Mark 12A Vehicle Specification


Vehicle Specification for Charmichael Mark 12A


I am slowly collecting information about my Carmichael Mark 12A fire engine from a wide variety of sources. This includes the manufacturer and part and equipment providers. Where possible I have acknowledged the provider of the information. Frequently it is the vehicle itself that has provided the raw data. As it is a unique vehicle there is very little published information to which I can refer. However, over time I expect this section to expand and hope that it will become the definitive source of information regarding the Mark 12A. It is the elevating platform that distinguishes it from a normal Mark 12.

I phoned Carmichael in June 2010, and as I found earlier when I needed some parts, they were extraordinarily helpful. The person I had dealt with earlier had retired about eight weeks prior to my call in June. Colin helped by providing dimensions directly off of the desk sized paper drawings. He also read through the hand written workshop journal of the time for any references to my Mark 12A. The information he provided is reproduced below.

Also in June 2010 I managed to locate a manual for the 903 engine. I bought a copy from Cummins, the engine manufacture. Unfortunately it was only available form the USA so the postage was almost as much as the manual. It is still under copyright so I cannot reproduce it here.

 To see  Scammell Crash Fire Rescue Chassis 6x6 dimensioned drawing, click the link. Opens in a new window. Zoom in for detail.

400 BHP and 500 BHP 6x6 Crash tender
A 6 x 6 rear engined chassis for airfield/cross country use with automatic gearbox and multi plate clutch PTO. There are no operational restrictions on the PTO engagement and by selecting 1st gear and low range in the auxiliary gearbox a slow crawl can be achieved whilst making full use of the fire pump. 400 BHP and 500 BHP engines are available and optional tyre equipment is offered and it is envisaged that this vehicle will operate as a major rescue appliance. The expected water capacity at a GVVV of approximately 26.41 tonne is 10,000 litres for 400 BHP models; and at a GVW of approximately 28.45 tonne ,s 11365 litres for 500 BHP models dependent on fire package.

In the tables below there is a mixture of imperial and metric measurements. The first stated measurement is as the source data with subsequent entries being conversions. This of course means that there is no consistent convention regarding the order of imperial and metric measurements.

Table of Base Vehicle Specifications

Base Vehicle


Carmichael Fire Limited


Mark 12A

Date of manufacture

16 March 1990

Serial Number

CH 4919


Chassis manufacturer

Unipower Vehicles Limited


Unipower were previously Scammell

Chassis number

LJ 72395

Number of axles



6x6 Rigid

Maximum Weights


Front axle

8130 kg - 8 Ton

Rear axle - 1st

10160 kg - 10 Ton

Rear axle - 2nd

10160 kg - 10 Ton


28450 kg - 28 Ton

Unladen weight




Model Code


Current tyres Michelin X 395/85r20 XZL
 Environmental Conditions  The vehicle in standard loon will operate at any temperature between -12° and 46" C.
At any altitude abowl 3668m the engine is derated by 4% per 306m,
 Crawl and Pump Mode  At 3000 Pump RPM Crawling Speed is less than 6 KPH in all cases



Table of Base Vehicle Specifications

Vehicle Dimensions


The following length dimensions were provided from the original drawings,
by Colin Nicklin of Carmichael Support Services Ltd. on 11 June 2010.

Gratefully acknowledged



From the back of the body excluding the mounting ladder
to the centre of the rear boggie.

3.185m - 124.918 in

10 ft 4 15/16  in

From last to centre of front axle.

4.750m - 186.299 in

15 ft 6 5/16 in

From last to front of bumper

2.059m - 80.756 in

6 ft 8 12/16 in

Total body length

9.994m - 391.973 in

32 ft 7 31/32 in

From the back of the body excluding the mounting ladder
to the front of the monitor flaps
when locked in the forward position

10.511m - 413.819 in

34 ft 5 13/16 in

Height - (laden) to top of monitor

3.370m - 132.174 in

11 ft 0 3/16 in

Height - (laden) to top of; platform (lowered and stowed)


Height - (laden) to top of airport light


Height - (un-laden) to top of  platform (lowered and stowed)
(airport light removed)


Height - (laden) to top of airport light




Ground clearance


Angle of approach


Angle of departure

 27 1/2 o

Track (at ground)

 F 2.010 R 2.080


Table of Engine Specifications

Cummins 903 Engine



Cummins VTA 903 500

Serial Number


Date of manufacture


S.O. No.





500 hp - (373 kW) at  2,800rpm


1,127 lb-ft at 2,200 rpm* (From spec sheet 1473 Nm (1060 lbf ft) at 2200 RPM)

Configuration and No. of Cylinders



Four cycle 90 degree V8 water cooled turbocharged and aftercooled


903 cu in (14.8L)



one, Turbocharged and aftercooled


51/2 in (140mm) (From spec sheet 139.7mm)


43/4 in  (121mm)  (From spec sheet 120.6mm)

Compression ratio

15.5 : 1

Injection timing code


Injector torque


Injector travel

0.187 inch(4.7498 mm)

Valve lash cold

0.012 inch Int. (0.3048 mm)

0.025 inch Exh. (0.635 mm)

Fuel rate at advertised HP

xxx mm3/stroke

Oil pan capacity

4.2 gals (19L)

Oil capacity

10 gals *

Coolant capacity

30 gals *


* = TBC


For information only
(from the Spec Sheet)

 Engine 400 BHP Models  All the same as the fitted 500 BHP except
 CumminsVT903  Turbocharged
 Power Gross  298.4 kW (400 BHP) at 2800 RPM
 Torque Gross  1247 Nm (920 lbf ft) @ l900 RPM
  (Ratings measured to BS Au 141a)


Table of Engine Auxiliaries

 Engine Auxiliaries 


CAVAC7 Type, 24 volt. 60 amp screened

 Starter Delco Remy. 24 volt, flange mounted
 Air Compressor Cummins Compact 374, litres/min
 Corrosion Resistor Cummins spin-on replaceable element
 Oil filter Cummins spin-on replaceable element
 Fuel Filter Cummins spin-on replaceable element
 Cold Start Aid Fleet Guard 24 volt Semi-Automatic Ether Cold Start Aid
 Steering Pump Dowty IP3090





Engine Manual

I received a copy of Cummins ‘Operation and Maintenance Manual Automotive Diesel Engines United States and Canada’ on 20th May 2010 direct from Cummins in the States.Cummins V903 front

My engine is a VTA 903-500. The manual translates this code as:

V = Type of engine

T = Turbocharged

A = Aftercooled

903 = Cubic Inch Displacement

500 = Maximum rated horsepower.

The manual also references the engine as a C.I.D. I assume this is Cubic Inches Displaced and not Compression Ignition Diesel.

Engine displacement is defined as the total volume of air/fuel mixture an engine can draw in during one complete engine cycle; it is normally stated in cubic centimeters, liters or cubic inches. In a piston engine, this is the volume that is swept as the pistons are moved from top dead center to bottom dead center. For conversions reference, 1 Liter = 61.02 cubic inches (C.I.D.). 1 cubic inch = 16 cm³ (C.C.). 1 liter = 1000 cubic centimeters.

The 903 is therefore 14.8 lts.

Cummins V903 rear

Engine output (power/unit displacement) is calculated as follows;

With a Hp of 500, (373Kw) this equates to 33.78Hp/lt or 25.19Kw/lt. This is relatively low in today’s terms, which can be 100 to 200hp/lt or 75 to 150Kw/lt.

The manual is 68 pages long and was ordered from Cummins QuickServe Store part number 3379137

On the right are two photos of a similar engine, a V903. This engine was found for sale at jobbersinc, and was at the bottom of the link. Presumably now sold.




Table of Intake / Exhaust / Cooling Specifications / Chassis / Undercarriage / Electrical

Intake / Exhaust / Cooling / Chassis / Undercarriage / Electrical

Air Cleaner   GKN Farr replaceable paper element, mounted high al the rear of lhe chassis.
 Exhaust system 127mm exhaust system with twin silence!l; mounted high at the rear of the chassis. 
 Cooling  The cooling sys(etn is remote mounted from the engine being positioned at the rear of the chassis on the RH side. Twin radiators. total face area 0.83 sq m are cooled by a Wilmot Breedon 813mm fan of the puller type. The fan is driven via a fail­safe Dynalr Thermo fan drive unit, to conserve power.
Frame Frame sidemembers are constructed from channel section high yield stress steel to BS 4360 508. The main sidemember section is 309 x 89 x 10mm.
Crossmembers are channel section and all bolted construction is used.
Front Bumper A heavy duty channel section front bumper is fitted.
Towing Front and rear towing loops are fitted.
Wheels and Tyres Michelin G20 Pilote on 3 piece disc wheels.
16.00-20 Michelin XL or XS (5.89: 1 Axle ratio)
Brakes  Air operated Kirkstall 'S'-cam 394 x 203mm brakes are fitted front and rear An EEC split system is installed. Spring brake units are fitted for parking and secondary braking. A snatch coupling is fitted to the rear.
Steering A ZF 8065 integral power steering box with ram assistance is fitted. It is equipped with hydraulic reaction valves to give superior steering characteristics.
Fuel Tank   A 200 Litre fuel tank of pressed and welded steel construction is fitted on the left hand side of the chassis at the r-. The tank is mounted on brackets bolted to the sidemember.
Electrical Equipment A 24-volt system with negative eanh. 4 off 12-Volt maintenance free batteries fitted wired in series parallel Batteries mounted at the rear of the chassis. A battery isolation switch is fitted. Full normal lighting is fitted (head, side, stop. tail, direction indicator, reversing and rear fog lamps).
Cold starting capability: - 12° standard - 23" optional.
Electrical system screening to enable VHF radio to be used.


Table of Transmission Specifications

Transmission Specifications

Gearbox Allison HT 750 DRD automatic transmission providing 5 forward speeds and 1 reverse 1st gear is manually selected and in conjunction with the low range of the auxiliary gearbox enables crawling al less than 6 KPH whilst pumping at 3000 Pump RPM. Gears 2 through 5 are shifted automatically. The gearbox is rated for 373 kW (500 BHP) and 1532 Nm 11130 lbf ft). The transmission includes a three element torque converter, a lock-up clutch and inhibitors to prevent harmful downshifts or reverse shifts.
Gear Ratios 1st; 7.97:1 Manual selection     2nd; 3.19:1     3rd; 2.07:1    4th; 1.40:1  5th; 1.00:1     Reverse;  4.47:1
Torque Converter Allison TC400 series
Engine Power Take Off Openings

400 BHP Models Standard - 500 BHP Models Optional

Number 2

Location  One on top, one on left hand side of converter housing at 7 o'clock position (as viewed from output)

PTO Openings Size SAE 8-bolt
Rating, Each opening; 194 kW (260 BHP) intermittent, 149 kW (200 BHP) continuous.
Rating, Combined; 298 kW (400 BHP) continuous.
Propshafts All Hardy Spicer needle roller shafts, 1710 series fitted between the auxiliary gearbox and the front axle. 1810 series fitted between the auxiliary gearbox and the rear axle, and 1810 series fitted between the main gearbox and the auxiliary gearbox.
Front Axle The driven front axle is a Kirkstall SD65 and is equipped wIth a cross differential lock. Suspension Is by semi-elliptic multi-leaf springs.
Axle ratio 5.36:1
Capacity   8.13 tonne
Maximum Lock   
Angles  Front 29.50 Rear 37.50
Turning Circle Kerb to kerb - 21m - 69ft
Rear Bogie   The driven rear axle is a Kirkstall D65 and is equipped with a cross differential lock. Suspension is by semi-elliptic multi-leaf springs.
Axle ratio 5.36: 1
Capacity 20.32 tonne
 Power Take Off

 400 BHP Models Standard -  500 BHP Models Optional
The PTO is a Scammell design, being a multi-plate clutch type and can be situated on the top or the side of the main gearbox. It is driven via an idler gear direct from the engine. There are no operation restrictions - the PTO can be engaged at any engine speed with the gearbox in neutral or in gear whilst the vehicle is stationary or in motion
PTO ratio = 1.421 x engine speed
HP rating = 194 kW (260 BHP) at 3000 Pump RPM

500 BHP Models Standard
The PTO is a Scammell design. being a Sandwich type positioned between the engine and gearbox. There are no operation restrictions -- the PTO can be engaged at any engine speed with the gearbox in neutral or in gear whilst the vehicle is stationary or in motion.
PTO ralio = 1.247 x engine speed.
HP rating 335.7 kW (450 BHP) at 3000 Pump RPM

Drive Modulator (Optional on Sandwich PTO) Available as an alternative is a vehicle/pump drive modulator. This provides. independent control of vehicle or pump drive by incorporating a friction clutch between the sandwich power take off and main transmission.
PTO ratio = 1.247 x engine speed.
HP rating • 335.7 kW (450 BHP) at 3000 Pump RPM
Auxiliary Gearbox   Kirkstall AGB 7000 gear unit, twin speed 1.0:1 and 1.96:1 reduction. Front wheel drive and range change selected by means of air cylinders. When 1.96: 1 ratio Is selected front wheel drive is automatically engaged



 Mark 12A arrival 1187


Table of Cab Description / Specifications

Cab / Controls / Instruments



 The steering position is in the centre of the cab surrounded my gauges, switches and lights. The driver’s seat is full suspension which is very good for cross country.
 Cab A three man steel cab. which is constructed to enable a crew compartment extension. is fitted. It is untrimmed but includes a full instrument panel, laminated windscreen. side windows, and windscreen wipers/washers. The cab is able to meet impending cab impact legislation. Cab height and noise levels are particularly low due to the rear engine installation. A temporary driving structure is available as an alternative to the cab. 

The two crew seats either side of the driver are designed to accommodate crew in full kit including breathing apparatus.

to the Rear seating and hatch

Controls All controls are arranged for use with protective clothing. Centre steer is standard. with options for LH or RH steer.
Instrumentation  - Instruments The instruments supplied are:­
Electric fuel gauge
Pressure gauge -hand brake system
Pressure gauge -service brake
Pressure gauge - auxiliary reservoir
Pressure gauge - engine oil
Temperature gauge - water
Temperature gauge - gearbox
Speedometer - MPH
Engine Hour meter
Instrumentation - Warning Lights Handbrake
Low Air
Front Wheel Drive
PTO engaged
Main Beam
Oil Pressure
Water Temperature
Direction Indicators
Rear Fog
Front Differential Lock
Rear Differential Lock
Instrumentation - Switches Inspection Lamp Sockets
Panel Light Switch
Hazard Flashers
Rear Fog Switch
Start Switch
Starter Button
Instrumentation - Column Mounted Switches Dip Switch
Headlight Flasher
Direction Indicators
Lighting Switch
Additional Equipment Carmichael Mark 12A interior Mast lights 1187 Mast light 110V switch and gauge
Additional Equipment

Carmichael Mark 12A Cab Emergency panelEmergency lights and sirens controls and indicators
Public address system (PA system) control (Tannoy)


Table of Optional Equipment

Optional Equipment

Kysor Radiator Shutter  
Heater and Demister (with cab)   
SAB Automatic Slack Adjusters  
Automatic Drain Valves  
Trickle Charger  
Engine Coolant Heater  
Engine Sump Heater  
Cold Start Aids to -23" C  
Spare Wheel No
Service Kit No
Roadside Tool Kit No
Engine Tool Kit No
Wheel Changing Equipment  
Tyre inflation Equipment Yes
Smiths Speedometer - KPH  
Quartz Halogen Headlamps  



 Table of Vehicle Performance (incl 400 BHP Model for comparison )

       Vehicle Performance

 GVW Tonne  Maximum Speed -KPM (MPH)  Typical Acceleration Times (Seconds) - 0-80 KPH (0-50 MPH)  Power to weight ratio
 5.36:1 - G20XL 5.89:1 - 16.00-20XL 400 BHP 500 BHP 400 BHP 500 BHP
 22.35  112 (70) 115 (71) 37.4  29.9  13.4kW/tonne (18.2 bhp/ton) 16.7kW/tonne (22.7 bhp/ton) 
 24.38  112 (70) 115 (71) 40.8   32.6   12.3kW/tonne (16.7 bhp/ton)  15.3kW/tonne (20.0 bhp/ton) 
 28.41  112 (70) 115 (71)  44.2  35.4   11.3kW/tonne (15.4 bhp/ton)  14.1kW/tonne (19.2 bhp/ton) 
 28,46  112 (70) 115 (71)  Not applicable  29.9  Not applicable  13.1kW/tonne (17.9 bhp/ton) 



Rather than put a small selection of many photos here, please see the Carmichael Mark 12A galleries below, either by watching the slideshows or following the links. This is a repeat of the gallery about the Mark 12A containted in Mark 12A and TM Purchase and Arrival for ease of reference


Photo galleries powered by SmugMug

To see the photos of post delivery inspection of the Carmichael Mark 12A in HD follow this link to my photo gallery site. Click here.







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