Sexton R975-C1 a mess

[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