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Broken exhaust valve

20K views 35 replies 19 participants last post by  Power Smoker 
#1 ·
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.
 
#2 ·
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.
 
#3 ·
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.
 
#8 ·
UPDATE

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.
 
#9 ·
Sounds like Luke's motor. Were the heads and deck surfaced when it was put together>
 
#19 ·
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.

Sounds more like a pre-existing condition.
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?
Weren't you trying out a new cam? Could a bad cam as well as tighter clearance due to the decking of the head cause this mess?
 
#13 ·
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?
 
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