What causes a valve to “burn”?

What causes a valve to burn in a normally aspirated engine? And what causes it to break, I mean losing a smal piece at the valve rim?

 rspi » I found this thread while trolling the web about burnt valves. Some of you know that I’m the “OCTANE” monitor and we all want to prevent problems. Of late, over the past 2 years, I have heard several people saying that a motor was bad because of a burnt valve.

Most of us know that these motors, especially the I5, was built to last 500,000 miles. So why are some of them dieing at 130k and 180k for burnt valves. From what I have found, it has mainly been the NA cars. Over the past week or so I have read numerous thread, articles, ask.com, posting about burnt valves and what people think causes them. Bill really put most of what I read in a nut shell. The thing that stuck out most to me is his last paragraph about timing, pre-ignition and EGR info.

I would like for people that learn of BURNT VALVES to post their conditions here if possible. My bet is that 75% of them are occuring in cars that run low octane fuel. The Volvo I5’s and I6’s run compression at 10.5:1 and do require 91+ octane. Sure they are made, through the knock sensor technology. to run on 87, however, that messes with the timing and may even cause the car to run a little lean. Running a car lean causes burnt valves. Sure it may take a while but if a car has burnt valves at 170,000 when it was built to last 500,000, you have really cut it’s life short.

Yes I also read that overheating, exhaust leaks, and plain old engine wear causes burnt valves as well. However, I would like to know how many are running low octane fuel???

If you had a burn valve in your Volvo, please post your information here. What motor was in the car and what octane fuel did you use? How long did you have the car? If you got the car and 3 months later you learned that you had a burnt valve, you probably didn’t cause it. However, if you owned the car for 8 years and was the one fueling it and servicing it, you would have a better grip on the underlying cause.

erikv11 » +1 to leaky valve stem seals. This will nucleate the hotspots (speckles of burned oil) that lead to the snowball effect Bill describes so clearly.

Maybe Volvo designed the engines to run for 500k, but no rubber part (seal) is going to make that. It starts with the weak link … Anyway, a burned valve doesn’t equal a dead engine, it just equals one that needs a valve job 

For the record: bought the NA at 96k, always ran 89 octane, about 170k the valve stem seals started smoking in two of the cylinders (by 180k could see slight oil deposits on those plugs), at 195k had a burned exhaust valve in one of the leaky cylinders.

parkbro » 1996 850 (non-turbo) bought in 2006 with 120K one owner Volvo Maintained. I continued all maintenance and ran 87 octane, unless I was planning a vacation trip to the NC Mountains then I’d fillup and use High-Test through-out the trip. While on vacation last June I was ‘hammering up’ the ole Mountain at 65-70 mph, CEL appears, had a low idle miss. I dropped off at local Volvo Dealer for diagnosis. Verdict= no compression in cyl. 5, ruled Burned Valve. I had towed home and in the garage it sits. It has 172,000 miles on it. I was puzzled, why did my ‘built to last’ and ‘maintained to schedule’ volvo burn a valve? My mechanic said, like anything else, wear and tear, the valves would only hold up so long. Another mechanic questioned if the fuel became lean on that particular cylinder? Either way I have debated on whether to get a rebuilt head from Clearwater Heads and replace it myself.

Nice Car, drives excellent, newly reupholstered seat, new tires, trans maintained and shifts strong, everything works well. Before replacing the head I was going to take compression readings across the other (4) cyl., could someone tell me where the compression readings should be on an engine w/ 172K miles? If they are within range I will probably replace head. The other thing is the fuel injectors and whether they could stand to be cleaned as part of my overhaul. I believe they can be cleaned via a Sonic Cleaning System???? Not sure of the term used when they ‘bench clean’ fuel injectors. I would do this to rule out the fuel delivery possibly causing the burned valve. The other concern I have and would like your input. I have put about 150 to 200 miles on this car since this occured, could I have damaged the catalytic converter in that few of miles. Your input on these (3) questions and any suggestions would be appreciated. BTW I love this car, it handles like no other car I’ve owned.

What causes a valve to “burn”?Picture of my Burnt Valve