Chipped Piston - Mercury 60

[BassnKY]

I have a problem with my 1984-85 Mercury 60 that I hope someone can help me with.

The last time I was out on the lake, all of a sudden, I lost power. It seemed like I only had it at half throttle.

Upon inspection, I found a couple of very small pieces of aluminum on the plug (NGK-BUHW - This plug has an electrode in the middle and no protruding grounding electrode) between the center electrode and the outer ring that was shorting out the plug. This was on the top cylinder. The first thing that went through my mind was a blown-up piston.

Next, I checked for compression. I have good compression in all 3 cylinders.
Next, I removed the intake and exhaust port covers. Upon inspection, I discovered a very small chip (Approximately 3/16" wide and 1/32" deep , - this is as close as I could measure with a dial caliper) in the ridge of the top piston.

After I discovered the chip, my next step was to look for a source of a piece of metal that could have caused the chip. I looked in the cylinders, intakes, exhaust, and lower end. The only thing I could find was 2 small areas in the intake cover where it appeared that the metal (Even though there was no corrosion) was trying to flake. but, I did not see any missing pieces.

Also, I checked out the cylinder wall and could not see any scratches. The only thing I could see was the normal wear patterns.

My only thoughts on the cause would be metal fatigue or running slightly lean caused the piston to get too hot.

Does anybody have any idea what could have caused this?

 

[Faztbullet]

Re: Chipped Piston - Mercury 60

That is called piston erosion due to preignition. Several causes are: weak water pump,lean fuel mixture from (A)debris in high speed jet (B)float level misadjusted (C)needle and seat damaged from ethonal fuel restricting flow (D) max timing misadjusted.

 

[will941s]

Re: Chipped Piston - Mercury 60

Something caused the chip in the piston. Did you check your reeds to make sure everything was still intact? What was the compression on the motor (numbers)? The power loss while running indicated a problem at that time, like that cylinder dropped. If the compression was good, then now you have to find out what caused that cylinder to drop when the problem occured. Keep us posted.

 

[will941s]

Re: Chipped Piston - Mercury 60

Faztbullet is the expert! What he said probably caused the problem.

 

[BassnKY]

Re: Chipped Piston - Mercury 60

will941s: Thank You for the response. I did establish what caused the cylinder to drop. The aluminum in the plug. While the aluminum was was still in there, I cranked it over and the plug (No plugs in the head) and it would not spark. I took it out and it sparked fine.

Fatzbullet: Thank You. This is VERY helpful.

A, B, & C) I will need to check the carbs. I have not taken them off yet. I would think that A & C would be the most likely culprits. I would not think the float level could have changed (Other than from debris) since I have not touched them. I only recently started using Marine Formula Sta-Bil regularly (Except to winterize).
As I am typing this, a thought came to mind. Could the sudden use of Sta-Bil have caused something to come loose and get in the jets. My fuel tank is plastic but maybe some gunk that was settled on the bottom got through the filter on the engine. (I know, I should also use an in line filter. I got one last year but never installed it , :redface

D) As far as the timing is concerned, I will need to check that once I put it back together.

Do you think it will it hurt anything to run the engine with the chip out of the piston. I know that I have run motor cycle engine with a small chip in the top of the piston (Back when I was racing motocross and did all of my own work).

Thank You to everyone!!!

 

[BassnKY]

Re: Chipped Piston - Mercury 60

Anybody have a thought on my last post?

Any help is greatly appreciated!!!!!

 

[CRFan1]

Re: Chipped Piston - Mercury 60

What you described is definitely caused by detonation in that cylinder...I have had it happen on my 2 stroke dirt bike. I would make sure you figure out what caused that cylinder to go lean and if it were me, I would consider doing a top end (piston, rings, etc.). Sorry

 

[BassnKY]

Re: Chipped Piston - Mercury 60

CRFan1:
Thank You for the input. Unfortunately, my currant situation and economy does not allow for a total top end rebuild.
I think my first step is going to be to establish solid numbers on the compression and go from there. I am thinking that if I have good (And consistent) compression numbers, I am going to find out what caused the detonation, fix that, and try and get it to last the season. BUT, my big concern is that the piston comes apart and the power head is lost.
Then, I can do a complete rebuild over the winter where I can spread out the cost by picking up the parts over a period of time.
Have you got any idea what my risk is in losing the top piston (assuming I get the original problem fixed)? My previous experience with a chipped piston has been good as long as I get the initial cause corrected.

 

[BassnKY]

Re: Chipped Piston - Mercury 60

OK. guys... Here are the compression numbers:

Please keep in mind that these are withe the intake (Incl. the fuel pump) and exhaust covers removed.

Top: 137
Middle: 142
Bottom: 137

I think these number look pretty good.

Because they are high, I took another look at the pistons and there is only a small amount of carbon build-up on them.

Any ideas concerning this and my previous post?

 

[sschefer]

Re: Chipped Piston - Mercury 60

OK. guys... Here are the compression numbers:

Please keep in mind that these are withe the intake (Incl. the fuel pump) and exhaust covers removed.

Top: 137
Middle: 142
Bottom: 137

I think these number look pretty good.

Because they are high, I took another look at the pistons and there is only a small amount of carbon build-up on them.

Any ideas concerning this and my previous post?

Is the carbon tanish brown or black?

 

[BassnKY]

Re: Chipped Piston - Mercury 60

sschefer:
Thank You for the response.
The carbon is black.

 

[Faztbullet]

Re: Chipped Piston - Mercury 60

Do you think it will it hurt anything to run the engine with the chip out of the piston

No.. just retard timing 2 degrees

 

[BassnKY]

Re: Chipped Piston - Mercury 60

Fatzbullet"
Thank you for the response. I will definitely retard the timing. I just want to get through the season.
What is your opinion of the compression numbers?

 

[BassnKY]

Re: Chipped Piston - Mercury 60

UPDATE:
I got everything back together and went to set the timing per this post in another thread:
Set WOT timing while cranking with the starter.

Remove all the spark plugs to reduce the load on the starter.

Ground all the spark plug wires, rig paper clips, alligator clips, etc., and wires to a good ground(s).

Remove the prop or be VERY CAREFUL of the spinning prop while cranking.

Use a remote starter button to trigger the starter relay/solenoid.

Rig your timing light on #1 plug wire.

Set throttle control to WOT in Forward gear.

Hit the starter button, crank the motor and observe the WOT Timing, adjust as necessary.

WATCH OUT for that prop if you didn't bother to take it off! The light was flashing on the opposite side of TDC. I have attached a pic to show which mark it was on.

I made sure the light was on #1 and well grounded. ANY IDEAS??

However, when I got the light on the wheel, I got a surprise.

 

[BassnKY]

Re: Chipped Piston - Mercury 60

UPDATE:
I got everything back together and went to set the timing per this post in another thread:


"Set WOT timing while cranking with the starter.

Remove all the spark plugs to reduce the load on the starter.

Ground all the spark plug wires, rig paper clips, alligator clips, etc., and wires to a good ground(s).

Remove the prop or be VERY CAREFUL of the spinning prop while cranking.

Use a remote starter button to trigger the starter relay/solenoid.

Rig your timing light on #1 plug wire.

Set throttle control to WOT in Forward gear.

Hit the starter button, crank the motor and observe the WOT Timing, adjust as necessary.

WATCH OUT for that prop if you didn't bother to take it off! "


However, when I got the light on the wheel, I got a surprise.

The light was flashing on the opposite side of TDC. I have attached a pic to show which mark it was on (Yellow arrow)

I made sure the light was on #1 and well grounded.

Alos: I went ahead and fired it up. It seems to be running fine, has good acceleration, and a smooth idle.

Something is off I assume on the light. ANY IDEAS??