[TAQuest]

I talked with the Lunati tech that helped recommending the cam and he said that he thinks the cam is the problem. He thinks the break in went bad. He said he is fairly certain it's not the springs. What the engine is doing is exactly what it would do if the cam and lifters didn't break in properly. So I'm taking it apart and looking at the lifters. He said that will be the best move going forward.

[Stan Weiss]

What was the cranking compression with the new cam?

Did you check the lift at the valves like you said you were going to do?

Stan

[TAQuest]

Originally Posted by Stan Weiss

What was the cranking compression with the new cam?

Did you check the lift at the valves like you said you were going to do?

Stan

Did not do a compression check after the new cam.

Only got to the point of the video of the valves opening and closing, did not measure the lift.

I'm going to take out the lifters and verify the break in before I do anything else.

The tech was heavily leaning towards a bad break in. Not even anything I did. He said there's a small percentage of bad break ins in his experience and he's a Pontiac guy from way back. He said what I'm describing is exactly what happens. The sound. The pop out the carb.

["QUICK-SILVER"]

Engine turned backwards just a hair when you let off the starter.

If rocker movement is good on both sides...we can rule out backfire from trapped exhaust. Like you get when an exhaust lobe is wiped out.

How is the engine running , in general, at idle speed? If it's rough...You could have a vacuum leak. Enough leak could cause a lean backfire and not be the carb causing it. Repeated reving and letting off will get fuel mix in the intake all messed up. Some runners end up pig rich and others near dry. That could have caused the first backfire and blown a gasket out or vacuum hose or cap off.

That carb mounted with two gaskets and the thin adapter plate?
E-carbs on Performer intakes are famous/notorious for vacuum leaks without the plate. Not enough contact area for the square bore carb flange at the spread bore on the intake.

Still thinking about the click/whack moving around.

Clay

[TAQuest]

Originally Posted by "QUICK-SILVER"

Engine turned backwards just a hair when you let off the starter.

If rocker movement is good on both sides...we can rule out backfire from trapped exhaust. Like you get when an exhaust lobe is wiped out.

How is the engine running , in general, at idle speed? If it's rough...You could have a vacuum leak. Enough leak could cause a lean backfire and not be the carb causing it. Repeated reving and letting off will get fuel mix in the intake all messed up. Some runners end up pig rich and others near dry. That could have caused the first backfire and blown a gasket out or vacuum hose or cap off.

That carb mounted with two gaskets and the thin adapter plate?
E-carbs on Performer intakes are famous/notorious for vacuum leaks without the plate. Not enough contact area for the square bore carb flange at the spread bore on the intake.

Still thinking about the click/whack moving around.

Clay

The engine ran smooth. Perfect idle. Break in ran smooth. Sounded perfect. Lunati has you go to 3500 for a full minute towards the end of the break in and it sounded good at 3500. Everyone listening thought it sounded great at 2000 rpm and up. At the end of the break in period I backed off the idle screw down to 1000 rpm and that's when I heard the sounds that weren't normal. I let it cool off and thought about it. Called Lunati.
Changed the oil again. Started it up. Heard the sound. Reved it and then got the 'pop' out the carb. Moved the timing around, no change. Even hooked up a different fuel source. No change.

["QUICK-SILVER"]

Don't take things apart wild guessing at this.

CHECK ROCKER MOVEMENT ON BOTH SIDES.

Kind of surprised the lunati tech guy didn't say to check for rocker to retainer clearance first. Just a few thou smaller base circle on the new cam could cause contact that the old cam didn't have. That contact makes for some strange valve click/whack noises. Most of all...Contact is worse when the valve is closed because of the rocker body shape. That contact will also wedge out against the valve keeping it from seating good.

We're talking noise and backfire here

Clay

[TAQuest]

Originally Posted by "QUICK-SILVER"

Don't take things apart wild guessing at this.

CHECK ROCKER MOVEMENT ON BOTH SIDES.

Kind of surprised the lunati tech guy didn't say to check for rocker to retainer clearance first. Just a few thou smaller base circle on the new cam could cause contact that the old cam didn't have. That contact makes for some strange valve click/whack noises. Most of all...Contact is worse when the valve is closed because of the rocker body shape. That contact will also wedge out against the valve keeping it from seating good.

We're talking noise and backfire here

Clay

I took videos of both sides just posted the one side.

I will check for clearance between the rocker and retainer. Makes sense. Thanks.

This tech guy has a LOT of experience. I got the good one that is old and has GTO's. Pontiac guy. He heard my description of what happened and he went right to the cam and lifters being bad. Like he was sure. Maybe they have had a few bad ones? Or he was God sent to get me out the ditch on Good Friday.
Either way, he was very convincing. Knows the parts exactly. Knew all about the heads and springs.

[TAQuest]

Clay,
With the valves closed there's still an 1/8 inch clearance between the rockers and retainers.

["QUICK-SILVER"]

Originally Posted by TAQuest

I took videos of both sides just posted the one side.

Was rocker movement good on the other side? If yes..The wiped cam lobe guess from the tech guy was just that, a wild guess. Now if you've got an exhaust valve that stays closed or barely moving...Then backfire from wiped lobe would be definate and not a guess.

What about that carb mounting and how it runs now.

Clay

["QUICK-SILVER"]

Originally Posted by TAQuest

Clay,
With the valves closed there's still an 1/8 inch clearance between the rockers and retainers.

That on top or between where the body around the trunion bearing gets close to the retainer?

Clay

[TAQuest]

Originally Posted by "QUICK-SILVER"

Was rocker movement good on the other side? If yes..The wiped cam lobe guess from the tech guy was just that, a wild guess. Now if you've got an exhaust valve that stays closed or barely moving...Then backfire from wiped lobe would be definate and not a guess.

What about that carb mounting and how it runs now.

Clay

We think alike. I told the tech guy that I had videoed the valves opening and closing so the lobes must be fine.
Right then he said; I don't want to be rude here but what you just said shows your lack of experience. The valves opening and closing only says you didn't go so far as to wipe the lobes clean off and fill your engine with metal. Good on you.

He says most will run it until the lobes are gone before they take a look at the lifters.

Carb has a perfect mount. No vacuum leak at all. No cobble jobs on this engine.

[TAQuest]

Originally Posted by "QUICK-SILVER"

That on top or between where the body around the trunion bearing gets close to the retainer?

Clay

I watched them move and they are not hitting anything.

["QUICK-SILVER"]

Originally Posted by TAQuest

We think alike. I told the tech guy that I had videoed the valves opening and closing so the lobes must be fine.
Right then he said; I don't want to be rude here but what you just said shows your lack of experience. The valves opening and closing only says you didn't go so far as to wipe the lobes clean off and fill your engine with metal. Good on you.

He says most will run it until the lobes are gone before they take a look at the lifters.

If it's got full rocker travel, lifter/lobe wear isn't causing the backfire. Wear on either one would be bad and mean something went wrong during breakin and all of it would need replaced....BUT that's not what your problem is since you say it's got good rocker travel.

Originally Posted by TAQuest

Carb has a perfect mount. No vacuum leak at all. No cobble jobs on this engine.

Have you got the thin adapter plate under the carb?
The lack of sealing area doesn't have anything to do with how well you did the install. A simple backfire can blow the gasket out. Or high vacuum from reving up and letting off can suck the gasket in. Just not enough there for it to get pinched/clamped between.

Clay

["QUICK-SILVER"]

Originally Posted by TAQuest

I watched them move and they are not hitting anything.

With a bright light and a one of those small magnifying pocket mirrors, I could see looking up under the rocker for a witness mark.
Hard to check with feeler guages because of the curve in the rocker body, where the retainer can hit right in the center of the arm. Not impossible just hard.

String/cord/wire that you could hold on both sides of the rocker, could be slid up to check for go/no go. Can't recall what minimum clearance is recommended for that.

Clay

[TAQuest]

Carb off. Gasket looks fine (see picture link below). One thing I did notice was the 5th rocker in the picture is a little crooked. The pushrod end of the rocker is to the right a little bit. When I push on the rocker to straighten it out, align it, it will not straighten out. Makes me wonder about the other end of the pushrod.

https://share.icloud.com/photos/0HOG...r_Township,_MI

["QUICK-SILVER"]

See that little tilt on the rocker fairly often. Usually doesn't hurt a thing. You can get adjustable pushrod guide plates to correct it. As long as the roller tip is on the valve stem good...usually not a problem.

Top of the gasket does look good. That gasket looks thicker/stronger than what comes with those carbs and intakes. Feel under the gasket with your finger, on the 4bbl end, and you can tell where there's lack of clamp area because of the spreadbore.

Here's a link to the plate Edelbrock says to use when putting their square bore carb on a their spread bore Performer intake.https://www.summitracing.com/parts/edl-2732?rrec=true

Clay

[TAQuest]

Basically, what the Lunati tech said was that if after break in you have any funny noises of any other problems like backfire you need to check the lifters.

So I'm checking them with a square. I'm done with one side and they are all square, no concave ones. Looks good. On cylinder #7 the poly lock was not set, intake valve. Maybe I missed that one? Would that make it pop out the carb? Finger tight and then went through the break in.

[Stan Weiss]

Shouldn't the lifter face be convex?

Stan

[NeighborsComplaint]

If you can rule out rocker/retainer interference, that is one variable out.

As others have said, that backwards rotation after cutting the ignition would normally indicate excessive cranking compression or too much initial advance. How did the engine crank on hot restart? If it "groaned" slowly before spinning, initial timing is too far advanced.

Retainer to rocker clearance needs to be ruled out as a cause. You should have daylight between the rocker bottom rail and retainer. Short Dport pushrods with a 1.7-1.8" installed height can be the cause. This will cause an intake valve to hold open and cause an intake backfire also. Longer pushrods and/or offset locks/keepers can correct this.

[TAQuest]

Originally Posted by Stan Weiss

Shouldn't the lifter face be convex?

Stan

Very slightly convex. Can't see it good with a square. I'm just using a square as the tech told me to do. He said if they are square or convex they are fine. If they are bad they will show concavity.

The other side is fine. All flat. Looking really nice. No witness marks on the spring retainers from interference from the rockers. Lash seemed still correct. The only thing I found wrong was on #7, I didn't set the lash and tighten the lock nut. It seemed like maybe a whole turn short of where it should have been. Two turns at most. Two turns loose. Like that through the break in.

The springs seem good. I can push them down with the heel of my hand. I have to lean on it to do it. They seem stout enough to seal the valve.

The break in was a success. Now just getting it to run right.