Service bay: Rover straight six
We lift the lid on the SD1’s 2300 and 2600 six-cylinder engine.
T his month we look at an engine design which was one of BL’s very own Greek tragedies and another story of a golden opportunity wasted – the 2300 and 2600 Rovers.
One of the reasons BMW and Mercedes do so well now is because they didn’t have any serious opposition in the late 1970s but it could have been different.
The basis for the development of the 2300 and 2600 Rovers goes back to BL’s need to replace both the ageing Rover 2200 P6 and the Triumph 2000 and 2500 range, both 1963 designs and getting long in the tooth despite various tweaks and facelifts.
The Rover 3500 SD1 had appeared in 1976 to critical acclaim but there was room between it and the 2200 Princess for a six-cylinder executive car to take on the V6 Granada along with other executive cars like BMW 520 and 525, Mercedes 230 and the forthcoming Opel Senator and five-cylinder Audi 100 as well as the Peugeot 604 and Renault 30. So, the arena into which the new six cylinder Rovers would enter was hotly contested.
Development of the new engine was entrusted to Triumph engineers and the bare bones of the new engine originally owed something to the old 2000/2500 Triumph straight six although nothing interchanged apart from a few nuts and bolts. A cleansheet design, the ‘PE166’ took many design cues from existing Triumph engines and the actual design process began in 1970 under Spen King, Jim Parkinson and Mike Loasby.
As early as 1970 thought was already being given to replacing the big Triumph. Originally, proposals were suggested to simply make an OHC version of the existing Triumph unit but the trouble with that was that its 74mm bore was small – modern designs such as the 2.5-litre BMW M30 had bores that were 86mm wide and big bores mean two big valves or four smaller ones – basically, the 2.5 block wasn’t up to it.
By 1972/3, development was well under way of an all-new engine which, given a free hand and a money-no-object budget, should have been something outstanding. However, BL was in the throes of financial troubles and the accountants insisted on
the usual cost cutting measures. The first of these came when the engineers involved were initially told to use the short stubby connecting rods from the Dolomite slant-four engine. To keep the connecting rod angularity within bounds this meant reducing the height of the block. Even so, with a bore size of 81mm (still fairly small) and a stroke of 76mm, the 2300 engine was nicely over square and the block was wide enough to accommodate a longer 84mm stroke to bring the engine up to 2597cc for the 2600 version. In the end, the Triumph rods were not used, but the block dimensions were set in stone by this point.
These early development engines were using a block very similar in dimensions to the 2500 Triumph unit – knowing BL they would probably have been thinking about reusing the old machining equipment to make the new engine much like they did with the O-Series/ B-Series saga. But they didn’t fall into that trap and were able to make the block some 20mm longer and that gave them the chance to increase the bore size at a later date to build a 3-litre version with 86mm bores. As it stood, Triumph engineers used the extra space to have extra cooling jackets around the cylinders.
Oddly for the 1970’s, the Rover six used a four-bearing crankshaft when just about everything else used a sevenbearing unit – the 1970s Mercedes 250 unit was a four-bearing unit and that was never considered one of their better engines. However, BL was interested in economy and one way to achieve that is to reduce friction. This was achieved, but the balance weights needed to make it run smoothly were massive and the result was still a very heavy crankshaft. Made from EN16 steel (suitable for Tutfriding) rather than the grey cast iron being increasingly used, the crank was nevertheless extremely strong and I can’t recall ever hearing of crank problems with this unit.
With the same block and connecting rods between the two, only the crankshaft and the pistons differed. The 2600 used forged Mahle pistons whilst the 2300 used cast Hepolite pistons from the Bradford piston manufacturer Hepworth and Grandage.
Up top, the Rover cylinder head design showed a lot of promise. Unlike most OHC designs, the Rover unit borrowed the combustion chamber and valvegear design from the Dolomite Sprint with the pent roof and the single camshaft opening both and inlet and an exhaust valve with one lobe – but rather than opening four valves per cylinder, there were only two in the Rover unit – an opportunity missed.
This also meant that that the same opening, lift and dwell were used on both inlet and exhaust valves – not ideal but not a major problem. What could have been a major problem was the fact that two valves were operating on one lobe. Contrary to popular belief, the cam to rocker relationship is the highest stressed part of an engine with just one valve – opening two puts huge pressure on the cam and so plenty of oil is needed – and therein lay one of the engine’s major downfalls, as we’ll see.
The fact that the bores were relatively small meant that the valves needed to open at an angle and the valvegear layout was perfect for this. In the end, valve sizes for both engines were set at 42mm inlet and 35.6mm exhaust – relatively small compared to 46/38 in the 2.5 BMW engine.
Unlike the Dolomite Sprint engine though, the head and cam carrier arrangements were different. The head was one layer of the sandwich whilst the cam carrier with the cam and rocker shaft was another with a big cast alloy cam cover that both looked neat and added strength to the whole set up.
A first for Leyland was the use of a rubber toothed belt to drive the cam. This was still rare in the UK although Vauxhall pioneered it in the UK with the 1967 FD Victor and Ford followed in 1970 with the Pinto engine. A viscous fan was also used along with a pair of SU HS carburettors and with the new engine came expensive new manufacturing facilities – for example, the head bolts that also secured the cam carrier were machinetigh tened to the correct torque all in one go.
Given the money that the new engine cost, the 2300 and 2600 Rovers should have been a winner from the word go – instead, it added to the SD1 tale of woe.
As a car, the 2600 Rover was pretty good. With 136bhp it wasn’t a lot slower than the 3500 and with the five-speed manual box it could return 30mpg on a run. Early bench tested 2600 engines had given over 150bhp – too close to the ageing 3500 V8 and so the engine was detuned, most likely by giving the camshaft very tame timing: the duration is just 238 degrees when the norm was around 256 degrees. That, added to fairly big valves meant that the 2600 didn’t have as much low down
grunt as perhaps it could have had, but all things considered it wasn’t a bad engine at all. The 2300 was smoother, but with just 122bhp it just wasn’t powerful enough to heave a heavy Rover along with any gusto. With manual steering, wind-up windows, no self levelling and far more basic trim and equipment it was obvious that BL wanted you to stump up the extra for the 2600.
The Rover sixes also had a distinctive sound, the combination of a slightly growly power unit allied to the familiar cam belt whine meaning that whilst they didn’t compare so well with the BMW and Mercedes sixes, they were comparable with the Ford Cologne V6 and Peugeot/Renault/ Volvo ‘PRV’ V6 units.
In service, it didn’t take long for the cracks to appear. Whilst the engine was impressively strong, it had chinks in the armour and the main one was the oil feed limiter valve in the cylinder head. This was fitted into the cylinder head to avoid flooding the top of the engine with oil and causing oil consumption issues and whilst the idea was commendable, the execution wasn’t.
The valve had a strange split pin type thing in the centre that could stick shut, normally as a result of being gummed up with ‘black death’ oil gunge due to the way the engine ran cold at the top end and the first thing an owner knew about it was when the car started to get noisy from the top end or slowed down and then stopped with the belt shredded and the cam seized in the carrier.
To repair this was a head-off job and if you were lucky the cam and carrier could be saved but many were scrap at that point. At the BL dealership I worked at in the mid ’80s, many mechanics would, when doing a top end rebuild, pull the centre pin from this
valve and chuck it in the bin. Once oil had a clear route to the top end of the engine the problem never happened again. Sales of Gold Seal replacement engines made BL plenty of money, but the car’s reputation was ruined. Mechanics often found that locating dowels were missing from the head and cam carrier assembly meaning that the head could ‘shift’, causing gasket failure.
Head gaskets were another common problem on these cars and the unusual, almost open deck design of the top of the block is thought to be to blame. But, if you have an 2300 or 2600 and rebuild the top end with the head skimmed, the block rubbed down to be perfectly flat and with a new quality gasket, it should be fine and to be fair head gasket problems were no more common than on many other cars of the era and they’re nothing like as prone as a K-Series.
MAINTENANCE
Given one of these cars with a noisy top end, you’d need to remove the head and do all you need to do – in fact, it’s almost worth doing it anyway. With the head off you can clean everything up, skim the head, recut the valve seats and fit new stem seals as well as removing the centre from the restrictor valve. The cam belt and tensioner need replacing every 30,000 miles, but given how easy they are we’d just do it every 18 months anyway although at present, the tensioner pulley is proving hard to find. A new belt is around £15 so is hardly expensive.
A good semi-synthetic oil and a Unipart filter every year or 6000 miles is a must – Rover later changed the oil change interval to 12,000 and that’s OK only if you have the restrictor valve with the centre removed. As stated earlier, these engines tended to run cold at the top resulting in ‘black death’, where the oil turns to black sludge. If the engine is still clean inside, then semi synthetic 10/40 is just the job. Spark plug threads in the alloy head are easy to cross thread so when changing them, a bit of WD40 on both the plug and the threads in the cylinder head and winding them in carefully is the answer.
The SU carbs were either the old type HS units with a side-mounted float chamber and a manual choke (with a plastic lever that used to snap) or later HIF type with the FASD (Fully Automatic Starting Device) or AED
(Automatic Enrichment Device) that are the same thing. Both were universally useless and the FA part of FASD had a different meaning to most owners and mechanics. A manual conversion kit is available, but a conversion to a pair of older HS type carbs is a better idea again.
One thing worth mentioning is that parts for these engines are almost ridiculously cheap. From Rimmer Bros, a cam kit is a mere £62 with VAT, a head gasket is 50 quid all in and even a new cam carrier is £134. That means that even if the top end of your engine is in serious trouble it can be rebuilt for relatively low cost and these engines are very simple and straightforward to work on with tons of room. Even a new 2300 crankshaft is just £42 with VAT.
CONCLUSION The Rover PE166 was sadly typical of BL (and Triumph’s) approach to building engines. Like the Stag and Dolomite Sprint units, it tried to be too clever for the crude and old fashioned manufacturing methods BL used and the questionable quality of some components. Had Mercedes built them, the 2300 and 2600 engines would have been manufactured with far greater precision and crude ideas like the oil restrictor valve would not have seen the light of day – you’d have to find the bloke at BL who thought of that and ask what on earth he was thinking of because it was just asking for trouble. It’s clear that the engine had a lot of potential – with such big cylinder head ports and such lame cam timing it’s clear that this engine was strangled to avoid competition with the 3500 and it could have developed a lot more power. With fuel injection and a better cam it could easily have achieved 170bhp or more and effectively relegated the 3500 to limited production status, becoming a rival to the German cars whilst the early reliability issues should have been swiftly cured.
However, they weren’t and the PE166 became known as a lemon. Today though, hindsight means that the major issues with the engine is easily fixed and that rather than replacing it with a V8, the straight six can be maintained, retained and used as something different to the ubiquitous 3500. Flawed it may have been, but it also an interesting unit that has a lot of character and you’d be surprised how good a sorted 2600 is.