R975 Radial engines

David Herbert · #1 24-12-20, 13:07

Lynn,
No indication of tensile strength. The description of the bolts is just that, not a full specification. "Alloy Steel" is the hint that these are not low grade material but that is not much help. Somewhere there will be a full specification of both the exact alloy and the properties required of the finished bolt but finding it will be a challenge. It might be possible to have a bolt analyzed but while real ones are still to be found it is cheaper to use them and be extra careful with torquing them up.
My personal opinion is that the failures are fatigue failures caused by the bolts flexing over a long period and not that they acted as a safety device. This could be due to them being wrongly torqued when the engine is built up (allowing a small angular movement of the gear) or that they were not really suitable for the constantly changing engine speed in an AFV and that this was not addressed until the '46' version. I wonder if one could fit a '46' crank and gear into a C4 ?

Dan,
I would strongly advise that one gives the engine some gas when downshifting, just as you would with a manual transmission. This is not a fully auto transmission, just easier than a manual - the driver has to help !

I agree with your views regarding fuel. You don't need the extra octane rating of AV gas but it will do no harm other than to your wallet. The ethanol content is certainly relevant though and I think that you have made a good call.

Have a safe Christmas everyone
David

Bob Phillips · #2 24-12-20, 15:23

Thanks again for all the comments and input. Dave and Lynn, I think the current rating for tensile strength in grade 8 bolts is 150KSI ( 150,000 pounds per square inch) vs 120 KSI for grade 5. Regardless of the actual value I am sure you would agree that modern high grade bolts would be preferable to the original and now stressed and aged bolts. I think that C4 ( and C1) owners should expect to replace these bolts at any point when they have their engine apart for overhaul or repair.
I have thought about trying to use the -46 improvements on the older style crank, indeed it may well be possible to simply use the rear of a -46 crank on the front of a C1 or C4. The issue I think may be one of correctly balancing miss matched parts, cranks, pistons etc. This is something outside my experience but as I have extra -46 cranks it may happen some day. Maybe this would be a good point of discussion for a future post.
Dan, thanks for your kind comments about this thread. There are not many places you will find informed discussion about 975s, and the goal is to keep as many of these fine old engines alive and running. You are also correct about my old C4- I take satisfaction in knowing it went to a good home.
Your comments about proactive measures to keep these engines alive and well ( high grade fuel, higher idling speeds etc) are right on. While radials are high maintenance powerplants there is nothing better than the sound of one starting up, with its coughing, belching and smoke. You gotta love it!
Best wishes to everyone for the Christmas season!

Bob Phillips · #3 25-12-20, 14:57

Here are dimensions for crankshaft bolts. If anyone has a source for 5/16 tapered washers please advise otherwise you may have to modify conventional cap screws or custom machine.
bolt3.jpg

Tony Smith · #4 26-12-20, 00:23

There is a company that makes high quality bolts, nuts and studs for performance cars and racing teams, which is also highly sought after by the aftermarket hot rod and muscle car industry:

https://arp-bolts.com/

On page 21 of their catalog (top right of the home page), they list the requirements for custom dimensioned bolts and studs. ARP are NOT hardware priced bolts and fasteners, but they are reasonably priced for the high quality items they are.

https://arpcatalog.com/20/

Don Phillips · #5 30-12-20, 21:16

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 · #6 04-01-21, 20:40

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 · #7 05-01-21, 00:54

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!!!