Hmmm! Now then, this little component has multiple problems and the ones highlighted here are new to me and just add to the list. Trying to explain it all is going to be tedious and you may find it boring but here goes!
Firstly, I have never seen chuck jaw marks on any Centa coupling I have dismantled and I can only say that this is totally unacceptable and the component should be returned to Morgan for replacement. Polishing it with scotchbrite is just not going to work. The machine turned finish may not be too much of a problem as the Centa hub is of soft steel and there is a chance that the steel will polish under the seal ring ( mine did ) and that is why, I believe, that there have been few failures here. As to grinding this is one way round the problem but grinding is a technique for achieving great accuracy and the surface finish is a by product of a process which is expensive due to having to carry out a second operation on another machine. Ford used to use a process called superfinishing on their crankshaft journals and this was done using emery cloth in a giant clothes peg while the crank was spun round - seems crazy but it worked because the finished journals were selectively mated up with shell bearings so finish was more important than accurate sizing. My point being that a good polish in the lathe would be as good as having the Centa hub re ground and a good bit cheaper.
The greater concern with this component is the face at the end which mates with the crank/ flywheel. This is sealed with some silicone sealer at the factory. I have seen some with saw marks still on the face where the billet was cut off too short to clean up properly in the lathe! This face is one of great importance and it must be clean, flat and absolutely square to the axis of the part. There have been some failures of the female splines which are due to the part being made to the same spec. as the original Harley type compensator. The Harley one is glass hard and moves freely up and down on the splines. To make this a free running fit, it only fits closely on the flanks of the splines not on the major or minor diameters - correct for a hardened component. The Centa version is a fixed spline and made of soft steel this means that it has to fit on the flanks and at least one of the major or minor diameters - ideally both, sadly it only fits on the flanks. The upshot of this is failure, which Morgan and their dealers seem to blame on the nut being too slack. Take it from me, if the splines are loose then the nut will come undone in the first minute of running the engine, regardless of how tight it is! Tightening the nut will not make up for a poor fit on the splines. The point of explaining this is that if the nut is very tight and the end face is even minutely out of true or if there is any foreign matter ( silicone sealer?) in between the faces, then the crankshaft will be bent out of true. This can easily be demonstrated with a clock gauge on the Centa coupling while the nut is tightened and slackened - who ever checks that? This might explain a few of the broken crankshafts that have been reported especially as it will make the Centa coupling run out and this will affect balance.
My answer to this is whenever I have a Centa coupling out of the machine, I cut an O ring recess in the face and check the face for flat and true. You then slide the O ring over the shaft and follow it up with the Centa hub to push it home - no silicone nor any speck of dust - this is important.
If you get involved with the splines be aware that, to my knowledge, there are two different crank shaft sizes with about 0.2 mm. Difference in the diameters. The replacement, tough, alloy steel inserts I have made (
www.bleazey.co.uk/M3W.html#Image )have to be matched to the individual engine - a real pain in the bum when supplying mail order.
To answer nippymogs query the oil is held in by a seal on the outside of the Centa hub and by the silicone sealer on the end of the hub to stop it creeping through the splines.
Finally, if anyone should have engine bearing failure and finds bits of silicone sealer blocking an oil way somewhere - now you will know where they came from. I just hope that the oil filter gets them first. I am not familiar with the oil circulation path so I can't be sure how likely this is - sorry.
