ERF's royal wedding
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The other half of the B-Series being Cummins' latest and lightest 14-litre engine, the best match so far on speed and fuel consumption over our Scottish test route. Tim Blakemore reports
HY is it that so many manufacrers, having finally got their rticular products "right," omptly stop production and roduce new models only to counter once again the seeingly inevitable spectre of ething troubles?
Despite frequent assurances at the "Mark 1" new model ill incorporate all the lessons arned from the "Mark 6" old odel, this does not always ork out in practice.
The main reason for this parently perverse logic is, of urse, that manufacturers feel ey have to keep up with the mpetition and many delopment teams are under pressure from sales and marketing forces to give them something new to sell.
If that something new turned out to be merely a cosmetic facelift, then rest assured the product would get a hammering from the technical press.
Both ERF and Cummins have products which have been around quite a while in the BSeries tractive unit and 14-litre in-line six engine, and the subject of our road test this week combines the latest, and probably the final, versions of both — and the results confirm that both manufacturers have now very definitely "got it right."
The NT250-powered lightweight ERF chalked up the remarkable double of the best fuel consumption and fastest average speed of any tractive unit to have pulled our van semi-trailer around the Scottish route so far. For records of any kind to be set, conditions have to be favourable and they certainly were this time with sunshine for most of the way and very low winds for the three-day period — certainly a completely different story from our last ERF lightweight test when snow bogged us down at Carter Bar (CM, May 9). But let's not take too much credit away from the vehicle, the performance itself deserves unqualified praise.
Even before the road test proper began, the ERF was impressive. On MIRA's weighbridge the uncoupled unit weighed in at just 5,969kg with the fuel tank three-quarters full and a 30kg fuel flowmeter on board. That puts it among the lightest of 36-tonners even without fitting aluminium wheels and front bumper and replacing the steel wings with thermoplas. tic.
Any ideas you had about the Shotts-built 14-litre engine being too heavy may need rethinking. Cummins' slimming exercise has brought the net dry weight of the NT250 down to 1,123kg (470 lb) — a reduction of 63.5kg (140 lb) compared to the NT240.
ERF's own slimming exercise on the chassis was described in detail last year (CM, November 1), but it is worth recapping.
Included in the list of weightsaving components are a cylindrical aluminium fuel tank; Kirkstall's D66-8-1S rear axle; a
-essed steel clutch cover in ace of a cast iron one and pered-leaf springs all round in option to semi-elliptic lultileaf. Carrying on down the 3t, there's a lighter type of ZF eering box; a pressed steel idiator with integral header Ink; a single air filter instead of Ivo with their attendant rackets; and last, but by no leans least, a chassis frame ghter by virtue.of its deeper but iinner longitudinal members id welded intermediate crossembers, not not bolted or riveted. Incidentally, a secondary adintage of the latest type of air ter for the more scrupulous )erator is that he can tell at a ance whether or not it has )en changed during a service. le exposed end cover is part id parcel of the filter element. We moved away from the 'eighbridge and the ERF contin
ued to impress. The park brake held without difficulty on the one in four test hill and the fully laden tractive unit easily pulled away from rest on that gradient.
For a vehicle geared to run comfortably at 60mph, that indicates an uncommon versatility.
Then came the timed acceleration runs, and once again the ERF Lightweight did better than it had any right to on paper. Up to 40mph it was actually faster than the 280hp 16-gear 1628 Mercedes-Benz though by the time 50mph was reached the Merc's fastest time was a second or so better than the ER F's. The E290 powered Seddon Atkinson 401 could only better the ERF's 0-50 time by about 11 seconds.
Using every gear (except crawler) in the nine speed Fuller gearbox it was not difficult to accelerate quickly with the NT250-powered unit. Often with higher-powered machines, one or two of the nine gears have to be skipped for the best acceleration times, and sometimes the same technique is needed with higher geared 230-250hp units.
We tried missing second with this ERF, and the times were slower.
In the everyday running life of a 32-ton tractive unit, though, its ability to accelerate quickly is relatively unimportant, but this test did give the first indication of how well matched the 4.96:1 rear axle ratio, Fuller gearbox and Cummins NT250 engine are in the B-Series. Cummins hasn't made a radical changes to the NT240 increase its gross power outp from 240bhp to 250bhp. T basic engine structure stays t same as the NT240 which its used the NHC 250's cylindi block head, pistons and valves Con rods, vibration damp and fillet hardened cranksh, come from the E290 "Big Car range, as do the Holset HC3 tt bocharger and its auxilliari though, like the NT240, t NT250 is a "small cam" engine The extra 10bhp simply com from "revised fueling characti istics" to quote Cummins' formation sheet.
Before driving the ERF, I vio inclined to believe that such marginal increase in power o. put would not be noticeat from the driver's seat but I vu wrong.
On long motorway inclines particular, the pulling strenth the NT250 was evident, clea reflected in the surprisingly svs journey times.
In December 1979 we test an NT240 engined B-Series the Scottish route with a f trailer and comparing some the section by section results interesting.
From Darrington on the Al our final fuel stop on the A5, t earlier B-Series averaged 8 km/h (5 0.2mph). On tt. predominantly motorway s, tion, which includes the lo drag up the M18, the lightweic
F averaged 9 0.91 km/h .5mph) and remember this a was pulling a van and havto overcome a lot more wind istance.
)n the Carter Bar hill climb, ere the road speed is too low wind drag to be an important ;tor, the latest B-Series rmed over in five minutes, ee seconds — over half a minfaster than the 1979 model d significantly only three ;onds slower than the E290Nered Seddon Atkinson 401), 'he speed of the climb corned to the 1979 ERF can be y attributed to two factors — additional power of the en e and the slightly lower rear e ratio, 4.959:1 as against 9:1.
: could be argued that the ytweighZ from Sandbach was :rifle undergeared for torway work. At 40mph in -drive top gear, the NT250 s working at 1,800rpm — ilously close to the tail that ds the "sting" in the fuel connotion curve.
lut our fuel consumption refs confounded this argument. a sure bet, though, that if the -nmins engine was driven at I throttle at speeds of 00rpm (62mph) and above, I consumption would suffer atly.
A distinctive feature of all the NT240-engined vehicles I have driven before has been the vibration at maximum torque — in some cases bad enough to cause annoyance. This particular bug seems to have been almost completely ironed out in the NT250.
A change of crankshaft vibration damper is apparently responsible for the improvement, still not enough to match the smoothness at peak torque of the Rolls-Royce 265L.
Whether the engine is the culprit or simply the mirror mountings I don't know, but this BSeries had a dancing offside mirror head when the engine was idling, irritating because rearward vision was blurred.
Also at odd times during the test, we noticed a buzzing when the engine reached 1,700rpm under load. This baffled us for some time, but close investigation on the third day revealed the cause to be nothing more serious than a loose grp fan cowling coming into contact with the fan blades.
A feature of this ERF which impressed me particularly was the effectiveness of the exhaust brake, I'm a convert to this type of retarder and use it whenever approiate to control speed dur
ing a road test, but all too often the exhaust brake control button is difficult to reach and its retarding effect is minimal.
Neither criticism could be applied to the Retro exhaust brake fitted to this B-Series. In fact this type has no separate control button but a dashboard-mounted rocker switch and micro switches fitted to the clutch pedal and throttle linkage.
When the rocker is switched on, the exhaust brake operate automatically whenever the throttle is returned to the "no fuel" position. If the throttle or clutch pedal is depressed, the circuit is opened and the brake can no longer operate.
The throttle micro switch prevents excessive pressure being built up in the exhaust manifold by the engine being revved and throttled at the same time.
ERF's B-Series cab has been described many times before in CM and, exhaust brake apart, there was nothing different about this one; but I was a little surprised to see the older type of steering wheel, with its smooth black finish, fitted in place of the later type with more acutely angled spokes and rougher finish.
ERF says the reason for reverting to this type is that there have been complaints about the abrasive feel of the other one. I had no idea that most lorry drivers' hands were so delicate! My personal preference is for the nonslip type for the very reason that it is non-slip.
Summary Putting Cummins' latest and lightest 14-litre engine with ERF's lightweight tractive unit is as natural a marriage as the slightly better publicised royal one that is soon to happen. The advantages seem to be kingsized too, with outstanding fuel economy, journey times andan unusually good payload being the characteristics of our test vehicle.
It isn't just the few extra horsepower but also the carefully matched gearing that makes the 35C — 2LT SBO such an attractive package. And the lightweight B-Series doesn't cost a king's ransom.
If the next stage in the development stories of Cummins and ERF are genuine improvements on the current products, then neither companies' customers will have cause for complaint.