Hi.

I agree with Spook on this noise being a broken valve spring or let say one that has collapsed.
I have often wondered over the years just how long valves springs should last?
The odds are twice as high than the chances of it being a connecting rod.

I surmise that some of the extra sound is in part due to “not following the cam” and is probably a nice unnerving noise.
Probably a sound that’s very much like not enough oil inside a hydraulic lifter within other engines.
That too creates a miss if it becomes bad enough.
Most of the time the hydraulic lifters do not have as much “pump up distances” and just stay noisy.
A collapsing (fatigued) or collapsed (cracked) valve spring can get there rather easily and it will not go away.


Either way if it is shorter than it should be, I would want to go that route and jump into any lower end problems.

A weak valve spring can in itself that make the engine miss as you have heard or felt it doing.
A worn bearing insert shouldn’t make it miss.
A stethoscope or better yet compression test will help confirm the problem is up top.
Besides you need to know in which cylinder has it.

I would also like to ask, How many miles are on this head or could it NOT be an original factory setup head?

Springs are made from coil of steel wire and then heat treated in a batches.
Yes One and only one can have a failure so it could be a fluke but I will suggest running them all under a spring compression tester for “some” peace of mind of consistency and specification.
Those that are in there now, have been tested by time and cycles.
Since this can be an issue to anyone at any time, I shall hope, the experience gained will be shared on the forums.

Just because you can replaced them all with NEW introduces other probabilities of untested quality issues.
What a dilemma that might be? 😳 as always!

Factories keep things grouped during production runs for quality control and warranty reasons.
They know what they have made and issues incurred or they get mitigation as they should.

It would be nice to correlate some ideas of how well the red blocks have lasted as long as they have.
I just know, in my heart, that these engines received a great amount of assembly “care” let alone being designed well with time based forethought.
I have kept my cars because they have paid me my due and I’m paying it back to a machine made by true craftsmen of that era.

Phil