impeller change Mark 55A?

[pxlxr]

I just picked up an apparently great running motor (for cheap!), but I am a little concerned about lack of water spitting from the unit. I've done a good bit of searching, and it seems most should come from near the prop, not the exhaust, right? I would like to change the impeller/pump unit, but I'm concerned I may need some of the "special tools" I've been reading about. Also, would this be doable without a service manual? Any Thoughts?

Also, do I need to remove the lower unit to grease with 105, or can I just use the fill screw hole? I'm a bit suspect of the seals, having no idea if they've been replaced after 50 years.

P.s. I'd like to thank all the contributors to this board. It is respectful and incredibly loaded with top-notch info. Good Work!

 

[mixerjv]

Re: impeller change Mark 55A?

"I just picked up an apparently great running motor (for cheap!), but I am a little concerned about lack of water spitting from the unit. I've done a good bit of searching, and it seems most should come from near the prop, not the exhaust, right?"

Not sure what you mean, but the Mark 55-58 are not jet prop exhaust units. When you have it in the water or a barrell, at idle the exhuast spits out the relief hole above the water line. The pee hole on these units clog very easily, especially under salt water use. The best way to tell is to put your hand on the smooth side of the block when the engine is running, it should be cool enough to touch with your hand. Ear muffs do not work on these units by the way, they must be run in a body of water, a barrell, or with the no longer available kit from Tempo.

"I would like to change the impeller/pump unit, but I'm concerned I may need some of the "special tools" I've been reading about."

The special tool to remove the water pump cover is easily manufactured with a CNC machine, and last I knew someone was selling them on Ebay. What is extremely rare, however, and hard to replicate is the water pump cartridge remover, but unless you're rebuilding the lower unit replacing just the impeller is fine.

"Also, would this be doable without a service manual? Any Thoughts?"

Yes, but do not destroy the water pump cover. It is no longer manufactured. Get the tool from ebay or another source.

"Also, do I need to remove the lower unit to grease with 105, or can I just use the fill screw hole? I'm a bit suspect of the seals, having no idea if they've been replaced after 50 years."

No, you don't need to remove the lower unit, there are two screw holes, remove both, fill from the bottom. New screws with the screw gasket are still made by Merc, get them. Definately replace the grease with 105. Don't worry about rest of the seals, to replace them you need to rebuild the lower unit, now you're talking a lot more NLA tools, arbor press, ect.

Good Luck!

 

[pxlxr]

Re: impeller change Mark 55A?

Thanks for the quick reply and good info, mixerjv. I'll look for the pump cover tool. I just took it out today for a test, and it idles nice, but I don't think I'm getting enough RPMs out of it (won't plane out on a 14ft p14). I'll have to fiddle with the jet screws and see what happens.

Anybody got keen ideas? Spark plugs are rusty, and I'll change them, but I wanted to open up the throttle as-is to see her current condition. Whats the best way to ensure maximized revs, short of a carb rebuild? Could it be points/condenser, even though idle is fine?

 

[mixerjv]

Re: impeller change Mark 55A?

Yes- a bad points condenser can make the engine run weak.

Be careful with the distribitor cap and rotor- both went NLA from Mercury just a couple of years ago. Further, at the end they went for a stuningly ridiculus $200 and $400 respectively, and those remaining in any dealer inventory will reflect that high price.

 

[pxlxr]

Re: impeller change Mark 55A?

I think I found the culprit. A COMPLETELY fouled plug. Hope she runs better after a full new set. Also, What's the best way to flush the cooling water lines clear? I suspect a blockage somewhere. I ran her in a tank for a bit and she got a bit warm, so I shut it down. Not sure if forward motion will force the water through the impeller or not. I'm going to replace the impeller as soon as I get the cap remover tool, but I'd like to gently drive her for a bit if I can.

 

[mixerjv]

Re: impeller change Mark 55A?

Forward motion will not force water through the impeller.

There is a screw hole on the upper part of the lower unit (the highest of the three screws) meant for a flushing adapter to hook to a garden hose for (for use when the engine is NOT running, also, FYI, these units do not have thermostats making flushing possible with cold engine). The adapter is long NLA but can be recreated with plumbing house supplies.

 

[mixerjv]

Re: impeller change Mark 55A?

Re-read my post above and I wasn't entirely clear on one part- You can flush this motor cold through the flushing adapter- there is no thermostat to block the water.

 

[pxlxr]

Re: impeller change Mark 55A?

I know I should get the service manual for this, but I'm trying to repair this one on a budget, and 80$ is steep. I'm pretty new to outboard repair, so a couple simple tips on impeller replacement from those in the know would help me greatly.

1- do I remove only the lower unit from the shaft, not the shaft from the powerhead?
2- when doing this, do I disconnect the shift lever, and from where?
3- what is the screw near the top of the lower unit on the starboard side?
4- do I remove/replace in fwd gear?
5- what is the easiest/best way to remove blockage in water lines?

 

[coolguy147]

Re: impeller change Mark 55A?

i believe the lower unit should drop right down after you take out 4 bolts. one is hidden in the exhaust. use a allan wrench to retrieve it.

there should be no shift rod to disconect. like i said it just drops down.

the screw is a hole for greasing the reverse lock lever if that is the screw your talking about.

they say to replace it in foward gear i would put it in foward gear then drop the lower unit.

remember where the gears are and do not move them.

to unblock the water lines i stick a hose of some sort up the water tube and under low pressure blow water through it.

when you get the motor running if your tele tale is block sitck some wire up the hole. it is right under the exhuast manifold.


you will probably ask me how to take the water pump cover off after you take the lower unit off.

the right tool is a spanner wrench and by looking at the cover it is pretty self explainatory on how to get it off. i used a punch because mine was already beat up.

 

[coolguy147]

Re: impeller change Mark 55A?

oh and when taking the impeller out use 2 flat head screw drivers. if it is really stuck in there then you may have to get the dremel on it. my motor didnt run for probably 20 years and it was rusted on the driveshaft. i had to grind it out.

dont bang on the water pump bowl(cup) it will break

dont lose the impeller key

 

[pxlxr]

Re: impeller change Mark 55A?

Thanks for the info. Getting a spanner, today. Hopefully all works out.