R975 Radial engines

[daninnm]

Thanks for the kind words Bob! When the machine is as valuable as they have gotten - I can see no reason to cut corners; saving a few bucks makes no sense in my way of thinking if the risk (however small) is damaging a rare and a hard to replace machine. So far my engine oil analysis is showing no metal being 'made' and it only costs $18 to get the results!!!

[Bob Phillips]

And so, here is the prototype crankshaft bolt in grade 5.
crankboltdon.jpg

[Bob Phillips]

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!

[Bob Phillips]

Here are some inspiring photos for radial engine fans ! From the book " Making Waves... Navy Women of WW2" Looks like P&W engines.

airgirls1.jpg airgirls2.jpg

[Bob Phillips]

Just a follow up on the discussion of suitable fuel grades for the 975. I have exchanged emails with retired engine builder and instructor Tom Henderson from down under. Tom owns and operates a beautifully restored C1 that he demonstrates at shows and events from time to time. He has been kind enough to respond in detail to a variety of newbie questions about fuels, oils, compression ratios and ring types and I really appreciate his patience! Tom tells me he is running 92 octane no alcohol fuel in his engine. He thinks this is a good compromise between lower alcohol infused fuels and higher aircraft oriented gas. While the dangers of using too low a grade of fuel in a higher compression engine are well known, there may also be consequences for running too high a grade as well. This may include elevated chamber temps and burnt valves for little gain in performance or economy. He also runs a semi synthetic 20-40 diesel oil which has better anti corrosion additives and detergents to try and offset corrosion in an engine that only runs occasionally. Cylinder temps (#1)! are about 400 degrees which are well within the acceptable range.
Another interesting thing Tom pointed out is that an aircraft engine runs a cam where there is higher cam lift and more overlap of valve opening, a cam which favors higher speed operation and which idles poorly, hence limiting their use in a land vehicle engine. Hmm, I wonder if I could get some -46 cams reground to C1-C4 specs? In this day and age it is unlikely that any of the 975 engines would get the abuse and hours of a vehicle actually involved in conflict. Hopefully with care and routine maintenance, a radial engine should run, for shows and events, for many years without major problems.

[Bob Phillips]

Here are the comparisons of a -46 cam on the left and a C1 cam on the right.You can clearly see the difference in the lobes. The closest lobes are for the intake valves and not surprisingly, the -46 has a lot more air/gas valve inlet time!
cams.jpg

[David Herbert]

Bob,
I know that C4 and C1 had different superchargers to each other but I thought that the cams were different too ?

David