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burned exhaust valve...AGAIN!!; 4000 miles since last burned valve
Topic Started: Aug 21 2014, 10:59 PM (2,654 Views)
kevinalbers
New Member
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My 91 Geo convertible 3 cyl. 1.0 has a #3 burned exhaust valve again. I just had a shop do the entire head, all new valves, valve guides etc 4000 miles ago. What is going on here? Why do these motors eat valves. Any suggestions on how to prevent this would be appreciated. I can't seem to locate the EGR valve on my motor. The pictures on this site are different than what my motor has. :rocker :banghead
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Coche Blanco
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Troll Certified

You don't have that valve. Have you rebuilt the bottom end?
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kevinalbers
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No. The bottom end has never been touched. Should it? Can that cause burned valves?
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96Geoman


The rebuilt head won't last too long without the bottom end being rebuilt. The passage ways to the EGR valve need to be clean too. I installed a rebuilt head on a worn out bottom end and the valves were eaten in less than 6 months.

I believe 3 Tech sells stainless steel valves (they may last longer but I'm not sure)
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GeoStalker
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"Chicks dig me and guys think I'm cool."

YES!

Secondly, did the "shop" replace the valves with stainless steel?
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geogonfa
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Most 91 verts did not come with an EGR valve...and I have to agree with everyone else, stainless steel valves and new rings... :type
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90 LSI
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GeeOh
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While metros do see their share of burned valves there is nothing inherent to the engine that make it prone to this failure mode. There must be some root cause and the most likely are common to all engines; running too lean, poorly ground valve seating surfaces, valve sticking in the guide keeping the valve from closing tightly...
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Justahoby
Unqualified informant

I put stainless in mine, and it is good insurance, however they are not 100% non burnable. Although not likely they can burn if conditions are right..
I just like valves I know are aren't going to be 1/3 missing if I am too lazy to do a tune up in time. I put long hard miles on mine, and am dependent on this car, and SS valves are not that expensive.
If you suspect rings aren't sealing , pull the pan, pistons, light hone , make sure no crap get on crank , new rings . Sealing the head with new valves does nothing to tired out rings.

I skipped the rings on mine only because when I got it from the junkyard I realized it was a low mileage engine when I pulled the head, then I put my milled head with good guides new seals and stainless exhaust valves with a fel pro gasket and head bolts. The exhaust valves were listed as stainless, and were not even $ 10 a piece, maybe $8 .
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freegeo
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I was thinking that the original valves were stainless and aftermarket valves were also. Are some that is available not stainless?
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Coche Blanco
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That's been kind of a question here for a while. We were sold SS valves as upgrades, when some people thought the OEM valves are stainless. I'm not sure we ever got a definitive answer.

Titanium is another option.
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myredvert
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myredvert

Quote:
 
While metros do see their share of burned valves there is nothing inherent to the engine that make it prone to this failure mode. There must be some root cause...
Other then having the misfortune of being installed in a very inexpensive "non-collector item" car that 20+ years after the fact would be even more prone to being maintained as cheaply as possible than when it was new?

I'm no automotive engineer, but a 3 cylinder engine intended to do what it do at ~200 psi compression is not exactly the "norm" either.

Maybe when you take a little engine that had a top end designed to work with a bottom end intended to produce what seems to be relatively high combustion chamber pressures, then only replace/rebuild that head but leave the bottom end in the low end of the design compression range (or lower), or rebuilding the head and bottom end without measuring and verifying valve, cylinder, piston, ring, etc. tolerances and/or using low quality parts may be a factor. :dunno

If every Metro engine was rebuilt to spec, at or before it reached the minimum specs, I suspect there would be substantially less occurrences of burnt valves. Just my personal theory guess, and I don't have a lot to back it up with except the glaring lack of anecdotal evidence that begins with "My engine was rebuilt to spec several thousand miles ago, and now...." :whistle
Edited by myredvert, Aug 22 2014, 11:42 AM.
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snowfish
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Basic GearHead

Stainless or not, they shouldn't burn in 4000 miles. :shake Even with a semi weak lower end. My money is on "the shop" didn't bleed the lifters. :hmm
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freegeo
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myredvert
Aug 22 2014, 11:41 AM
Quote:
 
While metros do see their share of burned valves there is nothing inherent to the engine that make it prone to this failure mode. There must be some root cause...
Other then having the misfortune of being installed in a very inexpensive "non-collector item" car that 20+ years after the fact would be even more prone to being maintained as cheaply as possible than when it was new?

I'm no automotive engineer, but a 3 cylinder engine intended to do what it do at ~200 psi compression is not exactly the "norm" either.

Maybe when you take a little engine that had a top end designed to work with a bottom end intended to produce what seems to be relatively high combustion chamber pressures, then only replace/rebuild that head but leave the bottom end in the low end of the design compression range (or lower), or rebuilding the head and bottom end without measuring and verifying valve, cylinder, piston, ring, etc. tolerances and/or using low quality parts may be a factor. :dunno

If every Metro engine was rebuilt to spec, at or before it reached the minimum specs, I suspect there would be substantially less occurrences of burnt valves. Just my personal theory guess, and I don't have a lot to back it up with except the glaring lack of anecdotal evidence that begins with "My engine was rebuilt to spec several thousand miles ago, and now...." :whistle
:gp

The engine really needs checked out to make sure you are going to get the most for your money. Normally if the head needs re-done the bottom end will need some work also. Not always but there is a good chance of it.

Did you do a compression test on the engine after doing the head rebuild?
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clarkdw


OEM intakes are fully magnetic. OEM exhausts have a magnetic stem and non-magnetic head.
3Tech sells only one piece stainless steel exhaust valves. They will stand up better than OEM valves but no valve will stand up to a g10 engine that is burning oil. Anyone who thinks any valves will is mistaken.
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freegeo
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snowfish
Aug 22 2014, 11:46 AM
Stainless or not, they shouldn't burn in 4000 miles. :shake Even with a semi weak lower end. My money is on "the shop" didn't bleed the lifters. :hmm
Will the engine still run fine with lifters in that condition? Normally the engine has a no start condition if the lifters get pumped up don't they?
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