Compression at 0 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.

'83 911 SC Cab
'85 944 I Class Track only
'73 914 Semi Tube Frame (work in progress)
'01 330 XI
'96 Grand Cherokee Tow Vehicle

First rule, do not panic. second, do not jump to the worst case scenario. It is a lot harder to bend valves our damage the motor than you think, especially turning by hand by some one who sounds as consciences as your self. More than likely you adjusted the valves on the "ramps" and not the "heal" of the cam and if you just readjust you will be OK. This time look on the cylinder on the opposite side of the one you or adjusting the boxers opponent if you will since it is a boxer engine by name and make sure the valves opposite of the ones you adjust or on "overlap" and you will know you or on compression stroke top dead center, double check by looking for marks on the pulley to line up. If you over shoot no problem as long as you go past and then go right direction to take up any slack, good luck, have a little confidence in your self and do not jump to the worst conclusions, unless of course you want an excuse for that new engine:D Fritz

Thanks Frtiz, but wouldn't the fact I backed off on the adjusting screws so there was slack in the rockers result in the valves sealing?

TIA

Sorry to hear of your troubles. From the sound of things, I would really suspect the testing unit...the valves appear to be seated well enough to prevent 100% leakage, from what you describe. Do you hear (not feel) a lot of air whooshing inside the engine (either by the rings into the crankcase, or via valves, but it already sounds like that is ruled out.)? How is the seal on the compression tester (with the spark plug hole)? Are the spark plug hole threads in OK shape (do they turn in easily )?

Might be easier to do a compression test instead of another leakdown.

Like ficke said, I think you are probably alright. I think the test is at fault, not the motor.

I have know way of knowing if this is the first leakdown test you've ever done or your 100th so just in case, I'll cover the fundamentals.

A leakdown gives you a partial picture of what is going on in the motor and IMO not a very accurate one when used in isolation. Bad motors have good leakdown and sometimes visa versa.

First make sure you are really at TDC i.e. you have the right pulley mark and the distributor is pointing to the correct cylinder.

With the valves closed and the leakdown tester hooked up you should hear the "sound of the ocean" at the oil tank (rings), exhaust pipe (ex valves) or air cleaner with throttle plate open (intake valves).

-Chris