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DS cam gear spun 90 what?

1321 Views 1 Reply 2 Participants Last post by  Freshmeat
hey folks -

we're working on a 94 P71 with around 100K.

the problem:
dad decelerated coming to a stop sign and the motor quit. no bang, no smoke, no sign of anything. just stalled out and wouldn't recrank. battery good, starter spinning, fuel good, spark, noid'd the injectors and they checked fine. checked crank sensor and camshaft sensor, both fine.

checked compression...PS pumped up fine, DS had nothing. not even a tick on the needle on the guage. double checked, thought maybe i changed something from one side to the other...same. no compression DS. hmmm...

pulled valve covers and that's when i found the bad news...DS camgear spun 80-90 degrees due to broken key in cam gear.

replaced the timing chain set and buttoned things back up. tried to crank...same symptoms. checked compression...again, nothing on DS, PS pumps up fine.

i pressurized the pistons, one at a time, with my air compressor (like i was going to change the valves) and spun the motor over with a breaker bar. on the PS, the air will quit and then begin again as the cam rotates...obviously the valves are closing properly. on the DS, air constantly leaks from somewhere. the tone will change, indicating the valves are moving, but the flow does not stop at all.

no bubbles in coolant when pressurizing any of the pistons and no coolant leaks anywhere on the outside of the motor that i can see.

what gives? did i munch the DS valves when the camgear spun? is the motor an "interference" motor, whatever that means?

thanks guys.

nate in NC
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When you did your timing, did you make sure you lined up the cam properly?
Pull it back off and verify the following motions:
Piston goes down / Intake valve opens
Intake valve closes
Piston comes up
Piston goes down
Piston comes up / Exhaust valve opens
Exhaust valve closes
Piston goes down / Intake valve opens
You get the point.

If any of the gears is not EXACTLY on the mark, it can be thrown off. It's possible you contacted some pistons with your valves, though. If nothing else, I'd say go ahead and tear it down to the shortblock and take a look.
I had almost the same problem with a 300ZX a while back. I put it back together and it didn't run, so I quit bothering- it was too expensive to fix, anyway. That's when I started getting serious about my wagon.

Good luck! Keep us posted...
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