R975 Radial engines

[Don Phillips]

A drawing of the bolt Bob had supplied dimensions for and an idea for making one from an ASTM F835 bolt. 120K PSI

[Bob Phillips]

Thanks Tony for the link to the ARP catalogue. Do they ever make NICE bolts and fasteners. I will try to get a quote from them on the costs of making some crankshaft bolts of the type we have been discussing. Meanwhile just waiting for some capscrews from Mcmaster-Carr to see if something useable can be put together at home. Will share the results when done.
I wanted to respond to Dan comments on the care and feeding of the C4 engine in his M18(post118). Now Dan has a really beautiful M18 and has had a hand in other high end, high quality restorations as well. When I was contemplating purchasing armour a decade ago he is one of the people I turned to for an opinion about the pros and cons of such an investment. In short, I value his opinion. Dan's M18 feeding regime is more of the champaine and caviar approach than the meat and potatoes, but as an owner operator he knows more about the need to pamper a 75 year old vehicle and its increasingly rare engine, than most people do. Aside from the higher costs of using AV gas and aviation oils I don't see how this could be an issue. In fairness, several years ago when I was anxious to start up and run both C1 and -46 engines I asked a US radial engine builder that I had known for many years, about fuel choices. His recommendation for both was to use the best pump gas you could get. That mean 91-93 octane but NO ALCOHOL.
In my current fleet of gas burning machines I run the regular slop only in a couple of daily drivers. Everything else;jeeps, trucks, lawn mowers, chainsaws, wood splitters, generators and my 4.2 L Jaguar ALL use no lead, high test fuel. I have had absolutely no fuel issues since I switched to high test. With respect to oil, Jaguar forums recommend the very best grade of synthetic oil you can find. So why not the best for your radial? Finally, at some point in the past I also recall Dan's recommendation to get oil tested for metal content from time to time as a way of preventative maintenance. Big rig owners do this all the time to diagnose the condition their engines are in and hopefully head off major problems before they can occur. Sounds like a very reasonable and prudent recommendation to me. So thanks to Dan for his input and first hand experiences in running his M18!

[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.