Dancing Vacuum Needle
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Joined: Dec 2007
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From: Boise, Idaho
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.
Post Fiend
Joined: Dec 2007
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From: Lost
Should have been. If the clearance was tighter than normal, then we may be on to something here. If it was fine, then could be related to valve sealing.
If the tips of the stems were a bit too tall when installed, it would lead to valve sealing issues, particularly after the engine is warm.
Could also be lifters pumping up once the engine is warm.
If the tips of the stems were a bit too tall when installed, it would lead to valve sealing issues, particularly after the engine is warm.
Could also be lifters pumping up once the engine is warm.
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From: Boise, Idaho
I measured the gap between all the valve stems and rocker arms on all of them with empty (bled down) lifters. 0.100" was the minimum, 0.200" was the max. 0.125" - 0.175" was preferred. I believe the lowest was 0.135" and the highest was 0.160". All very well in spec.
The popping is pretty much the same whether the engine's warm or cold.
The popping is pretty much the same whether the engine's warm or cold.
Post Fiend
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From: Lost
Silly question. Were the lifters used during the clearance test the exact same lifters in use now?
The valve stem length is critical on these ford engines with non-adjustable valvetrain. Even more so when the head and/or block has been decked, particularly if the entire valvetrain is being replaced with new parts (rockers, pushrods, cam & lifters) rather than older parts with a little wear on them.
I still think a good test would be to back off the rockers .5-1 turn, and see if the popping goes away. If it does, then you have a solid answer. If not, then the valves just aren't sealing, and the head will most likely need to come back off.
The valve stem length is critical on these ford engines with non-adjustable valvetrain. Even more so when the head and/or block has been decked, particularly if the entire valvetrain is being replaced with new parts (rockers, pushrods, cam & lifters) rather than older parts with a little wear on them.
I still think a good test would be to back off the rockers .5-1 turn, and see if the popping goes away. If it does, then you have a solid answer. If not, then the valves just aren't sealing, and the head will most likely need to come back off.
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From: Boise, Idaho
Yeah, they were the same lifters.
I'll give the test a try and back them off. They're the later pedestal style, so I'm not sure how well it'll work. It'll give me an idea though.
That does beg the question. If the lengths on something were off, why would the problem surface as time went on? There's always been somewhat of an issue with ticking (and the vacuum oscillating) but this popping is a new development. Wouldn't it have done it from the start?
I'll give the test a try and back them off. They're the later pedestal style, so I'm not sure how well it'll work. It'll give me an idea though.
That does beg the question. If the lengths on something were off, why would the problem surface as time went on? There's always been somewhat of an issue with ticking (and the vacuum oscillating) but this popping is a new development. Wouldn't it have done it from the start?
Post Fiend
Joined: Dec 2007
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From: Lost
If the valves were *barely* sealing at the seats, they could actually be starting to "burn" the valves and/or seats. As the combustion leaks out, it can accelerate/intensify the leaking.
Also, as the valves start lapping themselves in, it actually wears away a small portion of both the seat and valve, where they meet. Lapping compound for hand lapping the valves, is gritty paste that polishes the mating surfaces. This wears away a very minor amount of material from both surfaces.
Also, as the valves start lapping themselves in, it actually wears away a small portion of both the seat and valve, where they meet. Lapping compound for hand lapping the valves, is gritty paste that polishes the mating surfaces. This wears away a very minor amount of material from both surfaces.
Post Fiend
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From: Lost
A very viable possibility.
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From: In my own world
why not? he'll stand under the black cloud, you watch the rainbow, and get the pot of gold.Sorry. couldn't resist. I don't think crack in the head, because it is not doing it all the time, and I can't get past the noise it's making, that is definately mechanical.
Postmaster
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From: Earth
If there's something too long in the valve train, try some shims under the rocker pedestals. I bought a set of roller rockers for a SBF that came with two different thickness shims, but when I had to stack them to get the right preload I just bit the bullet and got shorter pushrods...
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From: Boise, Idaho
You guys crack me up. 
But hey, you can only have so much bad luck, right? Maybe I've already used all mine up.
Well, the problem's continually getting worse and worse (less and less throttle required) so I'm thinking a valve is burning or something. I imagine I'll have to pull the head here soon and have it R&Rd. Hopefully, after that, I'll be done with all of this.
As for the valve springs, would it be pretty easy to see if one's broken? They're brand new Comp springs, I'm not sure how one would have broke.
(Also, it's definitely not a mechanical knocking.)
But hey, you can only have so much bad luck, right? Maybe I've already used all mine up. Well, the problem's continually getting worse and worse (less and less throttle required) so I'm thinking a valve is burning or something. I imagine I'll have to pull the head here soon and have it R&Rd. Hopefully, after that, I'll be done with all of this.
As for the valve springs, would it be pretty easy to see if one's broken? They're brand new Comp springs, I'm not sure how one would have broke.
(Also, it's definitely not a mechanical knocking.)
Cargo Master
Joined: Jun 2008
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have you checked the linkage for the carb? sounds to me like either you are getting no pump shot or the secondaries are flopping open prematurely, or, if you have a choke it it closing somehow when you accelerate.
does the truck do the same with a different carb?
does the truck do the same with a different carb?
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From: In my own world
time to pull the valve cover, and run it, and watch the valve train. Your going to spurt oil all over everything, but you'll see if the valves are opening and closing. I wonder if you bent a valve when you locked up the valve train? Was it this head or the other one that happened too?