Sexton R975-C1 a mess
 

At the Oshawa military museum, we got the front covers off a sadly neglected R975-C1 out of the Sexton. We were expecting pistons rusted into bores but it was much worse. 5 of the 8 articulated rods are broken at the big ends (which, to my surprise, are actually the small ends because the knuckle pins are much smaller diameter than the wrist pins). The master rod bearing is also toast with about 1/16" clearance.

A number of pistons are all smashed up and each broken rod smacked the bottom of its liner on both sides as it was thrashing around so that the liner is mushroomed out, making it a pain to pull the jugs. The crank is a mess but surprisingly the crankcase looks intact.

Very disappointing. It probably makes a rebuild out of the question as we need a complete rotating assembly and probably 9 jugs. It's probably best to part it out and install a Detroit diesel to make the old girl mobile again.

Malcolm (using Cliff's sign-on)

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Malcolm,

That looks like serious damage, but for the C1 especially many spares can still be had. Maybe you spend more on the overhaul of the R975 than on a used diesel (ugh!), but you will save a lot in not having to convert the Sexton for the other engine to fit in. You will need to make engine mounts, cooling system, and change fire wall, prop shaft, fuel system etc. etc. - this is a huge job!

If I were you I would try to source the parts for the radial and find an aircraft / engine mechanics school and ask them to do the overhaul as a teaching project. I'm sure the students will like the ride in the Sexton afterwards!

Hanno

It might also be worth checking the aviation market for a complete engine that has reached the point of being too expensive to rebuilt for flight purposes, but will spec out just fine for a land vehicle.


David

I would recommend you talk to Carl Brown of C&C Military in England, great guy to deal with and tons of radial and Sexton experience and probably parts, if not complete engines. Hanno is right, converting to a liquid cooled diesel would be on par with simply replacing the radial. You could also try Andy Sanclamente at Northeast Military Vehicle Services near Boston, another great guy with lots of radial experience. I am pretty sure he is not currently doing restorations or rebuilds but he would still know where to find what you will need.

John

Bob Phillips, and Staman Trading had lots of parts for the C1's. Radial parts in general are getting hard to purchase (notice I said "purchase", there are parts out there, but collectors have been stocking up).
Converting to a more modern engine is doable. About the only diesel that will fit (and give you decent power) without modifying the hull is a 6V53 Detroit, about 300 HP with a turbo. You can use the original drive shaft, rear engine mounts, and clutch linkage. You will need a custom built rad, custom front engine mount, electric fans, No. 2 bell housing, flywheel, clutch and numerous linkages built. This will all fit in quite nicely, but will require many hours of machining and fabricating

So I sense some disapproval of the diesel swap. :) It's not our choice either, but I understand funds are a bit limited for what may be a $10-15,000 repair based on some prices presently on the North East Military site (and $23,000 for a C4 engine).

We have spare Detroit diesels here (although I need to confirm if any are 6V53's, Perry) and it sounds like a very interesting project to me. I really enjoy the design/fabrication stuff.

Anyway, I am working full time at a "real" job right now, but retiring in April so I will have more time then to follow up on the leads you all gave me above. In the meantime, we will continue dismantling to find out the full extent of the damage.

Malcolm,

It's not so much disapproval, we're just trying to change your mind.... Seriously, for a museum piece I believe one should try to keep it in it's original configuration. Frankly, the fact that you enjoy the design/fabrication stuff cannot be a decisive factor in the decision to fit it with a diesel. Unless the Sexton is your own, that is - you could even paint it pink :D
I think there are several options to repair or replace the radial nearer to the museum than having to go to the US or UK - please ask Cliff to check his PMs.

Good luck with your endeavours and I hope you get this Sexton running again.

Regards,
Hanno

I hope to come get it, I do not write very well the English, when there is no money for major repairs and always a problem and I appreciate the honesty, and I think a diesel is really the last cartridge to shoot the tank in question it is a important part of history, give an example, it's like putting on a ferrari GTO of 1956, the engine of a alfaromeo , lose all the historical and monetary value
louis

You might want to touch base with Wright Museum
 

Hi Malcolm

You might want to touch base with the Wright Museum in Wolfboro, NH http://www.wrightmuseum.org/. They have had the misfortune of blowing the radial in their Sherman twice. They may be able to provide some information and what to avoid. They have a complete Ford GAA they could put in but want to keep the correct radial. In there search for parts maybe they have come across the parts your engine needs.

Cheers Phil

OK, we'll do our best to get the R975 running again! I'm a very junior member at the museum (in fact I'm not a member yet, I just put in the application form) but what we can do is identify what needs to be repaired/replaced, source and price the parts needed, and make a case to the museum executive.
And we will NOT be farming out the rebuild! This is an in-house project (although a call to the Wright Museum seems like a good idea.:))

That thing must have made an awful clattering noise when it breathed its last. Talk about a catsarsetrophy.
It would be very interesting to know why it failed.

David

Actually they make a great deal of noise when they are running well ! This is partly because the exhaust manifolds are thin sheet metal and leak at the joints so the exhaust noise is very loud, also there is a balance weight free to float on the crank which rattles at low revs anyway. The reasion that so many radials fail in the hands of inexperienced operators is that they will idle smoothly at 500rpm and this makes driving them in close spaces much nicer.

However there is a reasion that the book tells you to never idle below 800rpm and even then not for long. That is that the oil pressure at the big end is mostly generated by centrifugal force in the drilling to that bearing from the main bearing. At low revs: not enough oil, bearing dies, lots of clearance, bearing rattles, con rods break, scrap engine. This engine is derived from an aircraft engine which spends its whole life at maximum revs, so it is not a problem. In tanks it was not a problem either as a driver abusing his engine could be put on a charge and had recieved proper training anyway. However most restored tanks are driven by people who have not read the book and in any case think they know better! It is NOT a car engine !!

There is another common failure that just stops the engine. That is that all the accessories on the back of the engine are driven from one gear that is screwed onto the end of the crankshaft by a number of socket head screws. These sometimes decide to all shear at once and the engine stops. It is a huge amount of work to fix but usually only requires replacement of the screws.

The parts are out there but people are asking a lot of money these days, good luck with the rebuild.

David

Interesting info, David. Thanks.

I see the manual specifies minimum 30 psi at 800 rpm immediately after a cold start. That's pretty low for a cold oil pressure. With hot oil I could see that dropping to 10 psi, and even lower at 500 rpm. That's not much to keep the big ends floating on the pins, especially if the engine is loaded.

Hard to say which domino fell first, but one guess based on the badly worn master rod big end is the master rod brg clearance increased to the point the end leakage starved the articulated rod bearings and they started seizing on the pins. The rods that broke all broke by tearing the big end apart, which looks very thin-walled and weak to me. But I'm not used to engines with 5.7:1 CR and 2400 rpm redline.

The crank feels looser than it should in the rear main bearing so another possibility is that it wore out and starved all the rod bearings.

The 30psi at 800rpm is the oil pressure generated by the pump. There is almost no pressure resulting from the pump actually at the big end. The pump gets it to the main bearing, from there it makes its way by centrifugal force. Even at 800rpm big end lubrication is marginal.

You must remember that this engine was designed to be started, warmed up in a very controlled way (1200rpm) and then run at max revs for the rest of the day. If allowed to idle at 500rpm it will destroy itself! There is no oil supply to either end of the slave con rods, they are lubricated only by splash. As there is quite a small angular movement in the joints between the master conrod and the slave conrods that is ok but they can not withstand the hammer action that results from huge play in the big end bearing. The damage you show was not caused by general wear, it was caused by idling at too low a speed.

Incidentaly the low compression ratio is effectively doubled by the action of the supercharger above about 1500rpm which is how it manages to make nearly 400hp.

You will have to completely dismantle the engine to make sure there is no swarf anywhere and to check / replace bearings that have been damaged.

Have fun, David

Malcolm
 

Somewhere here in town, there is a junk yard I have been passed so many times I have tuned it out at the moment, but it has had one of these engines leaning against a wall or fence in their yard for decades. It might have been the old Princess Auto yard, or a place across the street. If it comes to me shortly, I will let you know.

While it is in my mind, although Wright was the original company that designed this engine series as the R975, the same engine was also built under licence by Continental as the Continental R9-A and in Spain by Hispano-Suiza as the Hispano-Suiza 9Q, so lots of parts by various makers are out there.

In North America, the engine was used extensively by both Beechcraft and Cessna, so you may want to check their local dealerships for information as well.


David

It strikes me that the oil passing from the main bearing into the hollow crankshaft is having to fight against centrifugal force, although after that centrifugal force is certainly helping it get to the master rod brg.

Certainly - with a hot oil idle pressure maybe around 10 psi and weak centrifugal force, I can see that.

The attached extract from the C1 manual below shows passages for force feeding oil from the master rod bearing to the slave rod big end bearings.

Do you know what the boost is above 1500 rpm? The doubling of the compression ratio infers it is 10-15 psi. It seems such a small impeller for such a large engine, even with the 10.15:1 gearing.

We will be. And that brings up another problem - finding space for and keeping track of the parts!

We will. :)

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Sorry LRDG, I was wrong about the oil supply to the slave rods,I should have looked it up like you did ! And yes, I should have said 'greatly increased' rather than 'doubled' when trying to stress the value of the supercharger. The C4 had a different supercharger impeller and ratio in an attempt to widen the torque curve but it is hard to feel the difference between them when driving them.

David

David,
How interchangeable are C1 and C4 parts? I'm thinking about crankshaft, rods, pistons, rings, and jugs.

Malcolm

LRDG,

If you go by part nos there is not much interchangability but a lot of that reflects improvements in materials and fits. The difference in pistons seems to be primarily about wrist pin retention. Crank I think is interchangable, C4 still has the redundant front oil pump mount in the front housing. Rings need to go with the piston. Cylinders bolt on but there are lots of bits on the outside that are different (air deflectors, throttle linkage, rocker covers, oil recovery pipes) Supercharger gears and impeller are different but not sure about the housing. It is about 20 years since I looked at this in detail but complete engines were fairly cheap then so I never needed to build a mongrel.

You are about to become an expert in all this I think.

David

Your engine definitely failed due to a worn out crankshaft main bearing, resulting from no oil supply due to incorrect operation as David says.

You can fit a C1 crank in a C4 but not the other way round. The C4 crank isn't machined to take the C1 oil pump drive gear or lock ring.
Con Rods are the same in both engines but master rods different.
Pistons are basically the same but there are different rings depending on chrome or steel cylinders.
I can help you with parts if you can't find anything your side of the pond.
Carl

I definately bow to Carl's very much more recent experience with Sherman radials. As he is now involved I will keep quiet !

David

Thanks for the good information. As mentioned above, when I become a retiree in April, I will be in a much better position to follow up on all these tips.

More..R975
 

Not sure if I should weigh in here but..here goes..
Before you do anything else you need to strip that engine right down and see what you have to work with. If the case, crankshaft, gear case etc are rebuildable- all the rest of the parts are easy to obtain. You will need to really check for cracks and damage carefully. Second, while some parts between the C1 and C4 interchange, many do not. The crankshafts are different and use different bearing retention in the front, slightly different rear mains etc. Third there are many aircraft engines that have been flogged to people to use as spares- notably the post war R975 -46 which was a helicopter engine- though it looks a lot like a C4. It is an entirely different animal with few interchange parts. Be careful you don't get stung! Fourth, it is easy to destroy a C1 engine. I recall the overhauled engine in Bill Greggs Sexton having the bottom jugs damaged when safe start up procedures were not followed. Most of the many engines I have seen had bad main crankbearings- hardly surprising given the design and the design expectation that this would be an aircraft engine. Finally lots of parts and core engines are available right here. Tear that engine down and see what you need!

Andy over at northeast military is selling off everything he has. He has parts listed for this over at www.site.ww2mv.com/Engines-Parts_For_Sale.html

Andy (not the above andy :) )

Bob, the engine is coming apart as we speak - a complete teardown. The bottom of most the cylinder liners have been mushroomed out by the broken rods (red arrows) so it will take some time to get them out without damaging the case.

The rotating assembly is scrap, badly damaged. If I have it straight, the output spline damage shown would have been from the engine trying to stop the Sexton dead when it locked up.

The case may be OK. We'll check it with dye penetrant when apart.

I take your point about carefully checking we are buying usable parts.

Are the very thin, closely-spaced steel cylinder fins as-cast? If so, they are very high quality castings. Spin casting maybe?

Malcolm

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R975 Teardown
 

Malcolm- for whatever little bits its worth- those splayed out cylinder bottoms may be a pain to disassemble but maybe they will have saved the thin cast aluminium that makes up the crankcase. Later engines (eg the -46 helicopter) has much heavier castings in it. It also rated at 600 hp with much more blower and carb action. I cannot tell you about the fins, I always thought they were machined in but I don't know..Bob

Bob Phillips is your made for C1 stuff
 

last I heard he had lots of C1 cores avaiable and lots of parts....I even bought a C4 and a set of parts to rebuilt it but never had to do that.....I ahve his ph no if you need it....send me a note for the number..... :doh:

Good luck on your rebuild, glad they still have NOS Meteor engines in crates for my restoration!! When Rick had his original Meteor engine, the only known surviving example of a Mk1a Meteor, which was an aircraft Merlin converted to tank use but retaining it's original Merlin components, it sounds great. Not a radial but a V12.

https://www.youtube.com/watch?v=73u4GXB1TgU

https://www.youtube.com/watch?v=3sTt...re=c4-overview

https://www.youtube.com/watch?v=gYp1...re=c4-overview

Good point, Bob. You are right, they did save a lot of damage to the crankcase.

It's pretty well apart now and disassembly has stopped as there is some angst about repair costs.

There is some interesting damage to the crankcase in the raised web that supports the lifter bores. It's shown below. It lines up exactly with the inboard end of the starter drive shaft (last photo, 6 o'clock position). It's like the nut on the starter end of the shaft had come loose and allowed the shaft and small gear to move inboard and wear into the web. And it doesn't look like old damage because there is wear debris coated on the web that's not shown on the photo. It's like the nut came loose and when it was spotted (or heard), somebody just retightened the nut to pull everything back into place and hoped for the best. The weird thing is there absolutely no sign of damage or wear to the end of the shaft or the gear. It's a bit of a mystery to me.

Thanks again for all the suggestions on parts but things are on hold for a while.

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Hey Bob ;
I think you should clarify your comments on Bill's 975 :note: