No compression

[GoToGuy]

Ok, in aviation we do these often. It's one the primary tests for engine health.
And unfortunately, I'm not there to hear it, but if that loud on a posted video. That valve is either angled off the seat a lot, or is hanging open . With zero bleed resistance it's as if the valve is completely open.
I concur with above , the next step is pull the heads. See what's damaged, and type of damage. I believe this is beyond a simple lapping with that much blowby.
Look forward to your next progress report.

 

[Road Trip]

I will try the YouTube trick and will let you know what I find upon teardown

Well done, grasshopper!

Nice job talking while demonstrating to the viewer how the leakdown test process can isolate down to a specific problem/uploading those 2 YouTube videos.

I know for a fact that if I field any questions about leakdown testing in the future I will be linking them to these videos. (!)

Not IF but WHEN you get this engine repaired and reinstalled you should post a short victory video at the end of this thread
with the engine running as right as rain. (You know, I ran into a snag but I didn't give up on the fix story line. :0)

Dude, I am so happy to see a member of The Next Generation joining the engine building hobby. Watching you takes me
back ~50 years or so to when I was encountering difficulties but refused to take no joy as the final answer.

Keep us in the loop with status updates. And thanks for following through with the leakdown videos. (!)

 

[katwood16]

Update: I work at a dealership with a large service department and so I took the engine to work with me. My shop foreman is one of the most talented mechanics I've ever met and his work shows it. He told me before I pull heads he wanted to check it out. He then asked me to hook up the leakdown test again and put it to 90psi. Then he comes over with deadblow hammer, takes the rocker off along with the pushrod out and starts tapping on the valve springs with the dead blow, and almost instantly the cylinder starts to hold compression. I watched as the leakage went from 100% to less than 20 in just a few smacks. He did the same to the #8 cylinder and just like magic I watched the guage go from absolute leakage to almost none. I then told him I was concerned that the leakage was still too much and that I was still worried about valve issues. He told me they just need to seat and I should be good to run the engine. Once we were finished the #1 and #8 cylinders had less than 20% leakage. What do you guys think? Still pull heads, or run it as is? I really trust him but I always appreciate a second opinion. Maybe ill run the compression test tomorrow and see what it says but I don't want to be disrespectful as far as second guessing my foreman especially with how truly good he is. Maybe I'm just being overly cautious but I would like to hear what you guys think

 

[Road Trip]

What do you guys think? Still pull heads, or run it as is? I really trust him but I always appreciate a second opinion. Maybe ill run the compression test tomorrow and see what it says but I don't want to be disrespectful as far as second guessing my foreman especially with how truly good he is. Maybe I'm just being overly cautious but I would like to hear what you guys think

What are your goals with this engine? If this was a carbureted car and it really needed to be pressed into service
in a cab company that had way too many broken vehicles in the fleet, then getting the 1 cylinder close & the other up
to only 20% leakage?

Why not? We need something that will move under it's own power in order to pay the bills. Hammer it a few more times & Send it!
(No sarcasm. This kind of thing happens in the real world all the time.)

****

On the other hand, if this is going to be an engine under tight computer control, and is something that you
expect to be able to hop in, start it, and it runs without intermittently kicking codes, hesitation when taking off
from a light, worse than average gas mileage, and bringing driveability issues to this forum, only to have to
listen to us talk about misfires creating a 'false-lean' reporting by the O2 sensors misleading the computer,
etc...then getting a brand new engine to 'only' have 20% leakage in 1 cylinder? Given this scenario, I don't
think it's wise to push ahead with known issues with your valves/valve seats.

In English, back in the much looser tolerance days of carburation, mechanical centrifugal advance, and vacuum
advance canisters, any mechanic worth his salt could tune an engine around stuff like sticky valves and iffy
valve seating. Most engines started getting tired after 75,000 miles of use, and very few were ever in a
sharp state of tune. Richen up the jetting just a little, twist in a couple of degrees of advance, and if the
engine pinged on the highway, then run some 29¢/gallon Ethyl in it. But at the same time these engines
put out a lot more HC, CO, and NOx than today's engines do.

****

Let's stop and think about what your shop foreman did. By tapping on the tops of the valves he was
able to improve the valve seating? Now he didn't straighten any bent valve heads by doing this, so the
only other answer I can come up with is that the valve stem to valve stem guide clearance is *too tight*.

Tight enough that those valve springs couldn't overcome the friction between valve stem and guide, so
the valve stopped moving before being fully seated against the seat. Now keep in mind that you are
experiencing this at room temperature. When the engine fires and everything comes up to operating
temperature, hot valves get rid of heat in 2 places: the valve head at the valve seat, and the the valve
stem through the valve guide.

If there's a clearance issue at room temperature, given that metal expands when heated, it is only going to
get worse as the engine runs. If that exhaust valve hangs open, it will NOT cool properly, and there's a
good chance that it will burn up in short order. (See 1st attached for an exhaust valve I burned because
I neglected to perform the recommended valve lash adjustment at the scheduled maintenance interval.)

And I've worked on high mileage, tired motors with 20% leakage, and I could get them to run 'good enough',
but with anything I care about I want all the cylinders to read very close to each other, with a goal of maybe
5% leakage tops.

But it really doesn't matter what I do with my motors. What's more relevant is what are YOUR plans for
this powerplant?

* Flip it as-as, as shown, no guarantee that it will run without a SES light or passing emissions testing?
Then you get to use a hammer to help the valves to the home position & ship it.

* Put it together and get it to run smoothly on the computer, pass the emissions testing with ease, and
'get to drive it' instead of 'gotta drive it'? Then take the time to remove the heads, fix the clearances
issues, and put it back together. There is something to be said for putting an engine together in such a
way that it's pure pleasure to live with your own work. (!)

****

In the 2nd attachment is a TSB (Technical Service Bulletin) where GM addresses the recovery plan for
SBCs that experience misfire during heavy use due to too-tight valve stem/guide clearances.

And in the 3rd attachment is a frame grab from a YouTube video where a machine shop out in Colorado
is taking an engine apart in order to figure out why it only drove 10 miles after being reuilt by a different
machine shop before 'seizing'. Hint: The valve stuck open and the piston kissed it. I think that this video
will give you some insight as to how things go wrong when the valvetrain isn't running the proper clearances.
(JAMSI 235ci Chevy post-mortem disassembly)

Bonus viewing: Here's the video of the father/son machine shop fixing that same cylinder head, doing it in
such a way as to guarantee a long service life. Great viewing if you've heard some cylinder head terms
thrown about but would like to better understand what your machinist is trying to accomplish: (old 235 Chevy head machining perfection)

****

So you asked what do I think? Well, a phrase that I've learned from in this forum is "Buy Once, Cry Once."
In other words, "There's never time to do it right...but there's always time to do it over." Actually I'm mixing
metaphors a bit for effect. When it comes to engines, putting something together when it's telling you
that something isn't right is no recipe for long term success.

My elders would have told me to take it back apart and fix the obvious. Schurkey is on the record as saying that
0% leakage through the valves is the standard. GM would tell you in their TSB that too-tight valve
stem/guide clearance will end up setting DTCs for misfires when things heat up, expand, and not seat
properly when the going gets hot. And the machinists in those videos will tell you that they got to rebuild
a rebuilt motor because too-tight valve stem/guide clearances caused a valve to stick open with only
10 miles after a rebuild.

But ultimately it all depends upon what your goals are for your project.

For what it's worth --

 

[GoToGuy]

If we had low cylinder on differential test, and did well on run up and mag check, all temps in the green. We would " stake " a leaky valve in case some carbon or lead combustion material ( avgas low lead) got caught or flaked off in cool down. Bump the input pressure to 100 psi, then as your foreman did, strike the valve to clear whatever material that could be a problem. For me it was 50/50 . Pass / fail. I didn't mention it earlier , it's a you had to be there thing. Good luck!

 

[katwood16]

What are your goals with this engine? If this was a carbureted car and it really needed to be pressed into service
in a cab company that had way too many broken vehicles in the fleet, then getting the 1 cylinder close & the other up
to only 20% leakage?

Why not? We need something that will move under it's own power in order to pay the bills. Hammer it a few more times & Send it!
(No sarcasm. This kind of thing happens in the real world all the time.)

****

On the other hand, if this is going to be an engine under tight computer control, and is something that you
expect to be able to hop in, start it, and it runs without intermittently kicking codes, hesitation when taking off
from a light, worse than average gas mileage, and bringing driveability issues to this forum, only to have to
listen to us talk about misfires creating a 'false-lean' reporting by the O2 sensors misleading the computer,
etc...then getting a brand new engine to 'only' have 20% leakage in 1 cylinder? Given this scenario, I don't
think it's wise to push ahead with known issues with your valves/valve seats.

In English, back in the much looser tolerance days of carburation, mechanical centrifugal advance, and vacuum
advance canisters, any mechanic worth his salt could tune an engine around stuff like sticky valves and iffy
valve seating. Most engines started getting tired after 75,000 miles of use, and very few were ever in a
sharp state of tune. Richen up the jetting just a little, twist in a couple of degrees of advance, and if the
engine pinged on the highway, then run some 29¢/gallon Ethyl in it. But at the same time these engines
put out a lot more HC, CO, and NOx than today's engines do.

****

Let's stop and think about what your shop foreman did. By tapping on the tops of the valves he was
able to improve the valve seating? Now he didn't straighten any bent valve heads by doing this, so the
only other answer I can come up with is that the valve stem to valve stem guide clearance is *too tight*.

Tight enough that those valve springs couldn't overcome the friction between valve stem and guide, so
the valve stopped moving before being fully seated against the seat. Now keep in mind that you are
experiencing this at room temperature. When the engine fires and everything comes up to operating
temperature, hot valves get rid of heat in 2 places: the valve head at the valve seat, and the the valve
stem through the valve guide.

If there's a clearance issue at room temperature, given that metal expands when heated, it is only going to
get worse as the engine runs. If that exhaust valve hangs open, it will NOT cool properly, and there's a
good chance that it will burn up in short order. (See 1st attached for an exhaust valve I burned because
I neglected to perform the recommended valve lash adjustment at the scheduled maintenance interval.)

And I've worked on high mileage, tired motors with 20% leakage, and I could get them to run 'good enough',
but with anything I care about I want all the cylinders to read very close to each other, with a goal of maybe
5% leakage tops.

But it really doesn't matter what I do with my motors. What's more relevant is what are YOUR plans for
this powerplant?

* Flip it as-as, as shown, no guarantee that it will run without a SES light or passing emissions testing?
Then you get to use a hammer to help the valves to the home position & ship it.

* Put it together and get it to run smoothly on the computer, pass the emissions testing with ease, and
'get to drive it' instead of 'gotta drive it'? Then take the time to remove the heads, fix the clearances
issues, and put it back together. There is something to be said for putting an engine together in such a
way that it's pure pleasure to live with your own work. (!)

****

In the 2nd attachment is a TSB (Technical Service Bulletin) where GM addresses the recovery plan for
SBCs that experience misfire during heavy use due to too-tight valve stem/guide clearances.

And in the 3rd attachment is a frame grab from a YouTube video where a machine shop out in Colorado
is taking an engine apart in order to figure out why it only drove 10 miles after being reuilt by a different
machine shop before 'seizing'. Hint: The valve stuck open and the piston kissed it. I think that this video
will give you some insight as to how things go wrong when the valvetrain isn't running the proper clearances.
(JAMSI 235ci Chevy post-mortem disassembly)

Bonus viewing: Here's the video of the father/son machine shop fixing that same cylinder head, doing it in
such a way as to guarantee a long service life. Great viewing if you've heard some cylinder head terms
thrown about but would like to better understand what your machinist is trying to accomplish: (old 235 Chevy head machining perfection)

****

So you asked what do I think? Well, a phrase that I've learned from in this forum is "Buy Once, Cry Once."
In other words, "There's never time to do it right...but there's always time to do it over." Actually I'm mixing
metaphors a bit for effect. When it comes to engines, putting something together when it's telling you
that something isn't right is no recipe for long term success.

My elders would tell me to take it back apart and fix the obvious. Schurkey is on the record as saying that
0% leakage through the valves is the standard. GM would tell you in their TSB that too-tight valve
stem/guide clearance will end up setting DTCs for misfires when things heat up, expand, and not seat
properly when the going gets hot. And the machinists in those videos will tell you that they got to rebuild
a rebuilt motor because too-tight valve stem/guide clearances caused a valve to stick open with only
10 miles after a rebuild.

But ultimately it all depends upon what your goals are for your project.

For what it's worth --

No carb yet hopefully in the future, but i already deleted the egr and plan to do the same to the cats. I'm not sure what to. I want to make I did everything I can to ensure success but I'm really getting to the point where I just want my truck back. I will definitely talk to him about the tsb and possibly perform a compression test with a starter motor attached. I guess the reason I'm so skeptical is bc almost everyone was saying the heads will need to come off then he comes over with a hammer for 30 seconds and is like "it's all good send it". He was assuring me that whatever leakage is there will solve itself upon start up when the valves get some heat and find their home. But if this is an issue that won't just solve itself then I need to start thinking about pulling heads anyway.

 

[Erik the Awful]

The standard is 0% leakage. The valves shouldn't have to wear in to the seats, they should have been lapped in. But, would you rather tear into it, or would you rather just run it? Most likely it'll clear up and they'll seat themselves, but there's also a chance you have to go back into it.

 

[Road Trip]

No carb yet hopefully in the future, but i already deleted the egr and plan to do the same to the cats. I'm not sure what to. I want to make I did everything I can to ensure success but I'm really getting to the point where I just want my truck back. I will definitely talk to him about the tsb and possibly perform a compression test with a starter motor attached. I guess the reason I'm so skeptical is bc almost everyone was saying the heads will need to come off then he comes over with a hammer for 30 seconds and is like "it's all good send it". He was assuring me that whatever leakage is there will solve itself upon start up when the valves get some heat and find their home. But if this is an issue that won't just solve itself then I need to start thinking about pulling heads anyway.

Yup, I understand your situation. Face to face I come across as a fairly flexible "Let's make the best of what you have to work with."
Perfection is not always possible nor the best answer for every given situation. When I understand what the owner's
real needs are, then sometimes we declare that 90/10 rules are in play. (90% of perfection while only using 10% of the
time to do it." :0) But at the same time I make it very clear that there is also a 10% chance that the project will fall short
because we are relaxing the standards we are holding ourselves to on the fix in front of us. (!)

****

But I've discovered a distortion that occurs when I'm doing this remotely, especially in public. What little reputation you
build up over time you don't want to squander by offering less than a 'guaranteed' fix strategy. And I really want to help
someone who's stuck, but at the same time *not* lead them down an expensive garden path. And this is also explains
why I don't offer up any tips on automatic transmissions, for there are SMEs in here that can offer much better advice than I.
And I have seen in other forums where heated arguments crop up because one way or the other is the only way. And then
the troubleshooting turns into a turf war. And I rapidly lose interest. :0)

****

Having said all that, I feel that your plan to show your 'real life mentor' the GM TSB concerning the valve guide clearances is
a good plan. And if he reads it for comprehension and tells you to send it, then guess what? He is now it. If the engine
settles in and gives you good service, then his reputation is only strengthened from your perspective. But if the engine
is good only 90% of the time, but has issues 10% of the time, then either drive it in such a way as to avoid the issue,
or come back here and we'll kick it around a bit more. For all we know, maybe the valves aren't even the issue in this
hypothetical situation, for the root cause is actually elsewhere?

This is where you will hear someone in here ask for misfire counts & data streams in order to suss how to make things as
right as possible.

****

From my perspective over here in the finger lakes region of upstate NY, you have posed good questions, shown excellent
follow-through, and have done so with a professional demeanor. I in turn got a little more practice in remote diagnosis and
got to discuss one of my favorite troubleshooting techniques. (leakdown testing) And, I'm no longer it, your shop foreman is. :0)

Seriously, please do the forum a favor and report back with how all this turns out. I learn something from every experience.

Best of luck. And I mean that sincerely.

Cheers --

 

[katwood16]

Yup, I understand your situation. Face to face I come across as a "Let's make the best of what you have to work with."
Perfection is not always possible nor the best answer for every given situation. When I understand what the owner's
real needs are, then sometimes we declare that 90/10 rules are in play. (90% of perfection while only using 10% of the
time to do it." :0) But at the same time I make it very clear that there is also a 10% chance that the project will fall short
because we are relaxing the standards we are holding ourselves to on the fix in front of us. (!)

****

But I've discovered a distortion that occurs when I'm doing this remotely, especially in public. What little reputation you
build up over time you don't want to squander by offering less than a 'guaranteed' fix strategy. And I really want to help
someone who's stuck, but at the same time *not* lead them down an expensive garden path. And this is also explains
why I don't offer up any tips on automatic transmissions, for there are SMEs in here that can offer much better advice than I.
And I have seen in other forums where heated arguments crop up because one way or the other is the only way. And then
the troubleshooting turns into a turf war. And I lose interest. :0)

****

Having said all that, I feel that your plan to show your 'local mentor' the GM TSB concerning the valve guide clearances is
a good plan. And if he reads it for comprehension and tells you to send it, then guess what? He is now it. If the engine
settles in and gives you good service, then his reputation is only strengthened from your perspective. But if the engine
is good only 90% of the time, but has issues 10% of the time, then either drive it in such a way as to avoid the issue,
or come back here and we'll kick it around a bit more. Maybe the valves aren't the issue, but the problem is elsewhere?

This is where you will hear someone in here ask for misfire counts & data streams in order to make things as right as possible.

****

From my perspective over here in the finger lakes of upstate NY, you have posed good questions, shown excellent follow-through,
and have done so with a professional demeanor. I in turn got a little more practice in remote diagnosis and got to discuss
one of my favorite troubleshooting techniques. (leakdown testing) And, I'm no longer it, your shop foreman is. :0)

Seriously, please do the forum a favor and report back with how all this turns out. I learn something from every experience.

Best of luck. And I mean that sincerely.

Cheers --

Thank you man I surely appreciate all your advice and help it has been truly informative and educational.

 

[Road Trip]

I believe this is beyond a simple lapping with that much blowby.

Just wanted to clarify what I meant by lapping the valves.

* At one extreme, all 16 valves are replaced.
* At the other extreme, only the 2 leaky valves are replaced and the rest are not disturbed.

* I was recommending replacing both failing valves. But at the same time, in an abundance of
caution check the remaining 14 valves for straightness/behavior/concentricity via hand lapping.
Valves still in perfect condition get to stay, while valves showing any wobble at all get retired/replaced.

****

So I was using the valve lapping step as a diagnostic instead of attempting to correct the known-bad valves.
(But at the same time I *do* like just how smooth an engine runs on carefully hand-lapped valves. :0)

Sure, hand lapping doesn't beat a 5-angle valve job cut on a Serdi (cost no object valve jobs)
...but for us mere mortals it's a time-honored way to give yourself the best possible valve seating
while working within a budget.

****

Looks like the OP is going in a different direction, but just in case someone is researching all this
I thought I'd try to clarify the thought process.

Cheers --

EDIT: If you are interested in the state of the art when it comes to performing valve jobs, then
you might find this a good watch: (Serdi state of the art demo)