Timing wanders/retards on acceleration
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Joined: Nov 2011
Posts: 53
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From: Lynnwood WA
Timing wanders/retards on acceleration
My '69 350/350 4-speed has a timing issue: Timing wanders and retards 4 degrees on acceleration. The car is stock except for a Pertronix Ignitor III ignition, which is new. Any ideas on the cause would be appreciated. I suspect a worn distributor but am no expert. The car has 110K miles and the documentation I have which is since 1992 doesn't show distributor rebuild or replacement.
I've noticed while driving that there appear to be 'flat spots' in the acceleration: Progressive pushing of the gas pedal doesn't result in progressive acceleration and I don't think I'm getting full use of the engine's power. When the secondaries engage it appears OK.
Ideas?
I've noticed while driving that there appear to be 'flat spots' in the acceleration: Progressive pushing of the gas pedal doesn't result in progressive acceleration and I don't think I'm getting full use of the engine's power. When the secondaries engage it appears OK.
Ideas?
Pro
Joined: Feb 2009
Posts: 651
Likes: 33
From: North Port Florida
If you disconnect the vacuum advance and rev the engine, does the timing retard? If it does, it could be the distributor is a conglomeration of parts and perhaps the shaft with the flyweights came out of another engine that had a reverse rotation distributor in it. Only ran into it once, but it makes the vehicle driveability horrible. Hope this helps? Good luck.
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
I would have the distributor checked out on a sun machine to make sure the curve is right and more importantly make sure it is not OVER advancing when at higher rpms... The bushings may be getting worn in the weights.. Also a good time to inspect the gear. I would also be suspect of the Pertronix ignition.
Last but not least could be slop in the timing chain.
Last but not least could be slop in the timing chain.
Heel & Toe
Joined: Aug 2010
Posts: 17
Likes: 0
From: Mountain View California
I did the Pertronix conversion on my '72 SB. I had issues with trying to avoid changing out the resistor wire (engine would quit at low RPM). Finally gave in and added a copper lead which resolved the stalling.
My understanding is that the advance is not affected at all by the Pertronix conversion. If you just did the conversion and your advance is gone it makes me wonder if the springs or weight are moving freely and installed properly.
My understanding is that the advance is not affected at all by the Pertronix conversion. If you just did the conversion and your advance is gone it makes me wonder if the springs or weight are moving freely and installed properly.
Thread Starter
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Joined: Nov 2011
Posts: 53
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From: Lynnwood WA
Thanks all! Answers seem to point to the distributor. I'll have it checked out. I have heard that they need rebuilds at about the mileage mine has. FYI, there is no stalling at low RPM, in fact it idles great. The problem occurs during application of power.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Make sure the bolt holding the dist. is secure. I have seen or should say have run into a problem where the bolt was not tight enough and the distributor would lift a little and retard the timing due to the fact it runs off a helical gear connected to the camshaft. If it was a straight cut gear it wouldn't matter unless it lifted so much as to not be able to turn the oil pump, which I have also seen.
And one more is the wrong distributor hold down clamp where you can crank the bolt tight but there is a space left and the distributor can lift up, that's a tough one to find but at least you know about it now.
I would make sure it is not lifting then I would pull the distributor and look at the gear. Then make sure the weights under the cap are moving and not stuck due to rust or debris.
And one more is the wrong distributor hold down clamp where you can crank the bolt tight but there is a space left and the distributor can lift up, that's a tough one to find but at least you know about it now.
I would make sure it is not lifting then I would pull the distributor and look at the gear. Then make sure the weights under the cap are moving and not stuck due to rust or debris.
Last edited by MotorHead; Jul 9, 2012 at 09:05 AM.
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Racer
Joined: Aug 2000
Posts: 434
Likes: 3
From: Cleveland Ohio
If the timing chain is original to the motor then this is my guess. I just replaced a timing gear set that I could almost pinch the chain together between the sprockets. Was really surprise that the chain was not jumping teeth. Had wondering timing just as described. A double roller timing chain solved the problem. 
Burning Brakes
Joined: Dec 2010
Posts: 945
Likes: 10
From: Winston Salem NC
I have had similar problems to those described by Limey. I checked the dist shaft endplay and it was about 0.075-0.080". Stock play is much less, I think 0.010 or less. I added some shim washers and that helped but the timing still jumps around a bit. I also suspect the timing chain.
My car has 118k miles.
My car has 118k miles.
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
I have had similar problems to those described by Limey. I checked the dist shaft endplay and it was about 0.075-0.080". Stock play is much less, I think 0.010 or less. I added some shim washers and that helped but the timing still jumps around a bit. I also suspect the timing chain.
My car has 118k miles.
My car has 118k miles.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
I had a similar issue at high RPM. Could not figure it out. Changed out 3 distributors. Timing wandered and I was dropping 4 degrees timing(sound familiar?) between 4800 and 5300 RPM and worse as it increased in RPM. Ended up being weak valve springs. I know it sounds weird but you might have weak or broken springs. Valvetrain instability was knocking timing out. To this day I still don't have a scientific explanation why. Read this thread page 6 through 8 or 9 to go though what we did and how we found out.
Safety Car
Joined: Jan 2009
Posts: 3,736
Likes: 56
From: anchorage ak
My timing was erratic, I changed from copper to silver springs on the mechanical, it cured the issue. The copper springs seem to get weakened quick. I don't know if that was the case with you.
Race Director
Joined: Apr 2003
Posts: 19,352
Likes: 654
From: Tampa, Florida
My car did that and it was all in the distributor. With to much end play the center shaft raises and lowers under accelleration/decelleration. Timing changes because the gear splines are cut at an angle, as the center shaft rises it also turns, as it lowers it turns as well.
It could be something else but that's what it was on my car.
It could be something else but that's what it was on my car.
Melting Slicks
Joined: Jan 2012
Posts: 3,039
Likes: 504
From: myrtle beach sc
Army
Jcloving, My original timing chain went at about 42,000 miles. You are living on borrowed time! You do know that the stock gear is aluminum with nylon teeth. The teeth came off my gear, plugged up the oil pump intake and turned all of the main bearings blue. Lou.