High Speed Shutdown

[TexasSkeeter]

2001 VSX 225 on a Skeeter. Motor always ran good. Yesterday on way back to ramp decided to test top end. After maybe 30 seconds at WOT (68+ mph), the motor sound changed to a louder rattle sound. I throttled down and it quit as rpms dropped toward idle and boat slowed. No alarms.

Tried to restart and engine would not turnover. It tried, but seemed like too much compression for starter to overcome.

Maybe 10 minutes minutes later after *****ing to ramp and loading on trailer, I hit the key. It started immediately and I shut it down. What the heck???

Any ideas? I'm going to launch and test today. The loud rattle sound worries me. I'm wondering if I broke a reed....

[rodbolt17]

I am thinking you either lost the bottom bearing or suffered an overheated piston that swelled up and grabbed a cyl wall.
its not an automatic shutoff.
test the compression before water testing.

[TexasSkeeter]

I put the boat in water today and started it (I didn't see RodVolt's post until later). Immediately realized that the sound AND exhaust smoke seemed to be coming out from under the lower cowling. I am thinking the $20 gasket between the crankcase and the upper casing blew, but don't know. The "rattle" sound seemed like noise from an exhaust leak.

Does anyone know if that gasket blowing is a known issue? Maybe from loose bolts? Does the gasket just need replaced, or is there some other issue that likely caused the gasket to go?

Also, any guesses on cost to fix?

Thanks in advance!

[liliepad1]

Pull the spark plugs sounds like your gonna have 1 with metal on it . Compression test to confirm but sounds like u need to rebuild

[TexasSkeeter]

RodBolt, unfortunately you are right again. The middle cyl on the starboard side lost its rings. Have a couple mechanics say its ok to bore one cyl .03 and put in an oversized piston, while others kept standard size....is that an acceptable practice?

[99yam40]

exhaust smoke seemed to be coming out from under the lower cowling

Even if the rings broke on that piston you should not have exhaust/ smoke coming out from under the lower cowling unless there is a hole somewhere there is not suppose to be one.

Have you had it taken apart yet to see what all damage has been done?

[rodbolt17]

can it be patchem upped that way?
yes.
do I recommend it? no.

but scuffed rings/burned pistons are a symptom not a cause of a failure.

I would have the motor comepleatly torn down and ALL surfaces measured BEFORE even thinking rebuild at this point.

[TexasSkeeter]

Rod Bolt, please advise: If broke rings, scuffed piston are a symptom, what are the possible causes? I want to make sure my mechanic checks them all out before declaring this engine sound.

And as to boring one cyl out, do you advise doing them all to match?

[rodbolt17]

the two main causes, a cyl overheated or a cyl ran lean.
as that motor oils via the injectors I would pay close attention to the ENTIRE fuel system and carefully inspect the cooling system.
Yamaha only 0ffers pistons in .025mm and .050 mm.
roughly .010 and .020".
if your going to .030 your going aftermarket pistons.

typically,if not heat or lack of oil damaged, you can reuse the bearings.
myself I replace the lower ball bearing anytime I have the crank out for any reason.

the rest are roller type and simply go round and round.
the bottom is a ball bearing and accepts axial as well as radial thrust loads.

would not be the first time I have seen a leaking diaphragm on a 50 dollar fuel pump destroy a motor.

[TexasSkeeter]

Rod Bolt, you said "Leaking diaphragm on a $50 pump" can cause a motor failure.....let me get this straight: the fuel leaks into the crankcase from the leaking diaphragm, which is un-oiled gasoline. I'm guessing that dilutes the oil-gas mixture heading to the cylinders, causing lack of lubrication and ring failure. I'm also guessing the computer detects a rich condition, maybe thru the O2 sensor, and backs off the fuel flowing through the injectors (oiled fuel) to make up for the extra un-oiled fuel leaking into the crankcase. Which even further dilutes the oil ratio in the fuel heading to the cylinders.....am I on the right track?

I always thought a leaking fuel pump was just an annoyance(bad idle, etc...) but this sheds a whole different light on why you better not just let a leaking pump be.

[rodbolt17]

pretty much right about excessive fuel that isn't oiled.

a defective or unplugged O2 sensor can make it run lean above 4000 rpm as well.