yamaha 2 stroke 150tlrv

[riggo44]

I have a 1997 Yamaha 150 2 stroke. I've rebuilt carbs, fuel pumps, replaced fuel lines and it ran like a new motor for 2 days...then heard rapid tapping noise at 4700 rpms. shut it down and limped back to the trailer. Motor definitely runs and sounds different. Still starts and idles. Checked plugs and one is black. I tried to see in through the spark plug hole at the piston but couldn't really see much... I've spent two months restoring this boat and now I'm sick about this. Any ideas on where to go from here?

 

[ondarvr]

Check the compression, or just pull the head off that side.

 

[riggo44]

Yes, I probably need to pull that head. Today I noticed that when I push on the piston through the spark plug hole there is the slightest bit of play...and it makes a tapping noise that must be the sound I hear when it's running. Does that sound familiar to any specific issue?

 

[ondarvr]

Bad bearing on the crank or wrist pin, total rebuild time.

 

[riggo44]

so my grieving period is over...now what to do next? Ive rebuilt a 1980 evinrude 50 1 year ago and that went much easier than I would have thought. My biggest goal is "peace of mind" when it's all done. I know there are no certainties. I have the time to do the work but money is an issue.

1. buy rebuild kit and fix myself.
2. buy a powerhead and install myself.
3. take it to a service center.

And also what would have caused this? The motor was strong! Ran like it was brand new the day before. Should I try to find out what happened before I tear it down? Oiling system seems functional, I've only had this boat for two months. No oil hoses unhooked. I replaced the top half of the oil hoses on the top two cylinders above the one-way valves when I did the carbs about a week ago. Then ran premix through it until the top two lines were full of oil, no bubbles. Then it ran strong for 2 days Then disaster. Failure was not in one of those top two cylinders, it was middle passenger side, but I'm definitely feeling like it was something I did wrong. Thank you for your help.

 

[robert graham]

What was maximum throttle RPM's loaded and trimmed up?....should have been about 5500RPM's....I understand that the wrong prop can not allow upper RPM's causing the motor to lug can cause rod bearing failures.... Just a thought here...

 

[riggo44]

it did not seem to want to get up to 5500 RPMs but I was a little timid on the throttle as well. What would be the process of figuring out if that was a contributor.

 

[riggo44]

Since it is an older motor and I don't want to put a lot of money into it is fixing just the broken parts a bad idea? Would that even save me much? If it is a crank bearing would that mean the crank is likely ruined?

 

[riggo44]

well I got a quote of 7500 for a marine shop to install a new reconditioned powerhead. No way can I go that route...I'm hoping to stay under 4k. Now I have to decide between perform a rebuild or install powerhead myself. Any advice on this matter would be greatly appreciated.

 

[ondarvr]

Sell yours for parts and buy a different motor

 

[robert graham]

Maybe look around for a good running motor very similar in model and year of yours to buy cheap.....then keep your old motor for parts....what could be better than to have an entire parts motor handy for future use?.....

 

[riggo44]

I found a place called Tenkiller Marine in OK. They will pick up my powerhead rebuild it and send it back to me for 3100. If my crank needs rebuilt it's 550 more. I'm going to go pull the head off now. How can I determine whether or not the crank or rod has damage?

 

[riggo44]

maybe I'm in denial, but I tried to verify my findings and it seems there is no play in the piston when turning the flywheel. I turn flywheel back and forth but there is no play at all. Like the bearings are fine. Then I push on piston edge and there is the very slightest bit of movement. could this be from ring failure? The cylinder is not firing...could it be a fuel issue? Spark is good. I'm going to get a compression tester now...I am new to this so very appreciative of all the help.

 

[riggo44]

Or could the cylinder wall be trashed

 

[ondarvr]

The piston may rock from side to side slightly, that can be normal, up and down is bad.

 

[robert graham]

Maybe a wrist pin bearing failure....

 

[riggo44]

No Title

trying to diagnose my failure! I have been told it looks like a lean fuel issue. I had freshly cleaned carbs and rebuilt fuel pumps and it ran perfect for 2 days before this failure. Also is this cylinder head toast? Can this sleeve be bored even with the exhaust port damaged slightly? Can 1 cylinder be bored and the others left stock with original pistons. That is if the pistons, crank, and bearings look brand new can I reuse.

 

[riggo44]

any thoughts s on what would have caused this? the spark plug was black...

 

[ondarvr]

The cylinder needs to be measured to know if it's still good, or useable.

​You can just bore one cylinder, but then you have 3 cylinders in aged condition and one new, the old ones can self destruct at anytime. You need to totally dismantle the motor to do even one cylinder, so while you're there you might as well do the whole thing. Or do nothing and sell it for parts if the cost to rebuild is too high.

The damage isn't uncommon, the rings break for various reason and it destroys everything, frequently carbon build up or the locating pin backs out.

​You aren't supposed to reuse the head, but people do, make sure there aren't any small points sticking up, they can overheat and cause problems.