Rawlings R30

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This 3cc diesel is a companion to the Rawlings R-18, and like that engine, also appeared in 1948 as a product of GW RAWLINGS & Partners Ltd, Warwickshire, England. According to Fisher, a total of 147 R30's were made with production ceasing with the introduction of purchase tax on model engines in 1949. Priced at £6/5/0, it was distributed through Henry J Nichols. The photos on this page, and the description were kindly supplied by Richard Jackson of Dorset, England.

Like the smaller 1.8cc Rawlings R-18, the instructions for the R-30 say that is is to be treated as though it were a fixed compression diesel, only altering the compression for different fuel formulations. It shares bot the shape and unusual construction features of the R-18, having a contra-piston composed of a sandwich of lead alloy and steel which was free to move when cold, but expanded to give a gas tight seal when running. The recommended fuel has a high ether content: 6 parts Ether, 3 parts Diesel, 2 parts Castor oil. The oil content is low, but diesel fuel is �oily� which may have helped.
 
Bore 0.625" (15.88mm)
Stroke 0.625" (15.88mm)
Capacity 3.14cc (0.192 cuin)
Weight 202g
Height 3"
Length 5" (with spinner)
Width 2" (across bearers)

Performance with a 12x5 prop quoted by the maker was 7,500 RPM, providing 44 ounces of thrust. The implication was that it was a single speed engine as no mention of adjustment for different prop sizes is mentioned in the instructions.

Construction

The R-30 is constructed in an identical manner to the R-18, but has a larger bore to give the greater capacity of 3.14cc (although it was advertised as 3.0cc). It shared a number of parts with the smaller R18, namely:

In contrast to the sand casting used for the R-18, the R-30 crankcase is die cast, machined all over—apart from the underside. The differences are in the larger bulk of the crankcase and transfer block above the mounting lugs. The cylinder fins are of a larger diameter to fit the larger bore liner

On this example (unlike my R18) the cylinder head does not screw right down to the transfer block and the amount of contra piston left proud of the liner can be clearly seen in one of the pictures, hence the need for the guide spigot into the head. There is no serial No. on this engine although Fisher mentions that his had one

Test Run

For testing, I used an 11x6 plastic prop (nearest I had to the 12x5 recommended). In order to get sufficient compression to run the engine on standard diesel fuel (1/3 ether/kerosene/castor) it was necessary to insert a spacer .030" thick above the contra piston. With this in place the compression was gradually increased and the engine choked about four turns with the needle valve open three turns until it �popped�. The compression was increased another quarter turn and the engine started; then with the usual adjustments, it was soon running evenly and well. I measured 6,500 RPM but I was not really trying for the maximum as the engine was running quite hot. The needle needs to be open much more than the R18.

Comment

A very nice handling engine, easy to start and not fussy on the control adjustment. With the increased compression the contra piston is still approximately 1/16" out of the liner, so why use a high ether fuel and have the contra piston even further out? The contra piston was free to move hot or cold.

In my opinion, the R-30 is a much more handsome engine than the R-18 due to its better proportions. The fuel tank assembly is also more suited in size to this larger engine. Obviously as many parts as possible were used in common between the two engines to keep costs down, but why the R-18 crankcase was sand cast while this one die cast is a question that will never be answered. Perhaps they changed during the production run.

The power output of the R-30 was better according to the makers figures presumably as a result of the nearer to �square� bore/stroke ratio. On this one the transfer block joint did not leak unlike the R-18.

 


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