engine will not run - after valve adjustment
05-30-2006, 12:39 AM
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engine will not run - after valve adjustment
After dropping the motor in my '83 911 SC Cab for what I consider routine maintenance, the motor will not start. Not even a "pop". I have verified that the cylinders are getting fuel and there is a strong spark. A compression check found 0 PSI compression in #1 and #2. At this point I did not do a compression check on the remaining cylinders. Next, with #1 at TDC, I pulled the headers and #1 intake runner. The valves appear to be seated. Next I backed off the adjusting screws on the intake and exhaust rockers (to insure the valves were seated) until there was obviously free play, pressurized the #1 cylinder and performed a leak down test. The leakdown showed 100%. I could not feel any leakage as I held my hand to the open ports. I dribbled some oil into the intake and observed a few bubbles at the valve seat. Not enough to warrant (my opinion) 100% leak down. Next I plugged the exhaust with a plumbing test plug (this sealed tight) and gerry-rigged a similar plug for the intake (not as good a seal due to the shape) and repeated the leakdown test. Leak down still showed 100%.
Obviously the air is going "somewhere". I had the distributor out of the motor. If I adjusted the valves with the distributor 180-deg out of synch could this have caused the valves to hit the pistons as I was turning the motor? Do 911s have an interference fit? I broke the cardinal rule of not turning the motor clockwise. At one point I over shot the mark and turned the motor CCW for only a few degrees. Could this have caused the timing chain to jump a sprocket resulting in a valve hitting a piston?
As far as I know the motor has not had any mods. It has ~120K miles. I have not dropped the motor again for further inspection. I was hoping I might have overlooked something obvious.
If I have to redo the heads (assuming the pistons are OK) does it make sense to simply redo the heads or purchase a redone long block? IF I redo the heads what other mods would make sense at the same time? I have some SSI headers and Bursch muffler I planned to install when everything goes back together.
Thanks in advance for any input or direction.
Obviously the air is going "somewhere". I had the distributor out of the motor. If I adjusted the valves with the distributor 180-deg out of synch could this have caused the valves to hit the pistons as I was turning the motor? Do 911s have an interference fit? I broke the cardinal rule of not turning the motor clockwise. At one point I over shot the mark and turned the motor CCW for only a few degrees. Could this have caused the timing chain to jump a sprocket resulting in a valve hitting a piston?
As far as I know the motor has not had any mods. It has ~120K miles. I have not dropped the motor again for further inspection. I was hoping I might have overlooked something obvious.
If I have to redo the heads (assuming the pistons are OK) does it make sense to simply redo the heads or purchase a redone long block? IF I redo the heads what other mods would make sense at the same time? I have some SSI headers and Bursch muffler I planned to install when everything goes back together.
Thanks in advance for any input or direction.
05-30-2006, 12:58 AM
#2
Rennlist Junkie Forever
The ignition will have zero to due with the leak down. Rule that out.
The obvious problem is that you may have your valves too tight. Why is a different issue...
You should do a leak down on all 6 cylinders. Then on the cylinders that are showing 100% leak down, back out the adjusters far out, so that there is too much lash.
Then do another leak down on those cylinders.
With the lash set "too loose", is there still 100% leak down?
What is the leak down on the "other" cylinders that don't have the problem?
Report back....
TonyG
The obvious problem is that you may have your valves too tight. Why is a different issue...
You should do a leak down on all 6 cylinders. Then on the cylinders that are showing 100% leak down, back out the adjusters far out, so that there is too much lash.
Then do another leak down on those cylinders.
With the lash set "too loose", is there still 100% leak down?
What is the leak down on the "other" cylinders that don't have the problem?
Report back....
TonyG
05-30-2006, 10:39 AM
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RE: After dropping the motor in my '83 911 SC Cab for what I consider routine maintenance, the motor will not start.
More info. needed please. Why would you drop the engine for a valve adjustment? Or did you have the engine completely apart for other repairs?? If, in turning the engine over by hand, the valves indeed hit the pistons, that should have been obvious. But let us know more about ALL that was done (IE: just how much was the engine disassembled?) so we can think this through.
More info. needed please. Why would you drop the engine for a valve adjustment? Or did you have the engine completely apart for other repairs?? If, in turning the engine over by hand, the valves indeed hit the pistons, that should have been obvious. But let us know more about ALL that was done (IE: just how much was the engine disassembled?) so we can think this through.
