307 tapping thoughts?

[techg8]

I did replace the timing chain when I put it back together.

Today I ran a container of GUNK Valve Medic in the oil nice and hot for awhile, hoping it could be something gummed up or a sludge filled oil hole. No such luck. Its got to be something mechanical.

So I am looking at working my way into the lifter valley to see whats up. Ill start at the valve covers but I dont think Ill find much there.

It started after an evening of hard accellerations. I bet one of the lifters internal springs got tired or broke. Should be easy to spot once I get in there.

thanks for the input guys, I will keep you posted

 

[Peter]

does the engine have to be under load to make the noise or just at a certain rpm idling or driving?

 

[Bonnewagon]

Yeah, now it's sounding like a collapsed or stuck lifter. Sucks to open her up, but starting with the valve cover should pinpoint the problem. It could even be a broken valve spring or bent pushrod. Good luck with it.

 

[techg8]

does the engine have to be under load to make the noise or just at a certain rpm idling or driving?

it does not do it on startup or at idle.

at lean steady state cruise down the road it really makes a racket. From there if I get into or out of the gas it stops until the engine reaches steady state again.

It seems worse when the engine is hot than when cold

I can get it to happen in park or N by gently easing into the throttle.

So its more like a certain rpm than anything else.

 

[pontiacgp]

could be a carb knock, start the car and get it up to operatijng temp, slowly pour a trickle of distilled water down the carb and keep the engine running. See if that gets rid of it

 

[techg8]

well I tore it down to the lifter valley today. It wasnt a bad job. The new radiator even had a 1/2 full drain easily accessible that drained just enough coolant to remove the intake.

none of the pushrods were loose or sloppy. a quick visual inspection hasnt turned up any obvious causes.

I think I will clean up the rockers pushrods and lifters in my ultrasonic and then maybe disassemble the lifters for a full inspection. Theres got to be something going on in one of them.

 

[Bonnewagon]

How do the cam lobes look?"

 

[techg8]

I used a LED flashlight to peek down thru the lifter bores at the lobes.

The quick viusual turned up no unusual wear.

I mean they look worn but smooth, no pitting galling scarring or marks indicating trouble. Nothing "stood out"

same goes for the rollers on the lifters. They "look" pretty good.

I will clean them up and have another more detailed look.

 

[woody31]

at this point i would replace all the rocker arms and hold downs,,.even a few extra thousands will make a difference ,those are non adjustable,,,problem solved,,,, 8)

 

[techg8]

OK found it.

I inspected the pushrods while blowing them out and found a bent one.

I also found some small junk inside some of the lifters, likely leftover from the last build - I didnt disassemble the lifters when I overhauled the engine. Lesson learned.

My theory is that one of the small loose "bits" inside a lifter jammed it up long enough to bend the pushrod.

Anyhow I found the bent pushrod which provides a definitive answer to the question of what was wrong.

The lifters are all cleaned up and move smoothly.

The bent pushrod - well I dont know if I will just hammer it "straight" or replace it......

I will reassemble the engine then update the thread with a final outcome.