Sexton R975-C1 a mess

[David Herbert]

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

[LRDG]

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

Malcolm

[David Herbert]

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

[carl brown]

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

[David Herbert]

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

David

[LRDG]

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.

[Bob Phillips]

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!