Experiences of overhauling a Volkswagen air-cooled engine

Compiled and written by Nigel A Skeet, previously published in the club magazine.

Sometime in early 1983, our 1973 VW 1600 Type 2’s AD-series engine, developed a major oil leak, which we were unable to trace; leading us to completely dismantle the engine and renew every conceivable oil seal and gasket, plus the steel, pushrod tubes, which were noticeably rusty. Although by that time, I had quite a good selection of tools, including two click-stop torque wrenches, none of them were suitable for removing the 36 mm AF, flywheel gland bolt, which is tightened to a very large torque.
Fortunately, one of my engineering-student colleagues at Cranfield, named Jonathan Wells, loaned me his ¾ inch drive T-bar and 36 mm AF socket tool, which he used for the rear wheel hubs, of his VW based, autocross space frame buggies. Even with this tool, one needed to slide a long steel pipe (being several feet long, it is referred to in some quarters, as a scaffold pole), over the T-bar, in order to produce sufficient torque. When we later refitted the flywheel bolt, we were faced with the problem of how to obtain the correct tightening torque (which is critical for this engine); not having a torque wrench of sufficient capacity. This was finally resolved by weighing myself on the bathroom scales and then standing on the T-bar, pipe extension, the appropriate distance from the socket centre; ensuring that the pipe was horizontal.
Ten years later, in 1993, when we sold the 1600 engine, second-hand, in favour of a VW Type 4 style engine (the virtues of which, Jonathan Wells had extolled to me, in 1983), the buyer recounted a tale of woe, about his supposedly “reconditioned” 1600 exchange engine, whose flywheel bolt had not been adequately tightened. The flywheel subsequently came loose, resulting in a severely damaged engine, which was effectively written off.
On the whole, removing, dismantling, rebuilding and refitting the 1600 engine (my first ever attempt at such things) was child’s play (in many respects, simpler than doing a 200 piece jigsaw puzzle), but removing some of the cover-plates was a nightmare. Many of the cheese-head, slotted M6 screws had rusted in solid and needed to be drilled out very carefully. Noting that the screwdriver slots of conventional and Philips head screws were easily damaged, I later replaced them with 10 mm AF, hex-head M6 bolts, which would withstand higher torque. At a later date, I took the further precaution of coating the screw threads, with anti-seize copper grease. These days, I would also be inclined, to substitute stainless steel bolts and/or Allen socket-head screws, which are what I am using, on my transplanted VW Type 4 style engine.
Many of the cover-plates had corroded where they were exposed to the elements; having been given only a thin coat of paint at the factory. In some places, the steel had become wafer thin, necessitating repair. All the cover-plates were comprehensively treated with D-Rust (a phosphoric acid based rust treatment solution), to etch all the rust out of the pits, and repaired as necessary, by brazing on reinforcement sections, before repainting them with several coats of Finnigan’s Hammerite. When I sold the engine in 1993, these cover-plates were still in excellent overall condition, which I have since sold off piecemeal, during the following years; some as recently as 2010~12!
Removing the old exhaust silencer, proved to be no picnic either, and it was necessary to use a hacksaw and cold chisel, in order to disengage it from the heat exchangers. Had removal of the exhaust silencer not been necessary, it would probably have lasted a few more years. The original exhaust-manifold nuts, incorporated HeliCoil™ thread inserts, which did not rust, but the hexagonal outer portion had corroded badly and no spanner (neither metric nor imperial) would fit them snugly, so “copper exhaust-manifold-nuts”, were purchased as replacements.
We did initially obtain a stainless steel replacement silencer, from the local branch of Qwik Fit Euro, but this would not align correctly (may have been intended for a VW 1200 engine!?), with the cylinder head exhaust ports and/or the heat exchangers, so it was returned to the suppliers. Ultimately, we fitted a Scat ‘Monza’ style silencer, with two integral twin tail pipes, from the USA, purchased from the German Car Company, in Hadleigh, Essex. This lasted well, for nearly 8 years, until Easter 1991, when one of the twin tail pipes dropped off, somewhere on the M40 or M25 motorways. The so-called “copper exhaust-manifold-nuts”, which had been fitted nearly 8 years earlier, proved to be merely copper-plated steel nuts, and had rusted onto the screw studs; one of which sheared off and resulted in the need for an expensive repair to the cylinder head.
I had never been impressed with the standard, single-piece, exhaust-silencer clamps, intended for the VW 1600 Type 2, so instead I used a pair of two-piece, VW Beetle tailpipe clamps, which are more fiddly to fit (see Transporter Talk, Issue 27, February 1997, Pages 24~25), but provide a better seal between the heat exchangers and silencer. To be sure of a gas-tight seal, I also used a liberal quantity of Holts Firegum; a well-known brand of exhaust system sealant.
During the engine strip down, it was discovered that the valve guides were excessively worn, so the cylinder heads were taken to a local engine reconditioning workshop, in Basildon, Essex, for refurbishment. This proved to be yet another encounter with shoddy workmanship, resulting in one of our cylinder heads being consigned to the scrap bin. It was alleged that the damage had arisen, as the result of some earlier bodged attempt at replacing a single valve guide. The workshop manager disclaimed all responsibility, and showed us a cracked exhaust port, together with a rough-hewn valve guide, which had supposedly been removed from it. In our own minds, we were convinced that this was a deliberate falsehood, but could not prove it!
The cylinder head also exhibited deep bruising of the cooling fins, consistent with violent blows from a large ball-peen hammer; marks which we knew had not been present, when we submitted our cylinder heads for refurbishment. As a consequence of this episode, we were obliged to purchase a new, replacement cylinder head, from another supplier. Although this was for a VW 1600 engine, with the same sized valve heads as the original, the exhaust valve stem diameter was 9 mm, rather than 8 mm. I suspect there may have been other, more subtle differences, which were not apparent to my then untrained eye.
Such differences, may have contributed to cylinders 1 & 2, running hotter than cylinders 3 & 4, which I noticed some years later. Since then, I have learned that there are at least nine different VW 1600 ‘twin-port’ cylinder heads, with three different, standard combinations of valve head sizes, plus probably various differences in combustion chamber shape, volume and deck-height (i.e. squish or quench) clearance too. With hindsight, we should have noted the part number, cast into the rocker box of the defunct cylinder head (assuming it was originally ours!), but in those days, we believed there was only one type of VW 1600 cylinder head and were unacquainted with the significance of the suffix letters, in VW part numbers.
Whilst the engine was still out, it was a good opportunity to remove and inspect the petrol tank, which exhibited some corrosion around the fuel outlet, beneath the vehicle. Although there was slight pitting in places, the thickness of the steel had not been significantly compromised, so it was sufficient simply to etch out the rust pits, using D-Rust and repaint the refurbished surface. Other areas of the petrol tank were also showing signs of superficial rusting, which were similarly treated.
Having removed the bulkhead plate to gain access to the petrol tank, it was apparent that this too was rusting in places, so this was also refurbished before repainting. In common with the engine cover plates, the petrol tank and bulkhead plate, had received only a thin coat of paint at the factory, so all items received several coats of Hammerite; paying particular attention to those areas, which previously had rusted.
Prior to painting, I had twenty one, captive M6 nuts (with hindsight, M5 nuts might have been better!), welded onto the back of the bulkhead plate, coinciding with the top, middle and bottom, of the seven vertical ribs; anticipating that at some time in the future, I might wish to fit, electronic ignition and perhaps other accessories, which would need to be mounted in the engine compartment.

1973 VW 1600 Type 2, removeable fuel-tank compartment bulkhead, with nineteen M6 nuts, welded onto the back of the seven vertical ribs.
Note also, the additional holes in the bodywork, on either side of the bulkhead, for supplementary electrical cables, pipes or hoses, to enter the engine compartment.
Any accessories could then be fitted, using custom made mounting brackets; avoiding any later haphazard drilling of holes in the bulkhead (which might penetrate the petrol tank), to accommodate self-tapping screws. About ten years later, a local VW Type 2 owner of my acquaintance, who sadly lacked this kind of foresight, somehow managed to drill three holes in the forward face of his petrol tank, when fitting secondhand motorcaravan furniture, in his Microbus. Fortunately for him, I had a secondhand petrol tank for sale!