Difference b/w valve noise and spark knock?

[Anonymous]

Can anyone try to explain the difference b/w valves knocking and spark knock?

I've been hearing a knocking/rattling sound from the motor under load for the last couple of months.

I just installed a Pertronix ignition and replaced the plugs, roter and dis. cap. I readjusted the timing (it was soooo far off the scale!). It is now about 9 to 11 degrees BTDC and the knocking is much less. I'm just wondering if there is anything else I can do or am I due for a valve job?

Thanks,
Scott B.

 

[Anonymous]

First find out the source of your knocking/rattling.

If you can get it to replicate at all while stopped, you can remove spark plug wires one at a time see if it goes away,, the put the wire back and try next cylinder. That would eliminate or locate a bad cylinder...from there it could a bad piston rod or lower crank connections.

Try that first. A mechanics stethoscope can also help pinpoint the noise as it may be there at idle, but just not loud enough for you to hear yet.

Detonation or engine pinging does not sound like rattling or knocking as you describe...but it still could be it if timing is advanced and damper has shifted.

Good luck.

Steve-O

 

[Anonymous]

Steve-O

check your private message

Kelly

 

[66 Fastback]

Isuspect you have spark knock since it is occuring under load. Valve clatter would be present whether the engine is under load or not and probably at all engine rpm's.
Remove the #1 spark plug and check to see that the piston is at TDC when the timing marks and distributor rotor indicate it is at TDC. Your harmonic balancer ring may have slipped and your timig marks may be off. Or you may have too much total advance from either too much vacuum or centrifugal advance.
Doug

 

[Anonymous]

It idles perfectly, I can't hear any knocking while standing. It only seems to knock while excellerating. It may happen at high RPMs, as well, but I can't be sure because of excessive wind noise.

I'll see if I can get a stethoscope and check that way.

Scott B.

 

[Anonymous]

Thanks Doug,

Now the dumb question: How can I be sure if the piston is at TDC by removing the spark plug? What should I be looking at? I confess that I've never looked down the plug hole!

Thanks,

Scott B.

 

[66 Fastback]

Get a long screw driver and insert it in the hole. As you rotate the engine by hand, until the timing mark on the balancer/dampener indicates you are at TDC. You will see the screwdriver rise and fall. I think one time I put a piece of tape marking how far down I could insert the screwdriver and marked the depth as I got closer to TDC. Rotate it back and forth until it looks like you are at top dead center. Now the distributor rotor is should almost be lined up with the #1 spark plug wire tower on the cap. If the piston is not at the highest point in the rotation when the timing mark is lined up at TDC then the timing mark may have slipped. Using a screwdriver is not the most accurate method but you should be able to tell if the balancer has slipped a bunch. Keep in mind that the top of the stroke, it takes quite a bit of crankshaft rotation to produce much vertical movement of the piston.
Doug

 

[Anonymous]

to see if the piston is at TDC get a flash light and pull the number 1 spark plug, look down into the hole, turn the cranck until you see the piston rising and keep turning till it starts to go back down, then back it up till it is at it's highest point. That should get you close enough to TDC

 

[CZLN6]

Howdy Scott:

If it is pre-ignition, here is a list of things you can try, short of a valvee job.
*Make sure the advance mechanism in the distributor is free and rotates easily. make sure all vacuum lines are tight.
*reduce initial advance. (Yuk!)
*Try a tank of higher octane gas. (Yuk)
*reduce carbon build up in the chamber with a commercial additive.
*Try a colder plug
*reduce engine temperature.
*duct cold air to the air cleaner inlet.

Unless you do regular maintainance to your distributor, it's likely that the advance mechanism inside the distributor is sticking, and not allowing the vacuum advance to return to a low vacuum/high load setting, causing excessive advance under load situation.

That's my two cents. Hope it helps.

Adios, David