So for now, we are locked down for covid 19and it gives me the opportunity to stay home and get a few things done. One thing I have done is start rooting through some old magazines I have collected and I want to share some of the information I found with the forum. From the publication "Warbirds International", May 2000. There is a very interesting article about what kind of oil to use in large, hard working radial engined aircraft used to fight California wild fires. The main point of the article is that the California Dept of Agriculture decided to change the type of oil used in large radials ( like 1500HP Wright 2800s) from single grade 120 weight aviation oils to Phillips 25w-60 multigrade olis ( sorry no family connection!) the maintenance team reported " a decrease of 35-50% in oil consumption and a noticeable decrease in both cylinder head and oil temperature" . They indicated the multigrade oil offered better protection of the master rod bearings than did single weight oil.
With respect to diagnostics on the engines .."the biggest problem indicator had been metal in the oil screen..usually from main bearing failure" Further.." the type of metal found will give a good idea of whats going on in the engine and whether it needs to be pulled for preventive maintenance...if we find aluminium..its either from a scuffing piston or the blower rubbing on the ..case...if its brass or bronze it's most likely from the bushing ..inside the nose case or ..accessory gears..But if its silver, it's either from the master rod bearing or from the cam bearing- the only two engine parts that have silver.." Very useful diagnostic information, though I am not sure that our 975s have any silver bearings in them!
There is a final comment about the fuel used. " We used to use 115-145 octane fuel...(high lead) now, 100 octane low lead aviation fuel..this effectively drops horse power from 1525 to down to 1475.." but mechanics compensate somewhat for this fuel change by changing the spark advance from 25 to 20 degrees..". They claim the toll of damaged engines is typically about 3 per season, but there were no failures the season they started to use multigrade fuels. So fuel and oil quality clearly matter!
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