TOPIC: Mark 75 found

This past weekend I was surfing the local craigslist and I found an ad that just said “old mercury motors”. I texted the seller and he replied that he had two really old motors for sale. He said that one was white and one was black. He told me that one of them was 75 hp. It was obvious he had no idea what the motors were and I didn’t really want to ask a million questions over the phone, so we set up a time to go look at them the next day. They were only about 15 minutes from my house which was nice.
I got there and was sort of amazed to find a black Mark 75 60hp and a white 600el. The guy that was selling them had found them in an old semi trailer full of junk that the previous owner of his farm had left. He had mentioned that the semi trailer had not been opened up since around 1970, so they have been sitting for a very long time. The white 600 was completely seized, but the Mark 75 turns freely. I ended up buying both for $80. They also came with a large box of parts including two brass Michigan wheel props. I’ve been looking for a dock-buster for some time, so I was excited to get these for such a low price.
The lower units on both motors were completely apart and the guts are sitting in a separate box. The Mark 75 lower unit is cracked, which is why I assume the previous owner stopped running it. I think I should be able to weld it. The white lower unit is not cracked, but the scag is completely broken off the bottom. Does anyone have a blow-up of the lower units showing how the waterpump etc. go back together? These seem a bit different than anything I have ever worked on. Also , there are some rubber “duckbills” in the box, that I assume have something to do with the water pump, but not sure exactly what?
Im sure I will have a ton of questions over the next few weeks when I try to get it back running. I was reading that setting the timing on these is tricky, so im sure I will need help with that. Im also searching for controls as the guy couldn’t find them in the semi trailer.

Any other advice you guys have about these?

Sorry not sure why my message posted 3 times. I apologize. I cant figure out how to delete the 1st two.

scott

go back and get the other motor . the parts are the sane.

Id say you got a good deal. A good faceplate and a good wrap are worth more than $80. Setting points is a tedious game, but easily doable. If the one case is weldable you should have enough parts to make one good runner and the re-sell some of the leftovers.

Post pics of the lower units. You may have a good welder cut the good skeg off the cracked case and put it on the good case with no skeg. I never like welding skegs on surfacing fast boats. But with a MK 75 you would be fine to weld a skeg back on . Or find a good lower unit.

Good find.

thanks Milkdud. I have already contemplated cutting the skag off the cracked lower and welding it on the other. If I cant weld up the other one I think that is the route I will probably go.

I also need to replace the fuel lines as they are really stiff and brittle. It appears they have crimp fittings on them. What do you guys use when replacing them? Is there somewhere I can have them brought to be crimped?

Sorry for all the dumb questions. Im new to mercs.

motoscott,

I've got quite a few dockbusters sitting around and a number of good lower units.
PM me if you are interested in a lower unit.

Don

setting is easy. just spin the distributer with a drill and set at 60 degrees with a dwell meter.

Flying Fish wrote:

motoscott,

I've got quite a few dockbusters sitting around and a number of good lower units.
PM me if you are interested in a lower unit.

Don

HI Don, sent a PM but not sure if it went through? My computer is acting really funky today. Let me know if you received it.

Scott

I think the fuel hose fittings can be reused if you carefully dermal the crimp off. Then put a hose clamp or some other compression fitting back on it.

Is it charcoal grey or black?

the hoses are black on the mark 75. On the stuck 600el the hoses are grey. Are they made out of something different?

Not sure the differences in hose color.

I was asking if the motor was painted grey?

Someone may have replaced the hoses in the past. Most of the old hoses look like the ones in your 600.

Here are ferrules that can be used in making new hoses:

www.amazon.com/dp/B00ABZ3CAY/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=M9GY3Z46SKMB&coliid=IJJ1969H1HGCS

Here's one style of inexpensive hose crimpers:



Here are die sets which fit a different type of crimper:



These leave crimps that are more like the originals. I would imagine that if you were really careful, you could use a die set like this in a vise (instead of having the large crimper that fits the dies).

Hope that helps.........ed

edit: For those interested in digging further into fuel line restorations, here's the Fiberglassics discussion I got this info from:

www.fiberglassics.com/fiberglassics-forums/home/mercury-outpost/merc-fuel-line-parts

Scott,

I didn't get your message. Try this email address.
moparhemi34atintegradotnet

Don

So last night I decided to do a compression check on the motor and cylinders 2-5 were all right at 115 psi. I couldn't get my tester on cylinder 6 because of the cowl, but The bad news is that cylinder 1 was only at 70 psi. I opened up the small intake port cover on the side of the cylinder on #1 and found all the rings stuck in #1 piston.

I ended up pulling the powerhead and splitting the engine. Pulled the crank and all of the other piston and rings look beautiful. hardly even any carbon on the domes, I doubt this thing ran too long, but #1 has all stuck rings. New rings are already on order along with top and bottom seal and some gaskets.

Has anyone ever installed these without the special ring compressors? I called the local MERC dealer and they said that they could install them for me, but want $150 to do it. I read a post somewhere about someone using popcans and zip-tyes to compress the rings. Any other tricks?

Thanks,
Scott

for $150.00 you can get a used set of compressors.

Milkdud (Conrad) posted a "how to" thread on this subject here not long ago, using the right tools. (I think I'd be inclined to either beg, borrow, steal a set of the right tools rather than break a ring or piston land trying to cobble something together!) They (the classic Mercs) are glorious marvels of engineering mastery and mistery, but require the proper tools and techniques. Just my two cents, good luck with your project.

if your not looking to make a restored show quality engine... i have been using PEX clamps for all my fuel lines... i use these clamps on everything with a metal fitting..



and the tool...

Don't know if this well help or not on fuel lines, but in my Merc stash of info.

Get the proper manual for that engine and study it well, they are not for the faint of heart.

Thanks for the fuel line tip. Those pictures really helped to visualize what is actually under the crimp.

Good news on the ring compressors also. A close family friend, who is also a marine mechanic by trade, has a set that he is going to let me borrow. Parts are on order so in the meantime i'm going to clean everything up and get it ready for new rings with a hone job.

Hey All,

I started looking more closely at my lower unit parts this past weekend and I noticed a difference between the Merc 600 lower unit and my mark 75. The difference is a 3rd rear mounting stud at the back of the lower unit. The 600 has it, and the mark 75 doesn't. All of the lower units I see pictures of for dockbusters all have the 3rd stud.

Does anyone know at what point they changed? It looks like all of the other holes will line up between the merc 600 and the mark 75,so I assume I can run it by removing the rear stud?



here is a picture to try and better explain what I am talking about.

The 1957 Mark 75 didn't have the front stud, but the next year Mark 78 did.
The parts break-down for the '58 Mark 75 & Mark 78 suggest that they all had a front stud, but I don't have a '58 Mark 75 to go "hands on" to confirm this.
If the distance between the other (4) studs measure to be the same, and the driveshaft placement measures to be the same in the two drive shaft housings (DSH),...My guess is that you could remove the front stud from the 600DR lower unit and use its lower unit on the 75.
You can't simply drill a new hole in the Mark 75 DSH to accommodate the extra stud, because of the way the reverse lock rod is shaped where that front stud would come through the top of the DSH.
doc