£1.96 a Gallon
Practical Classics 1990 popped up this little ditty of long term Viva Owner Jonathan Gulliver and his Unleaded fuel modifications to his Viva Engine.
Everyone now knows that the age of unleaded petrol has finally arrived. If many readers of Practical Classics ask if they can put unleaded petrol in their cars, they will be met with laughter. Indeed, a recent oil company advert on television shows a Morris Minor and states quite categorically that it cannot be converted to run on unleaded petrol, although there is in fact a modified head available on exchange that enables it to do so. But what about cars for which exchange heads are not available? Can they be converted?
In most cases the answer is yes, if you’re prepared to fit hardened valves and seats. This feature explains how the work was done on my 1967 Vauxhall Viva. The principles involved arc similar for most cars and should help anyone considering doing so.
My Viva has the 1159cc pushrod the so-called ‘90’ engine which had a higher compression ratio and different carburettor among other things. Although the car looks much as it did on leaving the factory, it has electronic ignition, an alternator, a high ratio back axle and various other modifications – but they’re all other stories!
Let’s recap on the fuels. Unleaded petrol has been introduced because it does not include the lead said to be harmful to health and because it does not damage catalytic convertors. Lead is put in fuels because it boosts octane rating and thus stops the car from ‘knocking’. Originally, there was one grade of unleaded. This had an octane rating of 95, which is just lower than 4 star. Unleaded has never been given star numbers but if it had this would be about three and a half. Now there is a high octane unleaded too, with a rating of 97, the same as 4 star. Lead affects the car in several ways and let us consider them in two parts, first the ignition and compression and second the exhaust valves.
To run on 95 octane unleaded petrol, it is inadvisable to have a compression ratio of more than 8.5 to one. My car had a compression ratio of 9:1 and it seemed that the easiest way of lowering it was to use another head. For this engine, different compression ratios are allowed for by different thickness heads. This was no problem, having been given a similar car with a lower compression ratio by a friend for Christmas, so the head from that was used. Others may have to opt for thicker head gaskets or perhaps two. Alternatively, certain Viva van heads can be used. Apart from this, to use 95 octane petrol the ignition might need retarding, but not much. If pinking is not heard, all is probably well. If a car is to be run on 97 octane unleaded none of this is necessary but this petrol is almost as expensive as 4 star.
The exhaust valve area is normally protected and lubricated by lead from combustion. Remember that the inlet valve knows no different and can be left well alone. The big problem area is the exhaust valve seat. In a normal cast iron head such as fitted to the Viva, this is very soft and will be damaged quickly. Most oil company information referred to this as the problem area. A local machine shop, Saunders of Cadnam, fitted some hardened scats and we were off.
Ten thousand miles later, the head was removed to see how everything was. The valves looked fine and so did the seats – but the exhaust valve guides were badly worn. Clearly, something rather better was required in this department!
The cylinder head normally has cast in guides but these had already been machined out so that replacement guides could be fitted. It seemed a simple matter of finding a guide of a better material that would fit. A valve guide is rather like a thick walled tube. A valve guide manufacturer’s catalogue in a local trade motor factors very obligingly gave the material and size of all the guides they made. On consulting some of the manufacturers of special cylinder heads for unleaded petrol, recommendation was made to use an aluminium bronze material. Some manufacturers used such a material and a BMW guide was found which could be machined to suit. It was obtainable only from a BMW dealer and the price was a problem! A friend carried out the machining, the head was reamed out and the guides were pressed in. When doing this, it is easiest to put the head in the oven at about 130 degrees C for an hour or so and put the guides in the freezer. The head will expand and the guides will shrink and will not need to be hit so hard. If you are working on the Viva cylinder head, note that it is best to keep the diameter of guides you fit down to less than half an inch or there is a considerable risk of hitting the water passages.
The only areas of the exhaust porting which are untouched are the valves themselves. These seemed quite undamaged after 10,000 miles’ use, so it seems that they are up to the job. Problems may well occur with some other engines, though, in which case you’ll either have to fit a new set as and when required, have the existing valves hardened or have special valves made up; nothing like as impossible as it sounds!
It can be said that the environment friendly car is a contradiction in terms. However, we must do what we can and this is a small improvement. For whatever reasons you might undertake this work, it is good to be getting your petrol from the same pumps as the modern cars and not feel a bit of a motoring outcast. How long leaded petrol will be easily available no one really knows but modify your car like this and you won’t be worried.