Leak Down - 80% down via Exhaust Valves

[sacrileger]

I am installing 2g head on top of 1g 7bolt block. The head came off a donor motor. I dont wish to speculate re the history of this head/motor; however, I have visually inspected the head and tested the sealing of valves with the cams installed. This what it looked like after light cleaning:

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I rotated the cam for each cylinder to simulate TDC, poured water into the bowl and observed virtually no leakage into the chambers. Perhaps a teardrop or two via exhaust valves. Then I used compressed air blown at the valves via exhaust port and observed some bubbles, not really anything dramatic. Intake valves were fine. So I decided to put the head on and torque it to the block. I put the timing belt on and made sure all the timing marks (crank, pump, balance shaft and cam gear marks were dead on - level with top of the head and facing each other, dowel pins north).

Once it was bolted on, I performed a leak down test. Using stethoscope, I listened to the intake side and heard no hissing noise; however, I can hear air gushing out of the exhaust ports. My cylinder pressure drops from 100psi to 20psi in all 4 cylinders. Three cylinders are leaking via exhaust valves. I should also add that I also installed new rings into honed cylinders and those rings are not sealed yet so I did expect leakage via rings and I could hear (and feel) air escaping via dip stick hole.
Any idea what could have gone wrong? The only thing I can think of is that when I was putting the head on the block, I dinged the exhaust valves against the block and shifted their alignment. I cannot think of anything else. What am I missing here?

 

[SasaniFab]

Were the valve seals replaced? From what I gather you didnt have the deck milled or the valve seals replaced? Are you getting compression?

 

[boostdawd]

Valve seals would just cause oil to be burned not lose pressure......I think. If u saw a tear drop coming from the exhaust and bubbles why didn't u take it in for servicing? The valves are not sealing well and may even be bent.

 

[sacrileger]

Were the valve seals replaced? From what I gather you didnt have the deck milled or the valve seals replaced? Are you getting compression?

I have not done anything other than taken the head off the donor motor, cleaned the valves (they did not need much cleaning), checked for leakage and bolted the head on the 1g block. The head is not warped - I checked it with a straight edge - it's within factory spec.

 

[sacrileger]

Valve seals would just cause oil to be burned not lose pressure......I think. If u saw a tear drop coming from the exhaust and bubbles why didn't u take it in for servicing? The valves are not sealing well and may even be bent.

The teardrop was after a few hours of water sitting in the bowl and the bubbles from pressurized air were tiny, insignificant, certainly not justifying 80% drop in pressure. The compressed air is just gushing out through the exhaust valves now. There is a possibility that the valves are bent; however, there were no marks on the piston heads that would suggest any damage to the valves.....
Is there anything that can be done wrt testing the bolted on head other than unbolting the head and taking it all apart? I guess I am looking for a trick of the trade that will make my life easier.
BTW, how much force would be needed to bend valves?

 

[SasaniFab]

I'm assuming your running a composite gasket? How is the compression?

I have not done anything other than taken the head off the donor motor, cleaned the valves (they did not need much cleaning), checked for leakage and bolted the head on the 1g block. The head is not warped - I checked it with a straight edge - it's within factory spec.

 

[sacrileger]

I'm assuming your running a composite gasket? How is the compression?

I have everything disconnected, I cannot turn the engine over just yet. I would imagine the compression would be very low with 80% leak down test drop.

 

[SasaniFab]

If u can, I'd do a compression test to at least verify your test results before yanking the head off

I have everything disconnected, I cannot turn the engine over just yet. I would imagine the compression would very low with 80% leak down test drop.

 

[sacrileger]

If u can, I'd do a compression test to at least verify your test results before yanking the head off

Thanks for the suggestion; however, I suspect the compression would not be indicative of the valve issue because I honed the cylinders, put new rings in and have not run the engine yet. The rings are not set in yet. When I listen with my stethoscope, the intake valves are quiet (sealed), the exhaust valves hiss like crazy.

 

[SasaniFab]

It's strange that only the exhaust side is "leaking" is it possible the valve is not completely closed when your testing. The fact that it's a new engine is Irrelevant. When I built my engine I spun the oil pump gear prior to starting the car and once again when the car was together. When I did this I compression tested the engine. The cylinder were 100% even on all 4 cylinders. If you are certain that it's the valves, pull the head. I'm not with you so I cannot agree or disagree. It would just suck to pull the head if you don't have too. If you compression test it with leaking valves your def going to get variances from cylinder to cylinder. Like I said your there I'm not..... sounds like your pretty certain it's f***ed.

 

[SasaniFab]

Honestly man just pull the head, the minute that motor heats up your gunna have a nightmare on your hands getting that gasket back off.

 

[sacrileger]

It's strange that only the exhaust side is "leaking" is it possible the valve is not completely closed when your testing..

the history of the donor motor is checkered...big turbo, spun bearings, damaged ring lands on three cylinder heads, unknown work done on the head, etc. nevertheless, I have two theories here:
1) the exhaust valves are not completely closed for some (to me) unknown reason, i.e. the previous owner did not install the cams properly and once I timed it, the valves are out of sync.
2) I dinged the valve lobes against the block when I was putting the head on - I have no idea how much force is required to upset the valves though. Apparently they can kiss the piston at high RPM and still be ok.

Before I pull the head and start taking it everything out unnecessarily, I'd like to rule out some dumb mistake I made, i.e. the lifters are pumped up, etc. Perhaps there is some test that will reveal what the problem is. I can provide pics.

 

[SasaniFab]

the history of the donor motor is checkered...big turbo, spun bearings, damaged ring lands on three cylinder heads, unknown work done on the head, etc. nevertheless, I have two theories here:
1) the exhaust valves are not completely closed for some (to me) unknown reason, i.e. the previous owner did not install the cams properly and once I timed it, the valves are out of sync.
2) I dinged the valve lobes against the block when I was putting the head on - I have no idea how much force is required to upset the valves though. Apparently they can kiss the piston at high RPM and still be ok.

Before I pull the head and start taking it everything out unnecessarily, I'd like to rule out some dumb mistake I made, i.e. the lifters are pumped up, etc. Perhaps there is some test that will reveal what the problem is. I can provide pics.

The valve closure and opening events are controlled by the cam, when u do you leakdown you have the cylinder being tested near tdc correct? Make sure your performing the leakdown test properly.

 

[SasaniFab]

The valve closure and opening events are controlled by the cam, when u do you leakdown you have the cylinder being tested near tdc correct? Make sure your performing the leakdown test properly.

Holy hell that was a lot of problems..... who built that motor? Jesus

 

[gsxeclipse102]

If you filled the head with water and the valves didnt leak(a drop over an hr is nothing) then the head is fine. Your not gonna bend a valve by turning the motor by hand. Did you drain the lifters prior to install? If theyre pumped up solid they can cause horrible leak down tests. Honestly if you know the head is good( no leaks) timing is good then id start the engine.

 

[sacrileger]

Holy hell that was a lot of problems..... who built that motor? Jesus

I have no idea who built the motor, apparently over 500hp, I just saw the results. Just to give you an idea, here's the motor as I got it for $90:
https://tinyurl.com/jy8rgjh
and here are the three pistons and what they looked like after I pulled them out:

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But the head was in very good condition. My theory is that the previous owner did not figure out he could not get compression up because of broken ring lands and had the head done because the head was in excellent condition (virtually no carbon built up) compared to the condition of the pistons. I do not know how the spun bearings fit into this but they were spun so bad even the rods were chewed up. The rods are toast...no way new bearings could be installed into these rods.

 

[sacrileger]

The valve closure and opening events are controlled by the cam, when u do you leakdown you have the cylinder being tested near tdc correct? Make sure your performing the leakdown test properly.

Yes, absolutely, TDC dead on for every piston. I even used a dial gage to make sure the piston sits at it's TDC to make sure all four valves were closed.

 

[sacrileger]

If you filled the head with water and the valves didnt leak(a drop over an hr is nothing) then the head is fine. Your not gonna bend a valve by turning the motor by hand. Did you drain the lifters prior to install? If theyre pumped up solid they can cause horrible leak down tests. Honestly if you know the head is good( no leaks) timing is good then id start the engine.

I have done nothing to the head other than take it off donor motor (see above posts), test it and put it on my block. My concern is that I've done something to the valves while I was trying to place it on my block. I struggled. The head had the intake attached and I did have to rest the head on the block (meaning the head was sitting on the partially open exhaust valves) on the block and move it around to position it. It certainly was not a clean, one time, drop in.
I have searched this board to find anybody running into the same problem. Nada. It appears that the valves can take a lot of punishment before they bend. I wonder if I knocked the valves out of their alignment and all I have to do is take the head off and knock them back where they belong. Any idea if that is the thing to do?
I have not drained the lifters since I used the head fully assembled and I have rotated the cams at least two dozen times already.

 

[livedsm4g63]

I still dont understand why people use water when air molecules are smaller in size.

 

[sacrileger]

I still dont understand why people use water when air molecules are smaller in size.

I am not sure if your reply was meant sarcastically; however, I observed a small teardrop forming in some places and I took a note of the location. I also used compressed air to blow from the bottom and got a better idea by visual observation where other tiny leaks were located....so that's why water (or liquids in general).

 

[livedsm4g63]

Your reasoning for using water baffles me. And no, it was not meant to be sarcastic, its called science. If you want to know if they are sealing, lap the valves. If you are too lazy to do that, then take it somewhere and have it done.

 

[AdR]

Your reasoning for using water baffles me. And no, it was not meant to be sarcastic, its called science. If you want to know if they are sealing, lap the valves. If you are too lazy to do that, then take it somewhere and have it done.

Exactly, take off the head, remove the springs and lap the valves. If that doesn't fix your issue, you need to take it to get it serviced.

 

[livedsm4g63]

Exactly, take off the head, remove the springs and lap the valves. If that doesn't fix your issue, you need to take it to get it serviced.

Im sure you understand what you are talking about and just misspoke. Lapping valves will not fix anything, rather it would tell you if the valves are sealing or not. Machining would only fix this. Wanted to make sure the OP understood.

 

[AdR]

Im sure you understand what you are talking about and just misspoke. Lapping valves will not fix anything, rather it would tell you if the valves are sealing or not. Machining would only fix this. Wanted to make sure the OP understood.

Yup, that is what I meant. It should have said "If that confirms your issue, you need to take it to get it serviced." Sorry about that.

 

[sacrileger]

Your reasoning for using water baffles me. And no, it was not meant to be sarcastic, its called science. If you want to know if they are sealing, lap the valves. If you are too lazy to do that, then take it somewhere and have it done.

I am not lazy. At the same time there is no need to do something that is unnecessary and not smart. I am not building 600hp beast; just a daily driver which gives me room for a tiny degree of imperfection. When I had the head out and tested it, the tiny and minuscule leak did not warrant 80% drop in leak down..the valves are virtually open and I have no idea what happened between the test and bolting the head down or how to diagnose it. There's virtually no time involved in pulling the head off the block. But, my general question is this: do I mechanically take the head to pieces or do I find out if there's a trick of the trade to diagnose the problem and fix it - perhaps I knocked the valves out of alignment and there's a procedure to put them back where they belong w/i minutes; or perhaps the problem is with the cams once they are timed - I do not know what the previous owner did on the head. Do I have stock or custom cams? Did he not install them properly? I just do not know. I may end up with the same problem even after I lap the valves. The question here is why the exhaust valves are open now and not when they were tested.