The Rover K-Series engine was very advanced for its time when it went into production in 1988. Not only was it innovative in using an all-aluminium construction, it also used lean burn technology to give low emissions and good economy. It was also perfect timing for Caterham as the Ford Crossflow that had been the staple of its engine line-up was getting long in the tooth, though it would soldier on for some years still. The K-Series engine, coupled to a lighter bellhousing and gearbox, saved 35kg compared to the Crossflow motor.
Caterham employed the K-Series to great effect in the Seven with the motor inclined at 15-degrees to clear the bonnet. The first 111hp version could offer 0-60mph in 6.8 seconds and 103mph flat out. Early 1.4s did without a catalytic convertor, though it was an option and became standard in 1993 when Caterham obtained Single Vehicle Approval to sell fully built factory-made cars.
We won't detail the development of the K-Series engine in the Caterham Seven here as it's worth a whole book on its own, but its wasn't until 1996 that Caterham offered the 1.6-litre engine. This was a bored out version of the 1.4 that offered anything from 117- to 135hp in standard tune and was offered with a Ford-based five-speed gearbox as standard or Caterham's own six-speed unit.
Rover finally let Caterham buy its 1.8-litre K-Series in 1997 as supply caught up with demand for this motor. Caterham wasted no time in putting the engine into the Superlight R with 193hp, six-speed gearbox as standard and 0-62mph in 4.0 seconds. This car went on to take the production car lap record at the Nurburgring and covers 0-100mph in less than nine seconds. The 1.8 engine went on to be offered in power outputs starting at a modest 124hp and going all the way up the R500's 254hp.
When looking at a Caterham Seven with a K-Series engine, the first thing is to establish which engine is fitted to the car. Many owners have uprated their cars with larger engines, so ask for invoices and receipts to prove the motor in the car is what it claims to be if it has been modified. Also, many owners modify the engine for extra power, so again look for evidence and history of this work being carried out professionally or with proven parts from Caterham or a respected specialist.
Otherwise, the same rules apply across the K-Series range. The first thing you will hear about this engine is blown head gaskets. This has not proved to be a major problem with the Caterham, largely due to its light weight putting less strain on the motor in the first place. However, there have been some blown head gaskets, most often with more potent versions of the motor.
There are two key points to bear in mind with the head gaskets. The first is early engines had a head gasket design that was more prone to failure due to the design of the fire rings. This was largely fixed with a multi-layer gasket from Rover that was fitted to many Rover and Land Rover models under warranty. For the Caterham, it's a good idea to fit a new multi-layer head gasket whenever you have any work done to the cylinder head and most specialists will be able to recommend the best one for your engine's power output.
The second point to consider is the engine's coolant as the K-Series engine only has a small coolant capacity, so problems here can quickly escalate. Although the original head gaskets could fail with little or no warning, problems will be greatly reduced by using good quality coolant at the correct mix and quantity and making sure the whole cooling system is in tip-top condition.
As many Sevens spend the whole winter tucked up in the garage and then are used for weekend blasts, coolant pipes can be overlooked and left in perilously weak condition, so best to make a full check part of your regular service routine and replace any pipe that you're not sure about. Upgraded pipes are available from specialists and waterless coolant is another option to stop pressurisation in the system.
The cylinder head itself is easily modified to give more power through porting, though make sure you have the right cylinder head for your engine: a 1.4 head will not offer many gains with a 1.8 engine, while VVC heads are a popular upgrade. Not every engine block is the same, either, so look for a 1.8-litre block it you want big power. Also, whenever you remove the cylinder head, you will need to make sure new stretch bolts are used every time for reassembly as they are designed for one use only.
The K-Series cylinder head's aluminium can become porous over time, so look for signs of tiny pits in the surface with black spots as a clue to this, though a specialist assessment will be needed to determine the true conditions of the head.
It's a very light engine, the K-Series, and happy to rev, which means the quality and quantity of oil is vital. As it was designed originally for use as a transversely mounted engine, the oil pick-up in the sump can cause starvation on high speed corners as the oil is pushed to one side and away from the pick-up. To avoid problems with this, most owners simply keep a very close eye on the oil level, particularly during track days. The engine isn't especially thirsty for oil, so it should just need routine checks for road use.
However, it is worth checking the foam sump baffle is either in perfect condition or has been properly removed. The foam disintegrates over time and can block the oil feed pipe. A mechanical oil pressure gauge is a good idea to replace or supplement the original Caterham item, which is notoriously unreliable. A dry sump conversion is the way to go for serious track use and big power engines, though this is an expensive route to go down.
The exhaust manifold that comes as standard with the K-Series engines on non-Superlight models is a little restrictive, so many owners opt to upgrade to Superlight spec of fit an aftermarket item. This improves engine breathing, adds a little extra power and will give the engine a crisper sound.
There is some debate among Caterham K-Series-engined Sevens about which gearbox is best: the Ford-derived five-speeder or Caterham's own six-speed unit in manual or sequential forms. Most owners prefer the six-speed 'box as it has ratios specifically chosen for the Seven, while the sequential transmission only really offers a benefit for trackday or competition use thanks to its quicker shifts. The Ford 'box is tough, but its ratios are not as closely spaced to make the most of the K-Series' high revving nature.
Clutches are long-lived and easy to replace, but the cable can snap more readily than in most cars. A modified pedal box or improved cable will solve this.
Not every Seven comes with a limited-slip differential as part of its specification. A limited-slip diff will help on track days and is generally desirable, so check the specification of the car you're considering. Fitting a limited slip diff to a car that doesn't have one is straightforward as access to the rear axle is good and it's a job within the scope of the competent home mechanic. Replacements for the Ford Sierra-derived rear axle can be bought from a variety of suppliers such as Quaife and Raceline. Just ask to receipts and check the diff is what is claims to be by jacking up the rear axle to make sure both wheels turn in the same direction when one is rotated.
Lastly, check the battery turns the engine over quickly and all of the electrics work. Cars that have been left for long periods without being connected to a trickle charger are more likely to suffer battery faults. Luckily, the battery is light and compact to remove and cheap to replace.
PHer's view:
"You can do most of the work yourself - self-servicing is common, and almost any mechanical job is possible at home with a few tools. I've changed cambelts, starter motors, suspension components, fuel tanks, diffs. Apart from a few teething troubles, my car has been very reliable. I've done numerous road trips with it and it has never let me down. The odd broken spark plug and dodgy earthing strap have come up, but it's all part of the fun to mend what breaks."
Mark Andrews
