The Treatment of the BMW 801D-2 Radial Aero Engine Rescued From the Loiret River.

Engine Stand

An engine stand was constructed of box section mild steel. This was designed to hold the engine in the most appropriate position for placement in the treatment tank, keeping dimensions and volumes to a minimum. The devised treatment method called for the engine to remain on the stand during the entire treatment. Large lifting eyes were included in the design so that at no time would the hoist cables be in contact with treatment solutions.

Treatment Tank

A tank of mild steel sheet and box section reinforcing was designed and purpose built for this treatment (fig. 7.). The outside of the tank was protected with a coating of zinc anti-corrosion paint over which was applied several layers of outdoor gloss enamel.

Figure 7: Treatment tank showing the stainless steel anode and the PVC frame and flooring.

No surface treatment of the inside of the tank was undertaken other than descaling and degreasing. The rationale for this was that the base of the tank is isolated from the engine stand using rigid 7 mm PVC sheeting and the light gauge stainless steel mesh (the anode) is isolated from the walls of the tank by means of a frame constructed of 40 and 50 mm PVC tubing (fig.7.).

During the electrochemical process the tank is independently cathodically protected using an applied voltage. This was intended to prevent the dissolution of ferrous ions from the surface of the tank which would interfere with the chemical reactions. Further, the tank surface itself is protected from corrosion.


The structure of the engine was examined using sophisticated industrial X-radiographic equipment known as MINAC. This miniaturised system allows penetration of approximately 1 metre of concrete and can generate 4 MeV of power.

As several cylinders of the engine had become detached due to the impact of the crash, it was decided that a comprehensive structural examination was required. Cracks and breaks held together by only corrosion products, if present, could cause complications during the treatment process. The examination revealed however, that all major structural components were intact.

Internal Examination

An endoscopic examination of the inside of the engine was conducted to ascertain as to whether it was visually apparent that the corrosion products present inside the engine were of similar nature to those present on the outside. It should be noted that the engine was recovered from deep mud in which it had been “embedded” for some forty five years. Thus, it was possible that certain chemicals such as fuel, oil and combustion products sealed within the engine, may have initiated different chemical reaction paths. The examination was videotaped for subsequent detailed inspection. Results indicated that no unexpected reactions had taken place. Some signs of original lubricants were present, although none was sampled.


Any treatment of a composite object must be based on the results obtained from the detailed analysis of the various alloys, corrosion products and other materials which comprise the object. Analytical investigations were undertaken in which metal samples were examined by x-ray fluorescence spectroscopy and corrosion products were examined by x-ray diffraction analysis. Electron microscopy with Energy Dispersive Xray Analysis was also used to examine some samples. Due to the limitations of time and access to analytical facilities however, more comprehensive investigations could have been completed.

Of most interest to note was that no Al-Cu alloy appeared to be present (unlike the Pratt and Whitney engine). The composition of the cylinder head air-flow baffles was quite unusual, being an Al-Si alloy which was in very good condition. Inlet pipes are of almost pure aluminium, being comparable to the modern 2000 series designation. Significant amounts of magnesium corrosion products were also present, together with a small amount of residual magnesium alloy metal.

It was also apparent that a number of aluminium components manifested various applied surface treatments. Some wrought sheet appears to be covered with a chromate conversion coating and other intricate components appear to be anodised. These all appeared to be in remarkably good condition. Preliminary analytical investigations (Appendix 1) indeed indicated the presence of chromium but more sophisticated analytical techniques are required to distinguish the true nature of these coatings.

Examination of Organic Material.

Figure 8: Some of the components which appear to be anodised. Materials present on the engine include a semi-rigid plastic wrapping for electrical cables (fig. 8), reinforced rubber oil hose (fig. 9) and O ring gasket seals all in varying degrees of degradation. Although an infrared spectrum of the plastic material was obtained (Appendix 2) using a Perkin Elmer 1750 FTIP, at the time of publication, no further analysis has been undertaken to characterise these. Figure 9: Semi rigid plastic wrapping material.
anodised components
wrapping material

Test Treatments

Two parts of the engine, which have become separated from the bulk, a piston and an air-cleaner, were selected as specimens to be used to test the effectiveness of ultrasonic agitation during the treatment (fig. 10). A 12 litre “Sonoclean” ultrasonic bath was used during a pretreatment in a citric acid solution buffered to pH 5.4.

Fig. 10: Items which had become detached from the engine, used to test the effectiveness of ultrasonic agitation --- a piston and an air cleaner.
air cleaner

PH was monitored, as was the nature and appearance of the concretions and corrosion products. For example, after 4 days of treatment of the aircleaner most encrustations became quite soft, changing from solid to mud-like consistency, which could be easily removed. Interestingly, the pH of the solution rose from pH 5.41 to 8.61 probably due to the dissolution of ferrous ions. At this point the treatment was discontinued and the object thoroughly washed and dried.

These results proved most satisfactory. As with the Australian project, the usefulness of the technique was demonstrated. The high cost of an ultrasonic unit of sufficient size and power to be effective in the treatment of the engine as a whole proved to be inhibitive.

Abstract Introduction Perspective History FW190 BMW engine
Preparation Plan Treatment Conclusions Bibliography Appendices

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