Sexton R975-C1 a mess

[Hanno Spoelstra]

Originally Posted by LRDG

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
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

[pauletto luigi]

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

[Phil Waterman]

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

[LRDG]

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.)

[motto (RIP)]

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

[David Herbert]

Originally Posted by motto

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.

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

[LRDG]

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.