How did my outboard get holes in the pistons?

[BigB9000]

Outboard is a 75hp johnson, year is 81

pics:

I couldnt get a compression reading from the top 2 cylinders, but the bottom had 30psi (the one without the hole in it)

How does this happen? or are they supposed to be there? and whats with the clean spot on the pistons?

 

[F_R]

Re: How did my outboard get holes in the pistons?

Am I blind? I don't see any holes. Or are you looking at that little hole in the center of the piston? That is a centering hole to center the piston in a lathe when it was made. Absolutely normal. It doesn't go thru does it?

 

[BigB9000]

Re: How did my outboard get holes in the pistons?

all the way through. a needle go in untill it hits the connecting rod. But why is the 3rd cylinder different from the others? why have that dime sized area on it?

 

[lbentz]

Re: How did my outboard get holes in the pistons?

Well, let me get this straight. each of the cylinders have a hole in the center, that goes clear down to the connecting rod? Are these holes cleanly cut? Or are they like burned through?

Well, if they are machined through, as in drilled and such, then I wouldn't be too alarmed. I think your compression problem may be your reed valves.

Leon

 

[BigB9000]

Re: How did my outboard get holes in the pistons?

No, only 2 pistions have a hole in them. smack dab in the center. You can easialy see it in the pic.

2 cyl have them, 1 dosnt
(conviently the pistion without the hole was the ONLY pistion that has compression)

So, yes they are clean cut, almost like they were machined.
But, why would only 2 have hole, and not the 3rd?

And whats a reed valve?

(the thins on the inside of the intake manifold?)

 

[rupertmja]

Re: How did my outboard get holes in the pistons?

Looks like the holes are the original machined holes. My bet is they do not go right thru and that your rings were probably not sealing. Probably needs a rebore. The bottom piston - it has most likely been replaced at some point. Some people rebore one cylinder in two-stroke engines, leaving the other two as they were. Of course, it is best to rebore all of them at the same time. Does it have any oversize numbers on it? Shiny bit - looks like a bit of carbon has fallen off. Did you use some carb cleaner or anything before you dismantled it? Some carb cleaners are great at removing carbon.

PS I think you need to tidy up your garage. My mate's is the same and he can can never find anything. Tell me it ain't true.

 

[F_R]

Re: How did my outboard get holes in the pistons?

all the way through. a needle go in untill it hits the connecting rod. But why is the 3rd cylinder different from the others? why have that dime sized area on it?

OK, so they aren't centering holes. Whether or not pistons have centering holes depends on whatever manufacturing process they use to make them.

Now, the big mystery is why do your pistons have holes drilled all the way through the pistons? I don't have the slightest idea. By the carbon in the holes, it would seem that it has been running that way. Pistons burn holes through often enough. That is caused by pre-ignition. But in that situation it is an obvious burn-through, not neat little drilled holes smack in the center.

As I said, I don't have the slightest idea why your pistons have holes drilled through. It would seem like a very dumb thing to do.

 

[BigB9000]

Re: How did my outboard get holes in the pistons?

Yeah, the place is dirty. Its actually a lot worse than it looks, thats the trick photography for you. But thats from trying to put the (new to me) 19' boat, into the 18' garage. I had to throw things out of the way, off the racking, etc to get the thing to almost fit in there. If the racking wasnt there Im sure the boat would fit right in.

Now I just need to decide whats more important to me, the racking, or the boat fitting in the garage

 

[Pleasure Boat Junction]

Re: How did my outboard get holes in the pistons?

Looks like a former owner had an enemy who destroyed it on purpose by drilling through the spark plug holes. Bottom one doesn't have a hole because the pan is in the way. Just my guess?

 

[BaileysBoat]

Re: How did my outboard get holes in the pistons?

Are the holes the same size ?

 

[NelsonQ]

Re: How did my outboard get holes in the pistons?

Looks like a former owner had an enemy who destroyed it on purpose by drilling through the spark plug holes. Bottom one doesn't have a hole because the pan is in the way. Just my guess?

They'd be quite skilled to hit it that dead center and clean a hole. Certainly looks weird to me. Never heard of it. I think we're all in agreement this isn't normal.

Hoping some of the experts who've done years of this stuff can explain.

 

[Tim Frank]

Re: How did my outboard get holes in the pistons?

Bizarre!
If some sicko did get loose with a drill, the metal shavings would have fallen into the cylinder and there would be evidence of scoring at 6 o'clock on the cylinder wall. Might have messed with the rings, too.
Drilling through a spark plug hole and free-hand, that is a pretty precise job, though.
BigB, are there any longitudinal scratches on the cylinder wall?

 

[itsaboattime]

Re: How did my outboard get holes in the pistons?

The only holes I've ever seen in pistons have been burnt there by plugs that were too hot. They were big ol gnarley holes too!!! Not neat lil round ones that look machined.

Have you had this motor for a while?? Did it useta run?? If you just got it I would talk to the former owner and find out what happened.

 

[Joe Reeves]

Re: How did my outboard get holes in the pistons?

Those holes do not belong there. Somebody somewhere does not like somebody.

 

[CATransplant]

Re: How did my outboard get holes in the pistons?

Yup, it appears to me that someone has sabotaged that outboard. Not a good thing. You might want to speak to the previous owner and get the story of that outboard. I'm betting it quit running one day. He might even have an idea who did it...not that it does you any good.

 

[G DANE]

Re: How did my outboard get holes in the pistons?

Not relevant to your question, but it looks like an Evinrude to mee, most Johnsons are white. Sure looks like the common center marks on some piston brands. Are you perfectly sure they go thru the piston ?? Put a wire down as long as you can, and mesure how much. Your problem might be blown headgasked, sticking rings or something else, much simpler to adress.
Only way I can see anybody hit that well thru spark plug hole, is that they drill in a center mark that is already there, and there is almost no possibility thay can see where they hit, as spark plug hole is the only opening. Sounds weard if there shouldnt be marks beside the right dean in center hole. Better recheck. Cant imgine anyone taking head of to drill holes in 2 of 3 pistons, might do a lothers to sabotage.
Sorry for doubting.

 

[jonesg]

Re: How did my outboard get holes in the pistons?

fix it!
I think I'd at least try tapping it the next size up.
screw a bolt in and cut it off flush.

 

[noelm]

Re: How did my outboard get holes in the pistons?

not too sure I would be putting a bolt in my pistons and cutting it off, but to each their own I guess, first off, I guess it is really remotely possible that the pistons had the machine holes in the top from new, and it has been running way lean and burnt through the thinnest part (the tiny indent in the centre) very unlikely though, more than likely, you are mistaken and only think they go right through and there is some other problem causing your no compression on those cylinders, like it was rebuilt with 1 new piston (the odd one) and now something else has crapped out because of the cheap patch up rebuild!

 

[Pleasure Boat Junction]

Re: How did my outboard get holes in the pistons?

BigB, I don't think it is mentioned, but did you check to see if air would blow through the holes?

 

[BigB9000]

Re: How did my outboard get holes in the pistons?

A finishing nail will go 3/8 - 1/2 inch in before hitting something.

Other than carbon, it looks clean the 3rd piston was probably a replacement, it has numbers all over it. Inner cylinder walls look clean, no schraches. If the hole wasnt so deap, I would agreee its from a lathe. But Im not quite sure about that. But unless somebody drilled a perfect hole - this happened on its own.

I would also agree that engine failure lead to the weaking of the hole.

I Dont feel like putting my mouth on it to see if air goes through, and I couldnt tell with a little hose.

The outboard was/is a royal peice of crap. Somebody spray-painted it blue, and used random fastners all over to probably rebild it. None of the screwes were very tight, the flywheel pin was sheared off, carbs linkage was held together with zip ties.

Just all around a pile.

So I took It apart.