Timing slip?
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Mountain Pass
Joined: May 2021
Posts: 183
Likes: 21
Timing slip?
I drive my F350 (351W) CC every day. Yesterday it started hard like the battery was dying. Today it did the same thing and ran rough. Power was down too. I limped home and checked the alternator output—12V off, 14V running. Alternator is okay. Adjusted carb. Then I checked the timing. It was off. The 10 degree mark on the crank was well below the tang. I rotated the distributor counterclockwise and got the 10 degree mark back just above the metal tang. Ran great and started with ease again. My question is why or how? The distributor did not rotate. Can timing do this? Is there a potential problem with the timing chain or other component? Any sage advice would be appreciated.
Lead Driver
Joined: Nov 2013
Posts: 7,178
Likes: 1,174
My first thought was the outer sleeve on the crankshaft pulley had slipped. This would throw off the timing marks relative to the crankshaft. But this would not affect how the engine runs, only the indication for setting the timing.
I'd suggest checking for a loose timing chain. It may slipped a tooth. Set the parking brake and put the transmission in neutral or park. Remove the distributor cap. Use a socket and breaker bar to turn the crankshaft slightly in the normal direction of rotation. This takes up any slack in the timing chain. Make note where the rotor is pointing. Now turn the crankshaft in the opposite direction while watching the rotor. If the chain is good, the rotor will turn immediately. If the chain is loose, there will be a lag.
I'd suggest checking for a loose timing chain. It may slipped a tooth. Set the parking brake and put the transmission in neutral or park. Remove the distributor cap. Use a socket and breaker bar to turn the crankshaft slightly in the normal direction of rotation. This takes up any slack in the timing chain. Make note where the rotor is pointing. Now turn the crankshaft in the opposite direction while watching the rotor. If the chain is good, the rotor will turn immediately. If the chain is loose, there will be a lag.
Thread Starter
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Mountain Pass
Joined: May 2021
Posts: 183
Likes: 21
My first thought was the outer sleeve on the crankshaft pulley had slipped. This would throw off the timing marks relative to the crankshaft. But this would not affect how the engine runs, only the indication for setting the timing.
I'd suggest checking for a loose timing chain. It may slipped a tooth. Set the parking brake and put the transmission in neutral or park. Remove the distributor cap. Use a socket and breaker bar to turn the crankshaft slightly in the normal direction of rotation. This takes up any slack in the timing chain. Make note where the rotor is pointing. Now turn the crankshaft in the opposite direction while watching the rotor. If the chain is good, the rotor will turn immediately. If the chain is loose, there will be a lag.
I'd suggest checking for a loose timing chain. It may slipped a tooth. Set the parking brake and put the transmission in neutral or park. Remove the distributor cap. Use a socket and breaker bar to turn the crankshaft slightly in the normal direction of rotation. This takes up any slack in the timing chain. Make note where the rotor is pointing. Now turn the crankshaft in the opposite direction while watching the rotor. If the chain is good, the rotor will turn immediately. If the chain is loose, there will be a lag.
Logistics Pro
Joined: Dec 2003
Posts: 3,779
Likes: 873
From: Foothills of NC
I agree with above. I wouldn't drive the truck until you know if the chain jumped a tooth. I did this with a 302. Bumped the timing ahead until I could get to the chain replacement.
Big mistake. The chain jumped again several days later, and by then, had eaten the fiber cam gear up. This had filled up the oil pickup screen with timing gear grindings, ruined all the rod and main bearings, and left the crank in bad shape.
A hard lesson learned many years ago.
Big mistake. The chain jumped again several days later, and by then, had eaten the fiber cam gear up. This had filled up the oil pickup screen with timing gear grindings, ruined all the rod and main bearings, and left the crank in bad shape.
A hard lesson learned many years ago.
Moderator
Joined: Jan 2001
Posts: 56,997
Likes: 2,742
From: Virginia
I just had this happen to my 2.8. It got so bad it would not hardly run. When I did get it to run, I noticed too the timing marks were off, but when I tried to put my timing marks in the right place it would not run very well. I too thought my timing gear had stripped, they used plastic teeth on some of the 2.8"s. But no, it has been changed to an all aluminum one. So I put that all back together, the only thing left was the distributor. Pulled it out, it had a huge amount of end play in the shaft, and back and forth play at the top. I think the back and forth play is what made it quit, the little star wheel got too far away from the pickup. The timing was way off because of the end play. The gear teeth on the distributor are spiral shaped. If the gear has play up and down, the spiral makes the distributor rotor turn in relation to the cam gear, and that can throw the timing off.
Thread Starter
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Mountain Pass
Joined: May 2021
Posts: 183
Likes: 21
I agree with above. I wouldn't drive the truck until you know if the chain jumped a tooth. I did this with a 302. Bumped the timing ahead until I could get to the chain replacement.
Big mistake. The chain jumped again several days later, and by then, had eaten the fiber cam gear up. This had filled up the oil pickup screen with timing gear grindings, ruined all the rod and main bearings, and left the crank in bad shape.
A hard lesson learned many years ago.
Big mistake. The chain jumped again several days later, and by then, had eaten the fiber cam gear up. This had filled up the oil pickup screen with timing gear grindings, ruined all the rod and main bearings, and left the crank in bad shape.
A hard lesson learned many years ago.
Thread Starter
|
Mountain Pass
Joined: May 2021
Posts: 183
Likes: 21
I just had this happen to my 2.8. It got so bad it would not hardly run. When I did get it to run, I noticed too the timing marks were off, but when I tried to put my timing marks in the right place it would not run very well. I too thought my timing gear had stripped, they used plastic teeth on some of the 2.8"s. But no, it has been changed to an all aluminum one. So I put that all back together, the only thing left was the distributor. Pulled it out, it had a huge amount of end play in the shaft, and back and forth play at the top. I think the back and forth play is what made it quit, the little star wheel got too far away from the pickup. The timing was way off because of the end play. The gear teeth on the distributor are spiral shaped. If the gear has play up and down, the spiral makes the distributor rotor turn in relation to the cam gear, and that can throw the timing off.
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Logistics Pro
Joined: Dec 2003
Posts: 3,779
Likes: 873
From: Foothills of NC
When it jumped again, I was able to advance the timing enough again to drive it to my shop where I tore it down and replaced the chain and gears.
After getting it back together and test driving is when I noticed the very low/almost zero oil pressure on the factory gauge I didn't trust, for I had no lifter or bearing noise.
But, after removing the pan, plus one rod bearing and one main, I saw the damage done.
This was on a '79 F100, 302.
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Cargo Master
Joined: Aug 2007
Posts: 2,561
Likes: 69
From: New Zealand
You could rotate the distributor to correct the ignition timing......but the camshaft/valves would still be late
Thread Starter
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Mountain Pass
Joined: May 2021
Posts: 183
Likes: 21
Timing chain is tight in both directions. Never found a smoking gun, which bothers me. The distributor was tight, so I’m certain it didn’t rotate from being loose. After re-timing, adjusting the carb, and installing a new ignition box it runs better than before. I guess time will tell. Thanks for the suggestions.
4wd Low
Joined: Sep 2020
Posts: 14
Likes: 5
How is the helical gear on the dizzy attached to the shaft? Pretty sure the HEI unit I have on my 300 the gear is pressed on and then pinned in place. If the pin sheared but the bits of pin stayed stuck in the gear it could appear that this part of the system is fine when in fact the gear slipped a few degrees around the dizzy shaft? Does that make sense? If the problem reoccurs this would be my first suspect. Maybe even worth checking today if it is easy to pull the dizzy on your motor.
Thread Starter
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Mountain Pass
Joined: May 2021
Posts: 183
Likes: 21
How is the helical gear on the dizzy attached to the shaft? Pretty sure the HEI unit I have on my 300 the gear is pressed on and then pinned in place. If the pin sheared but the bits of pin stayed stuck in the gear it could appear that this part of the system is fine when in fact the gear slipped a few degrees around the dizzy shaft? Does that make sense? If the problem reoccurs this would be my first suspect. Maybe even worth checking today if it is easy to pull the dizzy on your motor.
Lead Driver
Joined: Nov 2013
Posts: 7,178
Likes: 1,174
Check the distributor’s centrifugal advance, too. If the springs broke or the mechanism jammed, that might explain the timing change.
Two easy methods to test:
1) Remove the distributor cap and twist the rotor by hand. It should turn about 30 degrees in the direction of normal rotation. When released, it should snap back consistently to the starting point.
2) Disconnect and plug the vacuum advance line. This makes sure you’re testing only the centrifugal advance. Connect your timing light and start the engine. Increase the RPM and watch the timing marks. Timing should increase smoothly and consistently return to the same point when at idle.
Two easy methods to test:
1) Remove the distributor cap and twist the rotor by hand. It should turn about 30 degrees in the direction of normal rotation. When released, it should snap back consistently to the starting point.
2) Disconnect and plug the vacuum advance line. This makes sure you’re testing only the centrifugal advance. Connect your timing light and start the engine. Increase the RPM and watch the timing marks. Timing should increase smoothly and consistently return to the same point when at idle.
Thread Starter
|
Mountain Pass
Joined: May 2021
Posts: 183
Likes: 21
Check the distributor’s centrifugal advance, too. If the springs broke or the mechanism jammed, that might explain the timing change.
Two easy methods to test:
1) Remove the distributor cap and twist the rotor by hand. It should turn about 30 degrees in the direction of normal rotation. When released, it should snap back consistently to the starting point.
2) Disconnect and plug the vacuum advance line. This makes sure you’re testing only the centrifugal advance. Connect your timing light and start the engine. Increase the RPM and watch the timing marks. Timing should increase smoothly and consistently return to the same point when at idle.
Two easy methods to test:
1) Remove the distributor cap and twist the rotor by hand. It should turn about 30 degrees in the direction of normal rotation. When released, it should snap back consistently to the starting point.
2) Disconnect and plug the vacuum advance line. This makes sure you’re testing only the centrifugal advance. Connect your timing light and start the engine. Increase the RPM and watch the timing marks. Timing should increase smoothly and consistently return to the same point when at idle.
Moderator
Joined: Jan 2001
Posts: 56,997
Likes: 2,742
From: Virginia
It should go up at a higher BTDC number. If you set the initial at 10BTDC, when you rev it it should go up 15 BTDC, 20BTDC, 30 BTDC. It's advancing the timing more and more. So it's firing Before Top Dead Center of the piston more and more.