Burnt Valve or Bad Lifter??? - JeepForum.com
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Unread 09-09-2009, 07:28 AM   #1
Chadrick454
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1977 CJ5 
 
Join Date: Apr 2009
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Burnt Valve or Bad Lifter???

Thought I would ask the experts on the CJ forum. My 77 CJ has an AMC 360 in it. Ever since I got this project Jeep running there has been a ticking/clicking noise, almost like an exhaust leak, coming from the passenger side of the engine. Long story short I can pull the plug wire off the back passenger side cylinder and nothing happens. No change in sound, RPM, or anything. Tried adjusting timing and that made no difference. Talked to a friend who has rebuilt a couple motors and he said it sounds like either a burnt valve or a bad lifter.

Has anyone here had the same/similar problem?
Can anyone suggest something to check or test?

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Unread 09-09-2009, 01:01 PM   #2
CJhollic
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Check compression on that cylinder.
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Unread 09-09-2009, 01:06 PM   #3
mudking_ky87
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i had that happen, was a cracked head, probably a valve though
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Unread 09-09-2009, 01:14 PM   #4
Coiz
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If you have a burnt valve, that means that combustion pressures are able to escape around the valve and seat. Move that cylinder to TDC compression and use a compression tester adapter with the shrader valve removed. Inject 100 psi of air into the cylinder. A small amount of blow by into the crankcase is normal. You will hear a light hiss from the dipstick tube or oil fill cap so don't worry about that. If one of the valves is burnt you will hear a heavy hiss from either the intake/carb or the exhaust pipe depending on which one is leaking. It should be fairly obvious if that is the cause.

If neither the intake or exhaust are hissing, you likely have a weak lifter that is not opening a valve and causing that cylinder to have low/no power. At that point you will have to at least pull the valve cover and push on the rocker/pushrod to check the lifter resistance.

I just helped a friend with a freshly built 331 stroker in a road course racing Mustang do this exact same thing just last week. We found the lifter on the exhaust valve felt like a sponge while the intake side was stiff as expected.
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Unread 09-09-2009, 01:50 PM   #5
Chadrick454
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Thanks for all the great advice guys! I will check compression and cylinder leakage next weekend when I get back from vacation.
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Unread 09-09-2009, 01:58 PM   #6
swatson454
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Quote:
Originally Posted by Coiz View Post
If you have a burnt valve, that means that combustion pressures are able to escape around the valve and seat. Move that cylinder to TDC compression and use a compression tester adapter with the shrader valve removed. Inject 100 psi of air into the cylinder. A small amount of blow by into the crankcase is normal. You will hear a light hiss from the dipstick tube or oil fill cap so don't worry about that. If one of the valves is burnt you will hear a heavy hiss from either the intake/carb or the exhaust pipe depending on which one is leaking. It should be fairly obvious if that is the cause.

If neither the intake or exhaust are hissing, you likely have a weak lifter that is not opening a valve and causing that cylinder to have low/no power. At that point you will have to at least pull the valve cover and push on the rocker/pushrod to check the lifter resistance.

I just helped a friend with a freshly built 331 stroker in a road course racing Mustang do this exact same thing just last week. We found the lifter on the exhaust valve felt like a sponge while the intake side was stiff as expected.
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