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#1
02-10-18, 00:56
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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! C1&-46 cs.jpg C1&-46cstop.jpg C4crankshaft.jpg 
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#2
02-10-18, 01:41
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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.
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#3
02-10-18, 01:44
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The Spider plate on the crank....is the lower pivot for each piston rod.
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#4
02-10-18, 01:48
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R975-ec1
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#5
02-10-18, 02:39
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975-46
Hi Des
Any idea about what caused this failure?
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#7
02-10-18, 04:30
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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
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#8
02-10-18, 05:09
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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 Sexton crankshaft.JPG
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#9
03-10-18, 01:47
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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.
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#10
03-10-18, 03:32
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975-46
I am inclined to agree- must have been quite a shock!
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