Air heard escaping through both manifolds when pressure applied to cylinder - need help/advice

[VT_4G63]

I am finishing up my build and getting ready to degree my cams in the engine from my 96 Spyder GST. I am in the process of swapping in checking springs to do so. My engine is on a stand with no cams or timing belt installed.

However, when I apply air pressure to the cylinders through the spark plug hole to keep the valves from falling, I can hear air escaping through both the intake manifold through the open throttle body port and through the exhaust manifold through the open O2 outlet.

If left long enough, all the air pressure will completely leak down, so I will never be able to swap out the springs as is.

Obviously it would seem the valves are not sealing. Air can be heard escaping through both manifolds on all four cylinders.

Prior to this, I had the engine completely apart to do a refresh. I replaced all gaskets, seals, timing, etc.

I lapped the valves when the head was off and I’m concerned I overlapped them. However, while lapping them I tested their sealing with a vacuum tester I made all throughout doing it to make sure I did it enough but didn’t go too far. All 16 valves on all four cylinders could be left with vacuum applied for a long period of time with very little leak down if any. So they were definitely sealing when the head was off.

Does anyone have any suggestions for why air can be heard escaping through both manifolds on all four cylinders and why they all won’t hold air pressure?

I would say I overlapped the valves and they aren’t sealing now, except they held vacuum really well when the head was off the block. Also it seems strange it’s on ALL valves on ALL four cylinders.

Could it be anything else I’m missing? What should I try/test next? I’m worried this head is done for and all my work up to this point is ruined.

 

[VT_4G63]

Here is a video of what I’m talking about

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[chrysler kid]

the next basic step is to remove the intake and exhaust manifolds and verify the valves are actually closed.

If you just want to send it and hope for the best, I typically use nylon rope fed into the plug hole, then rotate the crank to top dead center with a foot or two of nylon rope in the cylinder to cushion the valves with the piston at top dead center. You can do the valve stem seals without air, but you should verify this problem before that

 

[pauleyman]

I am finishing up my build and getting ready to degree my cams in the engine from my 96 Spyder GST. I am in the process of swapping in checking springs to do so. My engine is on a stand with no cams or timing belt installed.

However, when I apply air pressure to the cylinders through the spark plug hole to keep the valves from falling, I can hear air escaping through both the intake manifold through the open throttle body port and through the exhaust manifold through the open O2 outlet.

If left long enough, all the air pressure will completely leak down, so I will never be able to swap out the springs as is.

Obviously it would seem the valves are not sealing. Air can be heard escaping through both manifolds on all four cylinders.

Prior to this, I had the engine completely apart to do a refresh. I replaced all gaskets, seals, timing, etc.

I lapped the valves when the head was off and I’m concerned I overlapped them. However, while lapping them I tested their sealing with a vacuum tester I made all throughout doing it to make sure I did it enough but didn’t go too far. All 16 valves on all four cylinders could be left with vacuum applied for a long period of time with very little leak down if any. So they were definitely sealing when the head was off.

Does anyone have any suggestions for why air can be heard escaping through both manifolds on all four cylinders and why they all won’t hold air pressure?

I would say I overlapped the valves and they aren’t sealing now, except they held vacuum really well when the head was off the block. Also it seems strange it’s on ALL valves on ALL four cylinders.

Could it be anything else I’m missing? What should I try/test next? I’m worried this head is done for and all my work up to this point is ruined.

Did you bleed down the lifters?

 

[VT_4G63]

Did you bleed down the lifters?

The cams, lifters, and rockers are all out. Timing belt is off, as well.

The spring pressure should theoretically be holding the valves shut. I fear they’re overlapped and not sealing correctly.

Is there anything else it could be that I’m not thinking of?

 

[pauleyman]

The cams, lifters, and rockers are all out. Timing belt is off, as well.

The spring pressure should theoretically be holding the valves shut. I fear they’re overlapped and not sealing correctly.

Is there anything else it could be that I’m not thinking of?

I missed that. I assume you cleaned it all up, assembled etc.? Did you do any liquid testing? Fill the chamber or ports?

 

[VT_4G63]

I missed that. I assume you cleaned it all up, assembled etc.? Did you do any liquid testing? Fill the chamber or ports?

I cleaned everything up and assembled it very thoroughly and by the book. I always take my time.

I didn’t do any liquid testing, but I confirmed the valves held vacuum using a vacuum tester I made. I was able to build up vacuum on the intake/exhaust ports with the valves and springs installed and leave it sitting for an extended period of time with little to no leak down. If the valves weren’t capable of sealing then they wouldn’t have been able to hold that vacuum. This was with the head off the block.

This is what has me stumped. If the valves didn’t pass that vacuum test prior to mounting the head on the block I would say the issue is definitely my lap job and the valves aren’t sealing. I just can’t figure out how they could hold vacuum prior, but now aren’t sealing enough to hold air in the cylinder.

 

[VT_4G63]

the next basic step is to remove the intake and exhaust manifolds and verify the valves are actually closed.

If you just want to send it and hope for the best, I typically use nylon rope fed into the plug hole, then rotate the crank to top dead center with a foot or two of nylon rope in the cylinder to cushion the valves with the piston at top dead center. You can do the valve stem seals without air, but you should verify this problem before that

Removing the manifolds was going to be my next step tonight I think. I want to get eyes on the valves and see what is going on.

I thought of doing the rope trick to be able to proceed with installing the checking springs so I can degree the cams, and finish up this build without having to be able to hold air pressure in the cylinder. However, I really want to figure this out and get it squared away before I send it.

 

[99dsmer4g63]

Do you know if the head has been decked at all?

-Daniel

 

[diambo4life]

Better shot of the valves/springs from the topside? What valvesprings are in the head?

 

[VT_4G63]

Do you know if the head has been decked at all?

-Daniel

As far as I can tell the head has never been decked.

When I tore the engine down I saw no evidence of it having been worked on internally since the factory, original head-bolts, etc.

The bullseyes looked untouched.

 

[VT_4G63]

Better shot of the valves/springs from the topside? What valvesprings are in the head?

The valve springs are Brian Crower. The cheaper set with the steel retainers.

OEM keepers (reused)

GSC Viton valve seals

Stock valves (lapped by me)

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[VT_4G63]

Got the intake manifold off. This is a video through the open manifold port of air escaping past the valves….

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[DSMPT]

If left long enough, all the air pressure will completely leak down, so I will never be able to swap out the springs as is.

Even you remove the cams, the cylinders won't hold the pressure forever unless you keep applying the air while doing. A little and slow air leak is normal especially when you run a cold test. Most of the air actually leak down to the crank case. If you are worried about dropping the valves, you can also do it with the rope method.

I lapped the valves when the head was off and I’m concerned I overlapped them. However, while lapping them I tested their sealing with a vacuum tester I made all throughout doing it to make sure I did it enough but didn’t go too far. All 16 valves on all four cylinders could be left with vacuum applied for a long period of time with very little leak down if any. So they were definitely sealing when the head was off.

I don't know how much you lapped but as you mentioned that it passed a vacuum test after you lapped, then I wouldn't be worried too much. It may be have a better valve seating after running the engine and getting a couple of heat circles.

 

[VT_4G63]

Even you remove the cams, the cylinders won't hold the pressure forever unless you keep applying the air while doing. A little and slow air leak is normal especially when you run a cold test. Most of the air actually leak down to the crank case. If you are worried about dropping the valves, you can also do it with the rope method.

I don't know how much you lapped but as you mentioned that it passed a vacuum test after you lapped, then I wouldn't be worried too much. It may be have a better valve seating after running the engine and getting a couple of heat circles.

That’s a bit more reassuring, thank you.

What do you think of this video showing the air bubbling past the valves? This seems pretty bad, but maybe I’m wrong:

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[97egl]

It's hard to tell how much air is escaping from a video but you are probably ok if they passed a vacuum test before bolting it on. It's a metal to metal seal which just doesn't ever seal perfectly.

To answer why it passed the vacuum test but now is leaking more. The head and block deck are never perfectly flat unless you had them both machined. When you torque the head down the gasket takes up some of this imperfection, but the head also is going to bend to conform to the block. When it does the valve stem to valve seat geometry is going to change slightly.

 

[Anfurnyy]

I had / have a similar issue with mine except I had a 3 angle valve job done and it leaked pretty badly when bolted to the block. I took it back to the machine shop and they showed me in person the vacuum test and a fluid test ( fill the combustion chamber with water and shoot air into the port) and no bubbles and it pulled good vacuum.

As soon as I bolted it back to the block leaked air right passed the valves, mostly on the exhaust side. I gave up and said eff it and ran it. Seems to be doing fine but haven't checked it again since.

I think it might be from torquing the head down enough to make the valves not seal perfectly, IMO, but I'm also using L19s at 110lb/ft.

 

[chrysler kid]

It might also be better to have an external air pressure regulator to verify the valves are seeing a steady 100psi and can hold that psi for a while.

 

[1990TSIAWDTALON]

If the job was done right and you lapped them, a few hundred smacks from the valve to the seat (during startup) will eliminate the leaks. I smack my valve tops with a deadblow hammer a few times to seat the keepers and let the valves slap the seats. Normally tho, mine seal without springs on them at all. JS