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dues70's 1970 Pontiac Bonneville

2020 July
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Wrongway

Frustrated

Question

Posted (edited)

Hey guys, so I'm having a couple of issues. Or it may be 1 I'm really not sure. The 428 was running good but the vacuum was lower than what I thought it should be 7-8 in park and 4-5 in drive. I do have a small cam but I wouldn't think it should effect it that much. So I tried retuning the carb (edelbrock 1411 750cfm) to get more vacuum. was able to get as high as 8 in park, 5 in drive. Also I had issues with the motor holding prime. When its was running it was fine. When you shut it off you can see the fuel slowly creeping back down the fuel line and big air bubbles coming up it. Oh I put on a clear fuel line for now so I could as what was going on. No wet spots on the driveway either. So I figured that was a problem with the pump. 2 Days ago I replaced the pump, still doing the same thing. Yesterday I went out to give it another try. I use starting fluid to get the engine turning enough to pull fuel up and got it to the carb but she wouldn't run on her own. As soon as you take your foot of the pedal she dies. I forgot to mention, when she was running I had to set the RPM's between 1100- 1200 in park and in gear they would drop to 450- 550 RPM's. If I set it as say 800RPM's in park she would try to die when shifting to drive or reverse. The carb was rebuilt last year and everything on the car has been rebuilt or is new. Any thoughts?

Thank you

Edited by Wrongway
Added the RPM section

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Well, I’ve got good news & bad news. The good news is rain let up enough to do the compression check. The bad news is the rain let up enough to do the compression check. So the #5 and #6 cylinder have 0 compression. Hope you can read this, here’s what I found.

0CE8B596-F18A-4D98-BE29-05F25543925D.jpeg

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3 hours ago, Wrongway said:

Well, I’ve got good news & bad news. The good news is rain let up enough to do the compression check. The bad news is the rain let up enough to do the compression check. So the #5 and #6 cylinder have 0 compression. Hope you can read this, here’s what I found.

0CE8B596-F18A-4D98-BE29-05F25543925D.jpeg

wow !

wrongway, i think it would be worth doing a leak down test too, to find if its rings or valves causing the issue.

 the 2 pots with no compression suggests valves not sealing and possibly even cam timing too

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Yeah kiwi, just gotta find a set of gauges. My local parts house didn’t have them. 

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Posted (edited)
15 hours ago, Wrongway said:

Well, I’ve got good news & bad news. The good news is rain let up enough to do the compression check. The bad news is the rain let up enough to do the compression check. So the #5 and #6 cylinder have 0 compression. Hope you can read this, here’s what I found.

0CE8B596-F18A-4D98-BE29-05F25543925D.jpeg

Yeah, I don’t think a leak down is going to answer any questions! I also don’t think this is relative to the timing set! There may be a problem there, but that’s not causing this oddity of compression numbers! The first thing that comes to mind is the intake manifold! The odds of both heads having a gasket leak in matching position cylinders is highly doubtful. Plus the variation of cylinder pressures could be rings, but coupled with the zero pressure readings of 5 & 6!? If it were mine I would bite the bullet and pull the intake & drop the exhaust manifold! Then you can see the valves. 
When you if you pull the intake pay close attention to the intake gasket on both heads! Most likely there will be signs of leakage or poor sealing at 5 & 6 if there was gasket failure. If you find nothing there, you’re going to have to pull the heads!

If you do any or all of that let us know what you find & we’ll try to help you plan the next move.

Edited by Last Indian
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Lack of gasket seal on either intake or exhaust isn't going to cause zero compression.  Both of those spots are either before or after the valves, so as long as the valves are working and sealing properly you'll get a good compression test even with the intake manifold and exhaust manifolds completely removed and the ports open.

 

Wrongway, just to verify so please don't take offense... When you ran the compression test, you ran it with the throttle blocked wide open and all the spark plugs removed, right?  That's required to get valid numbers.  Otherwise the engine won't be able to pull enough air to fill the cylinders or spin fast enough to get a good reading.

Still though, the readings should just be low, not zero.

 I think I remember you said that you had to replace some valves because they got bent?   Were they on #5 and #6 by any chance?   I hate to say it, but considering the zero compression on those two, I bet if you pull the heads you'll find holes knocked into the tops of those pistons from when they hit the valves and bent them.

Bear

 

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Posted (edited)
42 minutes ago, BearGFR said:

Lack of gasket seal on either intake or exhaust isn't going to cause zero compression.  Both of those spots are either before or after the valves, so as long as the valves are working and sealing properly you'll get a good compression test even with the intake manifold and exhaust manifolds completely removed and the ports open.

 

Wrongway, just to verify so please don't take offense... When you ran the compression test, you ran it with the throttle blocked wide open and all the spark plugs removed, right?  That's required to get valid numbers.  Otherwise the engine won't be able to pull enough air to fill the cylinders or spin fast enough to get a good reading.

Still though, the readings should just be low, not zero.

 I think I remember you said that you had to replace some valves because they got bent?   Were they on #5 and #6 by any chance?   I hate to say it, but considering the zero compression on those two, I bet if you pull the heads you'll find holes knocked into the tops of those pistons from when they hit the valves and bent them.

Bear

 

I agree Bear, but I didn’t say the intake caused the compression issue. I said I would pull the intake and drop the exhaust manifolds so he could see the valves! 
Reason being without a borescope not many other ways the see the valves without pulling the heads. Because if it’s not valves it only leaves rings, and zero for a ring issue is not likely! And inspecting the gasket when removing it to me is just logical!

Edited by Last Indian

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27 minutes ago, Last Indian said:

I agree Bear, but I didn’t say the intake caused the compression issue. I said I would pull the intake and drop the exhaust manifolds so he could see the valves! 
Reason being without a borescope not many other ways the see the valves without pulling the heads. Because if it’s not valves it only leaves rings, and zero for a ring issue is not likely! And inspecting the gasket when removing it to me is just logical!

Sorry, Misunderstood did I

You know, I didn't even think about using a borescope, and I even have one.  Duh.  Wrongway, You might consider getting yourself one.  They are handy to have around for all kinds of things.

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16 minutes ago, BearGFR said:

Sorry, Misunderstood did I

You know, I didn't even think about using a borescope, and I even have one.  Duh.  Wrongway, You might consider getting yourself one.  They are handy to have around for all kinds of things.

Can you get a loaner borescope from the likes of AutoZone or O'Reillys? Just thinking out load.

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18 minutes ago, BearGFR said:

Sorry, Misunderstood did I

You know, I didn't even think about using a borescope, and I even have one.  Duh.  Wrongway, You might consider getting yourself one.  They are handy to have around for all kinds of things.

No sorry needed! I’m not the best writer in the world! Sometimes what’s in my head doesn’t always come out right in writing! So I easily may not have said it well enough!

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Posted (edited)

1st, "Wrongway, just to verify so please don't take offense... When you ran the compression test, you ran it with the throttle blocked wide open and all the spark plugs removed, right?  That's required to get valid numbers.  Otherwise the engine won't be able to pull enough air to fill the cylinders or spin fast enough to get a good reading." 

I take no offence at all bro. I forget, miss and do things wrong lol. Speaking of which, no Bear, I pulled a plug, ran test, replaced plug and moved to the next cylinder. I was not aware that all plugs needed to be removed. I figured they needed plugs in to build up pressure. Guess I need to redo it, sorry guys.

Yeah Bear you remember correctly. I broke 7 out of 8 exhaust valves. Snapped in 2 pieces. That was when I had ran the rockers down to 20lb. I was using OEM push rods, I ripped the tops off of 2. I replaced them with a new set of comp push rods. Reassembled and on 1st start up snapped 7 valves. That was when a comp tech supervisor told me they misinformed me about running them to 20lb and instead needed valve lash. I had the heads off, timing and pulled the cam to check it. Concerned it could have damaged it. I did not see any cam damage. The only damage other then the broken valve's was a small divet in the top of one of the pistons. I honestly don't remember which cylinder. It looked like the stem came down and stabbed it. Its about the diameter of a pencil eraser or a bit smaller. Maybe an 1/8" deep. It did not go threw the piston. I didn't think it would be enough to hurt anything. All off the other pistons still looked good. Replaced all 8 exhaust valves with stainless reassembled again. Started, drove it, no vacuum and y'all started helping me figure out why. 

So before I tear anything apart do another compression check with plugs removed?

Oh, and yes I did use new gaskets each time I reassembled the engine and I used Indian head shellack on the head gaskets and exhaust manifold gaskets.

thumbnail[1] (3).jpg

Edited by Wrongway
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Ok, new compression test. Plugs all removed. Wide open throttle. 

F321CBC9-D648-4117-9C87-3878F09A8A0D.jpeg

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7 hours ago, Wrongway said:

Ok, new compression test. Plugs all removed. Wide open throttle. 

F321CBC9-D648-4117-9C87-3878F09A8A0D.jpeg

Well done Wrong way. a good test:cheers: you have 2 pots with dodgee valves mate

2 hours ago, BearGFR said:

Well sir, that cylinder pressure is escaping to somewhere and that's a fact.  I assume that after you had the mishap with the exhaust valves that you had the heads redone including having all the guides checked, and the seats reground, so if that's the case  then it's not likely the leak happening at the valves.  You mentioned a divot in at least one of the pistons.  Maybe it weakened the metal there enough, made it thin enough, so that it wasn't able to hold up to combustion pressures.

Do you have an air compressor?  If so, maybe get a hose fitting you can connect to a spark plug hole and try to pressurize those cylinders.  You probably won't be able to - and you'll hear the air hissing out from somewhere.   Where you hear it leaking from will tell you where the leak is.  If it's loudest at the carb, it's an intake valve. etc.   If it's loudest at the dipstick tube, that means it's getting past the piston.

 

i am with bear here, compressed air will tell you where all that compression is going.( leak down test)

i had this same issue with my  96 dodge ram, i found a broken valve spring was causing the issue.

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have a really good look at the valve springs on those two pots Wrong way... you may find the issue :cheers:

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Posted (edited)

Two Lane, I honestly don't know what to suspect anymore bro. At this point I'm more following instructions from y"all that are helping me and hoping we can figure this out. 

No guys, since the motor only turned over 1/2 way and they broke I didn't have the heads rebuilt. They were completely rebuilt when I put the engine together the 1st time and only had maybe 50 miles on them. I thought I could just replace the broken valves and she'd be good.

I'll try to find a fitting that'll fit the plug hole also

Edited by Wrongway

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Fitting is ordered to air up cylinders, be here Friday. Do I still need to get a set of gauges for a leak down test? Or will airing up cylinders take care of that?

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13 minutes ago, Wrongway said:

Fitting is ordered to air up cylinders, be here Friday. Do I still need to get a set of gauges for a leak down test? Or will airing up cylinders take care of that?

Depends on what the fitting is or looks like! If the fitting is conducive to putting a gage on it and you use a female air chuck on the fill side that would surffice.

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24 minutes ago, Wrongway said:

Fitting is ordered to air up cylinders, be here Friday. Do I still need to get a set of gauges for a leak down test? Or will airing up cylinders take care of that?

I would just ensure you have a good air tight hose and connection to each of those cylinders in question mate and ensure that both the valves are completely shut  ( take covers off and check for broken springs turn motor over till you see both valves are shut) 

 And listen😜 you will either hear air coming back up the carb or out the tail pipe or both!

 i dont think you have a piston ring issue or you would still have had a better compression reading, Last indian is bang on, its valves not sealing or my gut feeling is broken spring maybe :cheers:

either way, the air wont lie:o haha

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I didn't see any kind of cracks or anything that looked out of sorts. Is it to late to disassemble and take pics or grind or lap valves or? Is that something I can do here in my shop? I know this probably isn't the "proper" fitting but its all I could find with the tread size I found. I figured I could connect pieces to do whatever y'll tell me to with it, hose, gauge, chuck, whatever. 

When I reran the valve's the other day as Bear advised I didn't see any broken springs but ill check again kiwi.

thumbnail[1] (4).jpg

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Posted (edited)

Wrongway..

You can use an old spark plug and knock the ceramic center and the metal electrode out of it with a hammer and a punch and grind or cut the electrode off the bottom and weld a Male fitting to the remaining outer part of the plug...That fits your chuck on the air hose and use it for pressurizing the cylinder..

Did the original valves have a three or four degree angle valve grind on them..?? What about the valve seats..??

It's not too late to disassemble the heads and grind And/or lap the valves in as there is only a very narrow area (only a few thousanths wide) that actually contacts the seat the other two or three angles are ground to facilitate efficient velocity and airflow..The thing is the expense of New Head and related gaskets...I would not reuse head gaskets once they have been torqued whether they have been run or not..

You should be able to determine the original valve angles by using the broken valve faces (hopefully you still have the broken parts) as a guide using a protractor to find the angles... If you duplicate the original angles they should match up with the valve seats...  You can have a machine shop grind the valves only (cheaply)...To your specs..Then lap them in  and reassemble the heads Yourself...You can also closely inspect the guides and the springs/locks/retainers while everything is apart...

But before you do all that do your air test first and then decide where to go from there... 

Edited by TWO LANE BLACK TOP
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Wrongway..

You can use an old spark plug and knock the ceramic center out of it with a hammer and a punch and grind or cut the electrode off and weld a Male fitting to the remaining outer part of the plug...That fits your chuck on the air hose and use it for pressurizing the cylinder..

Did the original valves have a three or four degree angle valve grind on them..?? What about the valve seats..??

It's not too late 

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