Going back to Bob's question in his post #21 about common failures in R975s, another one that I have come across more than once is that the eight small high tensile screws, that bolt the gear onto the rear section of the crank, fail and there is then no drive to anything on the back of the engine. This usually does not result in any seccondary damage, just a dead engine. It is a huge amount of work to replace them but doable by a competent person who reads the TM and can work very carefully.

This failure is easy to check for as nothing on the back of the engine goes round when the engine is turned by the fan. Also of course the starter does not turn the engine either.

David

975-46
 

Here is a picture of the gear (#9) from the -46 book, hope you can see it.
Attachment 102485

Rebuilding an R975 is not for the faint of heart, nor is it for one with little mechanical ability. Even though I was novice in radial engines, I had 30 plus years of mechanical, electronics training and experience. Using that experience, I CAUTIOUSLY undertook the project. I spent hundreds of hours reading every bit of information about the engine I could find. Read the manuals until you completely understand everything BEFORE you start the project; almost to the point you have them memorized. Measure EVERY part. Make sure EVERY part is serviceable, and clean. That includes every part of the accessories. The work area has to be spotless and dustless. Does that seem like a lot? It is. I would say a successful conclusion to a project like that requires a passion. No weekend warriors are going to do it. It was a privilege for me to be able to take on a radial rebuild. A once in a lifetime event.

Gotta disagree, Jesse. As far as I know, those holes are to reduce axial load on the pump, or in this case supercharger, bearings.
What can cause oil getting sucked in past the shaft seal on an overhung impeller design like this is having the impeller back shroud too close to the supercharger rear housing. The tight gap between the shroud and casing causes a pumping effect which can reduce the pressure down at the shaft below atmospheric.

Malcolm

975-46
 

So Rob, what do you know about the history of your radial? Was it installed as a govt rebuild or rebuilt by the previous owner? It is safe to assume that if someone stripped off the mags and wiring it had electrical issues ? If it has not suffered a catastrophic failure ( blown cylinder, broken piston, thrown rod, master rod fail etc) it may be a straight forward fix. Look forward to hearing more! Thanks for the comments and great pics Jesse!

We acquired a Sexton a few years ago and I pulled the R975 out of it and dismantled it. It was a total write-off, 5 of the 9 rods snapped. So the engine is quite an impressive static display in our museum now.

I would agree with Jesse. There's is nothing particularly high tech or mysterious about the design. But you would have to be SO careful with reassembly. I regret I didn't have the opportunity.

Malcolm

I am unsure as to the actual failure...too many rumours over the years to be sure. It was Bill Gregg's Sexton which came to the museum in the latter half of the 80s. At that time, there were a lot of artillery guys involved in the museum, and one story I heard was that the engine would not turn over so they tried to pull start it. If there was a hydrostatic lock, it could be bad. I came to the museum full time about 4 years ago now, and it is one of the many "taken apart" projects that I inherited. I think I have located the majority of the parts now, as they tend to move around much like the tide moves a piece of deadwood.

I have been warned before about these radials to read the manual twice, and if I think I got it, read it a third time. I am pretty sure it is one of those projects that, when the time comes, I will have to immerse myself in it. In the meantime, there are still many other vehicles, some operable and some not, that change the priorities of work. I have also warned my boss that whatever this engine does need, it will not be cheap.

The grizzly sitting next to it is in the same boat....too many years passed form the time it was operating. I heard a story form someone who was apparently visiting the museum almost 30 years ago that the museum was giving rides in it and the front end packed it in. Again, I can't be certain as I have been too busy to start diagnosing it. Summers are extremely full here between public displays and parades, sandblasting and painting, etc.

I am hoping that when my day comes to leave the museum, I am not leaving a bunch of torn apart stuff for the next guy.

Jessie, A tip of the hat for that rebuild. You have shown it can be done. Worked on radials at an aircraft engine shop. Here's a similar P&W R-985 on a test run. For anyone doing a rebuild for their MV..Get yourself a good quality torque wrench and follow the torque setting to the pound. The engine is held together with steel studs threaded into aluminum alloy..Really easy to over-torque and weaken the holding strength. Under-torquing allows bits and pieces to "squirm" into the soft alloy. Aircraft style engines are notorious for shock load damage...If a propellor strikes the ground...the whole engine has to be taken apart and inspected. That's why Dumping the Clutch in a radial powered AFV is a no-no. The engine is not capable of absorbing that sudden impact....

975-46
 

So in side that soft, squirmy aluminium case ( as Dennis put it ) there is a big heavy lump of steel rotating. The crankshafts for C1, C4 and -46 are similar the most obvious difference being their length. From the front counterweight a C1 and C4 crank sticks out about 11.5 inches. The -46 aircraft crank sticks out about 16 inches. I do not have an earlier Weight aircraft crankshaft to measure but I think it would about the same length as the -46. There is another important difference. Pleaser look at the (hopefully) attached photos. Two pictures compare a C1 crank to a -46 crank, while the third picture is a C4 crankshaft. There are two bearings on the shaft inside the nose case of these radials.
Note that the shorter C1 crankshaft (like Wright aircraft engines) have both bearings retained by a nut on threads cut into the shaft. If you look closely at the top view you can see the thin nut next to the bearing on the C1 crank. Note that the -46 crankshaft does not have this threaded portion to retain the inner bearing. You can see on the photo of the C4 crankshaft that the inner bearing is held in place by a sleeve which is pushed in place by the outer bearing and held by the outer bearing nut. Now could some of the metal wizards in this forum rework a -46 crankshaft into an ultra rare C4 crankshaft, your comments always appreciated!

Attachment 102602 Attachment 102603 Attachment 102604

Bob, You are very correct about the crank. Big chunk of rapidly rotating steel. Replacing the main crank bearing involved splitting the main crank. Then after measuring/grinding the main bearing surface to tolerance...a new main bearing was installed. The crank assembly was frozen in the freezer overnight...and the bearing slowly heated in the oven..Crank small...bearing large...You had one chance to get it on straight.

The Spider plate on the crank....is the lower pivot for each piston rod.

R975-ec1
 

Ex Grant Tank

Attachment 102605 Attachment 102606

975-46
 

Hi Des
Any idea about what caused this failure?

Failure !
 

Hi Bob - no it happened many yrs ago - was used for land clearing in Victoria - tank has been recovered. Motor sold to UK with NOS crankshaft

This link has some photos of the catastrophic failure of the engine in our Sexton and some suggestions as to what happened.

http://www.mapleleafup.net/forums/sh...t=21552&page=2

Malcolm

Here's a cross section of the C1 crankshaft that may shed some light on where stuff is located on the photos above.
Any machinist that was asked to convert a -46 crankshaft to a C1 or C4 would need a sample of each to see if it was feasible, I figure. Not to mention when the surface hardening was done.

Malcolm

Attachment 102611

Malcolm Towrie Having worked on engines like this...I would say this was a Prop Strike.... Dump the Clutch ...sort of incident. If it was engine oil trapped in the lower cylinders...we would have seen seen bent rods...And there are none. Unusual to have the balance end of the crank be broken off like that.

975-46
 

I am inclined to agree- must have been quite a shock!

Just for fun...

Gary Corns Radial Powered Plymouth truck...

Attachment 102695

I know its only 7 cylinders...but still have to give the guy some credit for thinking outside the box a bit!

Very interesting but kinda ugly, John, unless you're into the steam punk look.
No shrouding on the cylinders and no sign of the huge fan on the tank engines so how's he going to cool it, especially the lower 3 cylinders?
And try ordering at Timmy's.

Malcolm

I will go with you there Malcolm, it's not green and has no tracks...so besides some kind of engineering exercise seems like money wasted to me...and as for the Timmys drive thru I have begun a petition to widen those damn approaches and raise the menu board to commanders cupola height as tank drivers can never get even the simplest coffee order correct

My exact thought too. How the heck does he cool it....? Looked it up. Short answer is ..no cooling. Gary Corns says he runs it about 10 to 15 minutes. Before it gets too hot and he shut's it down. It's a Showboat..

John,
Got many (any) signatures yet??
Malcolm

They did a real interesting feature on an episode of Jay Leno's Garage on the truck, and you're right Dennis just an engineering exercise, no real function to it

I apologize to Bob for sending his very interesting and informative thread off a cliff



(PS: so far just one signature Malcolm, driver claims I have insulted his cognitive ability...)

Meanwhile, back to the thread. Here's the helicopter version of the engine, as talked about earlier. Continental R-975-46A being field changed in RCN HUP-3 "946" in the High Arctic. Summer 1955 transit of northern waters from BC to the Maritimes. Flew off #50 Labrador as part of proving trials to see if helicopters could be deployed on smaller sized ships. This lead to the invention of the the "Bear Trap" and successful deployment of the Sea King helicopters on RCN destroyers. Larry Zibitnew RCN Archives. (Go Navy)...grin...

Oops...obviously 246..

975-46
 

Great pictures Dennis!
can you imagine having to change an engine with equipment shown... lots of fun! Just like winter camping.
I believe one of these helicopters resides in an aviation museum near Ottawa.
Tims comments always welcome!

I wonder where they got the very long ladder from ? Too long to be needed locally or on the ship and even to transport easily. Very nice set of photos though Dennis.

David

975-46
 

Not only great pics but when you look closely...
in photos 2&3 you can see that an engine cooling shroud ( just like a tank engine) has been removed from the original engine and fitted onto the replacement in the can. This makes sense in this application where there is no propeller slipostream to cool the engine. Perhaps with a clutch assembly it could run a vehicle??
Also, in the background the original engine is stripped of its exhaust and mounts which will be refitted to the replacement.
Good point about the ladder in a land with no trees!

Just curious, was the engine installed with the crank in the normal horizontal orientation? Those photos give me the impression it might have been installed with the crank vertical, which would make me curious about oil scavenging and carb type.
Malcolm