Camshaft Knock? 305 V6. Please advise...

[restorevival]

SO.... Where to start... Not at the beginning because the story is too long. I'll start with my current frustration and see where the discussion goes from there.

I recently had the 305E v6 in my wife's '66 GMC rebuilt. Since getting it back from the shop and putting in lots of time adjusting, tuning, etc., it finally seems to be running right.

However, when idling, there is a distinct but fairly faint knocking sound. I drove it back to the machine shop and the guy that did all the machine work and put the engine back together says that the knock is coming from the camshaft. Here's his explanation: "These engines have no thrust plate on the camshaft, so at slow idle, the slack in the timing chain is allowing the camshaft to float and creates the knocking sound that you hear." He also said something about the movement of the camshaft being related to helical gear of (I think) the distributor? I may not be remembering that last part correctly.

His solution was to increase the idle speed until the knocking went away, which he did. The idle seemed a little fast to me, but I don't have a tach installed (yet) to know what it was idling at exactly. I drove it around a bit and it seemed fine, but then started dieseling/running-on whenever I turned it off...

I am starting to get into another topic so I will get back to the point. --Does the above explanation of the camshaft knock make sense?? At this point the conversation with the mechanic has gone beyond my understanding of the inner workings of this engine, so I lack the knowledge and vocabulary to question him further on it. I would really like some help from the community on this one.

My gut instinct is that the knocking is a problem, and that increasing the idle is only curing the symptom. I would love it if someone responded by saying that my instincts are wrong on this one, and that I have nothing to worry about... and then be able to explain why/why not.

Thank you in advance for your feedback.