I have a mostly stock 318 in my 86 Diplomat. The only mods are long tube headers and HEI ignition. Whenever I drive my car more than 20 minutes or so, enough to thoroughly "heat soak" it, I can shut off my engine, and if I immediately start it back I hear a knocking sound, much like spark knock, only while its cranking. It goes away immediately when the engine starts firing. There is never any knock while driving, and it never does it cold. Any ideas would be great!
Knocking sound on hot start
- Thread starter dankwiz
- Start date
MiradaMegacab
Well-Known Member
Maybe too much initial timing?
80 Aspen RT
Well-Known Member
Starter loose?
kkritsilas
Well-Known Member
Hi,
Has the timing chain ever been changed? Maybe it is loose enough that it has enough slack in it to rattle against the timing chain cover until the engine starts up and takes up the slack? Maybe this doesn't cover the cold start issue, though.
My old car, a 1993 Lincoln Mark VIII, had the 4.6L DOHC V8. Because of all the cams, the timing chain was extremely long. As time wore on, the accumulated slack from all of the links in the chain created enough slack that the timing chain would rattle on start up. Quieted right down when the engine started to run, because the forces of the running engine would take up all of the slack, and no more noise. Used to belong to a club dedicate to that car, and it used to happen with all of those cars. Never really created any sort of problem, just a rattle on startup.
Kostas
Has the timing chain ever been changed? Maybe it is loose enough that it has enough slack in it to rattle against the timing chain cover until the engine starts up and takes up the slack? Maybe this doesn't cover the cold start issue, though.
My old car, a 1993 Lincoln Mark VIII, had the 4.6L DOHC V8. Because of all the cams, the timing chain was extremely long. As time wore on, the accumulated slack from all of the links in the chain created enough slack that the timing chain would rattle on start up. Quieted right down when the engine started to run, because the forces of the running engine would take up all of the slack, and no more noise. Used to belong to a club dedicate to that car, and it used to happen with all of those cars. Never really created any sort of problem, just a rattle on startup.
Kostas
Mr.Lopar
Well-Known Member
If you gonna replace the starter, your best bet is to hit up a junkyard and get a mini starter off a 94+ dodge ram, Dakota, or full size van
Shorty Thompson
Well-Known Member
Sometimes a bent pushrod will be the culprit too .
My imp
Well-Known Member
Starter drive sticking when hot?
slant6billy
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Yep pull some pieces- valve covers- the easiest. Intake manifold next & look in the valley. You have a easteregg hunt for sure. I had a Jeep grand Cherokee with a 5.2 magnum that did that or close to that description. Turned out to be where the torqueconverter and engine came together. The Flexplate looked OK, but I changed it for shits and giggles (I had a 2nd jeep for parts, so it was readily available) The knock noise never came back afterwards.
Lets back up a bit. Do a cold compression test. Pull the coil wire, check each cylinder with a compression test ( I use the sparkplug type from sears). Write down what you have for each one (1 through 8). Put everything back (spark plugs and wires being careful not to mis-wire any plugs). Then run the engine and let it get to operating temps - that will produce this knock condition. Once you get it there, do your compression check again and note any weird numbers. the middle 4 cylinders get hotter faster, so comp numbers should be a little less, but over all not much. If you see a major drop- loss of more than 10, might be valve guide/ seal. If it was a "stuck" valve you would hear it more than just start up on hot. Again, I'm easteregging, but that is where I'd start, before pulling valvecovers or intake manifolds or trans. I really want a fiberoptic snake probe camera for Christmas to look inside the unknown of the engine. Good luck!
Lets back up a bit. Do a cold compression test. Pull the coil wire, check each cylinder with a compression test ( I use the sparkplug type from sears). Write down what you have for each one (1 through 8). Put everything back (spark plugs and wires being careful not to mis-wire any plugs). Then run the engine and let it get to operating temps - that will produce this knock condition. Once you get it there, do your compression check again and note any weird numbers. the middle 4 cylinders get hotter faster, so comp numbers should be a little less, but over all not much. If you see a major drop- loss of more than 10, might be valve guide/ seal. If it was a "stuck" valve you would hear it more than just start up on hot. Again, I'm easteregging, but that is where I'd start, before pulling valvecovers or intake manifolds or trans. I really want a fiberoptic snake probe camera for Christmas to look inside the unknown of the engine. Good luck!
My imp
Well-Known Member
Remove distributor cap, then manually turn engine reverse rotation to see how many degrees it takes for the rotor to start moving. Then manually turn engine forward rotation. That will show how loose your timing chain is.
Using the distributor method, i can hardly see any slack in the timing chain. I just ordered a recurve kit since the sound doesnt happen at 7 btdc initial. What are your recommendations for timing, i was thinking all in at 3000 (34-36 degrees) with around 15 degrees of vacuum advance.
