[HWYSTR455]

It's def not piston slap, I can attest to that, and have heard piston slap on a multitude of engines.

Although the cam gear was observed and considered not having a runout issue, that was a visual inspection, and could technically still have excessive runout. But that's a big reach there, I have never seen that, and I've done a lot of cams.

Looking closer at the vid where they turned it over with the dizzy out, not sure if it's an optical illusion, but the moment the starter is engaged, it looks like the cam gear kicks to the rear for a moment. It might show a little wear on the very corner of the tooth where it kicks out, too. Maybe slow the vid down?

https://www.youtube.com/watch?v=dDZKHIOGWcE

Maybe someone else can chime in and see what I'm seeing? That might explain the gear wear, but still can't see how that would cause a knock. It would have to kick the shaft over considerably, and consistently, and would need to have the shaft bushing worn out for it to go far enough to make contact. Or that's what I'm thinking.

More I think about pin knock, doesn't that actually change when you pull the plug wire? I think it gets quieter when you pull the plug wire?

.

[67gtospud]

To test and see if it is a cam gear machining issue could you get a roller cam to swap and see if the noise disappears? Maybe someone had a spare cam on the shelf you could borrow just to test.

[Sun Tuned]

Think about it. Something is egg shaped. And when it comes over it's shoving the drive rod over in the boss putting a witness mark on it.

It's locked in the oil pump and the distributor drive gear is meshed with cam gear teeth. Until u pull it out it really never changes.

I'd be looking at that cam real real closely.

[67gtospud]

Originally Posted by Sun Tuned

Think about it. Something is egg shaped. And when it comes over it's shoving the drive rod over in the boss putting a witness mark on it.

It's locked in the oil pump and the distributor drive gear is meshed with cam gear teeth. Until u pull it out it really never changes.

I'd be looking at that cam real real closely.

This does make a lot of sense. Also Paul checked the bottom end and said everything there was good. You tested everything else on the top end and say it's all good. What's really left? The cam can be swapped in the car easy enough.

[HWYSTR455]

Originally Posted by Sun Tuned

Think about it. Something is egg shaped. And when it comes over it's shoving the drive rod over in the boss putting a witness mark on it.

It's locked in the oil pump and the distributor drive gear is meshed with cam gear teeth. Until u pull it out it really never changes.

I'd be looking at that cam real real closely.

Yes, I get that, but the shaft being forced over enough to make contact would still have to be considerable, and the shaft is fixated between the upper and lower bushing in the dizzy housing. That would also be enough for the rotor to make contact with a tower post, no?

At least that's the way I'm thinking.

Has anyone looked closer at the vid, the point I'm talking about? Is that an illusion due to the cut of the gears?

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[Mike Davis]

Originally Posted by Sun Tuned

Think about it. Something is egg shaped. And when it comes over it's shoving the drive rod over in the boss putting a witness mark on it.

It's locked in the oil pump and the distributor drive gear is meshed with cam gear teeth. Until u pull it out it really never changes.

I'd be looking at that cam real real closely.

This sounds like the most likely culprit at this time.

[1968GTO421]

Central Virginia Machine. Hmmm. Here's a thread by a member who sent his GTO engine across country for reputable rebuilding there and had also had an unpleasant result. End result was a local shop got the engine done correctly.

https://www.gtoforum.com/f170/centra...review-106018/

I think our OP is right to work with the people currently involved, no sense adding more problems to the "stew".

[Va68goat]

At this point, the diagnosing and any part swap decision will be made by Paul, Jeff and the tech. I'm on the sideline and just observing. Pretty interesting stuff that you guys are posting though.

[grivera]

If the cam gear damaged the new/current BOP dizzy gear it should have also damaged the prior BOP dizzy gear.

Paul or Joe- was original gear damaged?

[Va68goat]

grivera,
Paul did say the old gear had some wear. He may be able to elaborate on that.

[Sun Tuned]

The tooth count on that cam gear looks not right to me.. which makes no sense, it's likely just the way the video looks on my phone.

I spent 4.5 hours washing something I can only call machining junk out of a brand new set of Comp 857S lifters one Sunday for a friend of mine. So the idea of a bad, sticky, or gunked up lifter is nowhere near out of the question. Especially out of the box. And I spent 4.5 hours housecleaning after we got em out of the box.

I think your issue is solely in that camshaft. You've changed distributors. No change.

Divide and conquer.

What's up with that cam gear? Get it out on some v blocks and let's look it over. Runout on backside of gear is one thing. Runout on outer circumference is another along with pitch and rake angle of gear teeth. Oil pump don't move around. Distributor is kinda stuck in block. Only thing in middle is drive rod and it's got witness marks on it and you've muncher one distributor bushing already.

We know the cam is straight. Paul didn't have to install it with a 5lb sledge, and it likely spins freely enough by hand??? If so it's straight in the block. Cause u know that 50 year old block and that 2 year old cam haven't met each other in a former life. I've seen cams bent before. Usually if they go in and spin fee they're fine.

Let's do some lookin at the cam gear. Or see if you got a trashed lifter plunger that's stuck at back of rear cyls.

[Sun Tuned]

Maybe if you start it again put your hand on distributor housing and feel for a thumping on housing. Indicative of a bent dist shaft, or egg shaped something else....

[Holeshot71]

Originally Posted by Va68goat

Holeshot71,
We've checked for exhaust leaks several times and it's definitely not an exhaust leak.

Ok thx. I do have another question, what's up with the counterweight on the cam in this video: https://www.youtube.com/watch?v=dDZKHIOGWcE
I've never ran a roller cam before but don't remember ever seeing that? Is there any chance it's interfering with the base of the distributor?

[STEELCITYFIREBIRD]

Originally Posted by Sun Tuned

The tooth count on that cam gear looks not right to me.. which makes no sense, it's likely just the way the video looks on my phone.



Divide and conquer.

What's up with that cam gear? Get it out on some v blocks and let's look it over. Runout on backside of gear is one thing. Runout on outer circumference is another along with pitch and rake angle of gear teeth. Oil pump don't move around. Distributor is kinda stuck in block. Only thing in middle is drive rod and it's got witness marks on it and you've muncher one distributor bushing already.

We know the cam is straight. Paul didn't have to install it with a 5lb sledge, and it likely spins freely enough by hand??? If so it's straight in the block. Cause u know that 50 year old block and that 2 year old cam haven't met each other in a former life. I've seen cams bent before. Usually if they go in and spin fee they're fine.

Let's do some lookin at the cam gear. Or see if you got a trashed lifter plunger that's stuck at back of rear cyls.

Agree, tooth count has to be correct or cam and dizzy would be out of sync right quick.

Assumed Cause of original dizzy bushing failure, soft bushing, never sat well with me, just too quick.
I agree ,there is a mesh problem with the gears that caused the first bushing failure....yet to be proven or found.
Bent dizzy shaft, not enough dizzy end play for correct mesh, dizzy drive gear concentricity to cam bearings or other drive gear mismachining , , poly dizzy gear problem, block problem, etc???

The water gets really muddy when a diagnosis goes this long. Like the introduction of the vacuum leak.

Myself, I start from scratch when I take over someone else's diagnosis, Assume nothing, install with confidence!

It will get figured out and will be a moment for more than just those $$$$$ involved!

[STEELCITYFIREBIRD]

Originally Posted by Holeshot71

Ok thx. I do have another question, what's up with the counterweight on the cam in this video: https://www.youtube.com/watch?v=dDZKHIOGWcE
I've never ran a roller cam before but don't remember ever seeing that? Is there any chance it's interfering with the base of the distributor?

That's the last lobe on the cam, and could be a possibility, would leave its marks on the same area of the gear or housing...+/- for ignition timing adjustments, if an interference does exist.

[HWYSTR455]

Originally Posted by Holeshot71

Ok thx. I do have another question, what's up with the counterweight on the cam in this video: https://www.youtube.com/watch?v=dDZKHIOGWcE
...?

What the!?! I was so focused on the gear it never occurred to me to look around!

What is that, a piece of a cam bearing or something!?!


/

[HWYSTR455]

Originally Posted by STEELCITYFIREBIRD

That's the last lobe on the cam, and could be a possibility, would leave its marks on the same area of the gear or housing...+/- for ignition timing adjustments, if an interference does exist.

Nope, the next lobe over from the gear should have plenty of space, like this:


.

[HWYSTR455]

It kind of looks like a plate of some kind?



.

[HWYSTR455]

It's moving around, it's not fixed on the cam.


/

[Va68goat]

I think that is some sort of reflection Mike