Did I kill it?

[treenester]

I have a 1974 MERC 500 that I just got. Was fishing a few miles upriver the other night. The motor ran fine. Started back to the landing & after about 1 mile, it just quit. I cranked it back up and it quit again. Kept trying & it finally cranked, but looked behind & it's smoking pretty bad (like a rich oil mix). I take off again & it doesn't go far till it quits again. I think it's out of gas, so I transfer some over from another tank. This takes a while so I crank it back up take off and it runs fine for about another 3/4 mile and then quits again. I try to crank now & it's tight (dragging). Oh no! It cranks & first thing I do is check the water discharge. It's hot, but not too hot to hold my hand under. Top of the motor is warm, and the back is warm through the cover (did not take the cover off). Starts idling rough, so I kill it. My fishing buddy pulls back around in his boat and I start it a few times just to show him what it's doing. We tow it in and I've not done anything to it. Was thinking about replacing the water pump impeller. When I first put the motor on the boat, I hooked the water hose to it & cranked it a few times to check the water pump & no water came out the discharge. I put it in the water & after about maybe 8 - 10 sconds water started discharging. My thought is that the water pump, though discharging a stream of water, was not pumping sufficient to keep the motor cool. What are some other things I could check? Anybody know what the compression should be on this model (ser#: 3817083)? I hope it isn't too late. Thanks.

 

[rickdb1boat]

Re: Did I kill it?

First thing is the compression. The readings are not as important as that they are all close to being even being the key. 5 or 6 miles with no cooling is not good, of course. But as you said, you may have had some cooling going on. If the compression numbers come up close, I would pull the head and check the cylinder walls out for scoring anyway. You may get lucky in that it did die out so quickly(Sort of) and did not run any longer. Post what you come up with and we'll go from there..

 

[Gus Mortimer]

Re: Did I kill it?

For starters, I am not a pro, but..<br /><br /> My telltale doesnt start peeing for a few seconds eithor, I think it takes a minute for the water to travel through the system. Also if you can keep your hand under it that doesnt sound too hot.<br /> My boat has recently had similar problems. it died the same way, would not start until I pumped the primer bulb, then would go for a few seconds then die again. I was able to drive back to the dock with a friend pumping the primer bulb the whole way. <br /> Obviosly a fuel issue with mine, could be with yours too.<br /> Lack of fuel is lack of lubricant so I guess you could have scored a piston, but lets hope not.<br /> Do the compression check first thing and let us know.

 

[treenester]

Re: Did I kill it?

I'll get a compression gauge and chk it out. If the head w/ come off I'll check the cylinders, too. Anybody know if the heads will come off that model?

 

[Nandy]

Re: Did I kill it?

Treenester, I have a 1968 500 mercury 50 hp. I had a similar problem but I hope yours is not as bad as mine was. My motor never had a strong stream coming off the tattletale water port. It actually dripped at high speed and nothing came out while idle. The owner told me that was the way it always worked and I took his word for it. Last season it broke 4 reed valves and mess up 2 pistons and scratch 2 cylinders walls. <br />Number one, get the book for the motor, number 2 get the book from the motor. It will help you and guide you. Also come to this board and asked anything that might not be covered or not clearly explained on the SELOC book.<br />Anyway, start by checking the compression. My compression is around 120 on all of the cylinders, once it warms up is about 115. You should have a generous stream of water at idle speed. My problem was due to a plugged outer exhaust plate. All the grooves were plugged to the point that there was not a way the water would come out of either water ports.<br />If your compression is ok and the water is flowing seems to be flowing ok you might have a gas pump problem or a carburetor problem. Post here your finding and somebody will be able to help you.

 

[Nandy]

Re: Did I kill it?

No, there is no cylinder head on this motor. What you see is a water jacket. To access the cylinders you would have to remove the cylinder block from the powerhead. Remove the carburators, inigtion, starter, flywheel and a whole lot more of stuff (sounds worst that it actually is), crank case and pull the crackshaft out with the pistons attached. Warning, you will need a special tool to put the piston back. If you get this far you better do the complete overhaul. Here is a list of some of the parts for my motor. Yours is a different year so the parts and prices might be different. Check with your local mercury dealer. Take the serial number with you.<br /><br />Water Impeller $14.95 47-89983T<br />Water Impeller Repair Kit $31.12 47-89983T1 <br />Inner Exaust Plate $66.05 Old 46109 - New 904211<br />Outer Exaust Plate Gasket $5.30 Old 27 46110 - New 27 854913<br />Inner Exaust Plate Gasket $5.90 Old 27 46111 - New 27 854924<br />Cylinder Block Gasket $4.40 Old 27 37816 - New 27 85487<br />Standard Size Piston Rings $45.70 39-27841A12<br />Piston Assembly $161.85 780-9229A 7<br />REED KIT $44.00 34-88498A 1<br />Needle Bearing Piston Pin $0.20 29-20063<br />Needle Bearing Crank Pin $0.20 29-20046T<br />O-Ring $1.15 25-20081<br />Seal $9.30 26-41953<br />Big Seal $18.65 26-29478<br /><br />Like I said before, the work sounds worst that it actually is, with all the parts and appropiate tools it will take you less than a day to do it. Good luck, have fun...

 

[tmcalavy]

Re: Did I kill it?

Do the compression test and check the fuel pump. I also have to ask if you had the right fuel/oil mix. I saw two guys run a Merc 500 once wth just straight gas. It would run a distance and then lock-up/shut down until it cooled off and then crank up and go a similar distance again. They were lucky we came along and gave them some of the right gas. Could also be an electrical problem...maybe. Taking a few seconds to discharge a stream of water is normal for these model Mercs...my 73 Merc 500 dribbles until the rpms go above idle speed and the water pump starts discharging at capacity. The compression test will tell you a lot. If you're lucky its just the fuel pump needing to be replaced. You did have the tank vented?

 

[treenester]

Re: Did I kill it?

Thanks for all the replies. I may get to check out my motor late tonight (have other obligations afer work). Going to try to get a compression gauge & an impeller sometime today. Thanks again for the responses.

 

[treenester]

Re: Did I kill it?

tim MC,<br />The tank is older, been cleaned out. The cap has the screw out vent, but I don't know how well it works, it (the cap) was kinda rusty when I got it. I cleaned it up. I had just put a fresh gas-oil mix (50:1) in the tank before the trip. As far as any other vents on the tank, I don't know.

 

[tmcalavy]

Re: Did I kill it?

You can check the tank venting by observing the bulb while running. If it collapses, the vent in the tank cap may be restricted. It will also get squishy if the fuel pump diaphragm is worn out, not collapse, just get mushy. Fuel pumps are a easy fix. Kits are cheap. Hope one of these is your problem.

 

[treenester]

Re: Did I kill it?

I got an impeller & a compression gauge earlier today. If I have time tonight, I'll try to at least chk it out & see about the compression.

 

[treenester]

Re: Did I kill it?

Well, the compression check was fine, so I pulled the gear housing to replace the water pump. Looks like the (upper) tapered roller bearing on the drive shaft just below the water pump assembly is going to have to be replaced.

 

[threecylinder]

Re: Did I kill it?

hey Dave, shoot me an e-mail if ya need help replacing the bearing

 

[i610288]

Re: Did I kill it?

I had a almost identical problem like yours.It turned out to be the fuel pump diaphram had tears in it and was making it run to rich.

 

[treenester]

Re: Did I kill it?

Took the motor out this weekend. Motor runs fine. It will go into reverse, but slips (grinds) under pressure. Before i took it apart, it would not even go into reverse. I was told that i probably had it a spline off when I put it back together. Another concern is, water is getting into the LU oil from somewhere. I guess it can be only two places, either the upper or lower seal on the water pump assembly. Overall I'm glad that the motor is not damaged. It ran fine all weekend. Now to address the reason for the stalling. My only guess is that the upper drive shaft bearing was seizing, which I replaced. Peices of this roller bearing were in the foot also, which prevented the shifting into reverse. Thanks again for the advice.

 

[profish00]

Re: Did I kill it?

did you replace the vent and fill gasket...water will enter there

 

[treenester]

Re: Did I kill it?

Vent? Don't know about the vent, but I used the same gasket, just put some permatex on it.