Rebuild 900 Hour 2006 Opti 175HP with a Melted #4 piston

[Fishinmymission]

477572477573477574477575 Typo supposed to be Piston #3 that melted, it's the middle starboard cylinder.
What are your guys recommendations for cleaning up the melted aluminum and then how do I figure out what the bore needs (hone or rebore) and choosing parts for new ring and piston. Also opinions on rod and rod bearings for that cylinder?
I already had some ccm reeds ill put in while apart but don't want to replace things that arn't needed unless you guys highly suggest it. I do failure analysis on transmissions for a living for the last 6 years but have never worked on a combustion engine cylinder or piston before.

I melted the number 3 piston in June and swapped to a 200 carb powerhead for the rest of the season. found the 200 Carb to make no more power over the 175 opti yet the fuel burn is not worth it for me to keep running it. Also not a fan of not being able to start the carb motor cold if im trimmed up in super shallow water.
I bought a spare fuel and air, injector used, and was thinking about sending all 7 air and fuel injectors to be flow tested, cleaned and re flow tested, hopefully confirming an obvious lean condition to the number 3 cylinder.

Engine ran fine and smoothly after the melt down just down the power from no compression in the one cylinder.


Thanks!

[InjectorService]

Definitely have the injectors and fuel rails cleaned and serviced. I would take a peek inside the compressor while your in there.

Blake

[FUJIMO]

https://www.screamandfly.com/attachment.php?attachmentid=477572&d=1606160618

[Chaz]

!!! Wear a painter's respirator ... !!!!

Go to the pools supply store , get a gallon of muriatic acid .. about $3.00

Small cup , and brush .. dab it on the cylinder wall .

Wear a respirator ... :eek:

Don't drip any down the ports ... it will eat that too .

Let it smolder a minute or two .. scrape the slag with an old knife.

Repeat if necessary .

Touch hone the hole , measure , top , bottom , along the thrust face . Then again at 90* , top and bottom. That will tell you if the hole is round and/or tapered .

Access from there ...

[FUJIMO]

...what chaz says can be done, but you need to do it after you tear the powerhead completely down & rebuild it. that piston, and possible another, has already transfered aluminum, so... a powerhead rebuild is so easy, and straight forward. i don't understand why anyone would be afraid to do them. on a two stroke, it also happens to be the right way to go. they turn too many rpm's not to. your then good to go, for a very long time again, worry free. and it won't cost a fortune, because you didn't wait until it grenaded, like some people.

[Fishinmymission]

If anyone has a list of certain bearings or seals that are absolutely a no brainer to replace (easy and cheap to do compared to chance of 1000 hour+failure)
I can grab a dial bore gauge and start inspecting per Chaz and the manual i feel like i can find some clean spots to find out if its tapered before i split and clean. I can handle the splitting the block and then cleaning the aluminum as well. I feel comfortable inspecting the rod and bearings on the number 3,replacing obvious seals while its apart. Ive never honed before but feel like I can find a friend or a shop or maybe buy or borrow the tool and do myself.

I'm 99.9% certain i had a lean condition melt out my piston so i have a good plan on making sure that I find the source of the fuel delivery issue and make sure its corrected. My compressor has no play and no leaking compression when rotated by hand it acts like a complete air spring until it surpasses the 90 psi regulator and releases pressure through the regulator.
I will note that over the three years I had this engine the alternator would heat up and stop working intermittently on only the warmest days causing some RPM drops at full throttle. This last summer in july when I had the melt down the alternator was shutting off for prolonged enough periods to figure out it was the culprit. I find it unlikely but I wonder if one injector could open more slowly while the engine was running completely off my strong dual batteries? Maybe unrelated to the meltdown but could have been related.
I ran the engine after the melt down to 4000 rpms and it was still having surging issues until i replaced the alternator and then became a smooth rpm but down a cylinder. I also performed drop tests all other cylinders seemed to be working after the melt down with the engine running. I checked compression in the number one cylinder and it was 115psi when the melted one was 0.
Do I need to compression check the others before i break it down further? I think I need new orings for the head i already removed first to check the number 5 cylinder.

[Chaz]

...what chaz says can be done, but you need to do it after you tear the powerhead completely down & rebuild it. that piston, and possible another, has already transfered aluminum, so...

Chaz = wunderin , how ya rebuild the powerhead ... and then clean and check the bores ... afterwards ... :eek: ;)

[Dave S]

Acid works but I am lookin for a faster way........I use a flappy wheel......just be carefull of the bore.......

[FUJIMO]

Chaz = wunderin , how ya rebuild the powerhead ... and then clean and check the bores ... afterwards ... :eek: ;)
...replace "&" with "to" in my sentence chaz... there, i fixed it. (jeeeeez louiiiiis...:rolleyes:;))

[Fishinmymission]

...replace "&" with "to" in my sentence chaz... there, i fixed it. (jeeeeez louiiiiis...:rolleyes:;))

I think we all knew it couldn't be cleaned and fully inspected till it was split. But fujimo when you say tear completely down and "rebuild" what does that mean? what do you consider a a rebuild versus only inspecting fixing up this one cylinder, piston and rod as needed.
Does a rebuild mean all new bearings, pistons and rings all bores drilled oversized?

[Dave S]

Pop one piston in ...... or 2 if needed.......cut your costs..... new every thing is a waste of $$$$$$$

[Chaz]

...replace "&" with "to" in my sentence chaz... there, i fixed it. (jeeeeez louiiiiis...:rolleyes:;))


Like you said .. "your sentence" ... your **** ~up , you fix it .. :D

BTW .. I'm familiar with jeeeez ... but who is Louis .. ???

Is he related to Thelma or Louise ... :p

[Chaz]

I think we all knew it couldn't be cleaned and fully inspected till it was split. But fujimo when you say tear completely down and "rebuild" what does that mean? what do you consider a a rebuild versus only inspecting fixing up this one cylinder, piston and rod as needed.
Does a rebuild mean all new bearings, pistons and rings all bores drilled oversized?

Not to put words in someone else's mouth . I'll stick to what I said ... ;)

You asked ....


What are your guys recommendations for cleaning up the melted aluminum and then how do I figure out what the bore needs (hone or rebore) and choosing parts for new ring and piston.

​!!! Wear a painter's respirator ... !!!!

Go to the pools supply store , get a gallon of muriatic acid .. about $3.00

Small cup , and brush .. dab it on the cylinder wall .

Wear a respirator ... :eek:

Don't drip any down the ports ... it will eat that too .

Let it smolder a minute or two .. scrape the slag with an old knife.

Repeat if necessary .

Touch hone the hole , measure , top , bottom , along the thrust face . Then again at 90* , top and bottom. That will tell you if the hole is round and/or tapered .


Also opinions on rod and rod bearings for that cylinder?
I already had some ccm reeds ill put in while apart but don't want to replace things that arn't needed unless you guys highly suggest it. I do failure analysis on transmissions for a living for the last 6 years but have never worked on a combustion engine cylinder or piston before.

So as a forensic pathologist on 8620 , 9310 , today it might be junk powdered metal .. :rolleyes: If you found a cracked gear next to the one that exploded , would you ignore it in your report ??? After all it was not the cause of failure ... :rolleyes:
You shouldn't need a pocket protector to conclude that .. it wuz the first-un to the scene of the accident .. an ifin it didnt cause it .. it wuz fixin ta foller .. next .. :smiletest:

No one here can tell you what the rest looks like .. and if you dont take a look , your only guessing .... 900 hours , it don't owe you anything. :nonod: If you deicide to go as cheap as possible .. it might deicide it don't owe ya a ride back to the dock ... :thumbsup:

[FUJIMO]

I think we all knew it couldn't be cleaned and fully inspected till it was split. But fujimo when you say tear completely down and "rebuild" what does that mean? what do you consider a a rebuild versus only inspecting fixing up this one cylinder, piston and rod as needed.
Does a rebuild mean all new bearings, pistons and rings all bores drilled oversized?
...send the thing out & have a pro recondition/rebuild the powerhead top to bottom. they will know what to do.

[Chaz]

Welp, there's always that ... :thumbsup:

[FUJIMO]

...they can warranty they're work for a period of time as well...

[InjectorService]

If you tear it down to the block and pull the powerhead, it should be pretty cheap for someone to do the rebuild and then you can pop the powerhead back on. Just make sure you use someone reputable. Ill give you a hint, the reputable guy isn't the one telling you "I can do it for less"

Do all that along with finding the cause of the meltdown, and you should get another 900 out of er. Id still pull that compressor apart though, regardless of whether it makes pressure or not. There's more to it than that.
:cheers:
Blake

[XstreamVking]

Better have two identical engines as a good parts source. The parts are not cheap. New injectors for air side are 200+ Fuel is "only" 90. Cleaning inj is 250. And reeds, better get some ccms composites. 130 Get a new style compressor now. 1000 Did I forget the coils? Might need some 90 ea X6. Fuel pumps, you have 3. 600 Rubber fuel rail parts? Yep....400. This is how I survive in the "opti" world. I have 5 to keep 2 running on my charter boats.

[Fishinmymission]

This summer when i bought a "running drop on" 200 carb powerhead from someone on long island NY who happens to be a member on this forum and works at an actual machine shop where is saw over 20 merc outboards around the shop when I bought mine for $2800, I got sold a complete lemon that took me months to find all the issues lose wiring, carbs that ran too rich when warm, vacuum leaks at oil injection plug, water leak at the exhaust divider plate, loose nut on one coil, rectifiers blown and no crimps just electrical tape connections to the stator which pulled loose, and a stator or switchboxes that intermittently have trouble transferring from the low rpm ignition to the high speed stator coil ignition source at 3000 rpm.
Who are the reputable guys nea CT/NY? I think i can manage myself especially with measuring the bore, will likely find a buddy or a shop to do the hone or bore depending once I find out what's needed.
InjectorService can you send me a quote to Flow test 7 air and 7 fuel injectors, clean, and reflow test? Also how do you clean the injectors? is there a way for you to trap save and send me all the debris from the #3 air and fuel injectors. I'm an engineer in a failure analysis for a helicopter company and will look at it with microscopes and maybe some compositional analysis.

[Fishinmymission]

Better have two identical engines as a good parts source. The parts are not cheap. New injectors for air side are 200+ Fuel is "only" 90. Cleaning inj is 250. And reeds, better get some ccms composites. 130 Get a new style compressor now. 1000 Did I forget the coils? Might need some 90 ea X6. Fuel pumps, you have 3. 600 Rubber fuel rail parts? Yep....400. This is how I survive in the "opti" world. I have 5 to keep 2 running on my charter boats.

I have ccm reeds never installed will this winter. Its a 2006 and I'm pretty sure its the new style compressor. This engine had the craziest issue for three years that drove me crazy where if it was hot enough after running for a while on only the hottest days it would get some intermittent rpm drops. The issue got progressively worse and started occuring cooler temps but still never acted up in the spring and fall only summer. I had fuel and air gaugues rigged to the helm, no pressure changes when the rpm drops occured. I replaced all the coils with used coils, then new coils and plug wires. Finally found out the alternator was intermittently not generating current when it would get hot but would start again once cooled off. I melted the piston on July fourth this year while my alternator was probably off and the engine was running on my dual battery bank. I think but am not positive that rpm drops were still happening after i melted the piston with the old alternator. I figured out what the alternator was doing finally thinking it was the smoking gun so I replaced it and I think the rpm drops stopped occuring but i was also only getting 4000 rpm, at this point i found no compression in that cylinder.

I think i'll just approach this with understanding the piston lean melt failure as best as possible and going from their reusing or using used components. I'm thinking its debris related but I'm also not ruling out that maybe this one injector had higher resistance and at insufficient voltage it did not open as fast or as long/ all the way making it lean. This has to be a lean condition because its obviously melted aluminum and there is no possible way for the cooling to have been insufficient at only that middle cylinder.

[XstreamVking]

Usual bad inj will just zero out or. New comp. will be black. Original for an 06 will be natural. I doubt the low volts was the culprit. I have run hours with no alt on 2 big batts. Down to 11.5 volts b4 I got back.

[Fishinmymission]

Usual bad inj will just zero out or. New comp. will be black. Original for an 06 will be natural. I doubt the low volts was the culprit. I have run hours with no alt on 2 big batts. Down to 11.5 volts b4 I got back.

When you were running on the 2 batteries did you notice that you were not getting full rpms (weaker spark)? this could confirm that my alternator kicking in and out without my knowledge was the source of my rpm drops at full throttle on my hot days. I drove a truck once without a serpentine and could feel the weak spark and misfires. Also I tend to agree with you and thank you for your first hand experience that a single injector would not run lean if voltage was low.

Good to know my compressor is painted black! I remember reading all the forum posts about spalled piston cranks and bad single bearing designs, bad castings etc on the early design.

[XstreamVking]

It would drop r's when I hit the trim. I wasn't running over 4k since on a charter. Seemed normal. That's all except the smart gauge saying low volts.

[Fishinmymission]

Ok I will say extremely rarely i would also have an rpm drop when trimming over those three years i think it happened twice i couldn't replicate it though because When it happened those two time I didn't know my alternator was momentarily not working. Also I would really only get the intermittent rpm drops over 4500 rpm, either the alternator only got hot enough to stop at those rpms, or the batteries couldn't keep up with my electronics, the fuel pumps and making that many much sparks at the higher rpms. Also a weaker spark may be fine on a lower fuel mixture but poorly ignite a richer fuel mixture.
Do optis run lean or leaner fuel curve below a certain rpm I wonder when there is no risk of melting?

[XstreamVking]

INJ. service or CHAZ would know the fuel curve. I'm just a fish guide that works on his own stuff.

[Dave S]

I have kept my mouth shut on this one......But... optis are just waiting to blow up. Too much Chit to go wrong....running on the ragged edge of lean out...give me 6 carbs and some oil and.......15 years later still going. If you want a Opti..... learn how to twist bolts..... clean injtors.....fix air pumps....And then the 2.5 optis have a big wrist pin that ...... makes for less piston pin boss in the slug..... just waiting to pull out and hacksaw the block. Save on gas get kicked in the arss.

[Fishinmymission]

Ill take the 175 opti that idles smoothly and never stalls and always starts every day of the year no matter the trim and so I don't have to fill up my 120 gallon tank every trip even if it does randomly melt a piston every 300 to 3000 hours. No lie way too many complex components on these engines that make things complicated and to easy to get a failure but worth the weight cost and efficiency.
I just pulled off the rail no debris in the rail or on the fuel injector filter. The only debris anywhere is carbon buildup on the tip of the air injector. I left my multimeter on the boat will ohm check all my injectors next chance I get.
Nothing blaringly obvious yet.

[Dave S]

If ya need any parts for it ..... give me a PM......

[InjectorService]

Ohming them isn't enough. Doesn't tell you anything. If it was open it just wouldn't run on that cylinder, wouldn't burn a piston.

Optis are great motors, some of my favorite out there. The problem with them is exactly this: nobody wants to maintain there stuff. They are 100% a high maintenance motor, no 2 ways about it. If you maintain it properly, it won't leave you hanging but does require work. That means checking the air compressor properly, having the fuel rails and injectors cleaned professionally, cleaning the VST, all oil & fuel filters, cleaning the water inlet filter to the compressor, checking all oil feed and bleed lines, checking your fuel for water, etc.

I'm not calling you out specifically, but if any Optimax owner skips the above steps in this situation, or doesn't look at the above items regularly, then they are in fact running a ticking time bomb as Dave says.

Why do you think 4-strokes are so popular now? The main reason = people can run the crap out of them without maintenance and they will for the most part keep running without issue. Take a 2 stroke and do the same, your asking for trouble, take a DFI 2 stroke and do the same..... it will leave you hanging.

Also, trust me on this, the junk in your rails isn't hanging out where your injectors sit.

[Chaz]

Why do you think 4-strokes are so popular now? The main reason = people can run the crap out of them without maintenance and they will for the most part keep running without issue. Take a 2 stroke and do the same, your asking for trouble, take a DFI 2 stroke and do the same..... it will leave you hanging.


It's that same lackadaisical maintenance program that has them only "add" oil, never change it. Nor flush it out, just hang it from the davits .. it'll be fine. With way more nooks and cranny's for water to be "stored" in the cooling passages .. sometimes the four strokes develop a exhaust side water injection port.
Since these new motors are made from Alka~Seltzer .. the correct welding rod is still being developed .. it's best to just go down to the four stroke store and pay $3500.00 hundred dollars for a replacement head , don't forget to get gaskets , bolts , O-rings .. and of course anything else that's rotted out ... ;)

[InjectorService]

But Chaz, they saved so much money on maintenance that the powerhead is cheap! :rolleyes:

[Fishinmymission]

But Chaz, they saved so much money on maintenance that the powerhead is cheap! :rolleyes:
No doubt a flow test is the best way to do this but I'm quickly approaching exceeding the value of what this engine is worth to me(there is a 200 carb currently running and all hooked up) and if I don't find the culprit in the flow test I could be out the money for the flow test and feel like it's not worth risking the rebuilding the opti.
I'm actually reaching out to a bunch of injector services to get quotes to see if someone will do the dirty flow rate test for free and then ill pay for cleaning and the clean flow test once that piece of mind of that the culprit is found and its worth rebuilding. InjectorService I'll send you a DM.


It's all a balance of value and I have months. It's a 2006 saltwater opti head on a 1995 saltwater mid. It my personal engine things are not lasting forever and I don't have time to brush out, alodine, and paint, or replace everytime some part gets corroded scratched or worn, but I occasionally do if I think the work is worth extending the life of this Frankenstein engine. You could spend 1000s replacing bunch of components and testing all the injectors just to have something else completely out of your control go wrong and lean out a cylinder its the nature of the opti beast. I got this fully dressed opti head for $1600 originally on ebay so deals can be found.