Yamaha 90 Two Stroke with 10 hours. Do I need to camera the pistons before buying.

[Graham Anderson]

I have a chance to buy a 90 Yamaha two stroke with 6-10 hours on it. The boat was tarped so we didn't crawl under and look at the tach.This engine is about 8 years old and was tarped and under covered all its life, and they say it was fogged but I am not sure if it was fogged the whole time. I would imagine that the humidity in the air would have got in and around the cylinder walls so I was wondering if I should try and camera the walls? Would there be any use to have somebody pull the head off and have a look. I'd pay extra now to ensure reliability in the future if need be.
I have heard some not so great stories about engines that have sat too long.
Thanks for any comments or ideas.

 

[robert graham]

The best proof of the motor's good mechanical health would be a sea trial out on the water....check for starting, idle, mid range and wide open throttle of about 5500 RPM's, trimmed up....a bore scope won't show you the insides of the crankshaft/bearing area or the inside of the carbs...if the motor will turn over normally then the pistons, rings and cylinders are all probably fine.....can you arrange a sea trial?....

 

[tommarvin]

I would do a leak down test. Much faster and easier to do than a compression test and safer, your not going to get shocked on the spark plug wires, you don't even start the motor.

Youtube explains HF leak down tool perfectly ,costs 40bucks,worth every penny, you have to be at Top Dead Center each cylinder for the test.

When you buy a used outboard you change water pump / rubber impeller, open the drain on the LU did water come out? if so don't buy it . Drain and fill with 100% synthetic marine gear lube,tested with 10% water contamination. Put t-stat in a pan of water,heat it up slowly, did it open around 110F.Spray 100% synthetic fogging oil in each cylinder for 5 seconds, make sure piston in all the way back in spray up at the top,turn flywheel by hand before you turn the key, lube it up first.

Please add a 10 micron spin on water separating filter to remove all the water and bad stuff in the gas.

 

[flyingscott]

WHAT leak down test is neither easier or faster than a compression test. You will be fine as long as it spins over smoothly. Go through the carbs and replace the water pump. Put more fogging oil in the cyl spin it a couple of times and then compression test it. Also if you don't want to get shocked pull the lanyard shuts the ignition right down. They are a really great motor follow Robert Grahams advice.

 

[tommarvin]

Do the sea trials and the leak down test to make sure the rings are ok cover everything.

 

[flyingscott]

Why is a leak down test easier and safer than a compression test.

 

[yamatech43]

That's right you're allll wrong..lol Look, you do a simple easy compression test and make sure all cylinders are within 15 percent of each other, and if they aren't then worry about the leakdown test to identify where the leak is. But I do agree spray a little oil in spark plug holes(a LITTLE), hook it up to a portable tank(don't run old gas in boat thru it, even if you add gas, you need to drain and clean out old gas and water from tank) and run the boat....run the hell out of it...don't ever ever ever buy a motor you don't run AT LOAD, not on a stand or on muffs. Good luck