Ideas on powerhead failure? Yamaha 150

scjmc · Nov 8, 2009

I took apart my failed powerhead today. I found cylinder 4 (I think 4 its the port side middle hole) dry of oil. The connecting rod to crank bearing was melted and that portion of the crank was rusted and looked ike it got very hot. There was a small piece of the piston skit broken off floating around in there too. The piston rings are intact and the cylinder walls look OK. Does anyone think tha tthe oiler could stop oil to one hole? Could combustion possibly burn the gas/oil mix in the crankcase? Just looking for opinions thanks.

reeldutch · Nov 9, 2009

Re: Ideas on powerhead failure? Yamaha 150

is this a carburated engine if so check out the carb for a clogged main jet.

cousinabe · Nov 9, 2009

Re: Ideas on powerhead failure? Yamaha 150

Agree. Your previous post indicates a 99 150 carb'd motor.
sounds like a clogged main jet for that cylinder.
motors blow due to lean conditions. Sorry to hear that.

robert graham · Nov 9, 2009

Re: Ideas on powerhead failure? Yamaha 150

Maybe the use of Stabil Marine all the time and a fuel/water seperator might have prevented this failure? Draining the carbs a couple of times a year could also help. Sorry about your motor, seems like the fuel/water/ethanol issues continue to cause a lot of problems. Good Luck!

scjmc · Nov 9, 2009

Re: Ideas on powerhead failure? Yamaha 150

I will check the carb jet, but the carbs are brand new yamaha as of about 3 months ago. There are good clean racor drainable fuel water seperators, and ethanol fuel has never been used in this boat. Whats the best way to check the jet? Actuate the linkage and see if it spras like the other ones? The oil is injected into the intake manifold after the carbs, so is it still possible that the absence of fuel could have caused this? Thanks again!! I would check this post more often, but I had a rough day at work today!!

99yam40 · Nov 10, 2009

Re: Ideas on powerhead failure? Yamaha 150

I have read somewhere that lack of oil will get a bearing and lean fuel mix will get a piston.
Sounds like you had a lack of oil problem, but that is just my opinion.

scjmc · Nov 10, 2009

Re: Ideas on powerhead failure? Yamaha 150

I am going to check the oil lines for blockage. Do those check valves ever get stuck I wonder? Can the oiler stop oiling only 1 cylinder?

cousinabe · Nov 10, 2009

Re: Ideas on powerhead failure? Yamaha 150

http://www.boats.net/parts/search/Yamaha/Outboard/1999/S150TXRX/OIL PUMP 1 150 L150 175/parts.html

oil lines can get blocked with sludge. my oil tank had condensation/water in it over the years, caused the filters to gum up. cleaned them out with carb cleaner. i would guess the same thing could happen to the check valves.

rodbolt · Nov 10, 2009

Re: Ideas on powerhead failure? Yamaha 150

rod bearing failure is normaly due to lack of lubrication.
can be caused by water injestion,clogged check valve in the oil line or a bad lift pump diaphram squirting fuel into that cylinder making the oil mix way to lean.
but if its rusty my bet is water intrusion.

reeldutch · Nov 10, 2009

Re: Ideas on powerhead failure? Yamaha 150

he said it melted a rod to crank bearing.
how can it melt if theres water involved. rust yes and breaking stuff yes but a lot of heat to melt a rod is very extreme and i believe only a extreme lean mixture of gas can melt it.
its hard to say if you cant see it in front of you.

just my 2 cents

rodbolt · Nov 10, 2009

Re: Ideas on powerhead failure? Yamaha 150

cause water and heat tend to wash lubricating oil off of the intended surfaces.
gas from the carbs wont have didly to do with rod bearings on a two stroke 150 oil injected yamaha.
oil is injected aft of the carbs.
lean air fuel mix will take out a piston.
however a leaking lift pump diapram will sqiurt raw gas with no additional oil into the crankcase and severly dilute the oil thats injected and cause a lubrication failure.
and water will wash the oil off and create heat causing the crank to turn blue,melt rod bearings then rust.

scjmc · Nov 10, 2009

Re: Ideas on powerhead failure? Yamaha 150

I cannot blow through the oil lines with my mouth. I tried the failed cylinder and I cant blow through it. I also tried blowing through another oil line and I couldnt. Should it be easy to do so? I afraid to use compressed air because I dont want to hurt the check valve. How much pressure does it take to open it? I will check the diaphram on that pump. The pump was replaced with the carbs a few months ago, but that doesnt mean that it is ok. Where should I look for water intrusion? The piston top and liner looked OK, just a little scorched from the heat in that cylinder.

scjmc · Nov 15, 2009

Re: Ideas on powerhead failure? Yamaha 150

I checked the fuel pump diaphram on that cylinder and it is good. I looked t the water jacket and did not see any signs of a leak into the block. Any other suggestions? I need to figure out of that oil line is blocked, but I cant blow through it with low pressure.

reeldutch · Nov 16, 2009

Re: Ideas on powerhead failure? Yamaha 150

what puzzles me is that most of the time when there is a no oil failure the piston will score the hell out of the cylinder wall.
there is no water evidense inside the cylinder.
only the bearing and connecting rod and piston skirt have damage.
you would think that if there was water inside the crank to wash away the oil, it defenatly would be going trough the intake ports of the cylinder and do some damage there to.
may be for some reason the bearing failed and overheated the hack out of it.
may be the connecting rod caps were not seated propper?

scjmc · Nov 17, 2009

Re: Ideas on powerhead failure? Yamaha 150

I know the circumstances are very strange. I wish I could figure out what caused the failure because I don't want a repeat adventure. I am probably going to have the power head professionally rebuilt. I am assuming that the water jacket will be checked more throughly than I can by eye.

scjmc · Nov 17, 2009

Re: Ideas on powerhead failure? Yamaha 150

When the failure happened the engine went from running fine to making a mechanical racket (3800RPM Cruise). I immediately brought the engine back to idle. Once at idle it shook for a few seconds and shut off. The entire event lasted 6-10 seconds. After it stopped it would not turn by hand clockwise, but it would turn about 3/4 of a turn counter clockwise. Once we took it apart it would rotate fine even with the rod cap on.

robert graham · Nov 17, 2009

Re: Ideas on powerhead failure? Yamaha 150

Sounds like the definite cause of this failure may remain a mystery. Was the motor ever laid up long without fogging and possibly corrosion started in the crank and rod bearings? It wouldn't take much corrosion/pitting on those needle rollers to fry the lower end. Please let us know if you find out for sure what happened. Good Luck!

rodbolt · Nov 17, 2009

Re: Ideas on powerhead failure? Yamaha 150

very rare to scuff a piston on a carbed oil injected V yamaha due to oil failure.
the oil is injected aft of the carb and usually if debris enters the pump and clogs a pump outlet nipple or a check valve you melt a bearing very rapidly.
piston simply doesnt require as much lube as a rod bearing.
if at any point the crank gets wet either from a blown gasket,water in the fuel or whatever the crank,rod and bearing will pit at the contact point.
once any surface is pitted the rollers can catch and become sliders.
even with lube sliders dont last but a few minutes at higher RPMs.
remember,E fuels can carry water right past any filtration system now in use.
after extended idle there isnt much oil in the system.
once the fuel evaporates now the water does its thing.
I reccomend if the engine is going to sit longer than 30 days either fog it or run it about 10 minutes at idle with the oil pump rod dissconected and the pump lever at wot position.
now we have plenty of oil to protect the shiney parts inside.

scjmc · Nov 17, 2009

Re: Ideas on powerhead failure? Yamaha 150

Thanks for the new input. The boat is normally used at least every 2 weeks. It has sat for maybe 4-6weeks on occasion, but not often. Many times it is used several times per week. It has never been fogged, but then the damage seems to be limited to the 1 cylinder. A few years ago there was a leak in the water jacket that was spraying water on the port side of the carbs. The carbs became corroded as a result, and the engine drank some water I am sure. That happened before we bought the boat though. THe failure occured after cruising for about 30 minutes.

HarmonAviation · Nov 19, 2009

Re: Ideas on powerhead failure? Yamaha 150

Dude, use Stabil in every tank of gas you mix up, it bonds to ethanol and takes away ethanols ability to attract water and break down oil. one bottle treats 25 gallons (autozone) add 2 qts 2 cycle oil to it and get the good stuff bottled in gallons from a big drum (available at most marine repair shops).

My engine compression runs from 90lbs to 120lbs, bad, right? after running this stabil/quality oil mix the compression in the two bottom cylinders actually rose to 105 - 120 going up a V6.

Lastly if you have pre 1993 oil injection, get rid of it and mix your fuel.

1985 Yammy 200 ETXK no oil injection

Ideas on powerhead failure? Yamaha 150

Petty Officer 2nd Class

Lieutenant

Senior Chief Petty Officer

Admiral

Petty Officer 2nd Class

Fleet Admiral

Petty Officer 2nd Class

Senior Chief Petty Officer

Supreme Mariner

Lieutenant

Supreme Mariner

Petty Officer 2nd Class

Petty Officer 2nd Class

Lieutenant

Petty Officer 2nd Class

Petty Officer 2nd Class

Admiral

Supreme Mariner

Petty Officer 2nd Class

Recruit