Burnt valve

CAT-TECH · 01-30-2008, 11:16 AM

When a valve "burns" it loses its sealing abilty. So why is it that on my 360 the valve only clacks when on start up? shouldnt it be at all rpms? you can tell there is a miss but it still runs very smooth.

440roadrunner · 01-30-2008, 06:25 PM

First, ( or have you checked?) the valve that is clacking on start may not be the same one that is burned.

Second, Valve lifters are flakey devices. You may have one a little sticky or gummed up, and if it IS the one that's burned, it just takes a little bit to pump up, take up the slack, and quiet down. The same thing can happen, whether the valve is burned, or not.

Also, if the engine has ever had a valve job, the valve stem height's may not have been properly dealt with by the head machinist, and one valve might be a little short, to start with.

Same thing is true of the cam, lifter, and pushrod. You might have one lobe that is starting to wear, samo for the pushrod and lifter(s)

If the noisy lifter is on the burned (or bent!!) valve, it may just be starting to 'burn'. Also, there are situations where valves get carbon or other "junk" caught in the valve. This could even be a piece of stuff that went down the intake!!

CAT-TECH · 01-30-2008, 08:46 PM

I know it is burnt cause of a compression check, bout 125 average with that one at 60. I new that late 70's and early 80's wore out cams fairly quick but i would be having other problems than just that. Also when the previous owner went for smog the hydrocarbons were through the ROOF! Ive seen some preaty weird stuff stuck between the valves and seats, anything from decent sized rocks to nozzle tips, just wondering why it only clacked at start up and not through the rpm range. Thanks

01-30-2008, 11:16 AM	#1 (permalink)
CAT-TECH Member Join Date: Jan 2008 Location: Cali Posts: 42	Burnt valve When a valve "burns" it loses its sealing abilty. So why is it that on my 360 the valve only clacks when on start up? shouldnt it be at all rpms? you can tell there is a miss but it still runs very smooth.

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01-30-2008, 06:25 PM	#2 (permalink)
440roadrunner Senior Member Join Date: Nov 2007 Posts: 272	First, ( or have you checked?) the valve that is clacking on start may not be the same one that is burned. Second, Valve lifters are flakey devices. You may have one a little sticky or gummed up, and if it IS the one that's burned, it just takes a little bit to pump up, take up the slack, and quiet down. The same thing can happen, whether the valve is burned, or not. Also, if the engine has ever had a valve job, the valve stem height's may not have been properly dealt with by the head machinist, and one valve might be a little short, to start with. Same thing is true of the cam, lifter, and pushrod. You might have one lobe that is starting to wear, samo for the pushrod and lifter(s) If the noisy lifter is on the burned (or bent!!) valve, it may just be starting to 'burn'. Also, there are situations where valves get carbon or other "junk" caught in the valve. This could even be a piece of stuff that went down the intake!!

01-30-2008, 08:46 PM	#3 (permalink)
CAT-TECH Member Join Date: Jan 2008 Location: Cali Posts: 42	I know it is burnt cause of a compression check, bout 125 average with that one at 60. I new that late 70's and early 80's wore out cams fairly quick but i would be having other problems than just that. Also when the previous owner went for smog the hydrocarbons were through the ROOF! Ive seen some preaty weird stuff stuck between the valves and seats, anything from decent sized rocks to nozzle tips, just wondering why it only clacked at start up and not through the rpm range. Thanks