Cause of cracked piston ?

BKool68 · Jun 24, 2002

I am working on an 99 225HP Evinrude. The top right piston cracked across the top in 2 places but did not hit the head. I am guessing water must have entered the cylinder? Or is there another possible problem someone knows about? I am honing the cylinder and ordering a piston and gaskets to put it back together maybe this weekend. Thanks for any help you can offer Brian

BKool68 · Jun 26, 2002

Re: Cause of cracked piston ?

Year of motor is 97 not 99. Does anyone have any input on this subject? Brian

BKool68 · Jun 26, 2002

Re: Cause of cracked piston ?

Dhadley any thoughts on the cause? Motor has been de-carboned each season and carbs done.

Hooty · Jun 26, 2002

Re: Cause of cracked piston ?

What was the orientation of the cracks in relation to the wrist pin? Parallel, perpendicular, at an angle? c/6 Hooty

BKool68 · Jun 26, 2002

Re: Cause of cracked piston ?

I believe they were paralell to the wrist pin.

Dhadley · Jun 26, 2002

Re: Cause of cracked piston ?

When you get the piston out can you post a pic? Good luck!

russthemuss · Jun 26, 2002

Re: Cause of cracked piston ?

Hi BK check out this site its got some good explanations. piston seizures ]

BKool68 · Jun 27, 2002

Re: Cause of cracked piston ?

The piston did not sieze and the rings were not broken. The piston is not melted on the top but the sides have some scoring. I will try to take a few pics tonight after work.

BKool68 · Jun 29, 2002

Re: Cause of cracked piston ?

I am unable to post pics yet. The cracks are not in any set orientation. The top of the piston appears to have an indentation near the center. I ordered the new piston, it is a Wiseco but has some slight differences from the original. On the stock piston there are 2 triangular pockets on each side of the piston above the wrist pin. The wiseco piston does not have these pockets. Other than that they appear to be the same. Should I send it back for another?

ShafferNY · Jun 29, 2002

Re: Cause of cracked piston ?

I don't know anything about wether that piston will work for you or not. My suggestion it to call Wiseco, they'll know. I tore down a 300hp evinrude that had a detonated piston. It so happens to have been one on the top right. My teacher in Marine Tech (High School) told us that it's common for that cylinder to run leaner than the rest because it's at the top of the engine. I think what probably happens is that the atomized fuel/air mixture in the crankcase may settle(due to gravity) and thats why the top one runs leaner. I'm not sure though.

BKool68 · Jun 30, 2002

Re: Cause of cracked piston ?

What you are saying is that a lean fuel mixture will cause combustion strong enough in the cylinder to dent the head of the piston and crack it without a meltdown of the piston? I have also been told that an early firing of the cylinder on the combustion stroke may have caused the damage. I am waiting for more input and a call to wiseco about the piston before I reassemble. Thanks to all who answer. Brian

ShafferNY · Jun 30, 2002

Re: Cause of cracked piston ?

I'm not sure if that would cause a dent or a crack. It sounds almost like it hit something. Maybe a spark plug, I don't know? I understand your logic, if there was water entering the cylinder it may cause the piston to crack, but why the dent?

Hooty · Jun 30, 2002

Re: Cause of cracked piston ?

The reason I asked about the crack orientation is because the strongest part of the piston is above and in line with the wrist pin thus the "breaking away" of the piston from the wrist pin. I think it got water-hammered. That's my opinion and it's worth exactly what you paid for it. Post foto if you can and keep us updated. c/6 Hooty

Dhadley · Jul 1, 2002

Re: Cause of cracked piston ?

The correct Wiseco number for your motor is 3043 or 3143. The letter P or S means port or starboard. The next number or letter is the bore size, ie. 2 = .020, 3 = .030, 4 = .040 or S for standard although obviously you will be boring at least that cylinder. The triangle holes you refer to are used to lighten the piston. The Wiseco total weight is matched to factory without using them. The most important thing is find out what made the dome of the piston cave in. Otherwise the new piston will do the same thing. It almost sounds like it was trying to go into detonation. Make sure you have the timing correct, use the correct spark plugs and have fresh 87 octane fuel. Keep us informed!

Dhadley · Jul 1, 2002

Re: Cause of cracked piston ?

Actually the hottest cylinders on a looper are the bottom cylinders. It has to do with exhaust routing. Just a thought.

Dhadley · Jul 1, 2002

Re: Cause of cracked piston ?

Just a little bump..................

Dhadley · Jul 2, 2002

Re: Cause of cracked piston ?

Or a little shove to get it to the top........

BKool68 · Jul 2, 2002

Re: Cause of cracked piston ?

We finished cleaning the cylinder and installed the new piston. Too hot to do much work. Still need to clean the block surfaces to seal her back together. One of the head gaskets was crushed a bit at the metal ring, but not sure if it was the bad one. We will be cleaning the high speed jet on that cylinder to make sure it was not leaning out. Thanks for all the advice on this job. If I get a chance I will try to take a pic of the piston and post it. Brian

BKool68 · Jul 2, 2002

Re: Cause of cracked piston ?

Sorry but still no pic... been too busy putting back together. The powerhead is assembled minus the heads. I just need to mount it on the leg and connect the hoses, wires and linkage. I also want to check the jet on top carb. I looked briefly at the Seloc manual for that but not sure of the job. Will read the book more tomorrow. Thanks for all the input. Brian

Cause of cracked piston ?

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