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burned exhaust valve
Topic Started: May 1 2011, 06:26 PM (2,621 Views)
ok guy
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I bought my 90 3cyl 5sp. about 3 years ago and drove about 30,000 miles trouble free getting 42 to 49 mpg driving mainly new mexico highways 70 mph. then #3 exhaust valve burned.I took the head to my favorite machine shop he replaced the valve and I put the thing back together and it ran great for about 10,000 more miles and then same thing again. So I took it in and let a profesional do the job and 750 miles later #3 cyl lost compression again and I'm pretty sure its that exhaust valve again! any ideas?
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idmetro
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Have you cleaned out the EGR passages? I understand the buildup of carbon in the EGR passages reduces the gas flow and may result in increased cylinder temperature which when combined with an engine that is burning oil does not bode well for exhaust valves - #3 seems to be the most common casualty. I'd also suggest a compression tst to get a general picture of your engines health, it may be time for a complete rebuild. Good Luck!
Edited by idmetro, May 1 2011, 06:40 PM.
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mcmancuso
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EGR is not to blame, either you're burning some oil(likely cause) and/or timing is retarded too much and you're sending still burning combustion mix past the valve. Advancing the ignition timing to 8 degrees will help slow burning in the future. You should have had rings done when you had the valve replaced, this is the #1 reason for repeated valve burning. Not doing rings will almost always result in repeated and steadily shorter valve burn intervals.
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Johnny Mullet
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Fear the Mullet

If the bottom end is worn out, it will continue to burn valves. It needs a ring job.
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mwebb
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FOG

it is not possible for bad or worn piston rings to have any effect at all on the exhaust valves or the intake valves .
because loss of "compression pressure" due to leakage past the piston rings also lowers Combustion Pressure and COMBUSTION TEMPERATURE which reduces the load / stress on the exhaust and intake valve .

will the partially or unburned HC and 02 burn in the exhaust ? probably maybe it depends on conditions at the time , and will exhaust gas temperature and cat converter temperature rise .... yes .
sorry folks - that is the way it is .

it is very possible for clogged or restricted EGR passages to have a negative effect on the exhaust valves and on fuel economy
because EGR (when active) lowers combustion temperature.
so when EGR is not present , Combustion Pressure and therefore COMBUSTION TEMPERATURE are increased .
resulting in and INcrease in NOX formation and early failure of exhaust valves .

and
overly advanced base ignition timing will also have a negative effect on exhaust valve because overly advanced ignition timing cause peak combustion pressure to happen too soon (before about 14 to 15 degrees ATDC)
so COMBUSTION PRESSURE and COMBUSTION TEMPERATURE
are INcreased
which does burn exhaust valves and piston tops and it also reduces available power output and reduces fuel economy .

now
some may say that if the engine is burning oil due to worn OR frozen piston rings that EGR passages may tend to clog sooner with unburned oil deposits and this may in fact be a contributing factor BUT
the excessive ring wear and frozen due to crap oil additives depositing out in the piston ring lands and EGR passages was originally caused by
using dogshnit oils that are NOT synthetic and NOT rated at
ACEA A3 B3 - A3 B4 .

so
in the long run
crap oil is the root cause of the problem and the negative effects causing increased COMBUSTION TEMPERATURE are very often installed by the owner of the car , because
they increased base ignition timing beyond specification .

moral of the story
use ACEA A3 B3 - A3 B4 5w30 or 0w 30 0w 0w40 synthetic engine oil
AND
DO NOT Tamper with your base ignition timing .

this was the KISS version
====================================
i welcome debate on this very topic or set of topics
bring facts , not myths and fables .

Edited by mwebb, May 1 2011, 08:22 PM.
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Woodie
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Burning oil absolutely helps burn exhaust valves, proven time and time again right here by our members.

Using 40 weight oil also contributes to valve burning, the factory says that, but I guess you think your theories carry more wight than the engineering team who designed our engines.
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Johnny Mullet
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Fear the Mullet

Out of the many rebuilds I have done I had a couple end up burning oil and burning valves again due to a weak bottom end. I no longer do head swaps because of this.
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ok guy
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I apologize I neglected to leave out a possible clue a couple of days ago the check engine light came on so I just went out and checked the code #51: EGR system circuit. Don't know if this will help with your diagnosis or not. Also up to now I can go 3000 miles between oil changes without adding oil, so its not using a lot. THANK YOU FOR ALL YOUR COMMENTS AND IDEAS!!!
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Deleted User
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OK guys. Let's regroup here. A 1990 is not supposed to have an EGR valve, right?
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mcmancuso
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Some california emissions cars had weird setups for their year, but typically no, EGR was not present on hatchbacks until mid '92, though convertible models built as early as mid '91 had them too. Can you take a snapshot of your engine bay and post it?
Edited by mcmancuso, May 2 2011, 10:16 AM.
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ok guy
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just went out and took a compression test (in 5 min.- amazing!)
#1:125dry - 175 wet
#2:120 dry -135 wet
#3:0 dry -0 wet
try to get a picture on if I can work out the technology
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Coche Blanco
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Troll Certified

You need a full rebuild. Approximately 500 dollars.
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ok guy
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just went out and looked and your right "this vehicle conforms to California regulations applicable to 1990 model year"...
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bogs
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Duct tape heals all wounds

-> Posting images <-
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Deleted User
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OK. Now we’re getting somewhere.

Fricking California Emissions Metro! Who would have guessed?

Idmetro is right. Oil burns hotter than gasoline. McMancuso had it right with should have done the rings with the burned valve the first time. That’s exactly what I did the second time it happened, and should have done it the first time. Johnny Mullet concurred with McMancuso. I’m pretty sure that mwebb concurs, although sometimes he’s hard to follow. The best advice from mwebb is to use really good oil – 5W-30. See ACEA A3/B3, etc oil in one of my topics. Woodie agrees, and admonishes the use of heavier oil. Coche? Got to love Coche! Not necessarily a full $500 rebuild, although while you have the head off, a new set of rings and rod bearings will take you a long, long way down the road.

Lots of good inexensive parts for Geo Metros on eBay, RockAuto, etc. Do not use a gaket on the oil pan. Mwebb has advocated the use of something better than RTV for oil pans, which is on my next list of things to research. Suburu oil pan sealant, I think. I'll get some and post a product review. I hate oil pan leaks. Getting good at oil pan R/R, though!

Have fun in the New Mexico sun!

Someone will chime in on the specifics on how to post pictures. It involves uploading to a photo hosting site like photobucket. My guess is that bogs will reply . . .

EDIT: bogs already replied. See previous . . .
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