ compared to the new (left) – and this with no weight on them

Engine mounts that show this degree of extension under load might in theory lower the car’s centre of gravity, but that will be more than offset by the movement of the entire power unit through fast corners. Imagine driving a front-engined car with a large sack of sand flailing about in the boot space as you change direction. First job was to loosen off the exhaust tailpipe, which had previously been adjusted within its aperture in order to compensate for the sagging mounts – and which would by definition end up too high. Next, remove the plastic plugs in the engine tinware for access to the mounts’ main M12 securing nuts. They simply push upward from beneath the car. Plastic undertray has to come off, too – where fitted; it was missing from this car

Undo and remove the two M12 nuts – first supporting the engine on your trolley jack, of course – and then the two hex-head screws securing the body of each mount to the car’s structure. Probably best to do just one side of the car at a time. Note the thick triangular washer beneath each screw head. After that, the mount simply lifts up and out of its aperture. Mounts in the 964 are handed left and right, as shown by their different part numbers (see text), but also by these crude but helpful factory-applied markings (far right)

The 964’s mounts are handed, such that the square shoulder on the underside fits neatly into the matching recess in the transverse engine bearer, placing the small tab next to one of the holes for the M8 securing screws in the right position to locate in the hole in the structure (below, far left). Our understanding is that significantly cheaper 993 mounts can be used, but without that tab (and not being handed left and right) they do need to be positioned with care. Be aware, too, that various grades of stiffness are available for all these devices – green, as here, denotes a standard Carrera coupé – and also that, strictly speaking, there are different items for Cabrios and Targas. Note aluminium grease on newly cleaned M8 screws – just in case you ever have to do the job again in the future...

Fit the M12 nut (upper row, far left) and the mount is secure. Same procedure on the left side of the car, here with one M8 screw accessible through the hole in the engine-cover slam panel. Here we also found it necessary to adjust the position of the mount very slightly, in order to line up one of the M8 screw holes with the threaded hole in the body. Take care not to damage the threads, of course, or you could be in big trouble. Job done, the new mounts show rather less extension with the weight of the engine on them again (lower row, far left). Last job of all, unsurprisingly, is to adjust the exhaust tailpipe again