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Discussion Starter #1
Sooo, :frown2: . Where do I start? I wanted to tune my carb and fix my head gasket leak. Before disassembling the head, I decided to check my valve lash, my intakes were off by 0.001 Inches so I use the Valve Shim Calculator to get my next shim size. I had 2.75 in both of my intakes valves, the calculator said that I should put a 2.72 inside, but I don't have that size, so I decided to put a 2.70 inside instead ( Just a 0.02 mm difference right). I put the copper spray on the head gasket and let it dry in the sun for about 35 mins and then started to reassemble the head. I put my carb on and went from a 172 main jet to a 170 main jet and increase my pilot jet. I started the quad, let it get warm and tune the pilot jet, and finally, with 3 turns out, there was a smooth idle with no backfiring.
I even rev limit it and it came back down very smooth. Here's the part that doesn't make sense to me... I then decided to go for a spin, and as soon I take off the bike felt slow to me and I was hearing louder air pressure from the engine than usual. then I shift to the second gear n opened the throttle 2/5, and suddenly i hear a chain noise spinning and my quad suddenly cut off :frown2:.
Rolled it back home opened the head and this happened:


How can my piston pull my valves out in second gear 2/5 throttle, but not when i hit the rev limiter in neutral, it doesnt make sense to me..

did my cam chain somehow got stretched, was it because my main jet was leaner, was it the the shims? Really don't understand how and i don't wanna buy another bbk and head and the same thing happenes. And no i did not check my valve lash after i changed my intake shims, i trusted the calculator.
 

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Did the timing chain snap? Or the valve head just snapped off?
 

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Discussion Starter #3
Timing chain seems fine, I always torque the head to spec. I'm also having trouble taking off the cylinder. IDK if it seizes as well or something.
 

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With that kind of force, I imagine its jammed in the cylinder. Try turning the crank while tapping the piston with a mallet.
 

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Discussion Starter #5
I will try that thanks. But I Still don't understand how it pulled the pistons out of the valves. Any other thoughts?
 

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It wouldn’t pull it out. I’m assuming the the valve stem is still in the head. Either the valve head snapped off of it’s stem or the timing was way off and they hit each other. Hard to tell which one it was in the pic since the result looks the same. Once you take the head apart, see if that valve’s guide is messed up or the stem is bent. That should tell you which one it was. If the valve head snapped (not from piston contact) then the guide shouldn’t show much in the way of damage.
If the entire valve fell out, it would be the keeper that failed.
 

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Discussion Starter #7
If the timing was off, wouldn't this occur when i rev limit it in neutral? The keepers didn't fail. I will take out the valve later today to inspect the guide and the stem. Thanks, I Appreciate the help
 

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It would, but could have jumped timing if the tensioner failed or a gear spun on one of the cams. The lower timing gear could also be loose. Without investigating further, probably a failed valve.
 

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Valve stem snapped.
 

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Discussion Starter #10
Valve stem snapped.
I recently changed the valves a year and a half ago to Ferrea Valves. How can it snap just like that?

When I first tore down the head to fix the leak, I noticed a very small clamp that managed to get in the intake side of the head. I removed it and can see that I ran the engine with it being inside there before.

When I took off the head I did a light and water test to see if the valves were sealed and it was. Could the clamp have affected it? if it did why didn't this happen when the clamp was in there?

And i'm thinking of buying a new head with +1 valves and putting in a 470 kit with a new +5 crank
 

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When you swapped the valves, were the springs replaced with dual-coil springs?
 

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Shouldn’t have been an issue then unless one failed. Maybe your clamp falling in there cracked one and it finally failed. 🤷Wooter♂
 

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I changed the springs to Ferrea racing valve springs
Valves steel or TI?

Springs Dual or Single?

New or uses springs?
 
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