TOPIC: 1959 Mercury Mark 75A questions

I just picked up a 1959 Mercury Mark 75A long shaft (SN 1112822) with the plans of using it on my G3 when it's done. I'm not very educated on outboards but I know this model is call the "dockbuster" because there is no neutral. What is the advantage in the long shaft (if any). I know to use it on my G3 the transom has to be modified for the added shaft length. It looks good cosmetically, haven't ran it yet, but here in Michigan boat motors typically don't get many hours due to short season. Any advice on the long shaft situation is appreaciated. Thanks, Mike

If the transom's good just get or make a jack-plate to raise the long shaft (Mike Moore Made one real cheap and Wade Swatzell made a nice one, both for the same reason as you). The cav plate just above the prop wants to be inline with the hull or keel bottom or just above, if its lower it will reduce your higher speeds. If you need to rebuild the transom later make it higher or find a complete short-shaft lower unit to stay original. If you don't have the Merc Service Manual, would be a good idea, PN. C-90-25500 Any pic's?

Thanks G3bill, Here are a coule of pictures. It looks really clean. I see the jackplates on some boats, they are usually aluminum right? I'd like to keep the transom stock. Mike

Right, Usually alum. Wade's was designed by himself and he happened to have a block of aluminum so didn't have to buy that, think it moved the motor out only about 1 1/2-2", the thickness of the transom. Nut and bolt adjustable as is Mike M's I think. I drew one on paper to have the motor mount above the transom with no or very little set back, don't know if it will work or where my plane is? Think I figured on using alum, and stainless.
'60 g3 with a MK78 all to be restored

Mike,


Make sure that transon is not rotten. I didn't check mine and first time out with Merc 650 it cracked down each side about 6 inches!!

If you have to replace the transom as many G-3 owners have, build it up to 21-22 inches at the top and use the nice motor without a jackplate. Good luck.