350 valvetran

kress1500 · 11-16-2006, 06:29 PM

i have a 92 k1500 with the TBI 350, stock heads, and the intake valve on #8 is stuck open. i havent pulled th head off, so can anyone tell me before hand if the valve would hit the piston? its the stock cam so it shouldnt be open more than .385 or so. thanks

maxwedge · 11-16-2006, 07:11 PM

Sure if the valve is stuck all the way open ( why?) it could hit the piston, you will see witness marks when you pull the head, maybe the valve is now bent, but how did this happen.

kress1500 · 11-16-2006, 07:38 PM

im not sure. i was gettin onto the highway, about 75% throttle, and at 70 MPH i let off the gas and my truck kept accelerating. i killed it and put it in neutral to fiddle with the pedal, and i thought i felt the cable click shut, but when i started it up the tach shot up past redline, so i killled it and got of the road. after i fiddled with the pedal i felt the cable return and was 100 percent sure, so i started it and it was normal. 10 miles later i was sittin at a red light and it just died. no violent shudder or noises, it just puttered out. it started up but was idling VERY lopey.

maxwedge · 11-16-2006, 07:48 PM

Do a leak down or compression test to pinpoint the cylinder then, pull that valve cover off and see if when the valves are closed on that cylinder is one down lower the the other, usually an exhaust valve would be the problem., valve is bent.

silicon212 · 11-16-2006, 09:15 PM

In the NASCAR world, they call that "dropping a valve". You can pull the valve covers off to look for a broken spring - this is usually how this happens and will be readily evident.

I did something stupid with mine on Saturday - while driving through the apartment parking lot, there was a car just stopped and after a few taps on the horn, bozo wasn't moving so I shifted into neutral and punched the gas. I got heart palpitations for the split second that the engine tached to 6700 RPM! It was never designed for that. I've put almost 400 miles on it since and it's fine as it has ever been, so I'm not going to sweat it. Spinning it that hard though, especially with over a quarter million miles on the clock, is not in the interest of longevity.

I'm so glad now that I went with the Competition Cams' valvetrain when I built that thing. A stock spring would have likely broke and broke my engine, or floated a valve and broke my engine.

kress1500 · 11-17-2006, 09:53 AM

i got the valve covers of and found the valve. it is an intake valve, and the spring is not broken. i can push the valve open more, but when i release it only goes to about half closed. im going to pull the head off today.

silicon212 · 11-17-2006, 11:00 AM

Sounds like you floated a valve at the high RPM and it got bent. Good luck!

randy78 · 11-20-2006, 04:08 PM

definitely sound sliek it probably got bent

remove the head put another one in

and try to find out what caused it so it doesnt happen again, or get another cyl head or have new guide put in on that cylinder and new spring too

but it could also have been caused by the lifter jamming, etc

good luck

kress1500 · 11-20-2006, 05:19 PM

ok. found out something fell in my intake somehow an got lodged in the valve. god knows how. i got it out and the head and piston looked fine.. it looked like a little brass thumb screw?? put it all back together and drove it to work today... it ran well but it idles high and i managed to get the timing off...i think i put the dist. in one tooth off.

kress1500 · 11-20-2006, 05:19 PM

ok. found out something fell in my intake somehow an got lodged in the valve. god knows how. i got it out and the head and piston looked fine.. it looked like a little brass thumb screw?? put it all back together and drove it to work today... it ran well but it idles high and i managed to get the timing off...i think i put the dist. in one tooth off.

silicon212 · 11-20-2006, 06:08 PM

You are VERY LUCKY, you should go buy a lottery ticket immediately!

Quote:

Originally Posted by randy78

and try to find out what caused it so it doesnt happen again

It has been established that sudden high RPM that exceeds the redline can float the valves, and on a system with hydraulic lifters, the lifters will fill up and hold the valve open, then the piston hits the open valve and the valve gets bent. He's lucky that a) that didn't happen, and b) whatever found its way into the intake was stopped cold by the intake valve which got held open by said object and didn't cause a bent valve.

jveik · 11-21-2006, 10:17 AM

i know a guy who had a screw from a throttle plate in his carb fall into the engine and it just basically went through it and is probably lodged somewhere in the exhaust now

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