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Q:
My outboard quit last week and tomorrow I start a rebuild. Lost compression on one cylinder. Its a 115 HP Merc and I haven't done a rebuild since I was a kid. I'm not a mechanic but I do have a shop manual and youtube. I also have more time than money right now. Has anyone else done one? Do you think it will be possible for a non-mechanic?

Question by DakotaMan. Uploaded on October 17, 2012

Answers (9)

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from Quinton Schmelz... wrote 1 year 26 weeks ago

We had 200 and 225 Mercs on our boat in Fiji. Did a lot of our own engine work... at one point my dad did replace the compressor on the port engine. He knows a hell of a lot about engines but is not a certified mechanic. If you have general engine know how, and have youtube, I say you should be able to do it. It really depends on your competency level. I've grown up on and around boat, taking apart both diesel and petrol engines (on boats and trucks and cars) I would have no problem diving into the project. If you feel confident, go for it.

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from Ontario Honker ... wrote 1 year 26 weeks ago

I wonder what a compressor would be used for on a boat motor?

Dakota, I'm guessing you blew a head gasket. Fairly common. Get an overhaul manual for your motor. You can probably order one on line. The tricky thing about outboards is the aluminum heads. Torquing them down properly is almost a science.

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from Josh Giannino wrote 1 year 26 weeks ago

Mercury has a bad habit of needing specialized tools to work on em. my grandfather was a certified mechanic but worked on all boat motors for years, and he hated working on mercs for that reason

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from Quinton Schmelz... wrote 1 year 26 weeks ago

Ontario Honker: I don't know either, but I do know for a fact that they have them. At one point, my dad even had to have one flown in to the nearest airstrip, find a way to get it to where he was, and replace it. I don't know if the Verados have them, but I know the Optimaxs do...
DakotaMan: I'm assuming you have an Optimax?

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from santa wrote 1 year 26 weeks ago

Back in the late 60's and early 70's, the Big Black Stacks from Fondulac that I ran and raced had to have the pistons and crankshaft installed as a complete assembly from the front of the case. It took special fingers to compress the rings on the pistons and were very hard to work on, whereas just about anyone could work on the JohnRudes. That is how the Merc's got the bad rap about being hard to work on, but even with all the special tools and hard to get to nuts, screws, and bolts, they were no real hill for a stepper back then. The newer Merc's are not built like that any more and are much easier to work on. Just pay attention during the disassembly because you will at some point have to reverse the procedure. Take a few pictures of the assembled motor before you start and watch carefully as you take it apart for problems. For example replacing a burnt piston without finding what caused it to burn in the first place is not fixing the real problems. Just think cause and effect while you disassemble and mark all parts as they come off. I find that a marked muffin pan is nice to put screws, nuts, and bolts into and keep them seperate so you will be able to put them back in the right places on reassembly. Good luck and do not be affraid to ask for help if you need it.

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from DakotaMan wrote 1 year 26 weeks ago

Thanks so much guys. The main thing I needed was encouragement I guess. It was not as bad to disassemble as I had suspected. I took pictures, videos and notes all the way through and think I should be able to get it back together. That was a great idea. I found two burned pistons; one with frozen rings and both cylinder walls scored. The cause was ethenol gas separating and plugging the #3 carborator jet (my bad), stopping the lubricant from going to these two cylinders (a 2-cycle). I had a mechanic completely dissassemble and rebuild the carbs but I am doing the engine rebuild.

I am going to hone the cylinders and so far it looks like the difficult part will be compressing the rings while I slide all six pistons back into the block. So far, that appears to be the only way to do it. I do need a special tool to remove the flywheel too... my gear pullers won't fit it.

It has been kind of fun. I still pray that it will run when I am done though. I will also test all systems (e.g. thermostat and water pump) to be certain that there is not a parallel cause still lurking. That was a great idea too. Thanks again all.

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from santa wrote 1 year 26 weeks ago

DakotaMan, You are lucky because I have had to deal with saltwater corrosion on the motors that I have worked on in my area. Just to get a few simple screws out, I have had to heat them with a torch. To clean any gaulded piston material from the cylinder bores before honing, mix up some Red devil lye (sodium hydroxide) as a paste and dab it on the aluminum stuck to the cylinder walls being carefull to not get any on the block itself. Some oven cleaners will also work but they are not as strong as the paste. Always be sure to rinse the areas where the sodium hydroxe was with a vinegar solution to neutralize the caustic soda. This keeps aluminum from getting in the honing stones and you get a much better finish. It is not necessay to remove all the scratches from the bore but it is neceassry to remove all traces of gauld. My racing merc was a 190hp twister built up on a 1969 125hp merc block. It had a bp 1:1 lower unit and run tilton floatless carbs with a dry exhaust. I ran only one piston ring per piston to cut down on friction because the motor far exceeded safe maximun piston speed every time I ran it. Thus I did have to break it down several times while I owned it and got pretty good at honing the cylinders with a Sunnen hone. I even finished the cylinders with pfte wiper stones so that there was no breakin period.

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from santa wrote 1 year 26 weeks ago

*ptfe*

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from DakotaMan wrote 1 year 25 weeks ago

Thanks Santa... honing went real well and I especially appreciate the advice that I don't have to remove all the scratches. I do have a problem with removing the cylinder head. It uses smaller bolts and I can't get them loose. They have a slight corrosion and both of the first two I tried to remove simply broke off. I guess I will have to take it to a machine shop to get them removed and repaired. I would not have had to remove the head... bummer.

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from Quinton Schmelz... wrote 1 year 26 weeks ago

We had 200 and 225 Mercs on our boat in Fiji. Did a lot of our own engine work... at one point my dad did replace the compressor on the port engine. He knows a hell of a lot about engines but is not a certified mechanic. If you have general engine know how, and have youtube, I say you should be able to do it. It really depends on your competency level. I've grown up on and around boat, taking apart both diesel and petrol engines (on boats and trucks and cars) I would have no problem diving into the project. If you feel confident, go for it.

+1 Good Comment? | | Report
from Ontario Honker ... wrote 1 year 26 weeks ago

I wonder what a compressor would be used for on a boat motor?

Dakota, I'm guessing you blew a head gasket. Fairly common. Get an overhaul manual for your motor. You can probably order one on line. The tricky thing about outboards is the aluminum heads. Torquing them down properly is almost a science.

+1 Good Comment? | | Report
from Josh Giannino wrote 1 year 26 weeks ago

Mercury has a bad habit of needing specialized tools to work on em. my grandfather was a certified mechanic but worked on all boat motors for years, and he hated working on mercs for that reason

+1 Good Comment? | | Report
from Quinton Schmelz... wrote 1 year 26 weeks ago

Ontario Honker: I don't know either, but I do know for a fact that they have them. At one point, my dad even had to have one flown in to the nearest airstrip, find a way to get it to where he was, and replace it. I don't know if the Verados have them, but I know the Optimaxs do...
DakotaMan: I'm assuming you have an Optimax?

+1 Good Comment? | | Report
from santa wrote 1 year 26 weeks ago

Back in the late 60's and early 70's, the Big Black Stacks from Fondulac that I ran and raced had to have the pistons and crankshaft installed as a complete assembly from the front of the case. It took special fingers to compress the rings on the pistons and were very hard to work on, whereas just about anyone could work on the JohnRudes. That is how the Merc's got the bad rap about being hard to work on, but even with all the special tools and hard to get to nuts, screws, and bolts, they were no real hill for a stepper back then. The newer Merc's are not built like that any more and are much easier to work on. Just pay attention during the disassembly because you will at some point have to reverse the procedure. Take a few pictures of the assembled motor before you start and watch carefully as you take it apart for problems. For example replacing a burnt piston without finding what caused it to burn in the first place is not fixing the real problems. Just think cause and effect while you disassemble and mark all parts as they come off. I find that a marked muffin pan is nice to put screws, nuts, and bolts into and keep them seperate so you will be able to put them back in the right places on reassembly. Good luck and do not be affraid to ask for help if you need it.

+1 Good Comment? | | Report
from santa wrote 1 year 26 weeks ago

DakotaMan, You are lucky because I have had to deal with saltwater corrosion on the motors that I have worked on in my area. Just to get a few simple screws out, I have had to heat them with a torch. To clean any gaulded piston material from the cylinder bores before honing, mix up some Red devil lye (sodium hydroxide) as a paste and dab it on the aluminum stuck to the cylinder walls being carefull to not get any on the block itself. Some oven cleaners will also work but they are not as strong as the paste. Always be sure to rinse the areas where the sodium hydroxe was with a vinegar solution to neutralize the caustic soda. This keeps aluminum from getting in the honing stones and you get a much better finish. It is not necessay to remove all the scratches from the bore but it is neceassry to remove all traces of gauld. My racing merc was a 190hp twister built up on a 1969 125hp merc block. It had a bp 1:1 lower unit and run tilton floatless carbs with a dry exhaust. I ran only one piston ring per piston to cut down on friction because the motor far exceeded safe maximun piston speed every time I ran it. Thus I did have to break it down several times while I owned it and got pretty good at honing the cylinders with a Sunnen hone. I even finished the cylinders with pfte wiper stones so that there was no breakin period.

+1 Good Comment? | | Report
from DakotaMan wrote 1 year 26 weeks ago

Thanks so much guys. The main thing I needed was encouragement I guess. It was not as bad to disassemble as I had suspected. I took pictures, videos and notes all the way through and think I should be able to get it back together. That was a great idea. I found two burned pistons; one with frozen rings and both cylinder walls scored. The cause was ethenol gas separating and plugging the #3 carborator jet (my bad), stopping the lubricant from going to these two cylinders (a 2-cycle). I had a mechanic completely dissassemble and rebuild the carbs but I am doing the engine rebuild.

I am going to hone the cylinders and so far it looks like the difficult part will be compressing the rings while I slide all six pistons back into the block. So far, that appears to be the only way to do it. I do need a special tool to remove the flywheel too... my gear pullers won't fit it.

It has been kind of fun. I still pray that it will run when I am done though. I will also test all systems (e.g. thermostat and water pump) to be certain that there is not a parallel cause still lurking. That was a great idea too. Thanks again all.

0 Good Comment? | | Report
from santa wrote 1 year 26 weeks ago

*ptfe*

0 Good Comment? | | Report
from DakotaMan wrote 1 year 25 weeks ago

Thanks Santa... honing went real well and I especially appreciate the advice that I don't have to remove all the scratches. I do have a problem with removing the cylinder head. It uses smaller bolts and I can't get them loose. They have a slight corrosion and both of the first two I tried to remove simply broke off. I guess I will have to take it to a machine shop to get them removed and repaired. I would not have had to remove the head... bummer.

0 Good Comment? | | Report

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