From: Dave Darling [darling@simlab.arc.nasa.gov] Sent: Wednesday, May 19, 1999 9:51 AM To: Tim Lavery Cc: 914 Subject: Re: [914] burned valve symptoms At 8:46 AM -0700 5/19/99, Tim Lavery wrote: >... What are symptoms of burned valves and/or dropped valve seats? I haven't BTDT on the burned valves, but I suspect the symp- toms are similar to one of the below... Dropped seat #1: Great big THWACK from the motor as I started to pull out of the garage. Then another. Then lots more as I got moving down the driveway. Shut it down immediately, coasted to park on the street. (Too much hill on the driveway to push back up solo.) Did a valve adjust, found 1/4" clearance on I#4. Oops. Dropped seat #2: Found the motor was running on 3 cylinders. Idled very unevenly, lost power, simply was an unhappy little car. A week of troubleshooting the ignition and FI, and then I tried a com- pression test. Zero compression on #3 cylinder. (I had examined the valve tips, no obvious 1/4" clearance.) The seat had been popping out of the head and back in. The valve would no longer seal against it, so no compression. When cranking the starter motor, had a characteristic 1-2-3-x-1-2-3-x change in the sound/speed/pattern of cranking. In ret- rospect, it was obvious that one cylinder had no compression. I confirmed it was a dropped seat (I#3) when I pulled the head off--the area around the seat was all banged up. Dropped seat #3: Very rich mixture. Spent a week troubleshoot- ing the ignition and FI. Did a compression test, couldn't get the gauge threaded into #4 easily (but the spark plug went in fine). Got lazy, blew off that one cylinder's test. After a week, I tried adjusting the valves. 1/8" + clearance on I#4. Uhh, I think I know what *this* is... I had also felt some "pfft-pfft-pfft" up through the throttle body when I put my hand over it. Upon thinking back, I also heard the 1-2-3-x cranking pattern when using the starter motor. I guess I just didn't want to think about that possibility... I would speculate that a burned valve would show up as zero com- pression, or very very low. Intakes can result in a very rich mixture on a D-jet car, as the gases in the cylinder get blown back up into the manifold, increasing manifold pressure, which the D-jet thinks is a wider open throttle. Not sure what a carbed car would do. Zero compression would result in an uneven idle, loss of power, and an odd cranking pattern (of the sound) when trying to start. Good luck, and I hope your problem isn't as bad as mine!!! --DD Dave Darling 74 914 2.0 (decapitated) darling@simlab.arc.nasa.gov "OFF WITH ITS HEADS!"