No Compression on one cylinder Mercury 200HP Outboard V6. Need Advice

Need some advice. I have a 2000 Mercury 200HP outboard (Carb) with no compression on one cylinder (top on Starboard side). Long story short, oil line came off, did not notice(dont know how), was running at ~3000 RPM and motor shut down and coasted to stall. Not sure if shut down with some safety interlock (temp, oil). There was no sudden lock of the motor. Repaired oil line, put oil in and started right up. HOWEVER, I could tell something was not quite right so idled to a dock in about 5 minutes and took out of water(30 miles around St Clair...lol)

I have worked on cars and 2 stroke motorcycles most of my life, but never tore into an outboard. I have searched through this forum and found some great info but wanted to throw this out to those of you who are more experienced.

So: I did compression test and found no compression on the one cylinder. All other cylinders were in spec. Sorry, lost numbers, but clearly the issue is the one cylinder that is dead. I did not see obvious "damage" in the cylinder, but feel certain that the cylinder is glazed and rings are gone. This motor was rebuilt by factory authorized dealer~5 yrs ago. It has ~4-500 hrs on it since that time.

I see no other choice than to pull the head and inspect the cylinders. In fact, I dont see any way around splitting the block.
So here are my questions for you all:
- Would your approach be to dive right in, pull the head and split block to inspect?
- Do you think it is possible that new rings and good crosshatch honing could do the trick?....or am I looking at an oversize bore. I know you cant tell for sure without numbers and a visual, but just a gut feel would do.
-Assuming I split the block and I can get by with rings and hone, wouldn't it make since to do all cylinders? Seems like a no brainer, but with 4-500 hrs and if they look good and compression is in spec....?
-What else should I be looking for? My thought is, if I dont "see" anything obvious, then dont mess with taking the crank out....but is that nieve?....I would inspect the rod bearing and piston pin bearing, and if visual ok then go with it.
-About splitting the block: I dont have the motor right with me now, but from the diagrams I assume the way to approach is from the intake plate side and leave the cylinder part of the power head attached to the drive shaft mount, then go at the rod bearing cap from there?

Sorry for the long post, but wanted to give and ask some details to start this thread.
Thanks for taking time to help.

Re: No Compression on one cylinder Mercury 200HP Outboard V6. Need Advice

Mine kept overheating because of a blown head gasket on that cylinder. Gasket is about 30 bucks at Merc dealer. Head is super simple to pull. Check in on a piece of glass for flatness and have shaved if necessary. Who knows? After you check for obvious cylinder damage, might get lucky!
Where was your oil line issue specifically? Need to check mine then :0)
Regards
Mike T

Re: No Compression on one cylinder Mercury 200HP Outboard V6. Need Advice

Long story short, oil line came off, did not notice(dont know how), was running at ~3000 RPM and motor shut down and coasted to stall. Not sure if shut down with some safety interlock (temp, oil). There was no sudden lock of the motor. Repaired oil line, put oil in and started right up.

Click to expand...

If it was oil line to oil pump/pump to fuel line and oil tank got low you should have had a alarm. If it was oil line its possible motor siezed due to oil stravation. If it was the small line to cylinder thats a recirc line and would not cause cylinder to lean out enough to cause failure if off.

I see no other choice than to pull the head and inspect the cylinders

Click to expand...

Your first step for basic inspection is pull heads(both) as a blown head gasket could fix it right up. If it has damage you will see it on piston/s and cylinder walls.

Would your approach be to dive right in, pull the head and split block to inspect?

Click to expand...

Only pull and split block if cylinder/s & pistons is damaged...

Do you think it is possible that new rings and good crosshatch honing could do the trick?....or am I looking at an oversize bore.

Click to expand...

If its lack of oil failure doubtful more likely to be bored...

Assuming I split the block and I can get by with rings and hone, wouldn't it make since to do all cylinders?

Click to expand...

Thats the correct way....

-About splitting the block: I dont have the motor right with me now, but from the diagrams I assume the way to approach is from the intake plate side and leave the cylinder part of the power head attached to the drive shaft mount, then go at the rod bearing cap from there?

Click to expand...

It will have to be totally removed from midsection and sent on a bench/table...

Re: No Compression on one cylinder Mercury 200HP Outboard V6. Need Advice

Thanks for the reply. About the oil line: I wish I could give you something really enlightening to check on your boat. Oil line from separate tank to engine oil reservoir was the issue. I preached many good sermons to my boys about safety and systems checks, but gun to my head, this one had to be me as I had worked in that area....nuff said, cant talk about that one any more. I havent looked at the boat since Aug.

Concerning the alarm: it is a very good question. bottom line is I did not get the alarm. The engine oil reservoir was...a....ouch, I cant say it.....empty. I suppose a good seaman would log each time they get the test alarm pulse upon startup....unfortunately, i just cant say that I did or did not.....sigh. Anyway I will find the answer.

Hopfully tomorrow I will be able to pull the heads.

The thing that has been eating at me is the manner that the motor shut down. It was like a kill switch and then a coast. Since all but one cylinder mesured in spec on compression, what stopped the motor? why didnt it keep going until 3 or 4 died? I dont see anything in the service manual descriptions that says the motor would be shut down upon low oil or high temp. Just that the alarm will sound (which did not happen). From the schematics, I can see that the temp signal and oil signal are inputs into the engine control unit, but cannnot tell what action is taken other than the audible alarm. Guess I'll know soon. I'll let you know what I find.

Thanks,

Where do you suggest I buy parts?

Re: No Compression on one cylinder Mercury 200HP Outboard V6. Need Advice

Here at iboats.com if available. If not, from any reliable source. For pistons, Wiseco have a good reputation. But don't throw any money in parts until you split it.

Re: No Compression on one cylinder Mercury 200HP Outboard V6. Need Advice

The only action from module is a series of beeps from horn,this is also tied into the overheat wiring. The reason it shut down is it siezed. For parts here at iBoats and pistons from Promarine or Mallory as Wiseco's if not broken in properly and bored a tad oversize will cold sieze....I myself do not install them in customers motors unless its a have to case(.064 oversize)

Re: No Compression on one cylinder Mercury 200HP Outboard V6. Need Advice

Update for today:
Startboard head is off. I was wrong on the bad cylinder #. 1 and 3 look ok. #5 is the issue. Havent pulled the other head as we jumped directly into preparing to remove the powerhead. Should have it off tomorrow if I can find an lifting eyelet to hoist it off the adaptor plate.
#5 Cylinder clearly an issue as I can see and feel scores in the cylinder along the axis of the rod. There is one small spot of "buildup" (small lump of metal), but no visible damage to piston. Motor is not seized.

Head gasket was perfectly fine.
Found wires from oil level sensor wires not connected !! @#@$%&*!

Thanks for parts info. I assume buying a kit is the way to go but need to investigate contents.

Thanks again guys.

Re: No Compression on one cylinder Mercury 200HP Outboard V6. Need Advice

Update:
Pulled Powerhead off and it is now stripped down to the block. Plan to spilt block this week.
I did not buy a powerhead stand (the vertical one, that has a spine welded to a plate. That might have been nice, but I just drilled some holes in the workbench and sat the powerhead vertical while I did the sub-component disassembly.
Now that I am near the point of splitting the block I need to get this thing horizontal. This obviously leads me back to the stand question. Im sure there is an expensive wiz-bang Merc stand out there to do this, but I'm wondering what suggestions you all may have for an improvised solution?
I assume I will need to rotate between crank side and head side with powerhead horizontal during assembly of rods, pistons, crank, etc. I got rid of my car engine stand. Could by a simple one and make an adaptor plate? The studs coming from the bottom of the powerhead dont have threads for the ~4" so large spacers,etc are needed. Also, this motor is not really designed to cantilever, so I assume I would have to grab 6 studs. I dont know how the Merc horizontal stand works(no pictures) What am I missing here? Im sure one of you guys have an improvised solution....maybe not, just but the darn stand? Would appiciate any advice you may have.

Re: No Compression on one cylinder Mercury 200HP Outboard V6. Need Advice

Just wondering how this went... (right, just wondering... NOT... I am in the same situation and want to know my course of action...)

My situation:
Running 4000RPM pulling a skier. Loses power and stops. Nurse it alive and get part way home then it seizes... no alarms or anything. back at the dock I find the oil line has simply broken AFTER the resevoir. Between the pump and the fuel, basically the last 6 inches of line before it hits the gas. No alarms in there at all.

Park it for a couple of weeks until I can get to it. Finally get free time. Pull plugs, spray oil in each cylinder and try to turn it over, it turns over. Put plugs in for yuks and try it, it runs. Shocked and amazed, but not convinced this is just a happy ending. Compression test. 5 cylinders 100 PSI. Top port cylinder 0 PSI. Bubble bursts. Recheck. Same. Get a little endoscope camera from ebay and view inside the offending cylinder. Lots of aluminum on the cylinder wall.

Winter project.

Winter is over, never got to it.

I have the block off and am about to split it.
I have a few theories and would like others wisdom to help direct me. your experience is nearly identical so I was hoping your outcome might help me decide, and I am open to others opinions.

My theory is that if its just the piston/rings then it might be worth it but if the crankshaft is involved I would buy a used motor of the similar vintage (1995 200 EFI) for $4000 and get boating and have mine for spare parts for the inevitable next disaster. That seems more logical to me than a new block for $3500-$4000.

But assuming a repair I still have questions...
Can I clean up and lightly hone the one cylinder and replace the one piston and go?
Can I bore out the one cylinder and put in one oversized piston and go?
Should I more out all cylinders and put oversized pistons in all 6 cylinders and go? If I go with this option, I am looking at about $400 in boring and $1000 in pistons and rings and gaskets and such for the rebuild kit and thats getting to be a significant portion of a used motor.

Any opinions welcome. Thanks in advance.

Re: No Compression on one cylinder Mercury 200HP Outboard V6. Need Advice

Rebore and go oversize for that hole only. They do it all the time.