911 3.2 to 3.4 engine build by Peter simpson

MOTORFACTORS

There’s more to a successful air-cooled engine build than simply the skill needed to bolt it together. First you have to decide what you want to achieve, and then where to source all the bits that will do the business Story and photographs by Chris Horton

e have talked often before in these pages about ‘mission creep’; when what starts as a relatively simple job ultimately becomes a task akin to reconstructing the Great Wall of China. And that’s pretty much how it turned out for art editor Peter Simpson’s 911 Carrera 3.2 engine build. Even with 106,000 miles on the odometer it was still running well enough. It’s a remarkably tough engine, the 3.2. But there was sufficient tell-tale oil smoke in the exhaust – especially after a coldstart, and when idling in

911 & PORSCHE WORLD

traffic – to suggest that, like most of these units at that kind of mileage, it could do with a top-end overhaul: new valve guides and seals, recut and/or reground valve seats, and obviously the subsequent careful setting of the operating clearances. In the end it had all that, and – as you have probably deduced already from the photos – a great deal more besides. This feature – with the second and final part in the February issue – is by no means intended as a comprehensive, step-bystep guide to this complex process. You will need a

good workshop manual for that, never mind both the skills and the experience that come from having cut your teeth on a few simpler power units first. You will have to gather a number of special tools, too. We hope, though, that like the recipe for a good curry it will give you a fairly accurate idea of what’s involved (and why it could cost so much!), and no less importantly, perhaps, a shopping-list of the basic ingredients you will require should you wish to create something similar. And not least what you might expect to achieve with them.

The catalyst for what turned out to be such a far-reaching overhaul was Francis Tuthill’s Workshop, the well-known and highly respected early-911 and rally-car preparation specialist near Banbury, Oxfordshire. A methodical man, Peter Simpson had already bought a set of second-hand cylinder heads, to send away and have rebuilt while the car was still in use as his daily transport. It was when this work was being done – by Rob Walker Engineering, also based in Oxfordshire – that Peter happened to mention the project to Tuthill’s MD, Richard Tuthill.

Standard 3.2 cylinder heads were reconditioned by Rob Walker Engineering, and then assembled by Tuthill’s. Barrels and pistons – from LN and JE, respectively – look almost too beautiful to hide away inside the finished engine. Two views of the split crankcase halves (bottom) show how good the engine was, even before the rebuild – and that was with over 100,000 miles on the clock. The 3.2 is as tough as old boots!

Richard, bless him, immediately offered to reassemble and refit the reconditioned heads – or have his engine builders reassemble and fit them, anyway – but then suggested that given both the car’s mileage and the work involved in replacing the heads (which in all 911s means taking the engine out), it would be well worth doing just a little more than that. It’s the WYAIT – While You Are In There – principle.

The clutch would almost certainly be quite worn, for a start, argued Richard. The barrels and pistons – or at the very least the piston rings – would be past their best (and particularly so if later working with rebuilt cylinder heads). And if Pete was going to the trouble of taking off all six of those for inspection and possible replacement, then it would be as well to consider the possibility of fitting new ones – and even (because it

would then be dead easy) increasing the capacity. And if he was doing all that it would be only a little more work to split the crankcases and fit new bearing shells and timing chains... and that would be the ideal opportunity to fit both uprated con-rods and stronger through-bolts and cylinder-head studs. You probably get the picture. Peter, no doubt seeing pound symbols flashing through his mind like an

insomniac counts sheep, was understandably reluctant to commit himself to too much expenditure. But Richard was very persuasive. He felt – and let’s be blunt about this – that many of the suppliers of the necessary standard and uprated parts would be happy to do deals in return for some exposure in the world’s most widely read Porsche magazine (as, of course, they were), and

Lightweight flywheel and paddle-style clutch came from Patrick Motorsports. The six individual throttle bodies are another work of art, from UK-based Jenvey. More on these next time

The secret of a successful bottom-end build is accuracy, cleanliness, topquality new parts where necessary – and making sure all the oil remains where it’s meant to be

911 & PORSCHE WORLD

finally Peter began to capitulate. The decider, he recalls now with a smile, was the photo that Richard e-mailed him of a similar engine, complete with another set of those iconic British-made Jenvey throttle bodies. (See the previous page.) ‘It was a bit like a drug dealer handing out free samples at the college gates,’ he jokes. ‘How could I refuse...?’ If that soon became the basic gameplan, then the next task was actually to source all the bits, and then to decide how to make them all work happily together. You’ll see next time, for instance, that by

911 & PORSCHE WORLD

virtue of fitting SSI heatexchangers, and in the interests of a ‘retro’ look doing away with the 3.2’s rear blower motor, Peter had to find some small sections of early-style tinware in order to retain a functioning cabin heater. Likewise the choice of an Omex electronic engine management system – in part to eliminate the conventional distributor – meant obtaining from Clewett Engineering in the US both a crankshaft position sensor and a blanking plug for the now redundant distributor drive. There were several more fundamental decisions to

be made first, though; ones that would between them determine the overall character of the engine. Thus both barrels and pistons (the latter made by JE ) would come from LN Engineering in the US; capacity, as suggested by Richard Tuthill, would be 3.4 litres from a bore of 98.0mm. LN would also supply a set of six lighter but stronger con-rods. Induction and exhaust systems we’ve already touched upon – and we’ll come back to them next time, too – but crucial to managing the gases within the ports and combustion chambers, and thus

defining the engine’s power and torque, would be the camshafts. Peter, again with advice from Richard Tuthill and his team, went for Kent Cams’ Rally items. If the top end of the engine had been basically serviceable, then the bottom end – everything between the crankcase halves, in other words – was near-perfect. Thus the crank itself would need only a thorough clean and a light polish before being fitted into new bearing shells from Euro Car Parts, which also supplied the vast majority of the seals and gaskets required. The oil pump, too, was checked

Oil pump – identified by the two green ‘O’-rings – was easily good enough simply to be cleaned and refitted. Specially bent strips of aluminium hold both the timing chains and the connecting-rods in the correct position while the ‘upper’ crankcase half is lowered over them (below)

Beautifully made ARP through-bolts and head studs, with special washers and domed nuts, will keep engine oil-tight for many years and miles to come

It’s vital to use the correct new sealing ‘O’-rings on the through-bolts (middle pic, above), and then – not surprisingly – to torque all the fastenings to the specified figures, and in the right order, too. Make sure while you do so that the crankshaft still rotates – and investigate if it won’t...

Completed crankcase (below) awaits the second stage: pistons, barrels, and then heads, cam carriers, and other ancillary parts. More on all these next time

and found to be fit for further duty. Fasteners – 911-specific through-bolts, cylinder-head studs and washers – would come from another US-based company, ARP. (You’ll find full details of all these products on the various manufacturers’ websites; see panel, right.) So-called ‘endless’ timing chains came from ECP, but their tensioners, like the oil pump, were fine. External oil lines – to clear the SSIs – came from Elephant Racing. The M&K exhaust silencer was from Cool Cava Racing. Oh, and the ultra-lightweight clutch, from which would later

come the engine’s hairtrigger throttle response, from Patrick Motorsports. The painstakingly careful assembly process was handled by Tuthill’s Mike Fletcher and Anthony Whitehead. It’s the next instalment, showing the fitting of all the really sexy bits, that will probably get most of you truly enthused about this project. But just as the heart of any successful building is solid foundations, then so, in its own way, is the secret of a powerful, reliable and above all durable air-cooled 911 engine. And they don’t come a lot better than a Tuthill-built Carrera 3.2! PW

CONTACTS

www.francistuthill.co.uk Tel: (UK) 01296 750514 Supplied: the many hours of labour to put it all together www.robwalkerengineering.com Tel: (UK) 01993 868683 Supplied: cylinder heads www.jenvey.co.uk Tel: (UK) 01746 768810 Supplied: throttle-body kit www.omextechnology.co.uk Tel: (UK) 01242 260656 Supplied: engine management and ignition system www.clewett.com Tel: (US) 310 406 8788 Supplied: crankshaft sensor; distributor-drive blanking plug www.lnengineering.com Tel: (US) 815 472 2939 Supplied: Nickies cylinder barrels, plus con-rods and JE pistons (www.jepistons.com; tel: (US) 714 898 9763)

www.kentcams.com Tel: (UK) 01303 248666 Supplied: modified camshafts www.eurocarparts.com Tel: (UK) 020 8956 5000 Supplied: bearing shells, timing chains, plus seals, gaskets and various other ancillary parts www.arp-bolts.com Tel: (US) 805 339 2200 Supplied: crankcase throughbolts and cylinder-head studs www.elephantracing.com Tel: (US) 408 297 2789 Supplied: external oil lines www.coolcavaracing.com Tel: (Sweden) 070 793 5952 Supplied: M&K exhaust silencer (www.mkexhaust.com; tel: (US) 262 364 7426) www.patrickmotorsports.com Tel: (US) 602 244 0911 Supplied: uprated clutch kit and lightweight flywheel

911 & PORSCHE WORLD

MAXIMUMPOWER Last month we looked at the logic behind Pete Simpson’s nut-and-bolt 3.2 engine overhaul, and the beginning of the assembly process. This time we see it right through to its beautifully finished conclusion. Well, almost... Story and photographs by Chris Horton

f the heart of any good Porsche 911 engine is its crankcase, and all of the rotating and reciprocating parts within it, then the six cylinders and their pistons, plus the cylinder heads and not least the two chain-driven overhead camshafts, can in many respects be likened to its lungs. It is, after all, the pistons’ and the valves’ movement – their ‘breathing’, if you like – and the resulting ingress, combustion and then egress of the now burned air/fuel mixture, that drives the whole process, and thus the car along the road. And thanks to the modular construction of the power unit – six

911 & PORSCHE WORLD

individual barrels, and six individual heads – it can be remarkably easy (if not necessarily inexpensive...) completely to alter the engine’s character. To give it a lung transplant, if you want to continue the anatomical analogy. And that’s essentially where Peter Simpson’s ambitious 3.2 rebuild headed next. We say ‘3.2’, but in truth the precisely 98.0mm diameter pistons and barrels (from American manufacturers JE Pistons and LN Engineering, respectively) would give it a swept volume of just about 3.4 litres – and a very slight but worthwhile increase in compression ratio, too. What’s more, fitting said pistons and barrels was as

(relatively....) easy as would have been the process for standard components: rings to pistons, making sure that the former were all the right way up, and in the correct order; pistons to connecting-rods, doublechecking that all of the gudgeon-pin circlips were securely located in their machined grooves. (And, of course, that all of the pistons were the right way round on the con-rods. Thanks to the shallow valve pockets in their crowns the pistons are by no means symmetrical.) Next, using a piston-ring compressor, squeeze the rings into their grooves in the piston skirts, and then, having given each piston a squirt of engine oil or a so-called

assembly lubricant, slide the barrels down over the rings – again making sure that all six of those, too, are the right way round. (And, of course, that you don’t break or otherwise damage any of the rather brittle rings in the process.) All pretty basic stuff, really. Er, not quite. In order to prevent oil (and gas) leaks from the base of each barrel, the latter are fitted with special shims (arrowed in the photo below left) to seal them against the crankcase. Crucially, these shims come in several different thicknesses – primarily 0.25mm and 0.50mm; some specialist engine builders have both slightly thinner and thicker items laser-cut to order –

Some 911 engine builders prefer to slide the pistons partially into the barrels (obviously leaving the gudgeon-pin journals exposed) before fitting the complete assembly to the con-rod, rather than fit pistons to rods, and then barrels to pistons, but it’s largely personal choice. Either way, it’s plainly vital not to drop any of the circlips into the open crankcase... Black powdercoated barrel ducts – correctly fitted – are vital to keep the engine cool, so don’t forget to fit them, and new oil-drain tubes are a sensible investment. Cam carriers (below) must sit perfectly flat and level on heads, or the shafts within them could bind or seize

and by selective assembly are additionally designed to provide a perfectly flat and level surface across the tops of the cylinder heads, when those are later fitted to the tops of the barrels. And why is that so vital? Because even a very slight discrepancy across these ‘faces’ could distort the camshaft carriers when those are torqued down, and cause the camshaft(s) to bind or partially to seize in their bearing journals.

No less important – or ingenious, come to that – is the precisely calculated engineering science by which the barrels and the heads are secured to the crankcase. (And the layout of the finished engine is such, of course, that the relatively heavy ‘top end’ literally hangs from the side of the relevant crankcase half. That alone, never mind continual expansion and contraction, and not least the high pressure in the

combustion chambers, places a substantial load on the studs.) There are many opinions about 911 head studs, but the general consensus seems to be that uprated items, like the ARP ones shown here, can only be beneficial – they have a much higher tensile strength than the standard Porsche items, and intrinsically stronger ‘rolled’ threads, as opposed to the usual die-cut variety. For the same reason it’s also

vital to provide each stud with an unimpeachable anchor point in the crankcase, if necessary by reclaiming damaged or even simply suspect threads with a Würth Time-Sert threaded insert. Not that you need to – or, therefore, should – tighten the cylinder-head nuts to some huge torque figure. In fact, Porsche states a total of just 32Nm, and the truth of the matter is that even without any kind of

Solid-state ignition system from Omex eliminates the need for a distributor. The redundant mounting hole in the left-hand crankcase was filled with this neat blanking plug from Clewett

All parts of the assembly process are crucial to the engine’s reliability, but particularly so the cam chains and valve timing

911 & PORSCHE WORLD

conventional gasket this is normally perfectly sufficient to provide a fully gas-tight seal between barrels and heads. Like we said, it’s all clever stuff. With the cylinder heads and camshaft carriers on, the next big step was to fit the two timing cases and then attach the chains, via the two bolt-on sprockets, to the cams themselves. This, too, requires a little more care and attention than, say, the toothed rubber belt in a 944 (OK, then, a lot more care and

911 & PORSCHE WORLD

attention than the toothed rubber belt in a 944...), but Tuthill’s finest – Mike Fletcher and Anthony Whitehead – have done it many times before, accurately setting the sprockets in position with the aid of a dial gauge to measure valve lift (and obviously with the valve clearances first correctly set) against degrees of crankshaft rotation. With that hurdle out of the way Pete’s 911 engine was at last beginning to look less like some

abstract modernist installation and, well, more like a 911 engine, and now it was time to ‘dress’ it with the remaining goodies that he had acquired. Chief among those were the British-made Jenvey throttle bodies that would improve throttle response (a work of art, these, if quite timeconsuming to assemble) and the US-made stainless-steel heatexchangers from SSI. Tinware, too, played a

big role in both the engine’s appearance and its functionality. The main upper fan shroud is the original, powder-coated a rather fetching orange (ditto the fan itself), but because Pete had decided to do away with the 3.2’s rear heaterblower motor he had to source a different duct to connect the upper shroud, via a length of flexible tubing passing down through the outer ‘tray’, to the left-hand heat-exchanger.

With the core components of the engine proper assembled, the no less enjoyable task of ‘dressing’ it can begin. New piece of ducting (above, left) allows elimination of 3.2’s rear heater-blower motor. Exhaust headers (above) are stainless-steel items from SSI: no surprise that anyone building an engine (or a 911) to last wants these. Jenvey throttlebody kit (below) is a bit like a big Meccano set – but perhaps even more satisfying to put together!

CONTACTS

After that, on went the lightweight flywheel and the uprated clutch, the oil-cooler, the camshaft covers, the generator belt (its tension adjusted, as usual, by means of shims between the two halves of the upper pulley), and those big air filters. With the engine back in the car the Omex management system was hooked up

(that’s why there’s no distributor; see the photo below), the fuel and oil systems connected and primed, and for the first time in many months the 3.2 was alive once more. It was, as Pete himself admits, a long haul, and an extreme answer to what he had been told were ageing valve guides,

but then if a job’s worth doing it’s worth doing properly. And there can be no question that this was anything less than a

very proper job! In truth, the 3.2 isn’t back on the road even now – Pete has embarked on a similarly ambitious body restoration, as you’ll have read in his Our cars reports. But we have no doubt that when it is it will – thanks to all the topquality parts and expertise that have gone into it – run like the wind. Watch this space! PW

911 & PORSCHE WORLD