Concepts: Valve tapping back in the 60s and 70s


#1

Back in the old days, I owned a 1960s car that would have valve tap when going up hills.
Now, that I know more about cars and engines, I’d like to know what that was all about.
What was causing the chatter? Were the valves loose?
I never did get it fixed. What would have eventually happened?

Why don’t new cars have valve tapping issues?


#2

More than likely, what you were hearing was not. “valve tap”, but was actually, “pinging”, or, “pre-ignition”, or, “knocking”.

This could have been the result of…

using gas of too-low an octane
or
carbon build-up in the combustion chambers
or
badly-worn spark plugs
or
(most likely) ignition timing that was advanced too far.

Eventually, your valves would have been worn-down to something resembling pencil stubs, and your pistons would have had some serious damage done to them.

Modern cars have knock sensors that retard the ignition timing when knocking/pinging/pre-ignition is detected, and thus you are not likely to experience this problem with a modern car.

It wasn’t “valve-tapping”…


#3

My guess is it was not a valve tapping issue but pinging. One could if a perfectionist advance the timing for high altitude and mountain driving to eliminate the ping. Ping or knock sensors now automatically adjust the timing as needed.


#4

Aint technology great,Grandaddy had an 62’ Ford with a manual transmission that He would lug to death-the preignition sounded like pop bottles rattling-Kevin


#5

The EGR system can also be critical in preventing pinging.

To address your question about what could possibly have happened if allowed to continue then the answer would be that it all depends.

If severe enough and chronic enough the engine can be destroyed; usually due to piston disentegration.


#6

Lack of oiling will cause valve clatter. If you were low on oil in the older cars, the valve would clatter.


#7

How would a piston disintegrate? What exactly is pinging? Is something actually hitting the valves, or just something about the timing is off? Does a piston actually get close enough to the valves to actually hit it (if the timing was off?)


#8

Last vehicle I drove with pinging was a USPS LLV with the Iron Duke 4. The Jeep that preceeded it didn’t ping with the same engine, so I’m guessing they leaned it out with the newer vehicle.

I was under the impression that light pinging under heavy acceleration was OK though.


#9

For distributor timing procedures, manufacturer service manuals of the 40’s and 50’s would often say you want a little bit of pinging. Those recommendations don’t hold true today.


#10

The way it was explained to me by an engineer for Chryco…was that the pinging is an unintended explosion of unused air/gas mix in the chamber. This can cause a shock wave (which is what you hear). This shock wave can have devastating effects on the engine. I’ve seen the internals of engines that were destroyed by engine knock. One engine had hole the size of quarter in two of it’s pistons.


#11

Yes, pinging is premature detonation of the fuel/air mixture. That can cause the tops of the pistons to be eroded - and in severe cases, it will destroy connecting rods