1987 yamaha 150 2-stroke blew again

[lime4x4]

Last year i blew the port engine. Spent the winter rebuilding it. Last year it was cylinder #3 that had a melt down. Couldn't find anything wrong with the oiling system so it looked like a carbon issue in the one cylinder. So i had cylinder#5 bored out .20". Replaced that piston and all the rings. Had the other 5 cylinders honed. The other day while heading offshore i noticed the port engine engine started to loose rpm so i backed off the throttles and the engine stalled. Wouldn't turn over. After it cooled it would crank but didn't sound right. So we spent the day fishing with only 1 engine. Took the cylinder heads off this morning and i found damage to cylinder #6 only. There is about 30 hours on this rebuild. Any ideas? The only thing i noticed was once i got the power head back on and running it on muffs i had more water coming out of the exhuast tube compared to the starboard engine but had a good strong pee stream and engine never overheated. It was an expensive day for 1 flounder...lol

 

[family affair]

Lime, that's terrible news. Sorry to hear that.
What does the damage look like?

Did you get a good look at the cooling jackets around the cylinder and head after #5 went kaboom? The only thought that comes to mind is corrosion is preventing cooling on that cylinder. I would think that localized overheating would not cause the overheat alarm. The high temp would cause pre-ignition/detonation causing mechanical damage like you saw on cylinder #5.

Keep us posted.

 

[lime4x4]

lets try this again

 

[lime4x4]

i edited my first post. Last year it was cylinder#3 that failed. For some reason google photo isn't playing nicely with image tags. I took the other cylinder head off the other side and found another damaged cylinder. Cylinders #6 and #5 are damaged. All other cylinders look fine.

 

[lime4x4]

Looking at the cylinder heads it appears cylinders 6 and 5 ran lean. Gonna order the pistons and gaskets unfortunately the machine shop can't do the block for another 6 to 8 weeks.

 

[gw204]

Why not find a used motor instead...or at least something with a good powerhead on it?

http://southjersey.craigslist.org/bpo/5120887964.html

 

[seasick]

Looking at the cylinder heads it appears cylinders 6 and 5 ran lean. Gonna order the pistons and gaskets unfortunately the machine shop can't do the block for another 6 to 8 weeks.

The pistons don't look like a lean condition. I would expect to see more damage to the tops and not necessarily the cylinder walls It looks like ring failure to me or lack of oil. Do you have photos of the plugs. They can tell a lot about mixture issues.
I just cant see spending more time and money on this power-head since whatever blew it up the first time is still an issue. Did you pull all pistons last time and check the rings and ring grooves for buildup or cracks?

 

[lime4x4]

Last year it was cylinder #3 that got destroyed this year it's cylinders #5 and #6. When the engine was rebuilt the other pistons and rings were checked. Since they checked out within spec they were re-used. They went back into the cylinder they came out of. This time around i'm gonna be replacing all the pistons and rings regardless. Below our pics of the cylinder head and plug. I agree if only cylinder #3 failed then it would have me wondering but since it's 2 other cylinders. Don't really mine the time involved. Last year my buddy bought a used outboard for his boat. Paid 1500 for it. Unfortunatly after 3 hours it becoame a very expensive anchor.

 

[family affair]

Statistically I would think it would be extremely unlikely to have mechanical failures in multiple cylinders based on component wear. Something else is going on IMO. Those pistons look awfully dry for a carbed 2 stroke.

 

[lime4x4]

Seeing how clean the cylinder head is that's what's leaning me to think those cylinders went lean

 

[lime4x4]

Got the engine off tonight. Took notice that there still was oil in the oil nozzles. Should'nt the intake side be coated with oil? Still didn't really find a reason for the failure

 

[lime4x4]

I just don't get it.. I c no reason why this engine failed. There was oil under the crank. There was oil in the nozzles and found nothing in the carb to cause a lean condition. None of the rings broke

 

[seasick]

I can't see any of the recent photos but am a bit surprised that no rings were broken. So that leaves a few other poosibilities: Something in the crank case or oil that scarred the walls (metal pieces perhaps) Pieces of the ports perhaps, pieces of the reed valves...
Another possibility is an oil issue. Although you same oil on the nozzles, that doesn't prove that there was enough or that oil rate was right for high speeds.
Do you log fuel use and oil use? That might give an indication of oil rate.
All things considered, you may not be able to determine what happened. The motor has served for a lot of years and may just have had it

I just can'r see dumping more parts and labor into it.

 

[lime4x4]

I don't know why the pics aren't showing up. I've been looking for a used 150 but they seem rare. finding alot of 175's and 225's thou. I really don't keep track of my oil usage. i just make sure sure the remote tanks are full when heading offshore. Parts are pretty cheap for these older 2-strokes and the only other cost i have is the machine shop bill. I did find that my low pressure fuel pumps are leaking thru the vacum port. Maybe too much fuel in the crankcase and it dulited the oil too much. Also heard that the exhuast inner cover has a habit of getting small holes in them allowing water into the exhaust side. Both lower cylinders were heavily damaged by the exhaust port. With machining and parts i'll be around 500 bucks which isn't too bad. Over the winter i want to find a set of newer 2 strokes

 

[lime4x4]

Well after getting everything disassembled and cleaned it looks like it was more then just a lean condition. Piston from cylinders 1,2,4 and 6 are showing shiny spots on the pistons skirts. The only piston that shows no sign of wear is cylinder #3 which was bored and had the piston replaced. I honestly don't know if the wear in the other pistons were there or not from the last rebuild. Not taking any chances this time. The other 5 cylinders are getting bored out with new pistons. After the break end of the engine i will also be running a slight premix in the main gas tank 2 gallons of 2 stroke oil to 100 gallons of fuel for the first 200 gallons of fuel then go back to just gas

 

[family affair]

IMO, I would run premix at the highest oil concentration possible until you 100% verify that your oil injection system is working properly. The photos you have posted would lead me to believe you are not getting enough oil. Another option would be to ditch the injection system completely and run only premix.

 

[seasick]

IMO, I would run premix at the highest oil concentration possible until you 100% verify that your oil injection system is working properly. The photos you have posted would lead me to believe you are not getting enough oil. Another option would be to ditch the injection system completely and run only premix.

There is a way to check the premix and that is documented in the service manual. Basically it requires running on a tank of premix, disconnecting the oil pump output line and using a measuring cup, see if the specified amount of oil is pumped in a specific amount of time.
I know a lot of folks say to disconnect the oil injection system and run premix but I don't feel the same. For the most part, the Yamaha oil system has been very reliable. In addition, one advantage is that the ratio of oil to gas is variable depending on throttle position. At low revs, the ratio is a lot less than at higher revs. That means less chance of fouling at lower speed like trolling.
Secondly, I am not a fan of hard wiring alarms so that they don't occur ( low oil alarm on main tank results in safe motor mode so the main tank has to have oil or the sensor has to be fooled).

 

[lime4x4]

I'm keeping the oil injection system. I will verify the output of the oil pump again. When i checked it in the spring it was within spec. The only thing that i found was the low pressure pumps were leaking gas into the vacum ports. So i'm thinking the gas was diluting the oil too much. I'm also replacing all the injection nozzles as well

 

[lime4x4]

Well i finally got the block and heads back from the machine shop. I finally found the cause of my failure. I was in the process of replacing the oil injection hoses and when i pulled them off the pump water came out. Found the pump was full of water. manually operated the pump in the remote tank and got 1/2 gallon of pure water before i got any oil. Found a slight knick in the oil seal on the deck oil fill.

 

[suzukidave]

Well i finally got the block and heads back from the machine shop. I finally found the cause of my failure. I was in the process of replacing the oil injection hoses and when i pulled them off the pump water came out. Found the pump was full of water. manually operated the pump in the remote tank and got 1/2 gallon of pure water before i got any oil. Found a slight knick in the oil seal on the deck oil fill.

ouch. sorry for your loss there. at least you know what caused it.