OK, I have a lot of interesting stuff going on lately. Here's my latest. It's a '67 Coupe 427 435 HP I've owned 6 yrs. I have never had a problem with the engine tuning, until today. The most I've ever had to do was very minor adjustments to anything on my periodical tune ups. Never, that is, until a dramatic shift today.Today the car was rolled out for driving and had a very serious preignition/backfire problem under load.Upon checking the engine over I found the idle ignition timing advance to be @32 deg.BTDC! Now honestly, all of the obvious checks good and I can see no reason for this occurance. I am scared to death that something has started to come loose inside the powerplant. Has anyone heard of this before? If the timing adjustment seems to take care of it, should I drive and see what happens? My Corvette manual says 5 degs. BTDC and my reliable Chiltons says 4 degs. BTDC. The car is @8,000 feet and tuning to @11 degs. BTDC helped quite a lot. Then the weather was done for the day and I await to see what further tuning will do. I'm not as knowledgeable as I would like to be about this powerplant. For all I know this is a sign of something to come that other enthusiests are aware of. So how about it? What do you know or what would you do? As usual, I very much appreciate your reading this, as well as any info you can offer. Please let us take a moment to think about and thank all of those over the years who have offered themselves up in the name of freedom so that you and I could sit here and do this today. Thank you and god bless to all of the veterans! You are not forgotten. Happy Memorial Day
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Re: Serious Timing Problems
Steve----
There are only 2 possibilities that I can think of. First, the distributor clamp may have been loose and the distributor rotated and resulted in faulty initial timing setting. If, after timing the engine, the distributor was in its "normal" alignment, I suspect that is what happened.
The other possibility is that the timing chain has "slipped" or stretched excessively. However, if this occurs, you should not be able to get the engine to run satisfactorily by adjusting the distributor/initial timing setting.
Timing chains are the "Achille's Heel" of Chevrolet V-8 engines, large and small. If yours is old or high mileage, I always recommend replacement. A failed timing chain can not only leave you stranded, but it can result in serious engine damage if it fails catastrophically.In Appreciation of John Hinckley -
Re: Serious Timing Problems
Steve----
There are only 2 possibilities that I can think of. First, the distributor clamp may have been loose and the distributor rotated and resulted in faulty initial timing setting. If, after timing the engine, the distributor was in its "normal" alignment, I suspect that is what happened.
The other possibility is that the timing chain has "slipped" or stretched excessively. However, if this occurs, you should not be able to get the engine to run satisfactorily by adjusting the distributor/initial timing setting.
Timing chains are the "Achille's Heel" of Chevrolet V-8 engines, large and small. If yours is old or high mileage, I always recommend replacement. A failed timing chain can not only leave you stranded, but it can result in serious engine damage if it fails catastrophically.In Appreciation of John HinckleyComment
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Re: Serious Timing Problems
Another, related, possibility is one/both of the timing gears 'shrank' allowing the chain to jump. Happened to me once -- looked like gear 'escaped' heat treat hardening. Gaps between teeth wore fast (shrinking toward of gear) and allowing enough slack in timing chain for it to 'jump' registration.
If either condition (chain stretches, gear(s) shrink) happens, owner should hear BRIEF warning -- 'tinkling' sound, like detonation, of the timing chain rattling agains the timing cover. Either is REAL serious and could grenade the engine (valves kiss pistons).
If it's a simple matter of distributor hold down being loose, be REAL grateful you found & corrected before doing any engine damage!Comment
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Re: Serious Timing Problems
Another, related, possibility is one/both of the timing gears 'shrank' allowing the chain to jump. Happened to me once -- looked like gear 'escaped' heat treat hardening. Gaps between teeth wore fast (shrinking toward of gear) and allowing enough slack in timing chain for it to 'jump' registration.
If either condition (chain stretches, gear(s) shrink) happens, owner should hear BRIEF warning -- 'tinkling' sound, like detonation, of the timing chain rattling agains the timing cover. Either is REAL serious and could grenade the engine (valves kiss pistons).
If it's a simple matter of distributor hold down being loose, be REAL grateful you found & corrected before doing any engine damage!Comment
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Re: Serious Timing Problems
Take a mechanics stethescope (about $10) at an auto sparts store and listen at the timing cover for any rattling or rubbing of the chain on the cover. If so, replace the chain and gears. One of the best tools I've ever purchased. Use it every day.Comment
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Re: Serious Timing Problems
Take a mechanics stethescope (about $10) at an auto sparts store and listen at the timing cover for any rattling or rubbing of the chain on the cover. If so, replace the chain and gears. One of the best tools I've ever purchased. Use it every day.Comment
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Re: Serious Timing Problems
One other thing to look at is the the vibration damper. The outer ring with the degree marks is attached to the hup with a rubber like material. Several years ago I had that material come loose and the outer ring would rotate some every time I drove the car. When I tuned up the car I noticed that the timing was way off so I adjusted it to the correct setting. The car ran very badly during the test drive so I rechecked everything and the apparent timing was way off again. I chased it for several days before a mechanic at a local Chevy dealer suggested that I had the above problem.Comment
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Re: Serious Timing Problems
One other thing to look at is the the vibration damper. The outer ring with the degree marks is attached to the hup with a rubber like material. Several years ago I had that material come loose and the outer ring would rotate some every time I drove the car. When I tuned up the car I noticed that the timing was way off so I adjusted it to the correct setting. The car ran very badly during the test drive so I rechecked everything and the apparent timing was way off again. I chased it for several days before a mechanic at a local Chevy dealer suggested that I had the above problem.Comment
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Re: Serious Timing Problems
Yeah! I find it a real handy piece for tracking down leaks in Shark vac systems....
On the $10, agree you can get 'em for this, but try 'em on at the store for comfort. The el cheapo jobbies can pinch so good you can't work with 'em for long....Comment
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Re: Serious Timing Problems
Yeah! I find it a real handy piece for tracking down leaks in Shark vac systems....
On the $10, agree you can get 'em for this, but try 'em on at the store for comfort. The el cheapo jobbies can pinch so good you can't work with 'em for long....Comment
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