Yamaha 250 OX66 Scorched Cylinders

[pstephens46]

I was referring to my own aging process. I just turned 50 so you know what is recommended at this point....

[boscoe99]

Not sure eating more fiber would have helped keeping the floaters away.

boscoe ,ever been driving down the road and end up with a blind spot when looking at road signs?

Did not last long but had me concerned.
Eye Dr said floater probably got in the way.
that was years ago, and has not happened again

Nope, I have not had any blind spots (yet I suppose) but I do see stuff fly across the sky due to floaters. Stuff that really is not there. Which brings me to a story about the past.

Many many years ago when I was in the Navy I was enlisted air crew. Sitting in the right seat minding my own business. We were cruising merrily along, about to doze off due to the drone of the motors, when all of a sudden the air plane pitched rapidly and greatly downward. What the hell? Scared the sh1t out of everyone but the piloti. Damn good thing we were all strapped in.

I did not know what a floater was at that time. Apparently the pilot had one come across his eye and he thought for just a nano-second that it was another air craft about to hit us. So he took evasive action to avoid a mid-air collision. With an air craft that was not there.

Better to not hit something not there than to hit something that was there.

[jfbetz01]

Ok, I may have stumbled onto something here. I was curious to see what exactly fuel-wise was being fed to the injectors; so I unscrewed the VST, and poured the fuel mixture into a glass. There appears to be a significant phase separation (glass on the right), with significant water content. The glass on the left was drained from my Racor upstream and shows no phase separation. Since the fuel is pulled from the bottom of the VST tank (I think), it would seem the injectors were being fed this contaminated fuel. So, is this enough to cause the detonation of the left bank of cylinders?

btw, pulled the right side heads...all cylinders appear normal.

[FabricGATOR]

How about your fuel... do you by any chance run pump gas with alcohol?
Do you by any chance use portable fuel cans that may have had diesel fuel in them at some point? (a little cross contamination)

E-10 gasoline will phase separate when a certain % of water gets into the tank and then the alcohol will drop out of the mix and cling to the water... The fuel left behind has low octane antiknock properties, so when you get water in your fuel filters (when we use regular pump gasoline for automotive consumption) we must consider what that quality of fuel is that is left behind.

I've read that many people around the country can not get the alcohol free recreational fuel.

As Boscoe pointed out that three of the six injectors, leaning out on the same bank of cylinders is unlikely. I would inspect the other pistons as well.

Cross fuel contamination in high compression aircraft engines (reciprocal) is much worse to get jet kerosene into your gasoline than gasoline into your jet engine. The Jet A contaminated gasoline will detonate prior to the spark plug based on compression and heat and just cause the engine to grenade.

If I die of old age... It sure is not going to be my fault!

[jfbetz01]

Gator-unfortunately, I do not have access to non E-10 gas, whether at my roadside gas station, or waterside fuel dock. I did top the tank off with roadside fuel prior to launching.

No, no portable fuel tanks ever...my main tank is 140 gallons. The fuel upstream of the engine is clean (glass on the left in the pic). But there was clearly a build-up of phase separated fuel in the VST tank (glass on the right).

Right bank of cylinders are all 3 without any issue.

I guess my question now is, among the likely culprits for detonation (lack of water cooling, lean fuel/clogged injector, poor fuel quality), what is most plausible. At this point...the fuel quality seems to be the only definite/verifiable indicator of the 3. And is this enough to detonate cylinders at this level? I would agree that 2 or 3 injectors having issues at the same time is unlikely, but I guess they would need to be flow tested.

And a lack of cooling water would probably not have an instantaneous affect like what I had...with no warning. It would seem to me, my temp gauge would have climbed up gradually above the normal range. The gauge read normal, even when the engine initially failed; then, as the engine seized and shut down, the needle pegged into the extreme hot range.

[FabricGATOR]

When you say top up the fuel just before boat racing (just kidding about racing) how much are we talking about? 30 or 40 gallons? and was that topped to full or just threw some fresh fuel in with what was left over from last season... or was it from last week? last month?

Now your picture shows about an estimated ounce to an ounce and a half of clear liquid under 6 or 7 ounces of fuel mix floating atop. But remember, that VST is a trap just like the Racor or the engine mounted fuel bowl/filter. So I believe that even though you show 10-12% by volume water(clear crap) in the VST sample glass, you probably don't necessarily have bad fuel floating atop of that sample.

You probably put at least 10 gallons through the VST that morning and it all just floated over the top of that clear crap. Now the injector pump does draw VST fluid from near the bottom, but that should be distributed to all the cylinders (injectors) evenly and I would imagine that if it got a slurp of that the engine would stumble but I doubt it would implode like that.

I just commissioned a trailer boat for a neighbor that had it sitting in his driveway for about a year since he bought it used from his friend. Supposedly, it had always been fed REC 90 (alcohol free) gasoline its whole life since new in 2005. We ended up getting about 2 1/2 gallons of water from the bottom of the 86 gallon fuel tank by siphoning the last of the liquid out through the fuel sending unit hole with the trailer jacked up high in the front. New fuel sending unit gasket kit and burned up all that old gasoline in the lawn mowers, pressure washers, and dirt bikes. That 2.5 gallons came out after the tank was siphoned empty through the Racor and we couldn't get any more gas out if it the way the engine would get it. That is when we cleaned the bottom of the tank out through the sending unit hole.

I would also consider/suspect funny fuel. The experts should chime in here soonly..

When was the last time the VST was serviced or checked for water/debris through the drain plug? Now you got me wanting to go check my two VST's...

[robert graham]

Looks to be text book detonation damage IMO.

Usually seen in the upper most cylinders. They run a bit hotter. In a big block HPDI it is usually (more than 50% of the time) the top left cylinder when looking at the motor from behind.

Usually seen on the exhaust side of the piston. Where temperatures are a bit hotter.

Yamaha has not said (that I know of) what kind of pistons they use. Hypereutectic pistons are known to be susceptible to detonation damage. I suspect that is what they are. They don't fare as well as old style forged pistons. Over on the bass boats boards they all use aftermarket pistons if and when a motor needs to be repaired.

Over propping, poor quality gasoline, an injector leaning out just a tad, inadequate cooling, etc. can all lead to the perfect storm of detonation.

All three pistons on the side shown appear to have detonation damage. You might as well remove the starboard side head and let us take a look at those pistons as well. I suspect some will show some damage.

Would there be any warning with detonation like pinging or knocking, like with an automobile engine? That's some nasty/catostrophic damage!!!

[boscoe99]

Would there be any warning with detonation like pinging or knocking, like with an automobile engine? That's some nasty/catostrophic damage!!!

In an automobile I can hear (even with my crappy ears) pinging. Years ago when pollution sh1t was first implemented I blocked off my exhaust gas recirculation valve. Damn that thing would knock in a heart beat.

In a boat with a loud motor on the back and air rushing by my ears I can't hear squat.

OP's motor has a knock sensor but detonation has to come first for the sensor to detect it. By the time the sensor hears the detonation it might be too damn late.

[99yam40]

running e 10 and finding that in the VST, leads me to believe that you have a pool of that phased out mixture of water/ethanol rolling around in the fuel tank.
the pick up tube picks up a little, but it does not sit on the very bottom.
there is a lot more rolling around on the bottom and that needs to come out. you will not get it all thru the normal pick up tube .

when you hammer down or make turns that stuff moves around and gets picked up . I am sure some of that has hit some injectors and will again if you do not drain and clean it all out

My opinion is that part of the motor tends to get warmer than the other parts so it is a combination of heat ,bad fuel, lean on fuel.
having injectors flow tested would help you see if they had anything to do with this problem

[robert graham]

running e 10 and finding that in the VST, leads me to believe that you have a pool of that phased out mixture of water/ethanol rolling around in the fuel tank.
the pick up tube picks up a little, but it does not sit on the very bottom.
there is a lot more rolling around on the bottom and that needs to come out. you will not get it all thru the normal pick up tube .

when you hammer down or make turns that stuff moves around and gets picked up . I am sure some of that has hit some injectors and will again if you do not drain and clean it all out

My opinion is that part of the motor tends to get warmer than the other parts so it is a combination of heat ,bad fuel, lean on fuel.
having injectors flow tested would help you see if they had anything to do with this problem

Sort of a perfect storm of conditions to do this kind of damage?!!

[pstephens46]

Damn shame all the boat owners who have no choice but E-10. Unless you have a work boat or retired, you can't burn enough of that crap to cycle it before it creates problems. Damn the government and bleeding heart fools!

And screw the Paris Accord....

Unless you want French wine, cheese or bushy women, I tend to avoid anything with France in the name...

Boscoe, thoughts?

[jfbetz01]

I may in fact look into draining the main fuel tank. But I would expect to have seen at least some ethanol come out of the racor or the port engine racor or port VST. I drew fuel from those other 3 places, and all were clean fuel.

Nontheless, somehow, that crap got past my racor and on board fuel filter. I'm wondering why only the port bank of cylinders was affected. Top was worst, middle was almost as bad, lower had only slight sign of issue; starboard cylinders were all good.

Not an expert on head gaskets, but both of these seem to have been functioning and tight.

[boscoe99]

Damn shame all the boat owners who have no choice but E-10. Unless you have a work boat or retired, you can't burn enough of that crap to cycle it before it creates problems. Damn the government and bleeding heart fools!

And screw the Paris Accord....

Unless you want French wine, cheese or bushy women, I tend to avoid anything with France in the name...

Boscoe, thoughts?

Boscoe's thoughts are Italian wine, Italian cheese and Italian smooth slick women.

Screw the french. I eat fried potatoes. I don't eat french fries.

[rodbolt17]

looks like another case of piss poor fuel coupled with excessive cooling system maint.

road eyes?????

left Mobile AL yesterday and the clock in the truck said 830.
arrived at the house here in KDH and it said 1215.
way to much windshield time.

[jfbetz01]

looks like another case of piss poor fuel coupled with excessive cooling system maint.

road eyes?????

left Mobile AL yesterday and the clock in the truck said 830.
arrived at the house here in KDH and it said 1215.
way to much windshield time.

What would be considered excessive cooling system maintenance?