Merc Mark 7

[Doug Wilson]

A big adjustable wrench will work. Soak the tank with either super clean or denatured alcohol and sea foam put some small chain in and shake that will usually knock the crud lose. If you use super clean make sure you rinse good with plenty of water then rinse with denatured alcohol to make sure all the water is out.
Doug

Doug

how is it motors multiply when the garage lights get
turned off?

[richardg]

myoldoutboard@aol.com has some of the impellers.

Hopefully the previous owner put some lube between the prop and the prop shaft so it will come off easily.

The water pump cover is behind the prop. Turn it clockwise to loosen.

Use 105 lube in the lower unit.

My favorite motor to work on.

[green-thumbs]

The work around is set hex head in vise and adjust jaws to firm but not too tight. Then rotate tank to unscrew filter. Usually works when you are too impatient to drop everything to go buy a socket or box end wrench.
Really gummy fuel residue can be rendered into a jelly with lacquer thinner. It works best
in warm weather out in the sun. After a couple days pour out the jelly, separate the liquid
and return it to tank for another few days. May take 3 or 4 cycles. Strong ammonia (extra strength) can then be used to finish cleaning.
The Green Tank Mercurys have aluminum tanks made from welded together stampings.
More usually the problem with them is they are beat up from from rough treatment.
Although they can be repaired it is usually more cost effective to find a better tank.
Louis

[cark-k]

Got the prop off no problem but it looks like the water pump cover requires a special tool to remove it. Is the pump cover threaded? Also, should I get the motor running and see if it pumps water or replace the impeller now. Thanks again for all the help.

Does anyone know if this manual will be of use? http://store.oldmercs.com/product_p/90-26140d.htm

[green-thumbs]

The 1965 and Prior Models manual is mostly about later models. If you can find a used one
at a reasonable price there is useful information but you have to dig for it. As it is not all
in one place.
I have take a number of KE4 and Mark 7 Mercs apart. I have not yet found a good impeller.
The water pump cover is a left hand thread that is opposite of usual threads. Reason for that is propshaft and propeller turn counter clockwise (CCW) and might tend to unwind a clockwise (CW) threaded cover. If the cover is not corroded in place the Mercury Service
Tool or a reasonable workaround will remove cover just like in manual….after 5 or 6
decades many are solidly stuck so you may have to resort to one of more of the several
techniques that are not in the manual….heat, beat and juice…sometimes destroy
cover in extreme circumstances. I have the tool…sometimes that is all that is needed
more often it ain’t that easy.
Everyone who has worked on covers has their own favored technique.
Louis

[cark-k]

Thanks GT. Right now I’m trying to remove the slotted lube fill screw and it’s really seized, thinking of drilling a 5/16 hole through it, tap it and use a bronze round-head machine screw to plug the new hole after filling. Luckily, the motor has good spark and compression.

[cark-k]

Yay! I had success removing the impeller cover plate after soaking and striking with a screwdriver in both holes with a hammer. How do I determine if the impeller is worn and needs to be replaced? Also, how do you remove the impeller, is it a press fit? Thanks.

[dave-bernard]

looks to be ok but if you are going to use it I would replace it for safety

[chuckw]

Just pull the impeller out with a pliers, but don’t lose the pin.

[cark-k]

I’m having a bear of a time trying to remove the lube fill screw. I’m using the correct screwdriver but it won’t budge and I’m rolling over the slot enough to know when to quit. Would applying heat help or could I do damage to the aluminum? I’ve been soaking it with Liquid Wrench also.

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