vz300tlrc melted piston #4

[muller2357]

04 300 hp vmax hpdi....246 hours.....running fine then started clacking away...shut her down got home pulled plugs...#4 melted...all other cylinders look good...have block completely tore down and sending to machine shop this week for inspection and hopefully boring out #4 hole...have some questions for the experts....possible causes and what to look for...i will be taking my injectors to a place in houston tx to be analyzed...im not a marine tech but am a proffesional gm tech, if i do my homework and take my time can i successfully rebuild this. where should i get my parts from..is there a gasket kit that will have all the seals i need..what is the diff between vmax and vmax series 2....forged pistons? should i go back with all forged pistons....sorry for the long post any help is appreciated
thanks

 

[robert graham]

Re: vz300tlrc melted piston #4

Most probably caused by a very lean fuel condition caused by plugged injector/screen on that #4 cylinder...maybe check around for prices for used or remanufactured power head to replace...could be less expensive alternative. I'd call several different boat shops/dealers to try to get a better idea of direction to take. It's winter and maybe some shops not so busy and would cut you a good deal on repair or replacement. Good Luck and let us know what you find!

 

[muller2357]

Re: vz300tlrc melted piston #4

no real off season here in south texas...i did some prelim pricing and if i can rebuild on my own ill save quite a bit....plus ill learn alot about my engine

 

[robert graham]

Re: vz300tlrc melted piston #4

Well good luck with it, and be sure and check the cause of that lean condition so it doesn't happen again after you fix it. I'd use Yamaha original equipment pistons, gaskets, etc.

 

[Capt Ken]

Re: vz300tlrc melted piston #4

So how are you going to check the pressure on the HP pump? You are going to have to cross all the T's and dot the I's or you will be doing it again. The HPDI is not an engine to learn on.

 

[muller2357]

Re: vz300tlrc melted piston #4

i was going to use yds and monitor the fuel rail pressure sensor...i would think the root problem would be something that would affect a single cylinder being as all the other pistons looked good on dissassembly.. i suppose i could still have an hp pump problem and it just happened to take out the weakest hole first....how else would i determine the health of the hp pump capt? if there is another better way let me know...i was planning on going after the mystery filters while everything is apart.

 

[multimech]

Re: vz300tlrc melted piston #4

Besides the injector (I agree that fuel pressure might not be the problem) look for blockages around that cylinder (cooling). Look to see the RPMs of the engine when planing (lugging?) Quaiity of fuel (Octane right? Been sitting?) Look for something that might have gotten hot in the cylinder, like a piece of the rings or a chip from a reed (abnormal combustion).

Check ignition to ensure you don't have a stray problem with #4.

Have all of the injectors sent out to be flow tested and cleaned. If the flow test shows you have full flow on #4, it is not the injector.

You can't check the pressure of the HP pump without YDS.

HPDIs have three fuel pumps (Lift, Low pressure to HP pump HP pump). Check the pressures on all of them.