Possibly a spring broke, hung a valve open and piston hit it repeatedly until it snapped, debris hung second valve open. Don't think your 3,000-mile break-in caused it.
Gonna tune him up! (Will it stay together)
- Thread starter Kevin frazier
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I wouldn't assume blame so easy, lasted 3,000 miles, and you know dyno 's are brutal, look for something mechanical. Sorry this happened to you, can't control everything, just what you can control. Assemble the best you can, with best parts you can afford, and twist your wrist.
Claviger
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Kevin, did you note the thickness of the shims in that hole? We're they both still in place atop the tappets?
Thing is, if it was doing 160/160 and made it 3k miles, it was running ok so everything had to have been close to correct at least. Since the other holes looked good, likely not knock/preignition.
One possibility:
If it spit a shim it would cause a violent beating to the valve and may have led to a snapped off valve head.
Thing is, if it was doing 160/160 and made it 3k miles, it was running ok so everything had to have been close to correct at least. Since the other holes looked good, likely not knock/preignition.
One possibility:
If it spit a shim it would cause a violent beating to the valve and may have led to a snapped off valve head.
Kevin frazier
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i dont know i just figured weakest link went first, me
Kevin frazier
Widowmaker!
yes i did note those shims as i had to buy some thinner, they were in place and springs and all on top was still locked down. Just the 2 snapped of exhaust valves, I will inspect that shim closer. Konrad felt engine was good after the beating he applied the day before.
Claviger
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Good to remove that as a point of failure.
Sucks when the sequence of events isn't obvious.
Sucks when the sequence of events isn't obvious.
Kevin frazier
Widowmaker!
Its not cracked but its the only one with an hour glass mark. Id say it even further points to a tight valve.
Claviger
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Tight or really loose, will get the same result in the end, but I suspect it was too loose.
Aluminum engines see clearances grow with heat, not shrink, the head expands faster than the valve. This would be consistent with a failure over time. As the clearance grows and the clearance ramp on the cam is never engaged because of too much clearance, the valve gets slammed against the seat instead of set down against the seat.
This would show as a good running engine right up until the head pops off the valve. It was, in fact, used as a trick for qualifying engines in NASCAR, but only in quals due to the abuse to the valves.
Too tight shouldn't cause any catastrophic issues unless it's zero clearance, at which point you should see weird AFR anomalies on the wideband, rough as hell idle, and poor power. Would've also been smokey out the tail pipe.
There's so much piston to valve clearance it's a null chance your adjustment was off enough to cause a collision with cam timing correct.
Aluminum engines see clearances grow with heat, not shrink, the head expands faster than the valve. This would be consistent with a failure over time. As the clearance grows and the clearance ramp on the cam is never engaged because of too much clearance, the valve gets slammed against the seat instead of set down against the seat.
This would show as a good running engine right up until the head pops off the valve. It was, in fact, used as a trick for qualifying engines in NASCAR, but only in quals due to the abuse to the valves.
Too tight shouldn't cause any catastrophic issues unless it's zero clearance, at which point you should see weird AFR anomalies on the wideband, rough as hell idle, and poor power. Would've also been smokey out the tail pipe.
There's so much piston to valve clearance it's a null chance your adjustment was off enough to cause a collision with cam timing correct.
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Kevin frazier
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, the afrs were good 11:7 at that point in tune, he started with cylinder 3 and he had set up on number 2 and had worked his way through tp to wot so probably an hour atleast before it happened
Claviger
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Here, a reference, from someone vastly more experienced than I about this whole thing ..
