Short Shaft / Long Shaft Exchange

Probably a stupid question. I have a 1967 500 Long Shaft Mercury that has crankshaft / piston problems. I have a 1967 500 Short Shaft Mercury that has lower unit issues.

Question: can I have a mechanic turn the two into one working Long Shaft motor? (That is, can the long shaft lower unit be attached to the short shaft "upper unit"?)

Sorry if this is a stupid or obvious question, and thanks in advance.

Re: Short Shaft / Long Shaft Exchange

Not a stupid question at all!

The simplest solution would be to pull the powerhead on the Shortie and install it on the Longshaft outboard. There's no difference in the upper ends, only in the length of the center section (exhaust tower) and driveshaft.

Another way would be to find a "longshaft kit" and use all the parts on the Shortie plus the longshaft lower unit. In this case, you wouldn't need to use the 5" driveshaft extension "stub" that comes with the kit, since the longshaft lower unit already has the correct-length driveshaft. These kits are not inexpensive and may not even be available any more (I haven't checked recently).

Realistically, the simplest and cheapest method would be the first. It'll cost a powerhead base gasket and not much else except labor.

HTH & let us know how it turns out.............ed

Re: Short Shaft / Long Shaft Exchange

Excellent! Thanks, Ed.

This old motor I have is absolutely beautiful cosmetically and in the lower end, but it just doesn't do anything (more than idle) worth a flip. It will be going back on an antique boat, and I love the way it looks so I hate to replace it with something newer.

Should be about 10-14 days before the thing's done and I'll let you know how it turns out.


Thanks again.

Re: Short Shaft / Long Shaft Exchange

My problem is just the oposite, I'm looking to buy a 2007 mercury 15HP big foot motor with the extra long shaft (25") and my questiion is can it be converted to a long shaft (20").