1981 Merc 200 MELTDOWN

Joined
May 17, 2003
Messages
22
81 Merc 200 with 390hrs just had a major meltdown! This thing was running great other than every once in a while it would just shut down. Had it to the dealer to try and find a problem but they could not find anything.

This past weekend we were headed back home when she did her mysterious shut down routine, no problem I'll just fire it back up. Motor starts but is running ruff, I put it into gear and give her some throttle and she starts to knock then quits. Now I am thinking that did not sound good! So we rowed that pig to the shore and got some help from some very nice people. (Thanks Jim)

Anyway the mechanic now has the heads off of the motor and the #1 piston is melted and the rest are in pretty messed up as well. Looks like the whole power head will need to be replaced! He's inspected the water pump which he said looked very good, and had a look through the carbs he said looked good and clean and now he is pointing the finger at the switch box.

Can a switch box cause this to happen? I want to be sure before I go and put 5000 dollars into this thing just to find out we never solved the original problem.

Anyone have a good used power head they would like to sell?:'(

Thanks,
Greg
 

KCLOST

Commander
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Jun 22, 2002
Messages
2,095
Re: 1981 Merc 200 MELTDOWN

A switchbox could cause the shut down problem you were having. But I don't think there is any way it will cause a meltdown... No way!

What about the oil pump? Did you have any alarms?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: 1981 Merc 200 MELTDOWN

Greg, What you have described is usually caused by the motor overheating, running without oil or running too lean a mixture (dirty carbs)or have a too advanced ignition. I have never heard of a switchbox doing any of these things.

Do you mix gas and oil and did you recently get that 10% ethylnol-gasoline mix fuel? If so, under certain conditions oil could have seperated from the alcohol, and you could have run your motor on plain alcohol. If you have oil injection, is it working?
 

andy6374

Lieutenant Commander
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Aug 4, 2005
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1,617
Re: 1981 Merc 200 MELTDOWN

I am in total agreement with KCLOST, no way it's the switchbox. If it is anything ignition related it is that the timing for the max spark advance was set too high.

Are you running a premix?

What were the condition of the other pistons...Carbon? What were you WOT RPMs, let me guess...around 5000.
 
Joined
May 17, 2003
Messages
22
Re: 1981 Merc 200 MELTDOWN

I've been getting the fuel at the local Shell station here at the lake, I am not too sure it its ethanol blended. Fuel was pre mixed 50 to 1.

The boat had a tendency to get hot when going slow (past the half way mark on the temp gauge) through the channel but would quickly cool off as soon as we were up to speed.

When the motor finally quit we were between 5000 and 5500 rpm, no alarms as I don't think this unit has that feature but I always thought it did.

When the motor died the first time I restarted it and tried to get under way, that is when it started to knock then died. After that I did notice the temp indicator almost all the way to the hot side of the gauge.

The plug that came out of the melted piston was white; all the others were black and oily. The cylinders on the other 5 were scored and the tops of the pistons looked eroded, for a lack of better term.

The mechanic working on is say's he's ruled out the overheating (even after I told him about he temp gauge showing hot) He said he had talked to some experienced marine mechanics and had told them the state of the engine. What he was told was that sometimes when the switch box begins to fail it can cause issues with the timing??

Can someone please tell me what the switch box's purpose is?
 

KCLOST

Commander
Joined
Jun 22, 2002
Messages
2,095
Re: 1981 Merc 200 MELTDOWN

The switchbox(s), there are two of them, recieve voltage from the stator under the flywheel. The trigger also under the flywheel sends a signal (trigger) to the switchbox for each cylinder to fire at the proper time. This trigger signal releases the charge from the switchbox to the coil so the sparkplugs will fire.

Normally when they go bad they just don't give off spark! So that explains why they would not cause a motor to melt down. Timing being messed up however will. A trigger signal at an improper time is a timing problem. Or a spark advance, advanced too much could also be it.

My guess is you have a problem with spark advance, timing, or lean carbs, or water blockages in the heads is another possibility...
 

andy6374

Lieutenant Commander
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Aug 4, 2005
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1,617
Re: 1981 Merc 200 MELTDOWN

At any rate if you are going to get it rebuilt find a good machine shop and a wrench that is over 40. Make sure they isolate what the problem was. Did he check the timing? It's just that I've never heard of a switchbox causing a meltdown. I'd go for a second opinion in regards to the cause of the failure.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: 1981 Merc 200 MELTDOWN

Greg, White plugs are likely the result of a lean fuel-air mixture. This can cause the damage you have. If you do decide to repair this motor, make sure you clean the carbs well, inspect the fuel pumps and lines, filters etc.
 

Deep_Blue

Seaman
Joined
Jul 19, 2006
Messages
66
Re: 1981 Merc 200 MELTDOWN

So if you’re not sure if your engine is tuned correctly or in my case it’s just been rebuilt, can you pull out the plugs to inspect them and look down inside the cylinders periodically to see if damage is occurring and fix it before a complete failure? Will the ominous signs of damage be noticeable before it’s critical or is it only noticeable after the point of no return (plugs turn white only a few minuets before complete engine failure)?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: 1981 Merc 200 MELTDOWN

Deep, I would think that damage in a multiple cylinder engine would occur in a few seconds of overheat, lean running or lack of lubrication. I do not think a visual inspection would allow you to see that damage is occuring.
 
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