Crossfire 700 meltdown - looking for root cause

[bedgar7]

Well after 14 years of riding and 17,500 miles later my trusty crossfire 700 decided to punch out. I am looking for some suggestions as to what caused the engine failure. I was riding at a steady 50 mph where the sled just shut off without warning. I pulled the jugs off to find the PTO piston/cylinder with some scoring. There is scoring in the back where the ring locating pin rides between the intake ports, then more scoring around the exhaust port. The APV looked to have been contacting the piston on the PTO side. The valve has a burr on the leading edge both on the top and bottom. I had happened to have just installed new plugs in the sled that morning. Both of the piston crowns are tan with a little wash the lighting makes the look lighter than they are, however they are not black.

 

[garageguy]

Spun a ring

 

[ezra]

Kind of surprised you could not ride it home like that .

 

[xcr440]

Is it possible an injector is not pushing what it should, and got lean? Saw a 700 similar to this a couple years ago, and that's what the issue was.

 

[Pmknman]

What do the reeds look like I cracked mine in my 700 and it went threw motor and well she never was the same after that

 

[bedgar7]

All of the rings were in place relative to their locating pins. After it had shut off I had restarted it for a few seconds but it was clattering so I shut it down and towed it out. I am guessing that was the APV hitting as the lower end seems fine. I did not pull it apart any further last night but I will check out the reeds. Looks like there is only a resistance measurement for the injector (without sending for flow testing) maybe ill pull the injector out and look for any blockage as that is the injector at the end of the line.

 

[fish633]

lean fuel condition,plugs show oil so injection pump was working,crank seal failure most likely.

 

[euphoric1]

Agree with fish633, its too late now that motor is already tore down, pulling some vacuum and introducing pressure to crankcase is the best way of diagnosis because if you dont do it, rebuild the top end it will only be miles down the trail before you will have the same problem if not more severe. being this wasnt done before disassembly I would replace seals, reseal crankcase and if still unsure afterwards, pull some vacuum and put some pressure just to be sure air tight. make sure you lubricate crank side of seal before installation.