Timing marks jumping around
03-28-2019, 12:40 AM
#46
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Thread Starter
timing belt and water pump have not been done - according to PO - 9 years old but only approx 3k miles.
I just bought a new gun hoping that was the problem. Reads exactly the same as my old gun
I just bought a new gun hoping that was the problem. Reads exactly the same as my old gun
03-28-2019, 05:01 PM
#47
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Dr. Bob - are you thinking maybe the TBelt is the issue ? I guess it kinda makes sense that if the belt is loose, it could cause this. Being almost 10 years old, I know it needs changing. I will remove the covers at the weekend and check on its condition. In the mean time Mark is sending me a used green wire and a coil so I can switch them out and see if there is any improvement.
03-28-2019, 10:56 PM
#48
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At this point we are kinda grasping at straws. It will be something that's loose and moving between the crankshaft dampener and the reluctor on the distributor.
There's nothing in a coil that will change timing more than a fraction of a degree but still be able to run the engine. That would be some internal arcing in the coil that changes the firing voltage slightly, but enough to affect the rotor to cap arc-over time. It's a real stretch.
Check for the belt tension. A stretched belt on a tensioner with no oil will move around some. Sticking bearings in the idlers or the water pump -may- affect this some, but again it's likely just fractions of a degree.
Look carefully at the harmonic balancer and the integrity of the rubber between the hub and the ring. If there are any cracks showing at all, the ring may be bouncing. The outer ring is loosely retained towards the engine by a lip that hides the rubber section. That lip will block any inspection from the front, so you may end up with an inspection camera with lights and a small mirror to see the rubber with the balancer in place. More than a few balancers have been pulled off with gear pullers with the fingers on the outer rim, often ruining an otherwise OK balancer. The rubber is the balancer is surely not stiff and dried out brittle after only forty years or more, to the point where almost any motion or abuse risks the rubber fracturing. For grins, grab the ring with your hands and try and move it.
There's nothing in a coil that will change timing more than a fraction of a degree but still be able to run the engine. That would be some internal arcing in the coil that changes the firing voltage slightly, but enough to affect the rotor to cap arc-over time. It's a real stretch.
Check for the belt tension. A stretched belt on a tensioner with no oil will move around some. Sticking bearings in the idlers or the water pump -may- affect this some, but again it's likely just fractions of a degree.
Look carefully at the harmonic balancer and the integrity of the rubber between the hub and the ring. If there are any cracks showing at all, the ring may be bouncing. The outer ring is loosely retained towards the engine by a lip that hides the rubber section. That lip will block any inspection from the front, so you may end up with an inspection camera with lights and a small mirror to see the rubber with the balancer in place. More than a few balancers have been pulled off with gear pullers with the fingers on the outer rim, often ruining an otherwise OK balancer. The rubber is the balancer is surely not stiff and dried out brittle after only forty years or more, to the point where almost any motion or abuse risks the rubber fracturing. For grins, grab the ring with your hands and try and move it.
03-28-2019, 11:04 PM
#49
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Put a new spark plug wire (without resistor ends) to #1 and recheck.
__________________
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Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
03-28-2019, 11:42 PM
#50
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Thread Starter
03-28-2019, 11:59 PM
#51
Team Owner
the resistor is in the plug that connects to the spark plug tip.
so you would get another wire with metal connectors on it and connect to the plug tip then to the distributor,
then test the wire signal
so you would get another wire with metal connectors on it and connect to the plug tip then to the distributor,
then test the wire signal
03-29-2019, 12:07 AM
#52
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Thread Starter
sounds good I will check. What is the thought process on this test ?
03-30-2019, 12:45 PM
#53
Chronic Tool Dropper
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There's a charge-discharge curve for the coil, with the point that the discharge (spark) starts determined by voltage available from the coil, vs. a combination of resistances in the system between the coil tower and the ground electrode on the plug. Stan's test takes the wire resistance out of the mix.
"Resistor" wires are used to reduce electrical noise and interference to the radio and other electronics in the car.
"Resistor" wires are used to reduce electrical noise and interference to the radio and other electronics in the car.
04-01-2019, 01:33 PM
#54
Rennlist Member
Thread Starter
At this point we are kinda grasping at straws. It will be something that's loose and moving between the crankshaft dampener and the reluctor on the distributor.
There's nothing in a coil that will change timing more than a fraction of a degree but still be able to run the engine. That would be some internal arcing in the coil that changes the firing voltage slightly, but enough to affect the rotor to cap arc-over time. It's a real stretch.
Check for the belt tension. A stretched belt on a tensioner with no oil will move around some. Sticking bearings in the idlers or the water pump -may- affect this some, but again it's likely just fractions of a degree.
Look carefully at the harmonic balancer and the integrity of the rubber between the hub and the ring. If there are any cracks showing at all, the ring may be bouncing. The outer ring is loosely retained towards the engine by a lip that hides the rubber section. That lip will block any inspection from the front, so you may end up with an inspection camera with lights and a small mirror to see the rubber with the balancer in place. More than a few balancers have been pulled off with gear pullers with the fingers on the outer rim, often ruining an otherwise OK balancer. The rubber is the balancer is surely not stiff and dried out brittle after only forty years or more, to the point where almost any motion or abuse risks the rubber fracturing. For grins, grab the ring with your hands and try and move it.
There's nothing in a coil that will change timing more than a fraction of a degree but still be able to run the engine. That would be some internal arcing in the coil that changes the firing voltage slightly, but enough to affect the rotor to cap arc-over time. It's a real stretch.
Check for the belt tension. A stretched belt on a tensioner with no oil will move around some. Sticking bearings in the idlers or the water pump -may- affect this some, but again it's likely just fractions of a degree.
Look carefully at the harmonic balancer and the integrity of the rubber between the hub and the ring. If there are any cracks showing at all, the ring may be bouncing. The outer ring is loosely retained towards the engine by a lip that hides the rubber section. That lip will block any inspection from the front, so you may end up with an inspection camera with lights and a small mirror to see the rubber with the balancer in place. More than a few balancers have been pulled off with gear pullers with the fingers on the outer rim, often ruining an otherwise OK balancer. The rubber is the balancer is surely not stiff and dried out brittle after only forty years or more, to the point where almost any motion or abuse risks the rubber fracturing. For grins, grab the ring with your hands and try and move it.
I didn't have much time this weekend but did have enough to pull the TBelt cover. The belt does seem to be pretty lose, it is 8 Years old but with only 6k miles. There is also some wobble when the engine is running. Here are a couple of short movies. One showing the Wobble and the other the timing mark movement. Could the lose belt be the cause of the moving timing mark ?
04-01-2019, 07:50 PM
#55
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Had to open the .mov files on my iPhone and view them on the very-small screen.
The belt is tracking OK, so maybe I'm just not seeing your wobble. And it doesn't make any difference -- you are looking for the belt advancing and retarding relative to the crank rotation. Better to shoot at the cam pulley with the timing light, after adding a paint mark at TDC #1 compression on the cam gears. For grins, make a match-mark on a pulley right in front of the balancer hub, lined up with the mark on the ring. Use your timing light to verify that the two lines stay together as shoot them with engine running. If they move relative to each other (hub/pulley vs ring) the balancer is toast.
Stooopid Stuff: The washer under the bolt in the crank nose has a stepped relief on the crankshaft (rear) face of the washer when installed. It fits slightly around the end of the crank to put a programmed clamping force on the balancer and the pulleys. If by chance the washer is backwards or the crank bolt is not tight enough (~235 lbs/ft IIRC), the balancer may be moving around on the crank snout. Remove the bolt after loosening the belts, so you can verify the washer installation. Correct if it's wrong now, then correctly tighten the bolt before restoring accessory belt tension.
The belt is tracking OK, so maybe I'm just not seeing your wobble. And it doesn't make any difference -- you are looking for the belt advancing and retarding relative to the crank rotation. Better to shoot at the cam pulley with the timing light, after adding a paint mark at TDC #1 compression on the cam gears. For grins, make a match-mark on a pulley right in front of the balancer hub, lined up with the mark on the ring. Use your timing light to verify that the two lines stay together as shoot them with engine running. If they move relative to each other (hub/pulley vs ring) the balancer is toast.
Stooopid Stuff: The washer under the bolt in the crank nose has a stepped relief on the crankshaft (rear) face of the washer when installed. It fits slightly around the end of the crank to put a programmed clamping force on the balancer and the pulleys. If by chance the washer is backwards or the crank bolt is not tight enough (~235 lbs/ft IIRC), the balancer may be moving around on the crank snout. Remove the bolt after loosening the belts, so you can verify the washer installation. Correct if it's wrong now, then correctly tighten the bolt before restoring accessory belt tension.
04-01-2019, 08:25 PM
#56
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Thread Starter
Had to open the .mov files on my iPhone and view them on the very-small screen.
The belt is tracking OK, so maybe I'm just not seeing your wobble. And it doesn't make any difference -- you are looking for the belt advancing and retarding relative to the crank rotation. Better to shoot at the cam pulley with the timing light, after adding a paint mark at TDC #1 compression on the cam gears. For grins, make a match-mark on a pulley right in front of the balancer hub, lined up with the mark on the ring. Use your timing light to verify that the two lines stay together as shoot them with engine running. If they move relative to each other (hub/pulley vs ring) the balancer is toast.
Stooopid Stuff: The washer under the bolt in the crank nose has a stepped relief on the crankshaft (rear) face of the washer when installed. It fits slightly around the end of the crank to put a programmed clamping force on the balancer and the pulleys. If by chance the washer is backwards or the crank bolt is not tight enough (~235 lbs/ft IIRC), the balancer may be moving around on the crank snout. Remove the bolt after loosening the belts, so you can verify the washer installation. Correct if it's wrong now, then correctly tighten the bolt before restoring accessory belt tension.
The belt is tracking OK, so maybe I'm just not seeing your wobble. And it doesn't make any difference -- you are looking for the belt advancing and retarding relative to the crank rotation. Better to shoot at the cam pulley with the timing light, after adding a paint mark at TDC #1 compression on the cam gears. For grins, make a match-mark on a pulley right in front of the balancer hub, lined up with the mark on the ring. Use your timing light to verify that the two lines stay together as shoot them with engine running. If they move relative to each other (hub/pulley vs ring) the balancer is toast.
Stooopid Stuff: The washer under the bolt in the crank nose has a stepped relief on the crankshaft (rear) face of the washer when installed. It fits slightly around the end of the crank to put a programmed clamping force on the balancer and the pulleys. If by chance the washer is backwards or the crank bolt is not tight enough (~235 lbs/ft IIRC), the balancer may be moving around on the crank snout. Remove the bolt after loosening the belts, so you can verify the washer installation. Correct if it's wrong now, then correctly tighten the bolt before restoring accessory belt tension.
The 2nd movie does show the timing light pointing at the crank and you can clearly see the timing mark jumping around at 3000rpm.
04-01-2019, 08:36 PM
#57
Chronic Tool Dropper
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Post the movies to yeautoob and embed the links in your post here.
I can see the timing marks jumping in the second video. Add a paint mark on the adjacent pulley rim them look again with the timing light. If the harmonic balancer ring is loose from the hub, the ring will continue to jump around but the mark on the pulley won't.
I can see the timing marks jumping in the second video. Add a paint mark on the adjacent pulley rim them look again with the timing light. If the harmonic balancer ring is loose from the hub, the ring will continue to jump around but the mark on the pulley won't.
04-03-2019, 05:15 PM
#58
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Thread Starter
Post the movies to yeautoob and embed the links in your post here.
I can see the timing marks jumping in the second video. Add a paint mark on the adjacent pulley rim them look again with the timing light. If the harmonic balancer ring is loose from the hub, the ring will continue to jump around but the mark on the pulley won't.
I can see the timing marks jumping in the second video. Add a paint mark on the adjacent pulley rim them look again with the timing light. If the harmonic balancer ring is loose from the hub, the ring will continue to jump around but the mark on the pulley won't.
Im still not sure on how to proceed with the spark plug wire idea. Is this something I need to go buy or can this be made ? After a brief search I could not find a wire without a resistor. Any chance you guys could elaborate a little more.
04-04-2019, 07:02 AM
#60
Rennlist Member
We've heard of the early 16v camshaft noses breaking off, maybe related to overtorquing. Really out there, but could such a failure occur such that the break allows the car to still run?