1993 Johnson TJ115TLETS burned Piston

[jstatham]

Hello everyone. Here is my current situation. I picked up a 1993 Johnson TJ115TLETS from a friend and I finally started messing with it 2 years later and here is what I found. It would crank up and idle fine but trying to get the boat on plane it was just dragging and you could tell it had nowhere near full power. I came home and performed a compression test and I had 100,100,100,80 lbs. I pulled the head off with the bad compression and found a burned piston.
Here are my questions

#1 what caused it? Lean Condition?
#2 If I rebuild will I need to have it bored or just replace rings and piston?
#3 If I do rebuild would you do all or just the burned one. From what I can tell the head on the bottom looks as bad as the top. I am wondering if someone already replaced the bottom piston.
#4 Is it worth Rebuilding? I can get parts as cost +10% but even with that we are talking 200-500 depending on what I do.

My friend sold it to me very cheap because he bought it for the boat and wanted rid of the motor and controls.My friend also told me he would buy it back but he is currently in hospice and I am not going to bother him. I know I can part it out and make my money back but I hate to do that do such a good looking engine. Any help will be greatly appreciated.

 

[interalian]

Looks like a ring broke and came through the piston top.

 

[flyingscott]

Something went through that motor tear it down to find out what.

 

[racerone]

All those motors will suffer the same fate !!!----This is such a common failure.-----Looks like one of the diverters may have blocked water flow too.

 

[emdsapmgr]

Agree. It's a little hard to see, but looks like the pictured water diverter may have severely restricted water flow around the cyls on that side of the block. Any excess heat can cause a lean condition in the cyl-causing the the top ring will disintegrate. Even if you have the correct fuel oil mixture. The water diverter pictured just to the left of center is correctly positioned. Visually compare it with your block. The right diverter is out of place.

 

[jstatham]

I agree. I spoke with my buddy who is a marine mechanic in Kentucky and he said that a piece of the ring broke and got beat around by the piston. My next task I guess is to measure the cyclinder bores and if they are way off and need to me bored I am going to just part it out. If the bores are OK and I can just buy new pistons, rings and hone it out I may go for it. What are your thoughts. I can get 4 new pistons and rings on jet.com for 229.68 other than a gasket set and some gel seal I should be good to go. I think.

 

[racerone]

It is hard for some to believe that this failure is due to the design of the top ring !----If you bore it out 0.020" and install a set of WISECO pistons you will have a motor that will run for many , many years.---A simple motor that you can maintain yourself too.

 

[jstatham]

It is hard for some to believe that this failure is due to the design of the top ring !----If you bore it out 0.020" and install a set of WISECO pistons you will have a motor that will run for many , many years.---A simple motor that you can maintain yourself too.

I am hoping I don't have to get it bored. What makes the Wiseco pistons better than OE or Sierra. If I don't have to bore it I see that Wiseco sells the OE replacements and well as .20,.30,.40 over. Like I said before the cost of having to bore it may make not feasible and turn into Parts motor.

 

[schematic]

I doubt you'll get away without a rebore. Not the end of the world....

 

[metriccrescentwrench]

You don't have to bore all holes, many many outboard engines have been repaired with only the bad cylinder(s) getting bored and an oversized piston installed.

 

[racerone]

The WISECO piston rings are totally different from factory original.----It is the extreme taper on the original equipment rings that is the problem as rings and pistons wear over time !!!!!!

 

[sutor623]

All those motors will suffer the same fate !!!----This is such a common failure.-----Looks like one of the diverters may have blocked water flow too.

Race, you feel this way about all the V4 crossflows, no?

 

[racerone]

They used these " pressure back " rings from 1973 to the last ones in 1998 or so.--------I have over 20 of these at the moment and all need rebuild due to failed rings.--Thus it is a common problem.---Many newbies fail to understand this.

 

[sutor623]

They used these " pressure back " rings from 1973 to the last ones in 1998 or so.--------I have over 20 of these at the moment and all need rebuild due to failed rings.--Thus it is a common problem.---Many newbies fail to understand this.

Even the loopers of this era?

 

[emdsapmgr]

There is another long-term ring failure factor which does not get much blame or recognition. That's the fact that the crossflow engines tend to accumulate carbon around the pistons skirts and the ringsets. Once this happens, the cooling intake fuel/oil can't get past the first ringset to lube/cool the top ringset. When this event occurs, it's an overheated top ring which then breaks and takes out the piston, even the head. The frequent decarb process and the use of Carbon Guard in the fuel just doesn't seem to get much press. These carbon-preventative techniques can keep a crossflow humming for many additional years. Certainly cheaper than a teardown and overhaul.

 

[jstatham]

I have one more question. I just talked to a supposedly 30 year OMC tech and he told me do not put Wiseco pistons in my motor. He said he has seen to many problems with them seizing. Does anyone have any experience with this and what pistons would you recommend. I have seen stuff posted all over the web from OE, Wiseco, Sierra, Vertex. I talked to another guy at a different shop and he said all he puts in is Wiseco pistons.

 

[racerone]

?????-------The WISECO piston company has been around for quite some time.----They did not start up in China last week !!----------If there was a problem it would have been corrected years ago.------Look for them via the internet and perhaps call the 1-800 number and talk to folks that know !!

 

[emdsapmgr]

The overhauler needs to know what he is doing when installing Wisecos. There is a difference in the thermal expansion rates between the forged pistons and the cast pistons. Both types of pistons will work-it depends on the piston-to liner clearances of each type. The installer needs to know which pistons you are installing. One thing you don't want to do is mix pistons from different manufacturers in the same block.

 

[ondarvr]

If you decide to fix it, do all new pistons, otherwise you have three that are past their normal lifespan and will fail soon. I had a 98' and when it ate a ring/piston I just got rid of it as is, just too many of these motors fail in this way. By the way, mine had zero carbon build up on anything. If it wasn't for this one major issue I would like these motors much more.

 

[Faztbullet]

I myself will not use a Wiseco piston in my customers engines. They are too soft(piston) and have to go thru several heat cycles to temper up. They take a long break-in and engine needs to be at temp before WOT operation. The only thing good about them is they work well in worn bores...below from,

http://www.klemmvintage.com/breakin.htm

In the 1970s, we made many attempts to use Wiseco pistons in two-stroke race motors?with very poor results. The truth is that Wiseco (at that time) had numerous materials and design issues that needed resolving. However, Wiseco has done a great job of evolving their materials and designs since the 70?s, and today?s Wiseco Pistons are an excellent choice for most high-performance two-stroke platforms. All that said, Wiseco pistons do have one design issue that they have intentionally have not tried to resolve ? longer than average piston-ring break-in times.
The forged material that Wiseco uses for their forged pistons does require ?a little? more clearance and a little longer break-in that typical ?cast? type pistons ? but that is not the unresolved design issue?. It?s the rings. The piston ring material that Wiseco uses is a very tough material that takes much longer than average to ?seal? to the bores. While the Wiseco pistons themselves are not a particularly close clearance fit to the bores, the Wiseco rings are. In truth, the Wiseco rings are made brand new with an end-gap that is much too small for full temperature high rpm operation. However if a Wiseco equipped engine gets the slightly longer than average break-in period it deserves, the outer-skin will wear off the rings to result in an ideal ?running? end-gap that will give excellent long term wear and service. If however, you try to run Wiseco piston rings prematurely hard, those rings will quickly expand until the ring ends make contact and literally ?bite? the full bore diameter in the ring path........JMO