50 horse merc questions

[LitlJohn]

OK here we go. Been twisting wrenches for years but new to boating. Recently purchased an old larson(mt third boat and fith motor) with an old(1967) mercury 50 hp 500 series. Took some PB blaster in the cyl. to get it to turn over nice. Big inline 4. Cleaned it up good, everything looks good but one plug tapped out to larger size. Give it some fresh gas(32:1) and she fired up quite well for having set for years. Ran good at idle and forward/reverse, good at higher rpm in nutral. So here we go with questions. Exhaust is through the prop, is that where cooling water goes too? Small slots just above the trim tab were weeping a little but not enough for this big a motor. Cyl. head stayed cool to the touch after several minutes in the tank. Where is the water pump and how do I specify the right impeller to order one? Should I worry about it? Should I replace it just for age and un use? any help would be appreciated. thanks.

 

[carholme]

Re: 50 horse merc questions

Do you know for sure it is a 1967? Do you have the s/n?

Gerry

 

[LitlJohn]

Re: 50 horse merc questions

Do you know for sure it is a 1967? Do you have the s/n?

Gerry

Yes sir, have the # and looked it up here. The boat is titled as a 1973 but the motor serial # correlates to 1967. Thanks for the reply

 

[gm280]

Re: 50 horse merc questions

If you plan on keeping it and using it, I would purchase a Mercury shop manual just for that year, horse power and model numbered motor. Don’t buy a cover-all type boat engine manual. They are too general and will not cover the unique issues with that exact outboard. The YES I'd replace the water pump impellor not actually knowing when it was last replaced. It is always good insurance to do that with older engines with no known history. The original shop manual will become your best friend with servicing that engine and doing any repairs you could have...

 

[LitlJohn]

Re: 50 horse merc questions

Shop manual is a good idea, will get one when finances allow. Just trying to learn a little now. Think the motor is cooling alright now but a new impeller is also a good idea. Still wondering if coolant flow is through the prop with the exhaust or if upper releifs are supposed to be flowing more. Thanks for the reply.
John

 

[LitlJohn]

Re: 50 horse merc questions

Just looking through parts listings for an impeller and found an upper and lower water pump repair kit, Does this motor have two water pumps? If so where are they located? Any help would be appreciated. Thanks John

 

[carholme]

Re: 50 horse merc questions

When I asked you for the s/n before, it was to verify the year and get the correct parts list for you.

However, here is a link to a 1967 50hp gearcase and you will see that item 37 is the only repair kit listed.

Mercury, Mercruiser, Force, etc. - GEAR HOUSING ASSEMBLY, COMPLETE (PAGE 1) - MERC 500

Gerry

 

[LitlJohn]

Re: 50 horse merc questions

Sorry sir, misunderstood. Ser #is 2103398. Still realy new at this, will get better. Diagram is a wealth of info, thanks. From the looks of it I better get the rebuild kit and not just an impeller. Still curious if that motor has two pumps and where most of the cooling water is ejected. If its out the prop with the exhaust and just overflow through the gills it's cooling now. I think it is because the head never got hot while running. Thanks a Bundle!

John

 

[carholme]

Re: 50 horse merc questions

The engine only has the one water pump.

Parts List:

MERC 500 - Mercury, Mercruiser, Force, etc. Parts Lookup

Service Manual P/N: 90-68647

90-68647 | eBay

In the interim, here is a link to the condensed version of the Clymer manual. Download it soonest to your computer as the link is short lived.

Small Engine Repair Reference Center Home: MERCURY - MERCURY 4 CYLINDER MODELS (1966-1968).

In the parts list, look at item 19 (plastic fitting) under CYLINDER BLOCK AND CRANKCASE ASSEMBLY MERC 500. You should see it by looking slightly to the left and down a little from the lowest sparkplug. It should have a tube attached to it, running to a position of the right side of the lower cowling. This is where water exits the engine for the telltale, which is a steady stream of water that you can see when the engine is running to show you that the impeller is working. Did you notice a stream of water from the cowling when you ran the engine?

It would probably be a wise move for you to drop the lower unit and have a look at and replace the impeller if it is in question.

Gerry

 

[LitlJohn]

Re: 50 horse merc questions

Another wealth of info, thanks. No, I never noticed any water flow from any where near the cowling on it's first run. Cant see the lower section of the motor for the cowling but will look for the fitting on it's next run. Gotten cold here again but will run it as soon as possible. What kind of telltale does it have? Temperature or flow or something else? Kinda thinking that for the 30 or so dollars a kit costs it would be cheap insurance. Have changed the impeller in two evinrudes and this doesn't look too much differant from the manual. Again, thanks for the reply and the links.

John