From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Issues with aluminum cylinder heads based on the experience of a Mack Truck Service Station.
| Identifier | ExFiles\Box 14\3\ Scan046 | |
| Date | 25th September 1929 | |
| COPY. September 25, 1929. TO: Mr. Olley (England) CC. Mr. Beaver Mr. Ainsworth. Mr. Burton. Mr. Ross. FROM: Mr. Allen. RE: ALUMINUM CYLINDER HEAD. On Tuesday, while in Long Island, I visited the Mack Truck Service Station and discussed with Mr.-----, the manager, the question of aluminum cylinder heads. He told me their experience with the aluminum head was a sad one and after struggling with the job for a considerable time and spending a lot of money they had finally given it up as unpractical. In an endeavor to use up some heads which they have on hand, machined, they are still putting aluminum on fire trucks on the theory that the job is subjected to little abuse and is well looked after. When the present supply is exhausted they will use cast iron even on fire equipment. They had trouble with the heads cracking through unequal expansion. Cold water carelessly poured into a hot motor and freezing were responsible for the majority of such failures. After the motor had been in operation a short time sludge formed in the head. In open pockets, this sludge became quite heavy while in restricted sections where the water was moving rapidly it was, naturally, thin. The variable insulation of the sludge, plus the high co-efficient of the aluminum, under the action of a sudden chill, resulted in cracks. The aluminum head would crack under a slight freezing which would not bother cast iron. They had trouble keeping the head tight. If the nuts were pulled down tightly the head would crack and if tightened with less pressure, by means of a ratchet wrench, it would only be a matter of a few days before leakage occurred around the gasket. In an endeavor to resist corrosion to a maximum they used a silicon-copper-aluminum alloy which does not have as high physical properties as the straight 8% copper-aluminum alloy which we are using. The low elastic limit on their material, plus the fact that it was bolted directly to cast iron, was probably responsible for most of this trouble. They also had trouble with high valves. The seats, which were made of aluminum-bronze, would hammer down into the casting and work loose. With the aluminum head the valves have to be adjusted at possibly 2,000 miles whereas with the cast iron head they expect the valves to stay put for 25 or 30,000 miles. Contd:-- | ||