84' merc 60 piston problem

[grp44]

First let me say thanks to the fourm for all the help.<br />I have a 60 #6429095, lost commpresion in the top hole. I pulled the ex. cover and found stuck and broken rings. Sent the block to be repaired, I didnt know what caused the problem, no signs of timing or fuel probs. <br />Got the powerhead back and after over ten tanks of fuel same thing, 30 lbs commpresion,stuck and broken rings.<br />After pulling the crank assy. I noticed that the newer piston was diffrent from the rest. The new piston does not have the large hole 90 degrees from the piston pin as on the others. <br />Could this be a problem,and any ideas on what could be eating the top piston.<br />Thanks Mike

 

[Clams Canino]

Re: 84' merc 60 piston problem

Actually... it not having the hole would tend to work "against" the problem, though it's kind of strange to mix and match like that.<br /><br />Past that you need to make sure timing is 21 max, good (midgrade) fuel to the top carb, and that it's propped to make the proper max RPM.<br /><br />Make sure the top float valve is opening up all the way. I ate a couple pistons when my middle carb wouldn't open wide enough to handle WOT over an extended period. Was flowing fine enough to handle 4500 all day or 5500 for 20 seconds or less.<br /><br />Lastly, examine cooling issues, check for new pump impeller, passages clean etc etc.<br /><br />Melted pistons never "happen" there IS always a cause.<br /><br />-W

 

[AMD Rules]

Re: 84' merc 60 piston problem

Was the top of the piston damaged from detonation (timing problems)?<br /><br />Was the wear on the skirt most notable 90° from the wrist pin (thermal expansion)?<br /><br />Any unusual noises prior to the problem(bearings)?<br /><br />Did the repair shop give you any indication what they found when they dismantled the motor, and what items were replaced with new?<br /><br />Does your motor use the autolube oil injection system?<br /><br />Have a peek at the links below in my signature... I can relate well to your situation.

 

[Laddies]

Re: 84' merc 60 piston problem

I have a couple of the 3 cyl 60 hps with the wrong main jet both came from the factory with them in the carbs and both suffered from preignition

 

[grp44]

Re: 84' merc 60 piston problem

Laddies what size should the jet be? There is no damage to the top of the piston, other than bits of ring stuck into it. I mixed the oil, and ran at 40 to 1. I'm thinking overheating in the top of the block some how.

 

[Laddies]

Re: 84' merc 60 piston problem

Both engines had .072 in the top carbs and should have been.0785 jets, both had alum. on the plugs from the pistion deflector, if the top isn't burned you have a differant problem. Look the ports over good to see if one may have snagged a ring

 

[grp44]

Re: 84' merc 60 piston problem

Thanks guys, taking the block to the machine shop to check bore. Forgot to mention that the upper o-ring was shereded when I lifted the bearing off.<br />I'll be back.<br />Mike

 

[AMD Rules]

Re: 84' merc 60 piston problem

If the upper bearing cap o-ring is shredded/damaged could the crankcase be pulling in air & run lean? Maybe it would affect the upper cylinder the most? <br /><br />I'm grasping at straws.

 

[grp44]

Re: 84' merc 60 piston problem

Any ideas are are welcome,thanks AMD. I should be getting it back togather next week. I hope it holds up better than last time. AMD, or any one, without having a Merc ring compresser, is it ok to use my fingers and work slow?

 

[AMD Rules]

Re: 84' merc 60 piston problem

Surely I am not the best one to give advice...BUT...<br /><br />The first time I assembled my motor by hand, alone. I thought for sure that it went together fine. Turns out I must have busted a ring.<br /><br />Second time around, I tried to get an assistant to help but I still found it easier alone. I checked the rings through the exhaust ports afterwards (forgot to do that the first time).<br /><br />So far all seems fine.<br /><br />Having 3 ring compressors is better, but it can be done by hand.

 

[grp44]

Re: 84' merc 60 piston problem

I just got the new piston I ordered, but its a low dome and only has 2 rings. I think the 2 rings are ok, but what about the low dome? should I mix the dome hight?.......... Laddies-Clams-AMD

 

[grp44]

Re: 84' merc 60 piston problem

I got the new piston installed. What a feat to get the piston pin in. I had to chill the pin and heat the piston.<br />Used some strips of 1/8 aluminum held with hose clamps to compress the rings, worked fine, slid the crank with pistons right in. Checked the rings through Ex. port, all was fine.<br />COMPRESSION<br />125 new low dome piston<br />130<br />130.<br />I will check the compression again after I burn this 6gal tank of fuel at 25 to 1.

 

[AMD Rules]

Re: 84' merc 60 piston problem

Congrats on the re-assembly. I'm not sure if the low dome is ok or not, but I bet it would be fine. You'd see a small amount of compression loss as a result. Did the new piston have the port on the side of the skirt?

 

[grp44]

Re: 84' merc 60 piston problem

The new piston does have the port on the side.<br />Going to drop her in the lake as we speak.<br />Later and thanks <br />Mike