DIESEL OR PETROL?

First we ditched thirsty petrol engines, but now the tide has turned against diesels. But converting back to petrol is a real challenge...

Ihad an interesting conversation the other day with a customer looking for a good petrol engine to replace the diesel in his Series III, and it set me thinking. For the last 30 years or more, the story of Land Rover engine conversions has been about pulling out old petrol engines and fitting diesels for better fuel economy. Now diesels are in the newspapers almost every day, and for all the wrong reasons. Older dieselengined commercial vehicles (including most pre-2001 Land Rovers) are already in effect banned from anywhere inside the M25 for emissions reasons, and several other cities are looking at introducing their own low emissions zones. Could we soon see people converting Series vehicles from diesel to petrol?

I have already done a handful of such conversions for customers living within the London Low Emissions Zone, using the 2.5 petrol engine (type 17H) offered as a factory option on the Ninety/one Ten range in the second half of the 1980s. It is a robust and durable engine, although a bit rough at high speeds, and works particularly well in Series vehicles where the extra torque (compared to the 2.25) makes for quite a brisk performance. The problem with the 2.5 is that there aren’t many about. By 1985 the demand for petrol-engined Land Rovers was falling fast, and the introduction of the 2.5 turbodiesel the following year killed the petrol market stone dead. The 2.25 petrol engines are rather easier to find, but most of them are the earlier three-bearing crank version which doesn’t much like being run at high speeds for long periods. Three-bearing engines were made for twenty-two years, the stronger five-bearing version for just five. Having said which, a freshly rebuilt three-bearing 2.25 is a lovely sweet engine and will give many years’ good service in a Series vehicle provided it is treated with at least a little respect and sympathy. Good second-hand examples are very hard to find, but the “two and a quarter” is not a difficult engine to rebuild, and spares availability (for all but the very early “151” variant) is excellent. I must have scrapped dozens of these engines over the years, just because no-one wanted them. I suspect I might end up regretting that: looking at how hard and expensive it is now to find Series One engines for rebuilding, I can easily imagine the 2.25s going the same way.

Straight sixes? Don’t make me laugh. There are a few 109s out there that have been converted from 2.6 petrol to diesel power and might convert back again, but a complete 2.6 engine is even harder to find than a Series One unit, and parts availability is terrible. Apart from being a rare option in itself, the 2.6 had the misfortune of sharing many mechanical components with the Series One two-litre “four”, which means that the Series One boys cleared the shelves of pistons and bearings years ago. There must be a lot of incomplete 2.6 bearing and piston ring sets gathering dust on shelves in Series One enthusiasts’ garages.

So that just leaves the Rover V8. I have a soft spot for these, having owned a succession of 109 V8s, an early five-door automatic Range Rover, and a 110 V8 Hicap that did around 12 mpg. But I’m not blind to their faults. The 3.5 isn’t an especially durable engine, with camshafts in particular having a fairly short life. In standard Land Rover tune (low compression pistons, twin Stromberg carburettors) it generates a lot of heat but not as much power as one might hope. V8s are expensive to rebuild when worn (which most of them are by now) due to the sheer number of components, and will only take one rebore before the block has to be sleeved. And they are a rather awkward shape to fit into a Land Rover engine bay. To drop one into a Ninety or One Ten you really need a long-stick gearbox from a 1980s Range Rover with its very long bellhousing to avoid bits of the engine getting tangled up with the footwells and front axle. And on a Series vehicle you are looking at significant engine bay surgery no matter what.

So there isn’t really an easy answer, if you are looking at moving from diesel to petrol. I have it in mind to see how many new bits would be required to convert a 2.5 naturally aspirated diesel into a 2.5 petrol. There are lots of 2.5 diesels lying around, and no-one really wants them. The crankshaft and camshaft are the same, as is the block (bar one oilway which is plugged on the diesel). The head and timing case from a three-bearing Series petrol engine will fit the 2.5 diesel block with no problems. A while ago I built up an experimental 2.25 petrol using a 2.5 diesel flywheel, backplate and starter motor and it was lovely; very smooth with good low-speed power delivery, although the clearance between the starter and the exhaust manifold was horribly tight. So that just leaves conrods and pistons. I have a slightly tired 2.5 diesel coming in early next year, so watch this space.

“There isn’t really an easy answer, if you are looking at moving from diesel to petrol”