Mercury 500 50hp 1980 powerhead help

[Rebel4.0]

Hi guys,

I bought my first boat last month and finally got it out on the water. A 14 foot sunray with a 1980 merc 50hp.

The problem was it had no power. top speed was like 8 mph. I started checking it over and found the cylinder washed.
Checked compression on all cylinders and it seems good.

After doing so reading it looks like my lower crank seals are bad and will have to pull the powerhead.

Ive removed the lower unit, removed the nuts off the engine mounting studs, removed the carbs and starter for weight.

I just dont know what to do with the shifter linkage. Ive ordered a manual but with the pandemic, im not sure when or if it will get to me.

does anyone have a step by step?

sorry for the long first post

 

[Texasmark]

I boats sells manuals. Ebay sells manuals. Get a service manual for your engine and go from there. There is a difference of opinions as to which is better Seloc or OEM.....folks that made the engine. I have/have had both for the same engine and have found that both have their strong points and sometimes it takes both to solve the problem.

 

[Rebel4.0]

I boats sells manuals. Ebay sells manuals. Get a service manual for your engine and go from there. There is a difference of opinions as to which is better Seloc or OEM.....folks that made the engine. I have/have had both for the same engine and have found that both have their strong points and sometimes it takes both to solve the problem.

I have a Seloc on order right now, ive been waiting 2 weeks now for it and i dont know when im going to see it. Shipping has been really bad lately with the Pandemic in Canada

 

[racerone]

Your location in Canada ?----You disconnect your throttle cable and shift cable.-------Remove the wee nut that attaches the arm the the shift rod.------Power head lifts off. ----Fairly easy to do.----How did you determine that lower seals are bad ?-----Do you have spark on all leads that jumps a gap of at least 3/8" ( 1 cm ) , very important test.---Carburetors confirmed to be clean ?------A bad lower seal on your motor might loose you a bit of power on the bottom cylinder.-----Certainly not so much that it will drop your speed to 8 mph !!

 

[Rebel4.0]

Your location in Canada ?----You disconnect your throttle cable and shift cable.-------Remove the wee nut that attaches the arm the the shift rod.------Power head lifts off. ----Fairly easy to do.----How did you determine that lower seals are bad ?-----Do you have spark on all leads that jumps a gap of at least 3/8" ( 1 cm ) , very important test.---Carburetors confirmed to be clean ?------A bad lower seal on your motor might loose you a bit of power on the bottom cylinder.-----Certainly not so much that it will drop your speed to 8 mph !!

I'm In Yarmouth Nova Scotia.
Running on a hose the motor runs fine, but in the lake it does not want to open up under load . When i pulled out the spark plugs to check them the lower one is covered in grey ( water and oil mix) Bottom cylinder

So there could be a problem with the carbs but i also know there should be no water getting in that lower cylinder. The spark is good

 

[racerone]

Could be the exhaust cover gaskets too.----Check exhaust tuner tube for blockage.---Have seen those plugged with carbon.----Did this issue show up suddenly ?----How did it run last year?----If there was water sitting on bearings inside the crankcase it is not good for bearings.---Best hurry to get this fixed !!------Oh, ---they all run fine on a hose.----It will bark and roar on 2 of 4 cylinders !

 

[Rebel4.0]

I just got it from a guy last month. That took it on trade from another guy... and he wasnt sure. I bought the boat and motor for $200 so im going to pull the power head and check a few things out. ill check the exhaust tube too

 

[Texasmark]

I have a Seloc on order right now, ive been waiting 2 weeks now for it and i dont know when im going to see it. Shipping has been really bad lately with the Pandemic in Canada

I boats electronic version of the Seloc is available as soon as you take your credit card and pay for it.

 

[AstroBoy913]

Rebel4.0 I'm having the same problem with the same motor. It runs great out of the water with muffs on it but when I get her in the water she max out at 7.5 mph and seems like the rpm isn't as high in the water. I checked all the sparks, fuel lines, got new prop for it also thinking that it might be a spun prop and cleaned out the carbs and the same thing. And I was on youtube one night and saw this https://www.youtube.com/watch?v=gkew5J0yIXo. And I haven't done this yet so I'm assuming that this is what racerone was telling you to do. I haven't messed with the lower unit yet, so I'll do that this weekend and see if I can get her back to normal.

 

[racerone]

I have seen that exhaust plugged.-----I did not make a video, I thought every body knows to check this sort of thing.-------Can't remember how many times I cleaned exhaust ports on Lawn Bow power mowers back in the day.-----Have not seen plugged ports on my own Lawn Boy for many years.-----Must be the quality oil I am using these days.

 

[Rebel4.0]

Just an update and a question,

I replaced the lower seals and the lower crank bearing. To my surprise it worked awesome. With my son, wife and I my top speed went from 8 mph to 26. It was just a small ride for about 45 minutes

So yesterday we went out again and it started out good. After about 20 minutes i lost speed again. once i got home i found water in my lower spark plug hole again.

Ive seen on line people are have had problems with the exhaust baffle plates rusting out.

l didnt check my exhaust baffle plate since from what ive seen you usually get water into more than one cylinder and my seals looked bad

Im now going to check it, just wondering if anyone had any other ideas?

thanks

 

[Rebel4.0]

Well i got the exhaust baffle off at noon today and its cracked. I guess i now know

 

[Willyclay]

Excellent troubling-shooting the issues with that great old motor. Good luck!