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#1 |
Registered User
Join Date: Jul 2017
Location: herminie, pa
Posts: 313
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Symptoms of a burnt exhuast valve?
Hello everyone,
What are the driving symptoms of a burnt exhuast valve? My truck idles and drives very well, and it still has good mid-range power. But recently it developed a high-load/ high rpm miss. I did a compression test, and cylinder 5 has 75 psi of cranking pressure, cylinder 2 has 95 psi of cranking pressure. The rest of the cylinders all have 120 psi while cranking. I then did a leak down test, and cylinder 5 is clearly leaking out of the exhuast valve. While cylinder 2 appears to be leaking past the rings, I also squirted some oil in number 2 and compression jumped from 95 pounds to 115. I guess my question is, what would these issues "feel like" while driving? Thank you!
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2009 GMC Sierra 1500 2006 Buick Lacrosse 1987 Chevrolet V10 1972 Chevrolet c20 350/350 1967 Chevrolet Biscayne ls3 swapped |
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#2 |
Registered User
Join Date: Jan 2011
Location: Chattanooga, TN
Posts: 1,108
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Re: Symptoms of a burnt exhuast valve?
The symptoms you’re likely to notice the most with a burnt exhaust valve is a loss of power from the engine and an increase of fuel consumption as the engine is run harder to do the work expected of it. Other symptoms will be dependent upon how badly burned the valve is.
When the edges of an exhaust valve burn, the combustion chamber no longer seals and not only do you lose compression in that cylinder, unburnt hydrocarbons will be exiting before they can be ignited. Running an engine low on oil will often burn one or more valves before the main bearings start to pound. Otherwise, a lean fuel mixture can cause this, too. On vehicles with a full exhaust system, the sound can be hard to detect. A cylinder leakage test will pinpoint it fairly well. Your pressure loss will be fairly high and you’ll hear the pressurized air escaping through the exhaust system, rather than through the intake or the crankcase. If you hook up a vacuum gauge, you may notice a steady loss of vacuum at idle if a valve is burnt or sticking. You’ll be looking at a valve job to correct it, or else swap out the cylinder head altogether. POP
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2016 RAM Laramie HEMI 1966 Fairlane GT/A, 390/335 HP If it costs you a dollar to make a friend, KEEP THE DOLLAR. If it costs you a friend to make a dollar, KEEP THE FRIEND. |
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#3 |
Registered User
Join Date: Oct 2005
Location: Overland Park, Ks.
Posts: 5,217
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Re: Symptoms of a burnt exhuast valve?
A burnt valve will be most notable at idle or low RPM. It will have a miss that seems to go away at higher rpm. If it is an auto trans, it will be very noticeable idling in drive. It will have a bad shake.
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#4 |
Registered User
Join Date: Jul 2017
Location: herminie, pa
Posts: 313
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Re: Symptoms of a burnt exhuast valve?
Huh, maybe my driveability issue is coming from somewhere else, becuase my truck sure does seem to idle and run good at low rpm. I don't have a problem until higher load/rpm
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2009 GMC Sierra 1500 2006 Buick Lacrosse 1987 Chevrolet V10 1972 Chevrolet c20 350/350 1967 Chevrolet Biscayne ls3 swapped |
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#5 |
Registered User
![]() Join Date: Nov 2006
Location: KINGSPORT,TN.
Posts: 3,035
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Re: Symptoms of a burnt exhuast valve?
More likely a sunken valve seat
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#6 |
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Location: Mt Airy, MD
Posts: 85,859
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Re: Symptoms of a burnt exhuast valve?
I think this could be unrelated. Your valve is probably not burned that bad yet, but you discovered it early by your test. Could be something like a lifter or rocker thing. Ignition, like plug wire?
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#7 | |
Registered User
Join Date: Jul 2017
Location: herminie, pa
Posts: 313
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Re: Symptoms of a burnt exhuast valve?
Quote:
I have a wideband o2 sensor, in going to put it in my exhuast just to be sure I'm not running out of fuel.
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2009 GMC Sierra 1500 2006 Buick Lacrosse 1987 Chevrolet V10 1972 Chevrolet c20 350/350 1967 Chevrolet Biscayne ls3 swapped |
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#8 |
Registered User
Join Date: Jul 2017
Location: herminie, pa
Posts: 313
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Re: Symptoms of a burnt exhuast valve?
Hello gents, I do believe I figured out why my truck has been running funny as described above. The other day, it started running really poorly, and it had fouled a set of plugs. From weak spark. I looked over my entire ignition system, and everything looked really good. But with my multimeter, I found that the yellow positive wire that powers my coil(resistance wire) has a short too ground. I haven't found the short yet, but with the wire removed from the coil, it has continuity to ground. So it looks like that circuit wasn't able to supply enough current to my coil on account of the short.
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2009 GMC Sierra 1500 2006 Buick Lacrosse 1987 Chevrolet V10 1972 Chevrolet c20 350/350 1967 Chevrolet Biscayne ls3 swapped |
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#9 |
Registered User
Join Date: Aug 2009
Location: Alden NY
Posts: 2,705
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Re: Symptoms of a burnt exhuast valve?
Compression is fairly low on all cylinders. Maybe time for a rebuild of both block and heads.
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1961 C1 Corvette 1959 El Camino 350 TPI, 9" 4 w disc 69 Blazer K5 - sold July '20 2021 Durango RT 5.7 |
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#10 |
Registered User
Join Date: Jul 2017
Location: herminie, pa
Posts: 313
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Re: Symptoms of a burnt exhuast valve?
That's actually my plan for this winter, I'm gonna pull the engine and give it a good going over. Rings, bearings, valve job, etc
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2009 GMC Sierra 1500 2006 Buick Lacrosse 1987 Chevrolet V10 1972 Chevrolet c20 350/350 1967 Chevrolet Biscayne ls3 swapped |
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#11 |
Registered User
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Location: KINGSPORT,TN.
Posts: 3,035
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Re: Symptoms of a burnt exhuast valve?
that points resistor wire is supposed to cut voltage
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I BELIEVE IN JOHN 3:16 |
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#12 |
Registered User
Join Date: Jul 2017
Location: herminie, pa
Posts: 313
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Re: Symptoms of a burnt exhuast valve?
I understand that part, the resistance wire is supposed to lower voltage to around 9 volts. But my resistance wire is shorted to ground, I don't think that's right
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#13 |
Registered User
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Location: KINGSPORT,TN.
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Re: Symptoms of a burnt exhuast valve?
does it drain the battery
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I BELIEVE IN JOHN 3:16 |
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#14 |
Registered User
Join Date: Jul 2017
Location: herminie, pa
Posts: 313
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Re: Symptoms of a burnt exhuast valve?
Nope, not yet. But I'm looking for a short or something stuck on
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2009 GMC Sierra 1500 2006 Buick Lacrosse 1987 Chevrolet V10 1972 Chevrolet c20 350/350 1967 Chevrolet Biscayne ls3 swapped |
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#15 |
Registered User
Join Date: Sep 2014
Location: Richfield, Oh
Posts: 112
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Re: Symptoms of a burnt exhuast valve?
yeah, a slight miss at idle is the first sign.
Disconnect the coil wire and crank it. You might hear a slight rise in cranking speed when it gets to that cylinder with the lower compression. That is another test. *edit* Ok never mind! ![]() |
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#16 |
Registered User
Join Date: Jul 2017
Location: herminie, pa
Posts: 313
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Re: Symptoms of a burnt exhuast valve?
I wanted to update my thread, as it turns out, the coil wire wasn't the problem. I did some checking and I have two cam lobes that are flat, one intake lobe on #4 and one exhuast lobe on #2 cylinder. So a new cam will be on the way shortly
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2009 GMC Sierra 1500 2006 Buick Lacrosse 1987 Chevrolet V10 1972 Chevrolet c20 350/350 1967 Chevrolet Biscayne ls3 swapped |
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#17 |
Registered User
Join Date: Jul 2009
Location: Space Coast, Fl.
Posts: 1,050
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Re: Symptoms of a burnt exhuast valve?
A new cam won't fix 75lb. cranking compression on #5 if the lobes on #'s 2 & 4 are wiped. Have you disassembled the engine & seen the cam or determine this from the rocker arm travel? If the cam is flat the metal went someplace.
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Dad always said, "Son, WISH IN ONE HAND, and ......." -------------------------------------- -------------------------------------- Current toy trucks: '71 GMC 1500 SUPER CUSTOM short/step, orig. dk. blue, 350/700r, ps,pb, A/C '72 Blazer 2wd, ochre & white, 454, tremecTKO 500 5spd. ps, pb, A/C, tilt Last 10yrs of hobby vehicles, had a FEW more in the 50yrs. before these: '66 Plymouth Belvedere City of Miami cop car clone. '70 Nova 406"sb, 13.5-1, solid roller, Brodix, p.glide/t.brake, back halved, 9" Ford, spool 4.88, cage,ladder bar/coilover, 10.5 tire....... SOLD!! '67 C10 short/step side mount spare -- SOLD!! '72 Jimmy 2wd, 350/350, ps, pb, fun driver, lots of bondo & a shiny red paint job..... SOLD!! '69 Nova 350, 4spd, A/C, ps, p.b, ...SOLD!! Last edited by RustyBucket; 08-24-2018 at 08:51 AM. |
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#18 | |
Registered User
Join Date: Jul 2017
Location: herminie, pa
Posts: 313
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Re: Symptoms of a burnt exhuast valve?
Quote:
I diagnosed the flat lobes on 2 and 4 by watching rocker arm travel, I actually used a dial indicator on them but it was really unnecessary. They only move about .050 of an inch at the pushrod. So I think after all, the miss I felt was from number #2 cylinders exhuast valve not opening and backfiring through the intake.
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2009 GMC Sierra 1500 2006 Buick Lacrosse 1987 Chevrolet V10 1972 Chevrolet c20 350/350 1967 Chevrolet Biscayne ls3 swapped |
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#19 |
Registered User
Join Date: Mar 2016
Location: Athens, AL
Posts: 80
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Re: Symptoms of a burnt exhuast valve?
It was stated earlier that a burned exhaust valve can be caused by an overly lean condition, and this is absolutely correct. Also, it can be caused by retarded timing; if there's not enough ignition lead, the mixture in the combustion chamber continues to burn as the exhaust valve is opening, and the valve overheats. If the lifter preload is set too tight, the same thing can happen...the exhaust valve hangs open, the valve edge overheats, and the valve fails. This is what it will eventually look like.
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#20 | |
Senior Member
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Location: Podunk, Texas
Posts: 748
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Re: Symptoms of a burnt exhuast valve?
Quote:
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#21 |
Registered User
Join Date: Aug 2009
Location: Alden NY
Posts: 2,705
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Re: Symptoms of a burnt exhuast valve?
If you wiped lobes, there was a lot of metal that went through the engine. Pull your oil filter and cut it in half so you can look at the element. If there are metal particles, there is a good chance that they have damaged your crank and bearing surfaces. Probably worth your while to pull the engine to at least look at the bottom end and the cylinder bores (you are going to have to remove a head to have it repaired and would normally do both heads at the same time). Sounds to me like this could be a more extensive than a cam and lifter replacement. Good luck with whatever you do.
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#22 | |
Registered User
Join Date: Jul 2017
Location: herminie, pa
Posts: 313
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Re: Symptoms of a burnt exhuast valve?
Quote:
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2009 GMC Sierra 1500 2006 Buick Lacrosse 1987 Chevrolet V10 1972 Chevrolet c20 350/350 1967 Chevrolet Biscayne ls3 swapped |
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#23 | |
Registered User
Join Date: Jul 2017
Location: herminie, pa
Posts: 313
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Re: Symptoms of a burnt exhuast valve?
Quote:
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2009 GMC Sierra 1500 2006 Buick Lacrosse 1987 Chevrolet V10 1972 Chevrolet c20 350/350 1967 Chevrolet Biscayne ls3 swapped |
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#24 |
Registered User
Join Date: Dec 2009
Location: bisbee, arizona
Posts: 1,529
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Re: Symptoms of a burnt exhuast valve?
two things;
learn how to use a vacuum guage. nobody knows how any more but it was an important tool back when our trucks were new...ish. Older chiltons manuals for 40's and 50's vehicles usually have a good instructional explaination on how they are used, read and understood. when you go shopping for a vacuum guage get the one with the biggest dial you can find. |
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#25 |
Registered User
Join Date: Jul 2017
Location: herminie, pa
Posts: 313
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Re: Symptoms of a burnt exhuast valve?
Just wanted to update my thread, after thinking it over, I just ordered a brand new 350/260 horsepower crate engine from radley chevrolet. They sell through ebay, It was 1839.99 shipped with a 50$ visa prepaid card. I thought that was a good deal for a brand new engine. I'll post some before and after pics of the engine swap. Thanks!
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