For Rolls-Royce small horsepower cars Rev July 2014
The reference numbers in blue are those on this Disc
(The DC0 references are the original camera ones and can be ignored.)
Rolls-Royce 25/30 chassis no: GRP 29 Image cooling-01.jpg
Cooling System
The R-R 25/30 has a well developed water cooling system which remains effective provided it is kept in good condition and free of sludge and corrosion. The parts in contact with the coolant are cast iron and bronze in the engine and copper in the radiator core.
The temperature gauge probe is mounted at the rear of the cylinder head and the Calorstat which controls the opening of the radiator shutters is mounted on the radiator header tank.
1.Capacity:
Coolant capacity: Total – 30 pints ( 17 litres) – according to original published data.
Individual capacities as measured :
Block and Head only – 9 pints ( 5.0 litres) excl. water pump and hoses
Radiator only – 13 pints (7.5 litres) film block type by
Searle Radiator Company Ltd., Camden Town NW1
This radiator core probably replaced the original honeycomb type.
2. Water Pump
The pump itself has a bronze body and rotor and is not susceptible to wear or corrosion.
The Impellor is mounted on a steel spindle which bears lightly on a pad thrust bearing in the centre of the inlet housing. If this is worn a new pad can be machined from PTFE or Tufnol. The purpose of the pad is to provide the smallest practical clearance between the impellor and the inlet housing when all is assembled.
See images cooling-02.jpg & cooling-03.jpg – waterpump disassembled
Water pump overhaul is also covered in a RREC Technical document.
2.1 Drive
The water pump is driven through a flexible coupling which eventually frays and, if so, should then be replaced, if only for cosmetic reasons.
Supplier: www.tgautospares.co.uk
The coupling is held between two ‘spiders’ which are retained by 4 – 3/16 BSF bolts and castle nuts with tiny split pins.
The water pump impellor shaft is driven by a floating spline within this ‘spider’.
Images cooling-04.jpg & cooling-05.jpg – coupling reassembled
3. Distributor
To improve access to the front cover plates it is recommended that the distributor cap is released and tied back in a plastic bag.
Undo the four ¼ BSF holding down nuts and lift the distributor body away. The ‘master’ tooth on the spline will ensure that the timing setting is not lost when removing and refitting the body of the distributor. To aid its reassembly in correct alignment it is suggested that a mark is made with a felt pen on the edge of the rotor and the adjacent edge of the body before lifting the assembly.
In order to prevent ingress of water or contaminants while working in the vicinity after removal of the distributor body, make a cover from plywood or rigid plastic to fix over the hole exposed by its removal.
4. Cylinder Head
The cast iron cylinder head is particularly vulnerable since water circulation in the narrow rearmost passages can be relatively sluggish which may have caused an accumulation of silt and corrosion which will exacerbate the problem. ( all original heads are now over 73 years old). This may result in inadequate cooling leading to cracking of the head in the region of numbers 5 and 6 spark plug holes. If there is any doubt about water flow in the head, removal and thorough cleaning of the passages is recommended. An indication of the condition of the passages can be gained by the removal of one or more of the rearmost core plugs on the off (sparkplug) side. There are 15 small and six large core plugs in the head itself. Each core plug has four holes. For core plug removal a special tool is needed with four prongs of hardened steel to locate in the holes in the head of the plug.
See image cooling-06.jpg – two core plugs removed
If a tool is to be made, effective prongs can be made from lengths of allen keys. A size of allen key must be selected which is a snug fit in the holes. A six to nine inch bar will provide adequate leverage. Remove as many plugs as will turn without excessive force. Do not use excessive force or a mallet which might risk cracking the thin walls of the head itself.
Image cooling-07.jpg – tool for core plug removal
If the head is removed from the engine then further access to the water passages can be gained by removal of the larger cast iron plates on the front and rear of the head (similar to the side-plates in the block) and each secured by eight screws.
Images cooling-08.jpg & cooling-09.jpg – end plate and core plug removed from head
Notes:1. The RREC offers a loan facility for special tools
2. All of the core plugs are sealed by aluminium washers. These are still available from Ristes www.ristesmotors.co.uk and others.
5. Cylinder Block
The block is fitted with four core plugs of similar type located within the pushrod galleries on the near side which can be removed as above. If these are removed, care needs to be taken to keep contaminants out of the oil ways.
Image cooling-10.jpg – core plugs in push rod galleries
To force the coolant to the vulnerable rear of the cylinder head the six forward holes in the off side top of the block may be advantageously sealed. The coolant will then be encouraged to flow up into the rear of the head and along it to the front where it passes into the top hose to the radiator.
Image cooling-11.jpg – top of block showing blanked holes along off-side front
5.1 Cover Plates on Block offside
There are six cast iron cover plates which provide access to the water jacket around the cylinders on the offside of the engine block. These are held in position by a series of
2 BA slot head screws which need to be removed by a screw driver.
Images cooling-12.jpg, cooling-13.jpg & cooling-14.jpg – access to block water jacket
5.1.1 Method:
To remove the 2BA screws ensure the screw driver blade is unworn and a tight fit in the slots. It is worth investing in a new screw driver if there is any doubt since it is essential to release the screws first time. A screw driver of about 16inches( 400mm) length is ideal and should be wedged by a bar of timber to ensure the blade does not slip out of the slot and damage the screw head. The timber should be approx 18 inches(450mm) long and of, say, 2inch x ¾ inch section. If a recess is bored in the timber at an appropriate place then one can apply considerable force on the head without risk of the screwdriver slipping.
Once the covers have been removed they expose the outside of the cylinders and the vertical copper tubes. The gaps between the tubes and the cylinders on one side and the block walls on the other, are quite small and easily blocked by corrosion and/or sludge. A high quality hacksaw blade ( i.e. one which is not likely to break) is ideal for clearing these slots by loosening the adhering scale so as to ensure good coolant flow around the cylinders.
5.2.2 Refitting.
The plates must be thoroughly cleaned and all corrosion removed to ensure the new gaskets sit flat on the mating surface. The countersunk holes should be thoroughly cleaned to provide optimum contact by the screw heads.
Gaskets can be made from 1.5 mm Klingerite .
The threads of the screws should be cleaned with a fine wire brush and the screws refitted using an anaerobic pipe thread sealant by Knorr Bremse or similar. Ideally, the threads in the CI block should first be cleaned by running a 2BA tap through them.
See Image cooling-15.jpg
Note: It has been suggested that new 2BA screws (stainless if available) are fitted, made with countersunk allen heads to ensure easier removal at a later date. Since this would be an easily reversible modification it might be deemed acceptable by purists.
5.2 Descaling
Before reconnecting the assembled engine to the radiator it will benefit from a good ‘soak’ for a minimum of 24 hours with a solution of Deox-C If the scale is significant then it is recommended to maintain the soak for several days. Deox-C is a crystalline corrosion removal product made by Bilt-Hamber laboratories of Billericay, Essex. Dissolve the contents of a one litre container in 5 litres of very hot tap water.
The lower inlet into the block from the water pump should be blanked off with an aluminium plate or similar. The solution can be introduced via the top outlet hose at the front of the cylinder head. The action of descaling the internals of the block and the head is accelerated at a raised temperature of up to 70 degrees C. The engine can be run briefly at, occasional intervals to maintain heat in the solution. Extreme care must be taken to avoid overheating the assembly since there will be no pumped circulation of coolant.
Finally, drain the solution and flush the head/block assembly with a garden hose for, say, 30 minutes.
Recommended chemicals Image cooling-16.jpg
6. Hoses
The top hose has an ID of 1-3/8 in (35mm) and the bottom hose of approx 1in (25mm). It is desirable to inset a metal tube in each to stiffen the assemblies, improve the coolant flow and shorten the actual lengths of hose. The top one is straight and the bottom one should have a gentle curve of about 135 degrees included angle. Stainless steel Jubilee, or similar, hose clamps should be used.
Images cooling-17.jpg & cooling-18.jpg – top and bottom hoses
7. Radiator
The radiator can be easily drained by rotating the tap at the outlet with a large spanner – a 5/8 BS (9/16 W) is an approx fit for the above radiator.
While the radiator is disconnected from the engine it is worth descaling it with a dose of concentrated washing soda (Sodium Carbonate- Na2 CO3 ), available very inexpensively from a supermarket.
Close the drain tap and seal the upper and lower outlets of the radiator.
Fill a series of Thermos flasks with boiling water to a total of about 7 ½ litres. Empty a bag of soda into a container and add the water to dissolve the powder. Pour the solution into the radiator as soon as possible while it is still hot. Leave overnight, drain and thoroughly flush with a hose.
Image cooling-19.jpg – car being flushed by garden hose
If the radiator core requires replacing this can be carried out by specialists.
Supplier: Tony Wild, Leeds Tel: 01132 872 946
7. Calorstat
If there is doubt about the correct functioning of the Calorstat control of radiator shutter opening then it is worth a partial disassembly of the system to clean and oil the mechanism.
Lift the knurled locking pin from the eye of the Calorstat rod and check that the shutters move freely. Another small pin connects the other end of the lever to the shutter mechanism and is retained by a small leaf spring.
Removal of this pin then enables the cast brass Calorstat coverplate with its attached pivots to be removed after undoing the five peripheral 3/16 BSF nuts. The other nut clamps the vertical pivot and should not be undone. The Calorstat bellows is now exposed in the radiator header tank, and hopefully will not need removal.
With the coverplate removed and the radiator cold, grip the central rod and pull axially. If there is resistance this suggests that the Calorstat is functioning. If it moves with little resistance then it is probably faulty and will need removal and rebuilding or complete replacement.
If removal of the Calorstat bellows is contemplated then first read: RREC Technical Manual No. 4 (1990). Page 105 ‘Rolls-Royce 20/25 automatic radiator shutters’.
The bellows housing is retained by a very thin brass flange and thus great care must be taken to prise it free with a flat bladed sharp ended tool before its withdrawal from the radiator header tank.
See Image cooling-20.jpg – header tank with Calorstat removed
See Image cooling-21.jpg – bellows and housing
The bellows can be tested by sitting it in a saucepan with water up to within 5mm of the flange. Note the position of the end of the central rod. Bring the water slowly up to the boil and noting when the rod starts to rise. At or near boiling note the height to which the rod has risen and measure the difference from its cold position. This difference should be at least 16 mm to ensure that the radiator shutters will fully open when hot.
See Image cooling-22.jpg – calorstat bellows in saucepan
If all is well then clean all the components and reassemble having oiled the various pivots and their bearings.
Manually close the shutters and then tighten the clamp which holds the pivoting lever connected to the shutter system. This sets the system in the cold position.
See Image cooling-23.jpg – linkage for calorstat
Suppliers: Calorstat repairs. Vintage Car Radiator Company, Towcester, Northants.
8. Thermometer
If the opportunity arises it is a good idea to extract the thermocouple from the rear of the head and check its accuracy in a container of water together with a thermometer of known accuracy and a portable heating element to bring the water steadily up to boiling point.
9. Filter:
It is recommended that a filter is fitted in the top radiator hose to collect any entrained flakes of corrosion or other contaminant before it can enter the radiator core. This filter should be inspected, and cleaned if necessary, every 6 months.
Suppliers:
Gano Filter Company, California
Cleanflow radiator filter sock (Australian origin) supplier- Ristes, Nottingham
10. Antifreeze:
Mono Ethylene Glycol antifreeze is recommended at a 33 % concentration to provide both winter and summer protection.
Suppliers:
Comma ‘Super Coldmaster’ or similar, available from www.hgvdirect.co.uk
Do not use a modern type antifreeze containing Organic Acid Technology (OAT) in this or any pre WW2 cars.
11. References for further reading:
Roll-Royce Small Horsepower Engines by R.Haynes & M.A. Grigsby RREC publication. Chapter 6
The Flying Lady, journal of the RROC, pages 289, 296, 297, 508 and 904.
Technical Manuals by RREC publications
12. Acknowledgments
Thanks for valuable practical advice and encouragement to Roy Brooks, John Hibbert , Stephen Wragg, Matthew Pickles and David Rochford.
Calorstat repairs: Vintage Car Radiator Company, Litchborough, Towcester, Northants.
Fiennes restoration www.fiennes.co.uk
These notes have been compiled in good faith by Bryan McGee, carry no official endorsement by the Club and are offered freely for reference by members to use at their own risk.
The attached document provides Workshop Hints for small horsepower Rolls-Royce cars – Rolls-Royce 25/30 – kindly provided by Bryan McGee. This particular document focuses on Bulkhead Shake
Last updated: July 2014
