That's what destroyed my engine this go-round. I'm trying to see if the insurance will still cover it. We'll find out soon enough. It's bitter/sweet since I thought it was vandalism where I saw metal flakes in the oil. I was fairly sure just because the sequence of symptoms, but with the engine out, it's clear what the problem is. rear exhaust valve, #6 cylinder. I also found a small piece of piston in the oil pan. Fun stuff.
Question: has anyone experienced this before? If so, what causes it? Was it totally random crappy luck, or what? The sucker just snapped randomly right about in the middle of the guide. I'm afraid to take off the head & see if the block is bad. Crossing my fingers & hoping the insurance will cover it, but it's looking bleak at this point.
Did it drop the valve? Were the retainers and everything still intact? Reason I'm asking is my other truck did nearly the same thing. It turned out that the retainers let loose and the valve dropped. It sheared off clean when the piston hit it. That was the verdict we came up with anyway, I guess it is possible that the valve just sheared off during operation or maybe it stuck in the guide and the piston hit it.
Those things are constantly being heated and cooled, so I'm sure they lose tensile strength over time.
everything on top was in place, held together by the rocker arm bridge. I've got the top 4" or so of the valve, along with the spring, keepers, and spring retainer. the truck was actually running when I ripped it apart. It just had a bad knock and lots of blowby. The bottom section of the valve dropped into the cylinder though, and destroyed lots of stuff.
IF this engine gets rebuilt, and I don't just stick another one in, I'll find out what caused it. I'll also be replacing all the valves with new ones, not just grinding them like I did last time. Thanks for the info.
The insurance told me too bad considering the circumstances. Curiosity finally got the best of me despite the discouragement tonight though. I pulled the cyl head off the driver side, where the broken valve was.
GET THIS: all the exhaust valves, not the intake valves, on that side (I haven't checked the pass. side yet) left marks in the pistons. They're between 1/32"ish to 3/32"ish deep. I guess I know why the one exhaust valve snapped.
I'll send pictures of the damage, but there's actually a chunk of valve in the piston, lots of deep marks, and a hole. The head has large gouges as well from the valve, and the glow plug is mashed over.
Question: Where does the responsibility lie? considering I got several hundred miles on the engine, and in the beginning, it ran amazingly, or so it seemed. Lots of bearing material throughout the engine probably from rods or crank because of extra stress of valves slapping. I haven't checked yet, but considering the evidence, could I have the timing off, is this a defective camshaft, or what is going on? At least I know why the exhaust valve broke.
The heads were resurfaced and valves ground about a year and a half ago, but not the block. Valve train is stock. The heads were checked out fine, and transfered from my bad block to the new one a couple months ago when I assembled everything.
Who assembled the motor? Whenever you switch heads from one block to another the valve clearence should be checked. Im no expert but did you run the rpms real high and maybe float the valves?
I would think it takes 7000-9000 rpms to float valves. These engines have two springs per valve they are also lighter and smaller than the 7.3 which gives them less mass to float.
I would think it takes 7000-9000 rpms to float valves. These engines have two springs per valve they are also lighter and smaller than the 7.3 which gives them less mass to float.
i have seen similar symptoms on a 4020 john deere years ago. in that case it was the cam driven gear and its keyway. the key was half worn away as was the keyway in the gear itself, this put the cam timing off enough for piston to valve contact.it was rebuilt at least two possibly 3 times before i saw it. i insisted that the piston marking was not normal and indicated a problem. these engines do have very little clearance between piston and valve to begin with, so if the head or block is shaved the valves should be recessed further into the head, but you already know that, i think?
i have seen similar symptoms on a 4020 john deere years ago. in that case it was the cam driven gear and its keyway. the key was half worn away as was the keyway in the gear itself, this put the cam timing off enough for piston to valve contact.it was rebuilt at least two possibly 3 times before i saw it. i insisted that the piston marking was not normal and indicated a problem. these engines do have very little clearance between piston and valve to begin with, so if the head or block is shaved the valves should be recessed further into the head, but you already know that, i think?
Since it appears to only be one set of valves, I would suspect an issue with the cam grind. I've seen the marks from too much being cut off of a head before and they were all 4 valves.
Generally it's the exhaust valves that hit when the recession is off or if the cam is retarded. Then recession spec I posted in another thread here - minimum is neg(-) .013"
that would suck...not sure how that would happen exactly...with a hood latch and all...but it would suck, nonetheless.
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