Newbie question 04 225 vmax

[twmotox17]

Good morning everyone. First post so forgive the ignorance. I recently purchased an 04 225 vmax and Im trying to figure out Yamahas model designations. What is the difference between the VX and VZ models? I bought this knowing it would have to be rebuilt. It has 120 psi on all cylinders except the lower left and it has 30. I ran a boroscope down into the cylinder and didnt see any scoring and the piston is intact. I have been ASE master certified for 30 years but marine engines are new to me. But why not jump right in lol. I didnt come with the wiring harness so i also need to find out what years and models will work. Thanks in advance for any replys

[99yam40]

scroll down a little and is shows what all the letters mean
Yamaha Outboard Parts

[twmotox17]

Awesome thank you

[TownsendsFJR1300]

Probably already know it, but I'd do a leak down test on that cylinder before yanking parts.

May be a bad head gasket, especially with no scoring seen..

[twmotox17]

Ive never done a leakdown on a 2 stroke outboard. On motorcycles but not marine. Wouldnt you have to block off the intake and exhaust like you do on a bike? How would you be able to do that?

[TownsendsFJR1300]

Nope, just bring it to TDC, lock up the crank and hook up gauges/air.

If you have major loss at TDC, could be rings, head gasket, or broke head.

Not sure where your thermostat is, but removing that (IF there is a large loss at TDC-head gasket), you should be able to hear it from inside the coolant passages.. Also, that failed cylinders spark plug would look clean with the water intrusion..

If it's the rings, you'll have air pressure NOW in the crankcase. You may have to remove the reeds to hear it.

There have been a few cases of the "pin" that locks the piston rings from moving, FAILING, (literally bent in the piston), then the rings rotated. With no scarring(in your case), probably not...


BTW, if you suspected, in the motorcycle, a lower crankcase leak, you could make Two plates to close off
the exhaust (one cylinder at a time) and a plate for the intake (remove carb). Now pressurizing NOT at TDC will pressurize the crankcase so you could check crankshaft seals, etc (I'd use a MUCH LOWER PRESSURE).

[99yam40]

leaking that bad the head will have to come off anyway to find out what is going on.

what all can cause it to be low on a 2 stroke?
piston rings stuck,broken, hole in piston, blown head gasket, hole in head?.

hard to believe you did not see anything with the bore scope.

you do not have to block off anything just bring piston to TDC and lock flywheel down so it does not turn.
do not let it hurt you if the pressure moves it

[twmotox17]

Thanks again. Got it mounted on the stand today and im going to get into it tomorrow

[twmotox17]

Turns out that the seller showed me the wrong cylinder. When i showed up and brought my boroscope he pulled the plug for me and told me which cylinder it was and it turns out that was not the cylinder that had no compression. My bad for not looking at them all but i took him at his word. It tore up the piston pretty good and the cylinder has some aluminum in it but no real scoring. Im going to clean it with muratic acid like i have done on motorcycles and then hone it and measure it. Hoping for the best but expecting the worse