What might of caused this?

Koltar

Cadet
Joined
Mar 18, 2002
Messages
21
This piston is out of a 115 1981 johnson V4 that came off a boat that i bought, im rebuilding the motor and was curious why the piston did this. And if i should look into why this happend and make sure it doesnt happen to the new pistons when i install them.<br /><br />if you look at the piston from the top you can see one edge of the dome looks burnt off, and all around the edge of the piston its very rough. Also it looks like there is melted metal flakes like on top of the piston.<br />
pistontop.jpg
<br /><br />If you look at it from one side you can see that the wristpin is recessed a little bit and some of the ring is actually gone. also there a lot of scratches in it.<br />
piston0.jpg
<br /><br />on this side of the piston it shows the wristpin out to the edge of the piston. there is also a cavity that you can see better from this angle than you can from top that actually goes behind the top ring. I think this is why i was getting 10psi. compression on that cyllinder =).<br />
piston1.jpg
<br /><br />Anyways i hope someone can fill me in on what i should look for and do before i put this motor back togather, i decided to just bore it .064 over and do all 4 pistons. This piston caused a pretty major scuff so i think i gotta go all the way on the boring =(.<br /><br />Koltar
 

butlp

Petty Officer 1st Class
Joined
Feb 26, 2002
Messages
302
Re: What might of caused this?

Koltar,<br />Was it by any chance the top left piston? I had a 235 OMC that looked very similar and it was caused by lack of cooling at WOT. Plastic bag covered the water intake. I had to replace the head as it was badly damaged too.<br /><br />Are the other three pistons OK?<br /><br />If I were rebuilding the motor, I would service and make sure the VOR was working properly, overhaul the carbs and check the ignition before you run the motor again. <br /><br />Good luck,<br />Peter
 

Koltar

Cadet
Joined
Mar 18, 2002
Messages
21
Re: What might of caused this?

no actually it was the bottom right piston, which would be the piston on the bottom on the drivers side.<br /><br />This motor doesnt have VRO, but i see what your saying this might of been caused by lack of water cooling.<br />thanks =)<br /><br />Koltar
 

Koltar

Cadet
Joined
Mar 18, 2002
Messages
21
Re: What might of caused this?

oh btw the piston above this one has some dings in it and some scuffin on it also but nothing near this bad. I think i still got 60psi out of it.<br />On the other side both pistons are fine, but im replacing them also because they are too loose in the bore and are kinda low on compression, i think they were 100psi. <br /><br />how much it cost to rebuild the carbs?<br />i was planning on cleaning them out just didnt know how easy it is and how much it cost to rebuild them.<br /><br />Thanks again<br />Koltar
 

butlp

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Feb 26, 2002
Messages
302
Re: What might of caused this?

Koltar,<br />I would be suspicious of bad fuel/oil mix then if no VOR. Make sur you put fresh gas/oil (for break-in) before you start the engine again. <br /><br />My motor was non VOR too and the other five pistons were perfect and I only re-ringed them. The bore on the bad piston was still good so I was lucky and only replaced the piston and new rings, plus a new head.<br /><br />I stripped and cleaned the carbs, making sure all the jets were nice and clear, the floats set to spec. and replaced the gaskets, which were not expensive.<br /><br />I replaced the plugs and set the timing as per the factory specs and fired it up and it ran perfectly and I sold it a couple of years later.<br /><br />I was lucky to have access to a clean room when I reassembled the motor, all those roller bearings don't like dirt or bits of piston. Make sure you use lots of fresh two stroke oil on all bearings and pistons when you re-assemble.<br /><br />If you don't have a OMC Parts Catalog or Service manual for your motor I would strongly recommend buying them as they are invaluable.<br /><br />Good luck <br />Peter
 

Beernutz

Petty Officer 1st Class
Joined
Aug 14, 2001
Messages
287
Re: What might of caused this?

You're on the right track, rebuilding the carburetors, Koltar. Looks like a serious lean condition on that side of the motor, for whatever reason. Main jets clogged?<br />OMC carb kits are comparatively cheap.
 

dick

Chief Petty Officer
Joined
Oct 4, 2001
Messages
433
Re: What might of caused this?

Looks like detonation to me .This could be caused by , WOT timing set wrong, over proping (engine not getting to WOT RPM ) , lean mixture or air leak, bad fuel, If it lack of oil you would notice crank and rod damage .
 

BKool68

Petty Officer 1st Class
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Oct 14, 2001
Messages
259
Re: What might of caused this?

Hi Koltar, I have an 1986 110 Evinrude with VRO with a piston like yours. My oil line broke and caused a lean mix that melted the piston. Before spending serious money with boring and 4 new pistons, hone the cylinders and measure the gap on new rings in the cylinder. You might not need to go through all the expense, unless you have alot of money to burn. If that is the case maybe you could send some my way. I would spend the money on a good carb rebuild though. Just my 2 cents.
 

Koltar

Cadet
Joined
Mar 18, 2002
Messages
21
Re: What might of caused this?

cool you know what i really dont have the money to rebuild this engine. im glad you mentioned that cause when i bring the pistons and block into the marina to get worked on im going to ask him if i actually am going to need to do all 4 pistons or coul di get away with just doing the 2 and honing the others and using the original pistons and getting new rings for them.<br /><br />could save me a few hundred bucks<br />which i really dont have at the moment, but what can i do, i dont want to leave my motor sitting in pieces. =(
 

BKool68

Petty Officer 1st Class
Joined
Oct 14, 2001
Messages
259
Re: What might of caused this?

When you said you had 100 psi on some pistons it sounded like honing and rings would work. I don't believe in spending money that is not needed. It saves some for more important things like fuel and bait. I have found this site helpfull in saving everyone a little money and agrivation.
 
D

DJ

Guest
Re: What might of caused this?

Koltar,<br /><br />She melted down. I would strongly suggest you go throught the carbs. Carb. kits are about $15.00-$20.00 each. You'll need two.<br /><br />Also make sure the thermostats are working. Probably would be cheap insurance to replace them.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: What might of caused this?

Had you run this motor or was it this way when you bought it?<br /><br />Let us know. Good luck!
 

Koltar

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Joined
Mar 18, 2002
Messages
21
Re: What might of caused this?

this was the way it was when i bought it, but i did go out and run the motor on the lake but it would only do about 30mph.<br /><br />I could tell something was wrong, the guy at the marina told me the motor might need to be rebuilt.
 

Koltar

Cadet
Joined
Mar 18, 2002
Messages
21
Re: What might of caused this?

hrmm im not sure wont know until friday, do you konw what ones should be in it?<br /><br />I cant look at them because they are sitting on my boat inside a garage, 100 miles away =). I go to work on it on the weekends.<br /><br />Koltar
 

novacane

Seaman
Joined
Mar 8, 2002
Messages
70
Re: What might of caused this?

yep that cylinder leaned out and than detention reared its ugly head bang thare goes the piston
 
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