96 Evinrude 115 - Help figuring out why it melted a piston

trendsetter240

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Hi folks,

I've got a new to me 1996 Evinrude 115 V4 looper that I bought as a rebuild project. The motor has one low piston at only 30psi. The rest of the cylinders are at 130-140 psi.

The previous owner stated that he was told it was the OMS/VRO that failed. I'm always sceptical of this so I wanted to dig deeper to find the real cause before I spend a bunch of money on the rebuild. The service history from this past summer shows the motor had the carbs rebuilt in July. At this time all cylinders were at 130-150 psi. Then, in August the motor was brought in again complaining of won't rev much past idle and stalls. The test report shows that the #3 cylinder reads 30psi with scored cylinder.


I have already completely torn down the motor and examined the pistons and cylinders. The number 3 cylinder is indeed scored and the rings are melted to the piston. I pulled apart all the carbs and checked each one. They are in perfect condition, and all passages are clean and clear.

I inspected the reed valves and they appear to be in excellent shape and leafs move as expected.

SO...I had suspected maybe the carb the #3 cylinder had failed causing a lean condition and the failure. But now I'm not so sure...Everything appears fine with that carb (and the others).

So is it possible that this failure was a result of the OMS pump? I plan on running mixed fuel after rebuild but I would feel much better if I could identify what the cause of failure was.

Pics to follow in the next post.

Any help would be much appreciated.

Cheers
 

trendsetter240

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

Here is a picture of the damaged piston. Anyone have thoughts on what this may have been caused by? I also can take pictures of any part if that helps to diagnose the problem.

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trendsetter240

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

Here is a picture of the scored cylinder.

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rolmops

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

Everything else being equal, the cooling water supply did not reach this cylinder and caused it to overheat and melt.This may be because of debris/blockage or a poorly functioning thermostat that did not allow enough water to go through the system.It could also be a matter of air locked in the cooling system around the cylinder.
Beyond that,you guess is as good as mine
 

trendsetter240

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

Hey rollmops thank you for the suggestion.

I've got the bare block here right now, is there anything I can do to clean out the passages without damaging things? Also if you look at the picture of the cylinder you can see there are some rubber plug type things in some of the passages. I've never seen them before, should that be cleaned out?

I'm going to toss the thermostats in a pot of boiling water and see if they open. They will be replaced anyways but it will be good to know.
 

boobie

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

Did you check the high speed jet in the carb for #3 cyl ??
 

trendsetter240

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

Did you check the high speed jet in the carb for #3 cyl ??

Hi Boobie,

I removed the screw plug and blew through the high-speed orifice and it was clear. I also used a piece of copper wire and pushed through but didn't find any blockage. Do I need to remove the actual jet from the orifice and check that too or should it be ok if I can blow air freely through it?

Cheers
 

trendsetter240

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

Here is a picture of the carb. I removed the large flat head screw from the bottom of the float bowl and blew through there.

Is the other brass screw in the top left to adjust the mixture (rich/lean)? This screw was all the way in.

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boobie

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

Are you sure you have the correct mod # ?? From the pic it looks like a fixed low speed jet. Vro's don't normally cause one cyl to fail but it can happen if that cyl is running hotter than the others.
 

rolmops

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

The rubber plug thingies are supposed to be there. They direct the water flow in the cooling system. If one is missing ,then it may have caused your problem. As for cleaning the cooling system; when you have that cylinder in a machine shop ask them to boil it. It will be in boiling water for a nice long time and it comes out sparkling clean inside and out. Just tell them what may have happened and they will make sure that all the passages are clear and all the rubber is where it should be.
 

trendsetter240

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

The engine model number, on the bracket, is E115ELEDR. When I look at the diagram of the carb on shop2.evinrude.com it looks identical.
 

trendsetter240

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

The rubber plug thingies are supposed to be there. They direct the water flow in the cooling system. If one is missing ,then it may have caused your problem. As for cleaning the cooling system; when you have that cylinder in a machine shop ask them to boil it. It will be in boiling water for a nice long time and it comes out sparkling clean inside and out. Just tell them what may have happened and they will make sure that all the passages are clear and all the rubber is where it should be.

Those rubber plugs are either missing or damaged in most of the holes. If they are required then they should all be replaced on this motor. Hopefully the machine shop knows what to do; they aren't an evinrude specialist shop but they do the boring and honing on 2-strokes all the time.
 

Joe Reeves

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

Two happenings can cause a piston to score as that one did..........

Either the carburetor is (or was) fouled which resulted in having that cylinder run lean... OR.....

That cylinder was not firiing due to no spark or some other reason which would result in what we call a "Wash Out" scenario. The proper fuel mixture would be entering the cylinder but would not be exploding. Eventually the incoming mixture (more fuel than oil) results in the fuel overcoming the oil portion of the mixture (improper lubrication) and the piston disintegrates.
 

trendsetter240

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

Two happenings can cause a piston to score as that one did..........

Either the carburetor is (or was) fouled which resulted in having that cylinder run lean... OR.....

That cylinder was not firiing due to no spark or some other reason which would result in what we call a "Wash Out" scenario. The proper fuel mixture would be entering the cylinder but would not be exploding. Eventually the incoming mixture (more fuel than oil) results in the fuel overcoming the oil portion of the mixture (improper lubrication) and the piston disintegrates.

Thanks Joe. With the carburetor pictured in my post above, do you think I'd need to remove the high speed jet or is it ok if I can blow air easily through the orifice? Also, could you identify the brass screw in the upper left of the picture? I'm not sure what the purpose of this is.

Cheers
 

Faztbullet

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

I blew up your pic and added lighting and from picture most of the damage is on the exhaust side. Also this head has been off before as someone used red RTV when they reinstalled it and this block does not have water deflectors like a crossflow.
That type of damage can occur from several possibility's:
1) Washed cylinder as Joe stated
2) Lean fuel mixture from clogged jet, float height incorrect, blocked inlet needle or screen in throttle body
3) Incorrect heat range plugs
4) Defective powerpack as could be double firing or firing advanced
5) Never seen a VRO/OMS lean just a single cylinder as fuel is common to all cylinders
6) Water intrusion from glueline in block, can be pressure tested to verify if so



scored cylinder.jpg
 

trendsetter240

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

Hey faztbullet,

You're right, someone has rebuilt this motor before. The piston and connecting rod in #2 are different then the rest. However, none of them are oversized so I guess they just replaced the one piston and honed the cylinder.

For your individual options:

1) Washed cylinder as Joe stated
--I am thinking this will need to be diagnosed after the motor has been rebuilt but that's ok because parts can be replaced at that point.
2) Lean fuel mixture from clogged jet, float height incorrect, blocked inlet needle or screen in throttle body
--I am confident that the carb jets are clear and there are no blocked passages or screens. Float height I will need to check.
3) Incorrect heat range plugs
--The plugs that were in when I bought it are champion QL78YC
4) Defective powerpack as could be double firing or firing advanced
--Not sure how to test this; I guess I'll have to wait for the manual to come I ordered.
5) Never seen a VRO/OMS lean just a single cylinder as fuel is common to all cylinders
--Me neither that's why I was questioning it. I have seen a pre-mix 2 stroke fail on one cylinder when run on straight gas so it's not impossible.
6) Water intrusion from glueline in block, can be pressure tested to verify if so
--This worries me. How does one pressure test a block? Is this something a certified evinrude shop should be able to do?

Cheers

P.S I can post High-resolution pics of anything that might help just ask.
 

boobie

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

Those black rubber plug thingies you're seeing in the block is probably left over black rtv sealer left over from the last time the mtr was torn apart. Looks like they put on to much as the sealer is not suppose to block the passage but just seal it.
 

trendsetter240

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

Those black rubber plug thingies you're seeing in the block is probably left over black rtv sealer left over from the last time the mtr was torn apart. Looks like they put on to much as the sealer is not suppose to block the passage but just seal it.

Now I'm confused, are those black plugs supposed to be in there or not? If you guys look at the picture, the smaller holes that surround the cylinder are the ones that were filled / partially filled with a black rubber substance. Should those holes be clear?

Cheers
 

dwco5051

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

Post was based on my misreading model and year, sorry :confused: :facepalm:
 

dwco5051

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Re: 96 Evinrude 115 - Help figuring out why it melted a piston

:facepalm: :facepalm: :facepalm:
 
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