How did my outboard get holes in the pistons?

[BigB9000]

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

...and the power trim/tilt dosnt work!

 

[SKEETR]

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

Clean up the holes, slap some jb in there and retest your comps. Should solve the mystery of two holes.

 

[lbentz]

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

Okay, as Pleasure Boat Junction mentioned, see if air can pass through the holes. If not, then I wouldn't worry about the pistons. You stated that the cylinders look good, so I would then check the reed valves. If the reed valves aren't working right, then you won't have any compression. Check the head and make sure that it is not warped, otherwise, you'll lose compression into the water jacket and yes, the reed valves are in the intake manifold. If you want a better look at the pistons for scoring, pull the bypass covers off the motor and you'll be able to get a visual through the intake ports. Typically, anything that will likely score the pistons will start there. If the pistons look good, then it's likely that they are not the problem.

 

[tx1961whaler]

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

Divorce Engine. The ex-wifey probably hated that boat.....
Had a buddy whose ex put carbide grinding powder in his Vettes' engine oil....

 

[iwombat]

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

Unless the exhaust is totally clogged up AND the reed valves are stuck shut, reed valves have nothing to do with compression - bad or otherwise. Bad ring seals, holes in the pistons, or a bad head seal (or bad head) are the only things that cause bad compression readings.

I think you're going to want to see if those holes actually do pass air. Strange beasties regardless.

 

[lbentz]

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

Reed valves have nothing to do with bad compression?? HAH!! I beg to differ. When your piston is going up to fire, it brings in fuel/air mixturethrough the intake at the same time. As soon as it fires and returns to the bottom gead center position. the pressure it creates in the block forces the fuel/air mixture into the cylinder again. If your reed valves are not working correctly, then you won't build the pressure that forces the the fuel/air mix to the cylinder. Did you ever know a 4 stroke engine to run on a cylinder that has a burnt valve? NO! It ain't happenin' All parts (what few there are) have to work correctly, in order to get the proper compression and fuel/air mix to flow right. Pressure in the block, is as important as compression in the cylinders. Since the head is off, you can crank the engine over with the starter to see, if there is fuel/air mix blowing out through the intake ports and out where the combustion chamber is.

It's hard to believe that neatly drilled holes were put into a pair of pistons to kill your compression. with holes that small, you should at least get a few pounds of compression.

Check the head gasket too, and see if there is any sign of pressure blowing through to the water jacket.

 

[Evinrude Boater]

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

If you don't want to blow through the holes you can tip the motor up so the top of the pistons are horizontal and put some fuel in the holes and see if it drains through.

 

[jonesg]

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

On the compression stroke, as soon as the piston closes the ports then cylinder compression begins, with bad reeds there would be slightly less due to intake not being charged but it will still be there ...unless the rings are stuck/broke.

 

[iwombat]

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

Yep, let's not forget air coming in through the exhaust too. You can do a compression test with the intake entirely removed. For that matter, you can do a compression test with the carb throttle plates closed too. It makes no real difference on a 2-stroke.

If you don't believe me, go try it.

 

[noelm]

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

well done Wombat, I was just started to get a tad peeved about the reed valves and compression thing, sounds to me like a backyard rebuild, still got my doubts on the holes going right through, and certainly don't go with the conspiracy theory that someone drilled them when he wasn't looking!! they are a good Motor, probably worth spending a bit of time (but not much money) and "poking" around a bit to see if you can find the compression "demon"

 

[iwombat]

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

diggers are tenacious lil buggers

 

[noelm]

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

OK I bentz on that particular Motor, you will get compression with the reed valves out and in your pocket, they do not need to be in place to create a compression stroke, their main purpose is to prevent lower crankcase compression (when the piston decends) from blowing out the carby/intake that's all, as mentioned, once the piston passes the cylinder ports, compression will take place, trust me on that one!

 

[noelm]

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

one thing I forgot to ask, did the Motor go when you got it, or has it always been dead? might explain a lot of things perhaps!

 

[G DANE]

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

There should be an inch or more down to connecting rods. Reed valves do not affect compression, when motor is turning as slowly as it is by startet or pulling rope, it will get air from exhaust if it has to. I once had a broken reed leaf that went inside the motor, and compression was just the same without a leaf on one cylinder. Found the bit inside the motor when it was apart, a new set in, and it ran fine on both cylinders again. I would vote for a blown headgasket, try with a new one, after correcting warp in head. Loopers do not have bypass covers, as I recall, so if you want to look at pistons and rings ( no bad idea ) it has to come apart.

 

[lbentz]

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

Well, if you check the reeds, and they check out, then I stand corrected, but if they are bad, then there will be a difference in the compression. Bad reeds can diliver a lousy compression test, simply because there is no pressure from the block, to force fuel/air mix into the cylinder. When the engine is cranking at high rpms, you'll be amazed at how much pressure will come screaming through those intake ports and into the cylinder. As I stated earlier, there are only a few moving parts in a two stroke, but the few there are will all matter greatly to make things right.

You may also check to see if there is any obstruction in the exhaust side. The exhaust side needs to flow freely as well. I've seen dirtbikes that had rat's nests in the exhaust pipes and people pulled their hair out trying to figure out why they had no compression or the bike wouldn't run.

Fuel/air has to flow in properly and freely and exhaust has to flow out properly and freely. It's that simple. Otherwise, it won't run.

 

[BigB9000]

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

The engine did -kind of- run when I got it. At full throttle & cranking it would fire for a second or 2. Just from the sound of it it wasnt going to run.

Ever cranked an engine with no spark plugs in? How fast and easy it turns? well, with the spark plugs in, this is how easy it was.

Im not going to rebuild it. I enjoy taking the things apart, so thats what I'm doing / did. Electrical parts are getting sold to help fund the rebuild of the boat. The rest will go to whoever wants it.

As far as the intake / reed valves, they look fine. They are all there an inplace

 

[asdasc]

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

Is there any way to get light under the pistons? Then you could check if you can see any light coming up thru them.

I don't buy the drilled hole theory, as you would have to be able to reach both pistons. I don't think you would have 2 side by side at the top together, right?

 

[Joe Reeves]

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

I just checked some pistons that are still on my shelf (remaining stock) and all of them have the factory centering indentations BUT none of them of course go more than a fraction of a inch deep.

If the centering holes on the pistons pictured in this discussion actually were drilled through, the compression loss when cranking would be quite minor as there is no way all of the compression could escape thru that tiny hole in the time allowed for compression at cranking speed.

The appearance of the sealing surface of the block looks to me that possibly the head gasket could have suffered blow by between #1 and #2, maybe even #3 cylinder.

Clean and resurface the surfaces of the block and cylinder head, install a new head gasket, and torque the head bolts to 18 to 20 foot pounds in the following sequence. If compression returns to normal, fine. If not, tear the engine down as you would be looking at a overhaul project.

9...10
5.....6
1.....2
4.....3
8.....7
12..11 (Continue on in an ever widening circle)

 

[BKS72]

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

BigB, if you're going to scrap the block and other parts you're not selling, I'd be interested. I have almost the same motor on my boat and am always looking for a winter project. I'm commuting from KC to Corona, CA weekly for work lately , so if you want to get rid of the block and whatever else, drop me an email at branden_stombaugh@yahoo.com and maybe we can work something out. I can't carry the block on the plane, but I could either check it or ship it home.

 

[BigB9000]

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

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