Worn distributor gear
Thread Starter
Racer
Joined: Aug 2021
Posts: 409
Likes: 82
From: NW Arkansas
Worn distributor gear
I pulled my distributor out today and discovered the gear at the bottom was badly worn, almost half the teeth were badly damaged.
This is following an event where the car suddenly stopped and won’t start again.
What might have caused this? Should I be worried about my engine?
it’s a 1991 base model.
This is following an event where the car suddenly stopped and won’t start again.
What might have caused this? Should I be worried about my engine?
it’s a 1991 base model.
Race Director
Joined: Jun 2020
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From: north of Chicago
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What color was the gear? Black or brass?
Thread Starter
Racer
Joined: Aug 2021
Posts: 409
Likes: 82
From: NW Arkansas
Sounds like the distributor has been changed, and a non "melonized" gear was on the replacement distributor. The gears are different heat treatments for use with hardened roller-lifter camshafts such as used in the 91 L98. The earlier non-melonized gear wears rapidly when placed on a roller lifter camshaft. The gears transmit a lot of torque to drive the oil pump. The oil pump load is what wears the gear.
Thread Starter
Racer
Joined: Aug 2021
Posts: 409
Likes: 82
From: NW Arkansas
The camshaft gear should be fine, it is harder than the distributor gear, as you've noticed.
Be advised that the two gear types generally have different shaft dimensions which are about .015 difference. The melonized gear has a smaller hole diameter. I am not familiar with availability of different shafts and gears dimensions in "large cap" HEI distributors, but the large cap distributor was used in both flat-tappet and roller-tappet camshaft applications, so it may be possible that there are two "different" distributors that appear identical, but the shaft diameter and the gear they use is different. Measure the shaft diameter. This is the kind of minutia that can drive you nuts if you don't know about it when sourcing parts.
Be advised that the two gear types generally have different shaft dimensions which are about .015 difference. The melonized gear has a smaller hole diameter. I am not familiar with availability of different shafts and gears dimensions in "large cap" HEI distributors, but the large cap distributor was used in both flat-tappet and roller-tappet camshaft applications, so it may be possible that there are two "different" distributors that appear identical, but the shaft diameter and the gear they use is different. Measure the shaft diameter. This is the kind of minutia that can drive you nuts if you don't know about it when sourcing parts.
Anyways I'll look into the shaft diameter, thanks again for telling me about that that'll save me a headache.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Since distributor is out make oil pump shaft spins. With key on gauge should register oil pressure.
if something happens were oil pump stop abruptly, distributor gear will lose teeth. It was more common when cam gears used nylon teeth. Teeth would break off and depending on pick up would wedge between the gears.
if something happens were oil pump stop abruptly, distributor gear will lose teeth. It was more common when cam gears used nylon teeth. Teeth would break off and depending on pick up would wedge between the gears.
Thread Starter
Racer
Joined: Aug 2021
Posts: 409
Likes: 82
From: NW Arkansas
I replaced the distributor. There is oil pressure on startup. It won’t fire still?? It just cranks, and our spark tester indicates it is getting spark. We tried rotating the rotor 180 degrees, that did nothing either. The brown wire (labeled tach) broke when removing it from the old distributor. Is this important? Would it cause this issue? Any help is appreciated,
thanks
thanks
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Thread Starter
Racer
Joined: Aug 2021
Posts: 409
Likes: 82
From: NW Arkansas
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Have you checked fuel pressure 42 psi and holding? Check plugs to besure they aren't fouled. Spray flammable aerosol in throttle body will engine run? Test light can be used to check for pulse. Connect alligator clip to battery positive. Test light will illuminate when probe is grounded. Ecm supplies ground. There are 2 fuses for injectors. You should Google for "no start trouble chart" for your car.
Thread Starter
Racer
Joined: Aug 2021
Posts: 409
Likes: 82
From: NW Arkansas
It's easy to check for Reference Pulses, which are required to fire the injectors:
Turn key to RUN, but do not crank. Fuel pump should run for 2 seconds and stop. If = YES:
Crank briefly. Just enough to turn the distributor a turn or so, and stop, but leave key in RUN. Listen for fuel pump, does it run 2 seconds and stop? If = YES, reference pulses were received.
Turn key to RUN, but do not crank. Fuel pump should run for 2 seconds and stop. If = YES:
Crank briefly. Just enough to turn the distributor a turn or so, and stop, but leave key in RUN. Listen for fuel pump, does it run 2 seconds and stop? If = YES, reference pulses were received.