TOPIC: Mk 75

Hey gents,

It’s been a while since I posted as I am out of the classic boat game (for now) but I still lurk frequently.

Anyway I’m eyeballing a 59 MK75 and the guy swears up and down that this unit has an actual reverse and not a direct reversing setup. He claims you can shift to reverse without killing the motor. It looks like a 59 and even has the funky starter.

Did they ever make one that was geared for reverse or does he just not know what he has? I’m gonna go look at it in a couple days but I’m just scratching my head on this right now.

Keep Chargin’
Andre

NEVER MADE A MARK 75 WITH FULL SHIFT ONLY DR

Thanks- that was what I thought.

Keep Chargin'
Andre

I had a 63 850 and I think that was one of first of the bigger Mercs with full gear shift. My dad had a Mark 58A and that was full gear shift, but that was only a 4 cylinder.
Bill

Earliest Inline Six that had a full gear shift was the Merc 700 "FGS" model. Then came the Merc 800, Merc 850, and Merc 1000.

MK75 and MK78 definitely did not have FGS, they were only made as Dockbusters.

Years ago I had a Merc 700 Dockbuster, the model with flow-thru prop exhaust. Bought it cheap out of the Little Nickel.

Repaired the water pump, synched the points, and once tuned, she ran like a Swiss watch. Best $25 outboard I ever bought!

Thanks guys-

I swung by and looked at the motor. It was completely restored and in beautiful condition. I am very very tempted to get it. He had it professionally restored and it looks it.

To the shifting thing- he says he was told by the guy he had restore it that you could just idle them low flip your DR switch and just pop them off in reverse without killing it. This sounds terribly wrong. Is that a thing?

Also really nice guy. I liked him a lot and he kept a very clean and tidy shop and pride in his work but he just didn’t know too much about the motor either.

Keep Chargin’

Nope, in Forward you'd pull the throttle back, which retards the timing to the point where the engine stops. Then you continue moving the control lever in the Reverse direction, until you get to the point where the reverse rotation of the starter motor will kick in and there's enough Reverse timing for the engine to run backwards when you hit the pushbutton.

I'd think it'd be really hard on the crankshaft if you were to "whip" the lever to the "R" position while the engine is running Forward, and try to start in Reverse. Got to be a bit of inertia there and a sudden reversal from Forward rotation couldn't be good for the moving parts.

The adjustment of the limit switches is important, as is the idle speed and mixture. If you get it all dialed-in, you should be able to just "tap" the key and she'll fire off. Note that dialing-in the dwell of the points, including getting the 2nd set of points to open up (i.e. "fire") exactly 90 deg after the 1st set of points opens, is very important to smooth operation of a Dockbuster Inline Six.

Glad I’m not crazy. It seemed like a sure fire way to start breaking things to me but what do I know?

In case you didn’t see this on Craigslist

seattle.craigslist.org/see/bpo/d/maple-valley-mercury-mark-75/7641510451.html

It's very Purty!

I’m very tempted but I’m worried I’m gonna have a terrible time finding decent controls.

Yeah, can't believe it doesn't come with controls, those engines are pretty much useless without the proper control box and harness.

I saw a few on eBay that might work, but as I recall there is some sort of difference between the earlier MK75 and the MK78 controls. Or it might have been between the very early and later models. Earlier boxes had the Forward and Reverse limit switches and adjusters inside. The later controls that definitely aren't compatible, IIRC, have the switches on the distributor and not in the boxes.

See the attached wiring diagram for MK75A - MK78A. If the MK75 you're looking at matches that configuration, then a 75/78 control box should work. The earliest boxes were green with pushbutton on top; then came black ones that were otherwise pretty much the same.

My old 700E Dockbuster had a white control box with the starter button on the underside of the control lever handrest. This engine has the limit switches on the distributor. So if you come across a white control box, it won't work on that MK75.

This eBay seller has (3) different MK78 boxes, that's about all I found:

www.ebay . com/sch/i.html?_dkr=1&iconV2Request=true&_blrs=recall_filtering&_ssn=heligroup&store_name=heligroup&_oac=1&_nkw=mercury

Note you'll have to copy that link and remove the spaces; this site still parses any eBay links for some strange reason.

HTH....................ed