bent valve

[mygreen98]

any ideas on what you may think caused this? i had to replace #8 cylinder exhaust valve after noticing a horrible misfire. after hooking up scanner and finding out more than one cylinder misfiring. i replaced a bad cap and rotor and spark plugs. still bad misfire. checked with scanner after cap rotor plugs, just cyl. 8 misfire. thus took compression , 0 ! upon removing upper manifold for head removal, found fuel pressure regulator leaking, replaced that as well.
truck runs fine now, but stumped what could have bent the valve. any thoughts.

 

[treepete]

man.. i dunno, maybe did the part itself fail? how could someting get in there to jam it up otherwise? thats weird..

 

[Razincayne]

Many Many things could of gone wrong to have the problem you experienced. Bent valves are usually the result of a close encounter of the worst kind with the valve and piston giving each other a little kiss. Causes typically include a broken timing chain or belt, weak or broken valve springs, overrevving the engine, valve sticking, insufficient guide clearance or lubrication (gunk buildup inside of engine) overheating, etc. Could also be insufficient valve-to-piston clearance, excessive valve lift, valve relief's not cut deeply enough into pistons, wrong pistons, not enough deck height, heads milled too much.

I really hope you did not just replace the bad valve and call it good. The bottom line to valve failure analysis is this, replacing a bad valve with a new one won't fix anything if there is an underlying problem that has not been corrected.

Then again as stated above in the other post...It very well could have just been a faulty valve and you got lucky.

 

[96ProCompTahoe]

i would go with the valve sticking / weak springs if it only bent one valve and you didn't just rebuild it or strap on new aftermarket heads/pistons/etc.

Pitt

 

[95TwinTT]

My experience has been over revving. I adoptrf the original setting of the hydraulic lifters when new. I just give them 1/4 turn after zeo clearence. that say, they don't hafe that far to pump up. Less floating. I have never had any trouble with this procedure. I also hafe not had any bent valves. Well, I take that back. I did have one bent valve, that the machine shiop set the valves. I bbacked them off and it's fine now. My valves float somewhere around 7200 rpm's.

When those twins get huffing, it's hard to keep them from over revving when in the lower gears. The rpm's come up so fas its hard to keep them from shooting over the rev limiter. I will keep working on the cure.


give it a try. Loosen those lifters to just 1/4 turn after zero clearance You will like the relsults. i should eliminae the float. Good luke.

Itis a inexpensive thing to try. Good lulck

 

[mygreen98]

i changed the spring as well as the valve. what baffled me was where it touched the piston. i was in between the valve cutouts on top of piston. therefore, i believe it bent then hit piston. i know of all the possiblities, just stumpped as to how. wasnt due to overrevving, didnt jump time, maybe valve stuck due to excessive carbon buildup on valve?

 

[mygreen98]

truck still going fine, drove it local, highway trip etc. no issues what so ever. better gas miliage too. must have been leaking fuel for awhile.