Dancing Vacuum Needle
Post Fiend
Joined: Dec 2007
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From: Lost
Just thought of another item that could be coming into play. If they knurled or replaced the valve guides, they could be just a shade tight. This can cause one (or more) valves to not fully close everytime.
Roadtrip it.
Roadtrip it.
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From: Boise, Idaho
Considering the symptoms that I have, that'd make perfect sense.
Heh, I didn't want to drive it too much until I figured this out. Looks like I was going about it the wrong way.
Heh, I didn't want to drive it too much until I figured this out. Looks like I was going about it the wrong way.
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From: Boise, Idaho
Well, and update. Things have gone from bad, to better to worse.
The vacuum needle finally steadied, and the vacuum signal was getting better with time. There was still some ticking in the engine which wasn't going away, and it still missed, but I figured it would eventually work itself through when everything seated, as was previously discussed.
However, about a week or so ago, I noticed it would pop if I got on it. This is at the high end, around 3000 RPMs and giving it a good amount of gas. It would barely do it.
Then, it started doing it more often, usually around 50% throttle or so.
Then 30%
Then 10%
Now, I can barely accelerate without it *BAP* *BAP* *BAP* BAP* inside the head, and it pops at idle and at cruise.
It's progressively getting worse and worse to the point where I can barely drive the vehicle.
The sound is a loud pop that sounds like it's coming from inside the head.
You can hear it in these videos.
YouTube - MOV062
YouTube - MOV063
Any idea what's going on? Or what I should do next?
The vacuum needle finally steadied, and the vacuum signal was getting better with time. There was still some ticking in the engine which wasn't going away, and it still missed, but I figured it would eventually work itself through when everything seated, as was previously discussed.
However, about a week or so ago, I noticed it would pop if I got on it. This is at the high end, around 3000 RPMs and giving it a good amount of gas. It would barely do it.
Then, it started doing it more often, usually around 50% throttle or so.
Then 30%
Then 10%
Now, I can barely accelerate without it *BAP* *BAP* *BAP* BAP* inside the head, and it pops at idle and at cruise.
It's progressively getting worse and worse to the point where I can barely drive the vehicle.
The sound is a loud pop that sounds like it's coming from inside the head.
You can hear it in these videos.
YouTube - MOV062
YouTube - MOV063
Any idea what's going on? Or what I should do next?
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From: In my own world
What is your oil pressure doing when it is ratteling like that? I wonder if the cam is walking back and forth. That is a new noise to me, never in 54 years have I heard that. Sounds like a woodpecker???
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From: Boise, Idaho
Funny you'd say that. When I was going through the multitude of ways I could describe the sound (wooden mallet, little drum, etc), a mentally slow woodpecker is what I finally concluded. I just forgot to say it when I finally wrote in on it.
By my cam walking back and forth, are you meaning moving front to rear to front in the engine? The only way I could see that is if the bolts that held the thrust plate on backed out. That'd suck. As for oil pressure, I don't think I've watched specifically while its doing that, but it seems like good solid pressure all the time while cruising. I'll have to keep a closer eye.
My other thought is that I timed it by vacuum. Maybe if the valves aren't closing all the way, it takes more timing to bring the vacuum up. Then, the sound we're hearing is actually pinging. Except when it "pings", it backs out the valve and POPs, instead of smacks down the piston. My theory anyway. I imagine I could test this by retarding the engine a good amount and going for a spin.
By my cam walking back and forth, are you meaning moving front to rear to front in the engine? The only way I could see that is if the bolts that held the thrust plate on backed out. That'd suck. As for oil pressure, I don't think I've watched specifically while its doing that, but it seems like good solid pressure all the time while cruising. I'll have to keep a closer eye.
My other thought is that I timed it by vacuum. Maybe if the valves aren't closing all the way, it takes more timing to bring the vacuum up. Then, the sound we're hearing is actually pinging. Except when it "pings", it backs out the valve and POPs, instead of smacks down the piston. My theory anyway. I imagine I could test this by retarding the engine a good amount and going for a spin.
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From: Boise, Idaho
Went and checked. The oil pressure is solid no matter what, and after experimenting more, it's completely load based. RPMs don't seem to factor in. Also, I didn't hear it at idle like I thought.
At idle, if I slowly increase the RPMs up to 3000, there's no popping. But if I throttle it hard it'll pop. Same with driving. The slower I accelerate, the less pop.
At idle, if I slowly increase the RPMs up to 3000, there's no popping. But if I throttle it hard it'll pop. Same with driving. The slower I accelerate, the less pop.
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From: In my own world
vaccum timing is actually better than a light[don't kill me for my .02 here]. Something in the rotating assy is the noisemaker, that's a metalic klunk. My buddy said maybe thrust bearings on the crank. The noise is when under power? What's it do if you let the clutch out a little too fast then push it back in while slightly rolling with medium throttle?
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From: Boise, Idaho
I'll try that.
However, the camcorder may be the culprit in why it sounds like a metallic clunk. It's definitely a pop, like an odd backfire. The way it echoes inside the head is what makes it sound weird. At less of a throttle (hard to hear in the video), its much more noticeable that it's a combustion/vacuum related popping.
I completely agree on the vacuum timing. I haven't used a light in a long time.
However, the camcorder may be the culprit in why it sounds like a metallic clunk. It's definitely a pop, like an odd backfire. The way it echoes inside the head is what makes it sound weird. At less of a throttle (hard to hear in the video), its much more noticeable that it's a combustion/vacuum related popping.
I completely agree on the vacuum timing. I haven't used a light in a long time.
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From: In my own world
Can you hear it through the carb with the air cleaner off, throttle by hand under the hood? If popping is heard, you have a bad seal on an intake valve.
Have you held a dollar bill by the edge at the tail pipe? If it blows out and stays out, you are ok. if it sucks in and out of the pipe, you have a bad exhaust valve seal.
Your truck has me baffeled, I wish I lived close, to be able to check it out.
Have you held a dollar bill by the edge at the tail pipe? If it blows out and stays out, you are ok. if it sucks in and out of the pipe, you have a bad exhaust valve seal.
Your truck has me baffeled, I wish I lived close, to be able to check it out.
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From: Boise, Idaho
Went out and did those tests.
The thing with the clutch (unless I did it wrong) didn't do much of anything.
Held a bill in front of the exhaust pipe, and for the most part, it steadily stayed out. I remember doing this one with my old head and it would definitely snap and suck back in, so I knew what I was looking for. Didn't do it, but occasionally it would falter, but nothing serious.
Then, took the air cleaner off, leaned in to listen, and gave it a rev. It popped out of the carb so loud that my ear hurt and rang for a good twenty minutes.
Oww.... So yeah, sounds like I have one or more bad intake valve seals.
Is that going to require removing the head?
The thing with the clutch (unless I did it wrong) didn't do much of anything.
Held a bill in front of the exhaust pipe, and for the most part, it steadily stayed out. I remember doing this one with my old head and it would definitely snap and suck back in, so I knew what I was looking for. Didn't do it, but occasionally it would falter, but nothing serious.
Then, took the air cleaner off, leaned in to listen, and gave it a rev. It popped out of the carb so loud that my ear hurt and rang for a good twenty minutes.
Oww.... So yeah, sounds like I have one or more bad intake valve seals. Is that going to require removing the head?
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From: In my own world
. Definately intake then. An old time fix was to wack the top of the valve with a no bounce hammer. Not hard enough to hit the piston[hehehehe}, but hard enough for the valve to center itself in it's seat. DO NOT USE A METAL HAMMER, PIECES COULD SHATTER, AND CUT YOUR EYES. If that don't work, then it's off with the head, and re grind the valves and seats, and then make sure to lap them back in. A test to see which cyl it is, would be to set each cyl, on tdc one at a time, remove the spark plug, and hook up a vaccum pump in the spark plug hole. Draw a vaccum, shut off the pump, and watch for the vaccum to drop. It will eventually drop on all of them, but the one your after will drop almost as fast as the pump is turned off. Kind of like looking for an A/C leak, using the same pump. If you don't have a pump, I guess a mighty vac [hand pump] would work.
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From: Boise, Idaho
I bet I can already tell you which cylinder it is.
Cylinder #1. Compression in the cylinder dropped by 15psi from before to after the head was installed. Plus, when I did a compression test, it would barely hold the psi long enough for me to get out of the cab and look at the reader. If I could get it to 140psi, it'd be at around 130 - 120 or so by the time I got to the engine bay.
Other than that, I just have a Mighty Vac to test with.
I'll have to see if I can track down a no bounce hammer. I have a rubber mallet, but that'll definitely bounce off. How well would putting a small wood block on the valve tip and hitting that with a metal hammer work?
Cylinder #1. Compression in the cylinder dropped by 15psi from before to after the head was installed. Plus, when I did a compression test, it would barely hold the psi long enough for me to get out of the cab and look at the reader. If I could get it to 140psi, it'd be at around 130 - 120 or so by the time I got to the engine bay.
Other than that, I just have a Mighty Vac to test with.
I'll have to see if I can track down a no bounce hammer. I have a rubber mallet, but that'll definitely bounce off. How well would putting a small wood block on the valve tip and hitting that with a metal hammer work?
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From: In my own world
You are looking for an imediate shock, that would susspend the valve in the air momentarily, and allow it to seat itself. I'm not sure if the wood would do that, but it beats $60 for a hammer you will probably never use again. I think I might try taping the he77 out of a hammer with electrical tape.
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From: Boise, Idaho
I gotcha, that makes sense. Yeah, for that price, it'd cost less to buy new head bolts and a gasket and remove the head. 
I'll see if I can fix something up.
If not, looks like it needs to come apart again. This is truly frustrating.
I'll see if I can fix something up. If not, looks like it needs to come apart again. This is truly frustrating.
Post Fiend
Joined: Dec 2007
Posts: 8,521
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From: Lost
Try another simple test. Back off the rockers just a bit. It could be as simple as the valve stems being a hair "too long" due to the seats having been ground. Generally, during a valve job, the tip of the valve stem is ground down as needed, to make up for it sitting a bit deeper in the seat. Perhaps the shop didn't quite get that part right.