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Discussion Starter #1
Here is what I found!

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Both exhaust valves snapped off, but both intake valves only suffered damage from the exhaust valves snapping. One exhaust rocker snapped in half. Both valve retainers are loose, with one completely broken. There's a hole through the piston, and the rod shows collison damage. One valve head was found in the exhaust manifold. Any guesses what caused this?
 

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Pic 6 with the broken rocker on the left... Is that valve intact? Can see one keeper is missing and the other is out of place.

Horrific damage, man that's bad! There's probably chunks in the exhaust, goat belly, etc.
 

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Discussion Starter #4
The broken rocker was over one of the destroyed valves. Interestingly enough, the intake cam and rockers have no signs of damage. The exhaust cam shows some dings but only in the ridge that locates it horizontally. The cam lobes are fine, as is one of the exhaust rockers. From the top side, the intake valves look completely normal. They're obviously chewed up on the bottom, but they weren't the cause of the damage.

I was pulling away from a intersection when I lost power around 4k or 5k RPM. I pulled the clutch and released the throttle and the engine promptly died along with a metallic clattering. It didn't sound nearly as bad as it looks here. At the same time, I had traffic around me so I was more concerned with pulling over safely.
 

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It's possible a valve stuck open while running, or the valve stem just broke.
 

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Discussion Starter #7
My current theory is the exhaust cam was off a tooth and the valves were just kissing the piston. Over time, this fatigued the valve(s) and they broke off and did all sorts of damage! I can't think of another reason why BOTH exhaust valves broke along with an exhaust rocker, but neither of the intake valves or rockers broke.

Photos of the front timing during assembly:

Photos of the rear timing during assembly:

The front cams were timed properly relative to each other, as are the rear.
BUT, were the correctly timed to the crankshaft?

The intake valves opens when the piston is near the top, so an early opening might collide. A delayed intake open means it would open as the piston was further down. It closes when the piston is near the bottom, so any timing error wouldn't cause collision.
The exhaust valves opens when the piston is near the bottom, so timing issues wouldn't matter here.
They close when the piston is near the top, so a delay here could mean collision. An early close would give extra clearance, so no issues.
 

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You should have felt the kissing as soon as the engine fired up. ... If they were hitting from the first start.
Did you notice anything?

I've seen a few of these engines that have died the same way, but I'm not sure what the cause is. Sticky valves seem to be somewhat common, but two at a time seems like really bad luck. I suppose once pieces started getting mulched, that could've taken out the other valve.
 

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FREEBIRDS MC CENTRAL NY
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Holy piston, Batman

Sent from my A501DL using Tapatalk
 

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Discussion Starter #10
I just saw this older post. Same thing! Seems awfully coincidental...

 
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