Need some expert opinions here. Blown Merc XR6

[4Bassin]

Hi, a little history. I have a friend who owns a Ranger boat that had a Mercury XR6 that burned a couple cylinders about 10 years ago. He had the block rebuilt and those same two cylinders blew again last year. He brought the boat to me and instead of rebuilding his block as it threw a rod and damaged the block. He bought a 2001 Mercury XR6 and I installed it on the boat. With my conversations with him I felt the motor was too high on the transom but he insisted it was correct. Needless to say I now have the boat back in the garage and #2 piston and cylinder is fried.

This time while I was tearing the motor apart I noticed that the oil pump driveshaft would turn with a screwdriver. I knew that couldn't be right so instead of blaming the problem on a motor too high on the transom I thought the engine may have starved for oil.
When I removed the carbs I dumped the fuel and it had oil in it so I am not convinced it was oil starvation. I finished the tear down and found the rest of the cylinders were ok and appeared to be oiled ok.
When I split the case I did find this:

Notice the oil drive worm gear is toast. I am starting to believe that it was possible that some of the debris from the piston disintegrating may have damaged the gear.

I am getting ready to send this block off for a new sleeve and anything else the machine shop deems necessary. I am back to believing that the motor overheated and this damage was caused. He did say he noticed 5lbs of water pressure when the motor started coming apart. The high temp alarm never sounded and I did ground the temp wire and the alarm does work.

What do you guys think??

Edit to add: I don't understand Mercurys thinking on this particular motor. My 97 EFI has a sensor that alarms if the oil pump shaft isn't moving. The previous XR6 that was on this boat had that same sensor. There was no alarm sensor on this motor and no place to put one. Why would Mercury remove that sensor?

 

[Karl_Childers]

Re: Need some expert opinions here. Blown Merc XR6

Which came first (chicken or egg) oil pump drive gear or piston meltdown, right? How did the pluggs look? How do you know if the carb was or was not leaned out? I'll bet the piston caused the gear failure, like you said. reason I say that is nothing else is torn up. Those cooling passages look like fresh water use, so most likely not an overheat, unless the motor was too high, which would also have torn up other things. Are all the bleed lines intact? could a ruptured bleed line cause it to suck air and run lean enough to melt down? How about carbon build up, causing detonation? I am just throwing out guesses really. If you want my opinion, I hate oil injection. When the system has a malfunction, your pistons look like that. Impossible if you premix! Although, pre-mix engines are horrible for the environment. I don't have all the answers, just some strong opinions. Good luck!

Rob

 

[cannonford57]

Re: Need some expert opinions here. Blown Merc XR6

karl is on the point on this one i think...with everything looking as good as it does i would agree with the carb leaning on that cyl.could be as simple as a bit of trash in the bowl lodging in the jet....i.ve seen it happen...take your time on the teardown and espically on the carbs...just my opinion

 

[4Bassin]

Re: Need some expert opinions here. Blown Merc XR6

Thanks for the responses. I doubt it was carbon detonation as all the pistons were clean with no residue at all. I gave the lean carb theory a thought but this is the third time a motor on this boat has blown the same cylinder. Different motors mean different carbs. I could understand a repeat of the same symptom if the same carbs were used. Even though the piston was toast the rod bearings still had a oily film on them. They weren't dry by any means. Upon dis-assembly all bleed lines were intact and didn't have any damage. I will check the carb that fed this cylinder but I am not optimistic that I will find a problem with it.

 

[Willyclay]

Re: Need some expert opinions here. Blown Merc XR6

I am NOT a professional but always like to learn from others. Looking at my service manual, I found that the temperature sensor range for a 2001 XR6 is 232-248F. That makes me think you could easily have an overheat situation without the warning horn ever being activated. Number 2 is also the highest point according to the coolant flow diagram. If the owner/friend reported 5PSI just before the latest incident, it sure sounds like the problem. I see a lot of bass rigs with the low-water pickup mod. Good luck!

 

[j_martin]

Re: Need some expert opinions here. Blown Merc XR6

In my humble opinion:
At WOT you should be running at least 10 - 15 lbs water pressure. If it's low, it's sucking a lot of air and that will tend to collect in the top, thus overheating #1 or #2.

The oil gear succumbed to a combination of flying debris and overheat, after the fact.

If you want to run the engine that high, especially in some waves, put a low water pickup on it.

hope it helps
John

 

[4Bassin]

Re: Need some expert opinions here. Blown Merc XR6

In my humble opinion:
At WOT you should be running at least 10 - 15 lbs water pressure. If it's low, it's sucking a lot of air and that will tend to collect in the top, thus overheating #1 or #2.

The oil gear succumbed to a combination of flying debris and overheat, after the fact.

If you want to run the engine that high, especially in some waves, put a low water pickup on it.

hope it helps
John

I'm pretty sure it was an overheat situation since it has happened with two different motors. I really don't like the jackplate setup on this rig as he is using two jackplates to get the motor back even further. I plan to lower the motor and run it on the lake and dial it in before returning the boat to the owner. I was fishing here for others expertise before I proceeded. Thanks

 

[familyboat]

Re: Need some expert opinions here. Blown Merc XR6

Hi - I had the same thing happen to me today

I was happily cruising along when suddenly the motor dropped 1000rpm and started to hammer. Then it died, and wouldn't start or turn. I pulled the plugs and all look fine except #2, which is a mass of molten metal.

I note that you sent for a new sleeve and are rebuilding. I wonder if it's worth to do that or just replace the powerhead?

As for why it happened, I'm feeling a bit guilty that I overrevved the thing, as we had an 18 pitch prop on and I was trying to get 40 mph out of it.

We had gone probably 10 miles at 35mph before I gunned it, and 5 minutes later it did its thing.

I haven't taken the head off yet. I could, having some mech. experience but none too much on outboards. I wonder tho how worthwhile that is.

By the looks of how blue it would smoke on startup I am doubting the oil injection was to blame. It could have got hot, since we had passed through some shallows earlier and were trimmed up and idling along. The telltale "pee stream" was coming out, but it's always a little spurty, and not a good strong stream. Perhaps I shud have replaced the water pump? Might as well do it now I guess.

Perhaps I should have kept it under 5500 also, but I've learned that lesson.

Please give me your advice.

 

[j_martin]

Re: Need some expert opinions here. Blown Merc XR6

The oiler is good for about 6500 rpm. The first thing that happens with a weak water pump is a bubble can develop in the top of the block, overheating 1 or 2. Also, when you pull in debris, it can plug small ports anywhere in the engine. I suspect that's what happened. #2 got hot and the rest stayed cool, including the overheat sender.

Tough luck. I've learned that it's just not worth it to try to motor through the slough.

John

 

[familyboat]

Re: Need some expert opinions here. Blown Merc XR6

Thanks for the reply! So, do you think it's cheaper to rebuild, or should I buy a powerhead?

 

[j_martin]

Re: Need some expert opinions here. Blown Merc XR6

Thanks for the reply! So, do you think it's cheaper to rebuild, or should I buy a powerhead?

Do I look like a fortune teller?

 

[familyboat]

Re: Need some expert opinions here. Blown Merc XR6

Can 't really see you from here, I'm afraid

I'm going to opt for the rebuilt powerhead. I took a head off and #2 is fried (lots of slag on the head from the burnt piston, bits of ring floating around) and #4 cylinder is badly scored. I get the feeling the rest of the motor had to work pretty hard to move #2 up and down after it disintegrated and tried to weld itself to the head.

Seems 6100 rpm was too much for this 2000 motor. Plus I realize now that the motor came from Colorado (5000ft) and we're at 3000ft, so I think the combination of WOT and thicker air probably did the motor in.

A rebuild will take too long, what with sending things out and getting parts and all that. Even tho the powerhead might be slightly more money it'll get done faster.

Has anyone got a recommendation for where to get one? I've noticed Hinkle Marine, Crowley Marine, RPI Marine, and Georgia Watersports so far. Any advice about good or bad experiences would be greatly appreciated.

I'll replace the powerhead, water pump, alarms, and tune the thing rich. Any other advice would be appreciated.

 

[familyboat]

Re: Need some expert opinions here. Blown Merc XR6

Well, I ended up buying a whole used motor, owned by a great person who installed it for me and also installed hydraulic steering for me. I really appreciate honest people who work hard and like what they do.

While installing the hydraulic steering, he found that the alarm beeper was stuffed with paper towel so as to silence it.

I believe the dealer who sold me the boat knew my melted motor had overheating issues when they sold it to me on June 19th. I can't believe that they would not take the time to replace the water pump but instead sold the boat to me with a defective one, and would stuff a paper towel in the alarm to silence it to boot. I would have gladly paid the extra money to have the water pump replaced, if they had just advised me to do so!

Now, I am going to sue them. Being a lawyer, I think this should be fun, but not for them. They are going to regret it.

 

[bdarbyups]

Re: Need some expert opinions here. Blown Merc XR6

I also blew my 2000 XR6, #1piston. I was told by K & K Marine Hot Springs , AR that the timing solinod stopped working and it put the motor timing up 40* blowing only the #1 piston. I had no warning signal and my water pressure was over 10lbs with all cylinders getting oil.