Need help on piston failure

[Cortes165]

I'm looking for opinions on this failure. All 4 pistons have the same damage all the way round. The cylinders were cleaned up and look ok. The engine stalled out while cruising at 4000 rpm.<br />This goes back to my engine failure last fall and we still have not resolved the issue. 1991 Evi 100<br /> Thanks <br /> piston pic

 

[reeldutch]

Re: Need help on piston failure

it smells to me like a fuel/oil related problem.<br />because you say it is on al 4 the same damage.<br /><br />but can you give some more info.<br />the pro's here need more info like<br />- type engine<br />-how you are setup size boat versus prop<br />-sparkplugs<br />-oiling system 50:1 or vro etc<br />-octane gasoline<br />-overheating alarm working?<br />- std bore and pistons???<br />- did you clean carburators<br />- etc<br /><br />they will need more cleus<br /><br />good luck and sorry to hear that<br /><br />reeldutch

 

[chuckz]

Re: Need help on piston failure

Those look like scored pistons. That means lack of lubrication.

 

[Harker]

Re: Need help on piston failure

Wow, are they like that all the way around? Somebody put sand in your gas?

 

[Cortes165]

Re: Need help on piston failure

I thought it would be better without all the details but you asked.<br />*91 Evinrude 100 HP VE100SLEIE<br />*16-1/2 ft ski boat<br />*plugs are OEM suggested<br />*vro (tested by dealer and says ok) <br />*vro was using oil by watching the tank <br />*87 oct fuel<br />*alarms were tested and worked (but did not alarm at the time of failure)<br />*.030 over bore<br />*carb kits and new water pump assy<br />*20hrs since rebuild. Ran excellent. Perfect rpm's.<br />*this happened after running straight fuel. First 2-3 tanks were vro and premix.

 

[walleyehed]

Re: Need help on piston failure

Looks like contamination to me...dirt, glass beads, etc....<br />It's verticle grooves, not a "smear" typical of no oil.

 

[reeldutch]

Re: Need help on piston failure

check the bearings if it is contamination i would think they would go first.<br /><br />i think you didnt get the right ratio of oil.<br /> but than again your alarm should go of. and with damage like that on all 4 pistons i think your motor would overheat and that alarm should be the last alarm you hear for that rebuild<br /><br />reeldutch

 

[chuckz]

Re: Need help on piston failure

*this happened after running straight fuel. First 2-3 tanks were vro and premix.

All four cylinders the same damage and the first tank of straight fuel. Lack of proper lubrication. I would think that the vertical scores are from the pistons going up and down without enough lubrication.

 

[Dhadley]

Re: Need help on piston failure

*plugs are OEM suggested<br />

Please be specific. Which plugs are you using?<br /><br />

*87 oct fuel<br />

How old is the fuel?<br /><br />

*.030 over bore<br />

What did the machinist use for a finished bore size? Please be specific to .0000<br /><br />

*20hrs since rebuild. Ran excellent. Perfect rpm's.

You mentioned about a rebuild last fall. Has the motor sat for any length of time? What was the top rpms?<br /><br />What was the timing set at? At what rpm? And by what proceedure?<br /><br />Did the previous failure have the same looking pistons?

 

[R.Johnson]

Re: Need help on piston failure

Here is an interesting thought! You are running the engine at 4000 RPM. In mechanic's, there is a point called harmonic impalance. At this point, rotating part's stop spinning around there center of mass, and start spinning around there center of gravity. When running an outboard in a test tank with a timing light held on the flywheel, you will see the flywheel start to take on a ripple, like the wave in a pond, when it takes on this imbalance. At this point, resonance is at the highest, and every thing start's to shake, and vibrate. If you listen closely, you can here the engine take on this sound as it goes through this transition. At 4000 rpm, you are probably running at this stage. Run the engine at it's proper RPM range, or at it's cruise throttle range. Those piston's could be from an engine that has been heavely lugged, or run at this stage of imbalance.

 

[rodbolt]

Re: Need help on piston failure

me I am looking at a lack of piston to wall clearence. could be due to improper machining or overheat. that motor should cruise for years at 4k if its propped so it can achive about 58k or so.<br /> just cause the carbs were rebuilt in the past is rather meaningless. they go bad from sitting. has anyone checked the t-stats and pressure control valves? and I am with Dhadley,how old was the fuel being used?a rebuild using an old VRO pump is pointless unless I am positive of the failure. its just to cheap to install a new one at the rebuild. I have seen a few that "tested" good but would not flow a correct amount of oil. that is why you mark the tank and measuere how much gas you used and do a rough calculation to see if the correct quantity of oil was in fact used from the tank. not super scientific but it does work. also what brand of pistons are you using?

 

[Cortes165]

Re: Need help on piston failure

I'll try to answer some of the questions:<br /><br />*Contamination? If there was something in the fuel tank, there is a filter.<br />*Age of fuel? I was on my 4th tank (10 gal built in) Fuel up on my way to the lake.<br />*Piston/cyl clearance. Good question. Were the cyl's fitted to the piston? I'll check into that.<br />*Carb rebuild? was done at time of engine rebuild<br />*Thermostats? I found they had not been changed. I removed them and found the therm a bit crusty. The plastic relief valves looked ok.<br />*Eng timing and setup? I can only assume if this is done at an Evinrude dealer that they setup to factory specs<br />*Max rpm? Not sure but I'm guessing 52-5400<br /><br />The thing that gets me is that the engine was running great (up to that point). Good compression, smooth, good pulling power, plugs had good color, even with the double oil. I was quite happy.<br /><br />Anyways, thanks for your response. I'm new to outboards so this is all good info.

 

[rayjay]

Re: Need help on piston failure

Originally posted by Cortes165:<br /> Good compression, smooth, good pulling power, plugs had good color, even with the double oil. I was quite happy.<br /><br />Anyways, thanks for your response. I'm new to outboards so this is all good info.

If the plugs didn't show some excess oil then you didn't really have double oil. Then when you went to straight gas you smoked the pistons.

 

[LubeDude]

Re: Need help on piston failure

Looking at the pictures, I have to side with Rodbolt, In the years of working on engines and failures Ive seen, It is my opinion that there was improper piston to cylinder clearence. Were these pistons posibly Wesco or Wysco, however you spell it? They seem to expand at a greater rate and need more piston to wall clearence.

 

[G DANE]

Re: Need help on piston failure

Did you check oil consumption by watching oil level sink in your tank, or did the mechanic check VRO function. It could look like it pumped water from bottum of oil tank instead of oil or if pickup filter in tank or tank vent was blocked, stopping oil from flowing, though I lean most against the water in oil thought.

 

[G DANE]

Re: Need help on piston failure

I'v had a bike that was bored with too small clearance, pistons had blank spots as well as scores. I dont think lack of clearance was the problem. Letting VRO pull oil from a clear hose with air bubbles isnt the same as pulling from boat tank. I would check the tank. Sad to see, I feel for you.

 

[Dhadley]

Re: Need help on piston failure

Start at the begining. Was the first failure the same? Then we need to know what the machinist used for a finished bore size (to .0000).

 

[reeldutch]

Re: Need help on piston failure

we are all second guessing here and it doesnt help cortes.<br />what ever caused it you don't want to have a repeat of it.<br />what i would do if this was my block<br />sinds you rebored the block 0.030 over<br />and you say the damage is on all 4 cylinders it is said to say but i think i would invest in a good new or used powerhead.<br />forget about your block. save all the good parts like stator,pp,coils,etc.<br />i realy feel bad for you i hope i'm wrong but after 0.030 i dont think you can rebore it much further. hophely i'm wrong. <br />i realy would think twice before sinking another grand in that motor.<br /><br />good luck reeldutch

 

[Cortes165]

Re: Need help on piston failure

Dhadley.........I have to dig to find that data but I will check it out. If the clearance was not correct, would the engine run for 20 hours and then fail???<br /><br />Dane.....I watched the tank consumption everytime I went out with the boat. The mechanic said he did the flow test, similar to the one in the Iboat FAQ.<br /><br />The tank was completely drained, cleaned and hoses checked. I witnessed that and don't see how water could get in after that. <br /><br />Piston type? Again I have to check that. I was assuming they were Evinrude genuine parts.

 

[Cortes165]

Re: Need help on piston failure

reeldutch.......another grand??? I wish.<br />The block was bored .030. I had the block inspected at a machine shop. They told me the damage was just the leftover piston stuck to the walls and the cyl walls were in good shape. <br />There are bigger pistons available but don't know if I have to go that route.<br /><br />I know you guys can't truly diagnose things over the internet. I just want some ideas, info or just ammo so I don't look like a total idiot when I chew on the shop.<br /><br />I have thought about rebuilt powerheads, different engine all together, but it's tough to do from where I live. <br />Where can I get info like that.?? How do you trust buying an engine over the internet.???