Predator 212 Valve Failure

[traxxasislife]

A friend of mine was riding my Dirt Bug with a modded Predator, not pushing it too hard (4600 rpm) when the was a pop then it locked up and had no compression. After tearing it down, the culprit was the intake valve had failed. Beware of this issue, i was running stock valves with 18lb springs and 1.3:1 rocker arms on a stock cam. Here is the damage:

 

[Stangrcr1]

Looks like a trophy for the wall! :laugh:

 

[vwfan79]

I had the same thing happen last year but my rocker broke too.

 

[astrowrench]

Trax;Quick Question did it break at or near the retainer cutout? I ask because it looks like it happened @ or near BDC to drive the stem thru the head; I do failure analysis so we can hopefully end these problems.
Thank Dave

 

[youngengines]

This is a common problem if the springs are Honda 18#. You gotta check for coil bind closely with 1.3 rockers. I don't run them anymore, unless I have the white stripe (listed at 26#) springs.

 

[astrowrench]

My thoughts are Exactly the same as Barry's; I was wondering how long it ran after you changed the springs and /or the rockers, Because I also have seen people do this Twice with the same Result Watch out with 18 lb springs;I use the Dyno 22LB as it is a much better spring, has a better spring ratio than the 26 Lb. white stripe spring, and is easier on the valve train and will run right with the 26 Lb to 8000 rpm.............:hammer:

 

[SnakePliscan]

valve failure or spring to soft?

Ii don't see a valve failure in these pictures, the op didn't mention whether the stem end separated or not but from the picture that shows the stem and were in hit the underside of the guide plate as it came through the head i would say its bent and in one piece.

So the retainer had to be shifted off the valve stem, for that to happen the valve has to be pushed up in the retainer.

Are we talking valve float were the valves are bouncing on the seats and the retainer and valve are traveling in different directions in split second time?

A 1.3:1 rocker is going to snap the valve off the seat and close it faster, more distance has to be traveled in any given duration.

 

[Dragbikemini]

18lbs springs are gx140 stock spings. if you look at the spring landing on a 140 its lower than all other gx heads so there would be no bind on a 140 head.

 

[traxxasislife]

I was running Honda 18lb springs, the motor had 6 hours on it, and it broke at the retainer. It didn't appear to have any coil bind issues but apparently I was wrong�� the holes in the head make it seem that the valve actually went through the head, came back down into the cylinder, then went through the head a second time, and now it is permanently stuck there. Also the rider at the time said it occurred after a speed run of ~6000rpm, then slowing down, then the valve let go at about half throttle (~4000rpm). I believe the valve stem actually sheared off at the retainer, because the entire spring/cap/rocker assembly was intact, and there were a few suspicious bits of metal in the head