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Burned Exhaust Valve?

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Truck has methodical ticking sound from driver side of the engine. I did the paper test where you place a piece of paper over the exhaust tips to see if it sucks back in. Sure enough, the paper would flow freely then would be violently sucked back in every few seconds. Truck does feel sluggish too when accelerating from a dead stop. My question is will the burned valve cause any more problems or will stay as is? On tuesday I'm going to call a mechanic i took my truck to for exhaust leaks that he fixed. He does all sorts of engine work on American cars, particularly muscle cars and muscle trucks. And what would I need to do to fix the problem? Sorry, I'm not a huge gear head. I know the basics.

Edited by ChinoHillian (see edit history)
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Burned exhaust valves do not make any sound that you can hear with the naked ear - they don't have a loud/audible tick. If an easily audible tick is present, it is VERY easy and QUICK to locate exactly which valve is the issue using a mechanic's stethescope - get one for $10-15 and with the motor running listen to each intake runner near where it is bolted to the engine head, you will hear the "singing" oscillation of the valvespring and each valvespring should sound exactly the same; do the same listening test with the exhaust by placing the probe on each of the 8 exhaust port primary tubes. If you are impatient or broke then make your own mechanic's stethescope using a 2-ft piece of wood dowell or super-long bar or screwdriver etc, placing your thumb over the end, and putting your knuckle into your ear (to transmit the ticking vibration into your eardrum - it works!). Since there is ticking I would bet that there is broken spring or a collapsed/failed lifter.


*IF* in-fact the exhaust valve is burned, yes it will cause MAJOR damage if you continue to run it for long - i.e. destroyed head gasket, warpage of cylinder wall, piston, etc because that cylinder is now running lean. Before you panic, some things you can look for to make sure the motor has in-fact a valve seat sealing issue:


* check engine vacuum using a vacuum gauge - on a normal engine with stock cam the vacuum reading should be dead steady at idle, if the needle 'bounces' more than 1-inch on the gauge then that is a sign of a valvetrain issue (the larger the 'bounce' the worse the problem); if you have access to a tuning tool and/or logging software, you can see the same exact thing in the MAP sensor reading

* cylinder kill test - if you have access to a diagnostic tool or tuning software, run a cylinder kill test to hunt-down the bad cylinder

* infrared gun - you can point it at each exhaust primary tube and get a reading at idle, if you find a tube colder than the rest then you have a missfire in that cylinder, else if it is hotter than the rest then that cylinder is combusting in the exhaust port (I got a little $8 infrared thermometer at Harbor Freight, nice ones are at Sears/Lowes/Home Depot for $90+)

* cylinder pressurization test - get a couple of adapter fittings so you can screw an air compressor hose into the spark plug hole, remove the oil fill cap, rotate the cylinder to TDC, and pressurize with air (don't use more than 50-psi or it will turn the motor over!) and if there is valve or ring leakage you will hear/feel the escaping air from either the throttle body, exhaust pipe, or oil fill cap, or any combination of each - turn the motor over by hand and repeat the test for each cylinder in the firing order

* cylinder leakdown test - BEST OPTION - same as cylinder pressurization test, but uses a purpose-built gauge that informs you to exactly how much air each cylinder is loosing.


My first car ('77 T/A) developed the same issue; I bought it modified and the original owner had overtightened an exhaust rocker arm (one valve was not completely closing) and within a few months things progressed to where I had to bore the motor 0.030-over, shave 8-thousandths off the block, and redo the heads. :( If you catch a failed exhaust valve early then you might be able to get away with just replacing the head, and it is very possible that you may find good 317-heads out there for cheap because guys upgrade to performance heads often, -or- you can choose to have yours rebuilt for a few hundred bucks. But if the lean cylinder condition is allowed to go for too long then when you put those fresh heads back on then the rings will go out after a couple months (because the piston crown & lands warped).


A cylinder leakdown test is ALWAYS a good idea to ascertain exactly what the physical condition of each cylinder is. If your mechanic does not have a cylinder leakdown tester I might let you borrow mine if you promise to return it promptly.


But do the listening test FIRST, get a mechanic's stethescope they are also invaluable for picking out bad accessory drive bearings too (idlers, pulleys, bearings etc).


Mr. P.


p.s. - the more I think about it, I would suspect a collapsed lifter - they happen all the time to the truck motors. :(

Edited by Mr. P. (see edit history)
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Thorough as always Steve :thumbs:


If you get a compression test kit at Sears or Harbor Freight, you can use it for the leak down if you remove the schrader valve. Sometimes 50 psi isn't enough to detect a leak. If you remove the rockers, slowly regulate the pressure to about 110 (the motor will turn to bdc on each cylinder you test) and listen for leaks. If it is a lifter, the heads still need to come off and you can also visually inspect the heads.

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Thanks for the responses guys! Mr. P, thanks for the very thorough response! I'm gonna pick up that gauge for the cylinder leak down test. Hopefully I catch it early.

Not discouraging you from purchasing a leakdown gauge, but get the mechanics stethescope first (cheaper, and more relevant in diagnosing this situation).


Mr. P.

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