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The design of stern gear that does not have a inboard bearing relies in part on the conventional stuffing box for shaft support. Remove that and the shaft can move as described and hit the tube - even if it is aligned properly.

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With all due respect, I think you are talking nonsense here. I replaced our stuffing box (Vega 27) with a Volvo seal and fitted a new Beta with centaflex coupling. The stern tube is approx. 1.75" and the shaft is 1".

I paid an alleged marine engineer to align the engine and the new Volvo seal leaked. Pulling it back I discovered that the shaft was almost touching the side of the stern tube, and would almost certainly have hit it under some load conditions.

I realigned the stern tube using a cone drilled for the shaft diameter then cut in half (easy enough to get made up in wood or metal by someone with a workshop and somewhat more effective than the roll of insulating tape mentioned above)

With the shaft now central in the tube the engine could be lined up and voila - no problems whatsoever in 550 hours running with a 2-blade varifold prop. Aligning the shaft with the stern tube is every bit as important as aligning the engine with the shaft, and is the first step.

Perhaps people do not take the trouble (simple enough using the split cone described above) to centralise the shaft properly . . . in which case problems are inevitable. The idea that the stuffing box (or any other form of seal) should in any way act as a bearing is absurd.

The use of a centaflex coupling also makes shaft alignment very easy using the 'clunk but not clunk-click' method (no point in messing about with feeler gauges if using one of these) and of course it helps dampen any vibration.

- W

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