Why then does Volvo list different props for short hub or long hub applications, as do all the places that sell Aquamatic propellers?
They are not being listed for short hub or long hub props......... they are being listed as short hub or long hub props.
If I've got the hardware for a 250 then according to you
either long or short should fit?
Well, not exactly.......look at my drawing again.
You'll see that I've put these shafts into 2 categories:
a...... the 280/285/290/SP etc. upper left hand corner (incorrectly refered to as the long shaft when/if the spacer is not considered)
b...... the 250/270/275 lower left hand corner (incorrectly refered to as the short shaft shaft when/if the spacer is not considered)
There is a caveat to this, and that is the spinner's center locking bolt threads.
The 250/270 shafts are not internally threaded for the keeper bolt.
The 275/280/285/290/SP are internally threaded for the keeper bolt.
At the right side, where I'm showing the short/long prop hubs (green rectangles), I'm using the same shafts and same spacer/line cutter to demenstrate how one sits "shy" and the other sits "proud".
And I'm having trouble with the math. If these dimensions are correct...
Your math is not accounting for the difference in spacer/line cutter lengths.
When the correct spacer/line cutter is used, all shafts net the same length of splines.
View attachment 11699
And I have what I think are both 250 and 280 line cutter/spacers.
The 250 measures .625
The 280 measures 1.375
Without actually measuring two of them..... that sounds about right.
It appears that both hubs (distance from line cutter to end of shaft splines) is 4"
But according to Volvo bushings are as follows,
Short hub - 3.071
Long hub - 3.661
So I guess there's another factor in the equation? That's why I was asking about the difference in hub length.
Look at my drawing again.
While I don't actually show the 1 pc spinner, you'll see the 2 pc spinner and my notation in that both parts of the 2 pc spinner = the 1 pc spinner.
Every prop I have measures about 4" of hub - from the front that rests on the spacer/line cutter, to the back that gets the bendy tab (250) or plastic washer (280). But in the case of the Amita they were (~1/8) too long to allow fitment of the bendy tab.
I think that we can safely say that the Amita prop is incorrect!
It should not have required any modification.
View attachment 11700
So I'm guessing that I don't have any true long hub props because they must protrude about 1/2" beyond the splines?
I don't know if the protrusion is exactly 1/2" or not.... but yes, the Volvo Penta long hub prop will protrude past the splines.
Therefor, the long hub propeller must use the AFT portion of the 2 pc spinner in order to grab enough threads.
And I see now, that short hub Amitas are no longer available for my 250 at the place the OP got his propeller, maybe because of the problem we are having with not being able to fit the bendy tab?
I may not be following you on that..... but if the long hub prop was used on a 250 drive prop shaft, you'd have no means of locking it... unless of course you did the SS safety wire thing.
I ordered an Amita long hub 280 - we'll see if it fits...
If the Amita long hub is intended to be used on a 250 prop shaft, you're going to be left with using the SS safety wire.
And..... if this Amita long hub prop has the large blades, the blades may interfere with the 250 style exhaust outlet housing.