Were surviving early Merlins rebuilt and upgraded?

[Engineman]

FWIW

In my notes (from sometime in the mid-1990s) I have the Merlin 266P and Merlin 69 carburetters being problematic, and the problem carburetters subsequently replaced with the same carburetter as used on the Merlin 266 and Merlin 66.

Yes, The Bendix Stromberg Injection PD18 carbs came with AUTO-RICH and AUTO-LEAN mixture options. I have read reports about them being problematic and, later fighter versions got a simplified single RUN setting for the Mixture control selector. The precise examples of which model PD18 Injection carbs were fitted by Packard to the new Merlin 69 and 266 or 266P engines that were modified in the UK is not known by me but, Rolls Royce modified the PD18 and called it the 8D/44/1 for the RR built Merlin 66 and the Merlin 266 version fitted to the Spitfire LF. 16. My guess would be that the Spitfire LF. 16 Packard built engines arrived in the UK with the PD18 carbs and there was a modification programme that cycled them through and refitted them as the 8D/44/1 for the Spitfire LF. 16. Quite what happened in the UK with RAF Merlin Mustangs and their engines/carbs, I am not certain.

Eng

 

[Engineman]

Hi again,

I have done a little more digging and found more information about the carburation development of the later Merlin 60-series engines with the Bendix Stromberg Injection carburettor adaptations. During RR development towards the Merlin 66 for the Spitfire Mk IX, RR found that it was advantageous to use the larger bore Stromberg carburettor, the PD 18, and had to advise Packard that they should use the larger PD 18 rather than the smaller PD 16 as previously used on the Packard Merlin 28, the larger carb having chokes 0.5 inch larger dia.
It would seem that RR worked with the PD 18 A-1 or PD 18 B-1 and that formed the basis of their modified 8D/44/1 designation for the modified Merlin 66 Stromberg injection carb.
A little later, RR were working with the early versions of the Mustang III with the Packard V-1650-3 engines fitted with the PD 18 A-1. David Birch wrote in the RRHT book Rolls-Royce and the Mustang, on page 75, that it was discovered that the engine would not run in Auto rich in FS gear etc! However, testing showed that Auto lean gave very satisfactory results and that the modification of the Mixture control to only allow Auto lean made the carburation operational (at that time).
Further details in the 1944 American Service Instructions for the V-1650-3, -7 and Merlin 68 and 69 engines are interesting. This detailed document lists the V-1650-3,-7 engines as fitted with the PD-18A1 and the Packard built Merlin 68, 69 engines built with the PD-18B1. The A-1 is listed as having all the mixture settings, Idle cut-off, Auto lean, Auto rich and Full rich,
the B-1 is listed as being limited to just 2 positions, Idle cut-off and Running.
So, overall, there are a lot of details in these carburation differences. Certainly, it would be interesting to find further details about the RR modifications to the standard 8D/44/1 that was developed to suit the Merlin 66.

Eng