Originally Posted by skipperpete
The only time you could ever get that lucky is if you were changing in the same engine and gearbox as original.
It gets worse if you go from say a Hurth on a Perkins
to a Hurth on a volvo....... for reasons best known to themselves, Volvo changed the register from male to female on the Hurths they supplied on the back of their marine engines.
A lot of the gearbox manufacturers came up with their own bolt pattern and as far as I know there is no uniform standard. Here’s a partial list of small marine gear output flange sizes. Attachment 215035
When Volvo Penta discontinued the production of their own gearboxes and made the decision to buy and private label ZF product, they asked ZF to change the configuration of the output flanges on the smaller models to match the flanges on the old Volvo gears (MS, MSB, MS2). This avoided the necessity of making changes to their line of driveline accessories such as solid and split couplings, flexible couplings, etc. It also made it just a bit easier for individuals with existing engines to repower
and not have to mess with the shaft and coupling.
For the larger VP engines up to 300+ h.p. range that use private label ZF product like the ZF 45A, 630A and 800, this change wasn’t done, because the existing VP product (MS3,4,5 & HS1) conformed to “industry norms”, namely the commonly found 5” Borg Warner coupling.