Norfolk Garage

Another rough-running Lightweight rears its ugly head for Britain’s favourite garage owner

Alittle while ago I had a customer ask me whether I would rebuild an engine for him. The vehicle was an ex military Series IIA, with a 2.25 petrol engine that the customer described as being on its last legs. Normally there is a fairly long turnaround time for this kind of job. I have to remove the engine, strip it down and assess the condition of the major bits, send the block, head and crank away for machining, then build it back up and refit it. All of this takes several weeks, mainly due to waiting for the machine shop. I use three different companies for my machining work: all are very good and reasonably priced, but permanently over-stretched, which means I have to take promised delivery dates with a pinch of salt.

So the little Series IIA had to wait until I had enough free space for it to be able to sit around engineless. I finally managed to chase a couple of long-termers off the premises, and a very sick-sounding Land Rover limped into the workshop, running on two cylinders at best and belching black smoke. The vehicle had been running well when the owner bought it but had gradually lost power until it would only do 35 mph. I opened the bonnet expecting to see the usual filth-encrusted old lump leaking oil from every joint and gasket. Instead I found a nice, clean Army-reconditioned engine, whose serial number identified it as having started life in a Series III Lightweight.

A couple of other signs pointed to the possibility that the engine might not be as bad as the owner thought. It was a three-bearing motor, and worn examples of these usually have a distinctive harsh rattle when revved from about 1500 rpm, caused by the centre main bearing shells wearing through to the backing metal and chewing up the crankshaft. This one was sweet, smooth and totally free of the three-bearing death rattle. It was also clean and oil-tight underneath, with no sign of any oil leaking past the rear crank seal. Three-bearing engines have a rather old-fashioned split seal which does not age especially well, and to find one which is not dripping oil from the bottom of the flywheel housing is unusual. I would have bet money on this engine not having covered many miles since it was rebuilt.

At this point my suspicion was that it had burned a couple of exhaust valves. The two and a quarter in standard form has the valve seats machined directly into the cast iron cylinder head, and should never be run on unleaded fuel unless an additive such as Castrol Valvemaster is used to protect the valve seats. If run on straight unleaded the valves will stick to the seats, tearing away microscopic fragments of metal until the seats become pitted and unable to seal properly. At the same time the erosion of the seats will result in the exhaust valve clearances closing up until the valves are no longer able to close fully. As the seal between valve and seat deteriorates, hot gases will start to flow through the gap, rapidly eating away at the edge of the valve until there is insufficient compression for that cylinder to fire.

It must be nearly 30 years since leaded petrol was phased out in the UK, but I reckon the majority of Series vehicles have still not been converted to run on unleaded. The conversion is technically fairly simple: the cylinder head is machined to accept hardened steel inserts for the exhaust valve seats, along with new valves and guides. However, this requires the cylinder head to be removed – for vehicles that cover relatively few miles each year, it makes better economic sense to carry on using a lead replacement fuel additive until the head needs to be removed for some other reason such as head gasket replacement.

I have also found that many owners of Series Land Rovers simply do not know that 2.25 petrol engines in standard form should not be run on straight unleaded. With a vehicle that is treated gently and not subjected to high speeds or heavy loads, it will take many thousands of miles before the symptoms of burned valve seats start to appear. Until then the engine will run just fine, which is how an assortment of charlatans and conmen over the years have persuaded people to spend good money on various magical devices that claim to allow older engines to run on unleaded. Fit one of these to your vehicle and by the time your valve seats burn out, the company that sold you the magical device will have long since disappeared along with your money.

Since burned valve seats cause a loss of compression, the first step is to carry out a compression test. This will not distinguish between burned valves or seats and other causes of compression loss such as a failed head gasket or holed piston, but a lack of compression will almost certainly require the head to be removed for further investigation, regardless of cause. A compression tester for a petrol engine consists of a pressure gauge, a flexible pipe with a threaded adapter on the end, and a one-way valve with a release button. They typically cost around £15 to £30, which is less than it will cost you to get a garage to carry out a compression test. The procedure I adopt is as follows: 1. Remove all four spark plugs, ensuring you mark the plug leads so you can refit them in the right order. 2. Disconnect the high tension lead on

the ignition coil. 3. Lock throttle lever in the open position

with a piece of wire or cable tie. 4. Spin the engine over on the starter for a few seconds to clear out any residual fuel or oil. 5. Screw the compression tester into number one plug hole and crank the engine over on the starter for about five seconds. Note the reading on the gauge. Release the pressure with the button, transfer the gauge to the next cylinder and repeat the process until you have tested all the cylinders. The actual figure you see on the gauge will vary according to several factors including engine design and specification, temperature, thickness of oil and the accuracy of the gauge itself. The workshop manual gives the following figures for the 2.25 petrol engine, tested hot: 145 psi for engines with the 7:1 compression ratio head, 160 to 170 psi for 8:1 engines. These are, of course, factory

figures for a perfectly unworn engine. My own experience is that anything much under 130 psi indicates a problem somewhere. Arguably more important is the variation between cylinders; as a general rule, all the readings should be within 10 per cent of each other – and preferably rather closer than that.

In the case of this particular engine, tested stone cold after standing for a couple of days I got one cylinder at 145 psi, two at 140 and one at 135. That was a slightly greater spread than I really like to see, and I made a mental note to check the valve clearances, but the figures overall were plenty good enough to allow the engine to run on all four cylinders. So just as with last month’s mysteriously rough-running Lightweight, the finger of suspicion had to point to the ignition system. The spark plugs I had removed were rather fancy: triple-electrode with gold-plated bodies and a totally unfamiliar brand name. I have had spark plugs fail before despite looking perfect, so I fitted a set of good old fashioned Champion plugs and turned my attention to the distributor. This was (as with the Lightweight) a Ducellier, and (as with the Lightweight) falling to bits internally. The springs for the centrifugal advance had either broken or detached themselves, allowing the timing to vary randomly.

In the passenger footwell of the vehicle were various items including a new, boxed Chinese-made electronic distributor. They are slightly tricky to fit in that (at least on the ones I have seen) there are no alignment marks between the rotor and pickup to allow an initial static timing. I turned the engine by hand until the top dead centre mark on the crankshaft pulley lined up with the pointer (with number one cylinder on the compression stroke), dropped the distributor into the mounting plate, engaged the drive dog and then rotated the body until the rotor arm was in line with the contact inside the distributor cap corresponding to number one cylinder. If all is well the vacuum advance unit should be pointing towards the rear of the engine.

The final job was to check the valve clearances, which turned out to be all over the place. Number three (cylinder with the lowest compression) had zero clearance on one of the inlet valves which explained the slightly low reading. I hit the starter button and the engine burst into life on all four cylinders. I checked the timing with a strobe gun and it was only a couple of degrees out, so my initial guesstimate for static timing was as close to correct as it could have been. A test drive revealed a healthy engine and after a service, various minor repairs and an MOT the IIA was reunited with its owner.

“The finger of suspicion had to point to the ignition system”