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440 ignition timing retarding when reving

Joske2

Joske2

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Hi guy's,

i have here a '74 Jensen Interceptor with the 440 engine.
Engine is still original. The strange thing is, when i set the initial timing to 20° at idle, which is 800 RPM, when you rev it up to 1000, it retards to 16°. vacuum is not connected. When i rev it up more to about 1300RPM then i have back the original 20°, and at 3000, i still had only 26°. This was with the original distributor with the original soft and heavy advance springs.

Now i changed the distributor to a new Firecore one, and use the softest advance springs,
it still does exactly the same at idle, but i have 26° all in AT 2400rpm and if you go higher,
it retards again to 24-25.

Could it be that the cam is moving in the block and so affects the timing curve?

any help appreciated.
 
I would doubt that it is a cam issue but look at a timing light issue or the outer ring on the harmonic balancer moving. Also a CD box like a MSD6A can affect some timing lights. How does it run? If it's running good I wouldn't be too concerned as long as the harmonic balancer isn't bad. Good luck.
 
Check the dist ground to the engine also see that on the dist machine on occasion.
 
If you have access to a second timing light, you can verify what yours is showing and eliminate it as a possibility easily.
Also make sure the distributor shaft bushing inside the block is not excessively worn and allowing for the distributor to "walk" a little.
 
Loose timing chain. Turn crank back and forth to feel slop.
 
eric383 said:
I would doubt that it is a cam issue but look at a timing light issue or the outer ring on the harmonic balancer moving. Also a CD box like a MSD6A can affect some timing lights. How does it run? If it's running good I wouldn't be too concerned as long as the harmonic balancer isn't bad. Good luck.
Click to expand...

Used 2 timing lights, both the same, check them again on my 383 Roadrunner, all perfect.

its running good until 2800-3000 , above that it starts to backfire and hesitate, light or full throttle makes no difference.
 
moparedtn said:
If you have access to a second timing light, you can verify what yours is showing and eliminate it as a possibility easily.
Also make sure the distributor shaft bushing inside the block is not excessively worn and allowing for the distributor to "walk" a little.
Click to expand...

timing light checked, and the play is normal, nothing excessive. Besides, once its running the cam pushes the shaft against the bushing, and
that looks all good.

have checked 2 other engine blocks, the same play on the shaft.
 
Coronet 500 said:
Loose timing chain. Turn crank back and forth to feel slop.
Click to expand...

Well, you should try that once on a Jensen :(, the steering gear is just in front of the damper and you can hardly get a socket on, let alone turn it.
 
may have one of those nylon timing gears. they used to be standard on all big blocks. if so it was probably wore out 35yrs ago.
 
Joske2 said:
Used 2 timing lights, both the same, check them again on my 383 Roadrunner, all perfect.

its running good until 2800-3000 , above that it starts to backfire and hesitate, light or full throttle makes no difference.
Click to expand...
That would have been good to know it sounds a lot like the mechanical advance is hanging up, take the cap off and turn the rotor it should move somewhat freely in a CCW direction then return back to where it was stared at, ever oil the mech advance? Should be done once a year.
 
Sorry the felt pad under the rotor in the shaft is where you oil.
 
eric383 said:
Do you have a Mopar electronic ignition system? A orange ignition box? I would start looking at these components if you had the same trouble with the old distributor. Make sure you have enough voltage going to the coil. Was there anything done to the car before this started happening?
http://www.forabodiesonly.com/mopar/threads/mopar-ecu-orange-box-strange-issues.204335/
Click to expand...


It has the Mopar electronic ignition. It uses the black and gold box. i changed it with my rev-o-nator box and coil from my roadrunner, and the problem
stays, i must say that the timing was more stable then before, but still had the same issues. Then i used an orange box, just to check and still the same.
 
lewtot184 said:
may have one of those nylon timing gears. they used to be standard on all big blocks. if so it was probably wore out 35yrs ago.
Click to expand...


I did not know that there where nylon timing gears? i thought that it was always with a chain ?
 
Joske2 said:
I did not know that there where nylon timing gears? i thought that it was always with a chain ?
Click to expand...
'Silent' sprockets were used on passenger car engines...318's especially. Not sure about the rest of the passenger car fleet....slept too many times since tearing a BB apart.
 
Cranky said:
'Silent' sprockets were used on passenger car engines...318's especially. Not sure about the rest of the passenger car fleet....slept too many times since tearing a BB apart.
Click to expand...
I believe I tore apart a 440 with nylon gears and timing chain. If I remember correctly it was from a 1972 vehicle. Make sure the grounds are good and clean for your box. Do you have any access to a old points style distributor? It would be nice to try and swap it in and eliminate all the electronic ignition parts before having to go further.
 
Joske2 said:
I did not know that there where nylon timing gears? i thought that it was always with a chain ?
Click to expand...

Yes a chain was used, and the cam timing gear was metal with a nylon coating on the teeth to reduce noise. After several years and miles the nylon would sometimes end up in the bottom of the oil pan.
At least that's what happened in my '69 Super Bee's 383 with 173,000 miles on it. The nylon pieces actually clogged the oil pick up twice on me. Fortunately I was diving slow each time it happened and heard the valve noise then saw no oil pressure reading on the gauge and I was able to shut down the engine before any damage was done. Let it sit for a few minutes then fire it back up and no valve noise and had good oil pressure. I was a little puzzled at the time.
The second time it happened I pulled the engine and that's when I found the nylon pieces in the pan and pick up screen.
 
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