The engine failed on my 2004 6MT Sedan on July 4th with 114K miles. Had just replaced the shocks, tires, brakes, spark plugs, valve covers, and changed motor, transmission, & differential fluid (synthetics), and updated the Navigation DVD in anticipation of a 1,600 mile trip I was taking the next day

Big puff of smoke when decelerating from 80 MPH on freeway, then bucking and snorting and missing, smoking like a chimney. My brother and I did a compression check, had 180+ Lbs. in 5 cylinders - ZERO compression in #4.

Let it sit for a month (disgusted, didn't even want look at it), then we took the heads off and took a look - this is what we found!

YEP - a large portion of an exhaust valve has gone AWOL and my engine ate it. !!

 

Took both heads off and delivered them to my local Hi-Perf machine shop. They reconditioned the heads, had to replace two valves in the process (besides the obviously broken one, another one was lightly bent).

No explanation or diagnosis as to WHY this valve broke. Theory is that the valve lost it's seal and began to leak at that point of contact, essentially creating a "blowtorch" effect that began to eat away at the metal on the edge of the valve, and also cause metal fatigue, which resulted in a large piece of the valve eventually breaking off and the sudden loss of all compression in that cylinder.

Machinist asked if I'd ever "over-revved" the engine. Yep - one time I was running about 130 MPH in 5th, went to drop into 6th and coast down, but she went into 4th instead and overrevved by maybe 2,000 RPM for a split second (I was fortunately able to stab the clutch and get it to disengage before the drivetrain locked up - it was already starting to rotate on me!). I coasted down to about 80 MPH and then slowly let the clutch out in 6th and she ran fine, so I thought I'd dodged a bullet - turns out I probably bent that valve in cylinder #4 and started the leaking process which eventually led to the valve failure. "Good a theory as any" was what the machinist said, guess we''ll never know if that was or was not the cause.

 

wow good luck, how much does that head job recondition run?

 

They charged me $475, which included two new valves, new valve guides, and a hi-performance 5-angle valve job (which costs approx. $100-$150 more in labor charge than the standard 3-angle valve job). Pretty fair deal, I thought,

Here they are, back from the shop and ready for our re-install.

 

Heads off the engine - shade tree mechanics at work!

Notice the scarring on the re-conditioned head - that chunk of valve did some damage on it's way out of the motor... and the likewise damage to the piston in cylinder #4. That valve didn't give up without a fight.

 

Curious to how much it costs to reinstall the engine?

 

I couldn't answer that, Prinny, as we did the work without removing the engine from my car (even though the Infiniti Workshop Manual says to begin the procedure by removing the engine AND transmission from the car). Although it would have made accessing some things easier, seemed like a lot of unnecessary work to us, and we were able to do the job without removing it..

I wouldn't pay more than $500 labor for someone to remove and re-install the engine in my G, though, if I supplied the new motor and/or parts needed.

 

That is crazy. On the bright side new motor I guess. Keep us posted on how it goes.

 

Very nice! Sub'd for updates

 

So then we put her back together and buttoned it up ....plenty of (red) assembly lube grease to avoid a dry startup .....gotta line those 4 cams up just right .... no room for error here, or you'll spend another whole day tearing it back down.

Amazingly, she fired and ran ....and now she runs like a scalded dawg ... chirps the new tires in 2nd & 3rd no problem ... all the power and torque are back, feels like 2007 again ...so now I rejoin all of you as a ... "G35 Driver" !!

Thanks for viewing.

DBarnes

 

Nice save and props for getting it done with the engine in the car!

 

Nice glad to hear you go it back on track. I have 173 on mine and waiting for it to so something like this