NEW! The Sheer Truth
Magnificent and no lorry!
(Photo Ken Gardiner, whose superb restoration of a Sheerline this is).
Auto enthusiasts always have something to learn. It is folly to think otherwise.
So I was delighted, a few weeks ago, to be corrected on my pet subject of Austin pre-1955 by Australian enthusiast, Ken Gardiner, on his pet subject, the Austin A125 Sheerline.
I had always thought the Sheerline’s four litre motor was a slightly modified incarnation of Longbridge’s 1940s lorry engine of that size.
Not so; as Ken explained.
Like the units for the Big Seven and Austin Eight, beneath the surface the A125/A135 and K Series truck engines are markedly different.
All Austin four litre petrol engined lorries from 1942 onwards (there were no diesels at that time); then BMC built Morrises, and finally, Leylands in the 30 cwt – five ton class until 1976, shared the same dimensions for their six cylinders. But not one of these commercial vehicle engines is interchageable with the A125/A135 car.
The primary reason for this is the latter’s motor has the two forward mounting points on the sides of the block. The lorries have their single attachment in the form of a plate bolted to the front of the block, under the timing case and extended at a right angle at the base to rest on a large rubber mounting fitted directly on top of the front chassis cross member.
Because, predictably, the camshaft is entirely different in the lorry engine, the location of the distributor is different from that of the car. The truck has the drive, and also that for the oil pump, passing through the second strengthening web in the cylinder block, while the Sheerline’s find their way through the third.
Of the four camshaft bearings only the first and fourth are interchangeable.
The position of the oil filter is also different. Austin lorry engines habitually intruded into the bulkhead and, to an extent, the cab, confining space at the rear. There is much more ‘air’ at the rear of the car’s unit and the filter bowl does not need to be moved forward as on the truck.
Next the manifolding, that, again predictably, is substantially altered. The lorry engine has a smaller diameter intake design and a single, as opposed to dual, exhaust outlet.
The cylinder head itself is entirely different. It may come as a surprise to learn that the lorries (with the exceptions of those powered by two later up-rated engines designated as 40E and 40V) are only classified as of 75 brake horsepower. That says a lot for gearing and what can be done when around 100 mph top speed is not required!
The cars get their 130 ‘horsepower’ from a head re-worked by consultant, Harry Weslake, to include larger valves, heart-shaped combustion chambers, enlarged manifolds and a Stromberg DBVA 42 carburettor on the Sheerline; three SU H4Ts on the Princess. The lorry used a Zenith 30 VM.
Sliding under the two engines we would notice the cars have a finned, aluminium sump with the oil pump cavity and reservoir at the rear behind the third crankcase web, while the lorries have a pressed steel sump with the cavity and reservoir at the front, ahead of the second web.
Thus, in essence, the only major parts that are interchangeable are those two camshaft bearings, the pistons, rings, and gudgeon pins, the connecting rods and the crankshaft.
Finally, the car engines have ‘4 LITRE CAR M’ cast into the bottom of the block on the right side, under, and slightly forward of, the word ‘Austin’.
I am extremely grateful to Ken for this interesting and illuminating description of the differences between these two power units. If you want to comment, please get in touch.
So I was delighted, a few weeks ago, to be corrected on my pet subject of Austin pre-1955 by Australian enthusiast, Ken Gardiner, on his pet subject, the Austin A125 Sheerline.
I had always thought the Sheerline’s four litre motor was a slightly modified incarnation of Longbridge’s 1940s lorry engine of that size.
Not so; as Ken explained.
Like the units for the Big Seven and Austin Eight, beneath the surface the A125/A135 and K Series truck engines are markedly different.
All Austin four litre petrol engined lorries from 1942 onwards (there were no diesels at that time); then BMC built Morrises, and finally, Leylands in the 30 cwt – five ton class until 1976, shared the same dimensions for their six cylinders. But not one of these commercial vehicle engines is interchageable with the A125/A135 car.
The primary reason for this is the latter’s motor has the two forward mounting points on the sides of the block. The lorries have their single attachment in the form of a plate bolted to the front of the block, under the timing case and extended at a right angle at the base to rest on a large rubber mounting fitted directly on top of the front chassis cross member.
Because, predictably, the camshaft is entirely different in the lorry engine, the location of the distributor is different from that of the car. The truck has the drive, and also that for the oil pump, passing through the second strengthening web in the cylinder block, while the Sheerline’s find their way through the third.
Of the four camshaft bearings only the first and fourth are interchangeable.
The position of the oil filter is also different. Austin lorry engines habitually intruded into the bulkhead and, to an extent, the cab, confining space at the rear. There is much more ‘air’ at the rear of the car’s unit and the filter bowl does not need to be moved forward as on the truck.
Next the manifolding, that, again predictably, is substantially altered. The lorry engine has a smaller diameter intake design and a single, as opposed to dual, exhaust outlet.
The cylinder head itself is entirely different. It may come as a surprise to learn that the lorries (with the exceptions of those powered by two later up-rated engines designated as 40E and 40V) are only classified as of 75 brake horsepower. That says a lot for gearing and what can be done when around 100 mph top speed is not required!
The cars get their 130 ‘horsepower’ from a head re-worked by consultant, Harry Weslake, to include larger valves, heart-shaped combustion chambers, enlarged manifolds and a Stromberg DBVA 42 carburettor on the Sheerline; three SU H4Ts on the Princess. The lorry used a Zenith 30 VM.
Sliding under the two engines we would notice the cars have a finned, aluminium sump with the oil pump cavity and reservoir at the rear behind the third crankcase web, while the lorries have a pressed steel sump with the cavity and reservoir at the front, ahead of the second web.
Thus, in essence, the only major parts that are interchangeable are those two camshaft bearings, the pistons, rings, and gudgeon pins, the connecting rods and the crankshaft.
Finally, the car engines have ‘4 LITRE CAR M’ cast into the bottom of the block on the right side, under, and slightly forward of, the word ‘Austin’.
I am extremely grateful to Ken for this interesting and illuminating description of the differences between these two power units. If you want to comment, please get in touch.
The forward mounting plate
of the lorry engine was entirely different
from that of the twin ‘side mounts’ on the cars.
On Austin ‘commercials’ the engine usually intruded into the cab, as shown here.