Post Valve Job Cylinder Head failing Leak Down test

jokem59 · Aug 21, 2020

Hi Everyone,

I wanted to get your opinion on my recent experience. I sent in some heads off a EJ205 subaru engine (DOHC) to get a valve job done and supplied new OEM valves. After the job was complete, I installed the heads on the the short block which is still on the engine stand and ran a leak down test. My target pressure was 70 PSI but I had no expectation of reaching that pressure as with a good seal, the pressure should start pushing the piston down from TDC and I would have to hold the crankshaft stationary.

I was disappointed to discover that 3 of the 4 cylinders exhibited 60% leakage while one cylinder held pressure to the point where I could no longer hold the crankshaft stationary. I brought the heads back to the machine shop to have them take a look and their claim was that everything looked good. I was told that after I run the engine, everything would seal back up and I would have no issues.

I'm a little hesitant to do this because it's a lot of work to put the engine in and pull it out if there are issues. Also, the fact that one cylinder passed the leakdown test while the other failed is reason for my skepticism.

What are your opinions on this? Just install them and run them? Or if the leak now, they'll leak after they're run?

Thanks!

dalmatiangirl61 · Aug 21, 2020

What was done to lower end? Are you sure it is not leaking past the rings? With heads removed either do a vacuum test on each valve, or pour some solvent into each runner and see if they leak. If they leak, I would take them back, or to another shop. If you find the valves are sealing, you have a ring sealing problem.

What all was done to heads? Are they grinding seats or cutting with carbide? Did they lap the valves/seats?

Edit: Do those heads use shims to set valve lash? If so you may need to check that they are shimmed correctly.

john.k · Aug 21, 2020

Exackerly....test the seats with petrol ,if they leak ,then ease the cam bolts a turn or so.....and again see if they seal........Ive been doing truck engines for many years ,and if the seats look good after machining ,and the blue smudge looks ok ,I dont bother testing ,just put it all together............Gotta remember some ally heads distort some when tightened down ,and may take a few miles for valves to wear in properly,and seal ...........I reckon if I cant hear hissing when the engine is turned over with a bar ,then all is OK .......New rings often take a while to seal ,too.

1953chevB · Aug 21, 2020

Was the work done on the piston? rings ?
was the head verified for flatness, was the head gasket sealed?
sometimes the valves when ground are not seating air tight, the valve faces need to be lapped to each other remove the high spots and seat properly.
my old man taught me this. extra work by it works,
during the leak down test where was the air leaking from EG EXHAUST or intake ports? the crank case, or the head gasket.
edit so if the air is leaking from the exhaust its the exhaust valves, air from the intake is the intake valves.
air in the crank case means the rings are worn or stuck and need cleaning. remove carbon.
can you disassemble the valve train? and mark the valve interface with bluing or a black or red marker
turn the valves and look to verify if there is full contact. could have been a shotty valve grind.

1953chevB · Aug 21, 2020

v

also is the fly wheel and starter installed, can you run a pressure test?
record the pressure for each cylinder , and compare to the book requirements.

markz528 · Aug 21, 2020

I was taught to put the valves in without the springs and then pour some kerosene in the chamber. Proper seal would not leak the kerosene - valve weight alone should seal it. I would do the same test with the heads assembled and see if any kerosene leaks by. If it does its no good.

Street · Aug 21, 2020

If you pull the heads and do the petrol test down the port...thats a basic mechanic test, check if it leaks between the valve and seat.

However if your a machinist you pull the valve and blue the valve, do the contact test, blue the seat do the contact test this checks concentricity of valve to seat and seat to valve.. if it is a nice contact seat and you can see it with the blue all is good...this is the ultimate test.
don't use too much bearing blue only a small amount.

Modern seat machines cut the seats and testing is done with a vacuum gauge to check the seat if it passes this it is generally reasonable.
If you want it spot on just grind the seat and blue test it so it lines up perfectly if gets it that little bit better. More labour involved to do this.

As any liquid is thicker than air if it leaks with a liquid it is a bad seat so needs to be fixed.

Leakdown does not identify which area is at fault, you need to eliminate a few things before you can pin it down to bad bore ring seal or bad seats so will need to pull the heads.
Ideally you need to check items before you assemble them when you do things in the future, cheers.

jokem59 · Aug 21, 2020

dalmatiangirl61 said:
What was done to lower end? Are you sure it is not leaking past the rings? With heads removed either do a vacuum test on each valve, or pour some solvent into each runner and see if they leak. If they leak, I would take them back, or to another shop. If you find the valves are sealing, you have a ring sealing problem.

What all was done to heads? Are they grinding seats or cutting with carbide? Did they lap the valves/seats?

Edit: Do those heads use shims to set valve lash? If so you may need to check that they are shimmed correctly.

Nothing was done to the lower end. Reason I pulled heads out and replaced all the valves is because one of the exhaust valves was burnt out. Prior to pulling the heads off, I ran a leak down test as well. And the cylinders WITHOUT the burnt valves all passed the leakdown test. This was done while the engine was still in the car.

Pressure leak is happening from intake/exhaust ports. Checking the PCV and oil fill tube and I don't feel any pressure escaping there.

The machinist did the solvent test and said things look good. Can you pass the solvent test and fail the leakdown test (before running the engine)?

john.k said:
Exackerly....test the seats with petrol ,if they leak ,then ease the cam bolts a turn or so.....and again see if they seal........Ive been doing truck engines for many years ,and if the seats look good after machining ,and the blue smudge looks ok ,I dont bother testing ,just put it all together............Gotta remember some ally heads distort some when tightened down ,and may take a few miles for valves to wear in properly,and seal ...........I reckon if I cant hear hissing when the engine is turned over with a bar ,then all is OK .......New rings often take a while to seal ,too.

Thanks for the feedback. Piston rings are already worn in. It sounds like you're in the camp of, if it passes the solvent test, then you're good to go!

1953chevb said:
Was the work done on the piston? rings ?
was the head verified for flatness, was the head gasket sealed?
sometimes the valves when ground are not seating air tight, the valve faces need to be lapped to each other remove the high spots and seat properly.
my old man taught me this. extra work by it works,
during the leak down test where was the air leaking from EG EXHAUST or intake ports? the crank case, or the head gasket.
edit so if the air is leaking from the exhaust its the exhaust valves, air from the intake is the intake valves.
air in the crank case means the rings are worn or stuck and need cleaning. remove carbon.
can you disassemble the valve train? and mark the valve interface with bluing or a black or red marker
turn the valves and look to verify if there is full contact. could have been a shotty valve grind.

also is the fly wheel and starter installed, can you run a pressure test?
record the pressure for each cylinder , and compare to the book requirements.

Head has been verified for flatness and head gasket was sealed - followed the FSM procedure.

Machinist lapped all the valves and showed me that even/thick grey banding on both the valves and the valve seats.

The leakdown test shows that the leak is coming from a mix of the intake/exhaust ports depending on the cylinder.

I can disassemble the heads and do some testing with Prussian Blue to get a warm and fuzzy, but the grey banding from the machinist's lap job looks thick and even.

Flywheel and starter are not installed. Engine is sitting on the engine stand at the moment.

jokem59 · Aug 21, 2020

Reposting reply - previous attempt didn't seem to take.

dalmatiangirl61 said:
What was done to lower end? Are you sure it is not leaking past the rings? With heads removed either do a vacuum test on each valve, or pour some solvent into each runner and see if they leak. If they leak, I would take them back, or to another shop. If you find the valves are sealing, you have a ring sealing problem.

What all was done to heads? Are they grinding seats or cutting with carbide? Did they lap the valves/seats?

Edit: Do those heads use shims to set valve lash? If so you may need to check that they are shimmed correctly.

Nothing was done to the lower end. Reason I pulled heads out and replaced all the valves is because one of the exhaust valves was burnt out. Prior to pulling the heads off, I ran a leak down test as well. And the cylinders WITHOUT the burnt valves all passed the leakdown test. This was done while the engine was still in the car.

Pressure leak is happening from intake/exhaust ports. Checking the PCV and oil fill tube and I don't feel any pressure escaping there.

The machinist did the solvent test and said things look good. Can you pass the solvent test and fail the leakdown test (before running the engine)?

john.k said:
Exackerly....test the seats with petrol ,if they leak ,then ease the cam bolts a turn or so.....and again see if they seal........Ive been doing truck engines for many years ,and if the seats look good after machining ,and the blue smudge looks ok ,I dont bother testing ,just put it all together............Gotta remember some ally heads distort some when tightened down ,and may take a few miles for valves to wear in properly,and seal ...........I reckon if I cant hear hissing when the engine is turned over with a bar ,then all is OK .......New rings often take a while to seal ,too.

Thanks for the feedback. Piston rings are already worn in. It sounds like you're in the camp of, if it passes the solvent test, then you're good to go!

1953chevb said:
Was the work done on the piston? rings ?
was the head verified for flatness, was the head gasket sealed?
sometimes the valves when ground are not seating air tight, the valve faces need to be lapped to each other remove the high spots and seat properly.
my old man taught me this. extra work by it works,
during the leak down test where was the air leaking from EG EXHAUST or intake ports? the crank case, or the head gasket.
edit so if the air is leaking from the exhaust its the exhaust valves, air from the intake is the intake valves.
air in the crank case means the rings are worn or stuck and need cleaning. remove carbon.
can you disassemble the valve train? and mark the valve interface with bluing or a black or red marker
turn the valves and look to verify if there is full contact. could have been a shotty valve grind.

also is the fly wheel and starter installed, can you run a pressure test?
record the pressure for each cylinder , and compare to the book requirements.

Head has been verified for flatness and head gasket was sealed - followed the FSM procedure.

Machinist lapped all the valves and showed me that even/thick grey banding on both the valves and the valve seats.

The leakdown test shows that the leak is coming from a mix of the intake/exhaust ports depending on the cylinder.

I can disassemble the heads and do some testing with Prussian Blue to get a warm and fuzzy, but the grey banding from the machinist's lap job looks thick and even.

Flywheel and starter are not installed. Engine is sitting on the engine stand at the moment.

dalmatiangirl61 · Aug 21, 2020

1953chevB said:
also is the fly wheel and starter installed, can you run a pressure test?
record the pressure for each cylinder , and compare to the book requirements.

Friend does lots of Subies, iirc the starter mounts thru the trans. He needs to mount flywheel and figure a way to lock it against case, friend uses a properly placed prybar, I think someone makes a bolt on tool too.

1953chevB · Aug 21, 2020

jokem59 said:
Reposting reply - previous attempt didn't seem to take.

Nothing was done to the lower end. Reason I pulled heads out and replaced all the valves is because one of the exhaust valves was burnt out. Prior to pulling the heads off, I ran a leak down test as well. And the cylinders WITHOUT the burnt valves all passed the leakdown test. This was done while the engine was still in the car.

Pressure leak is happening from intake/exhaust ports. Checking the PCV and oil fill tube and I don't feel any pressure escaping there.

The machinist did the solvent test and said things look good. Can you pass the solvent test and fail the leakdown test (before running the engine)?

Thanks for the feedback. Piston rings are already worn in. It sounds like you're in the camp of, if it passes the solvent test, then you're good to go!

Head has been verified for flatness and head gasket was sealed - followed the FSM procedure.

Machinist lapped all the valves and showed me that even/thick grey banding on both the valves and the valve seats.

The leakdown test shows that the leak is coming from a mix of the intake/exhaust ports depending on the cylinder.

I can disassemble the heads and do some testing with Prussian Blue to get a warm and fuzzy, but the grey banding from the machinist's lap job looks thick and even.

Flywheel and starter are not installed. Engine is sitting on the engine stand at the moment.

the lapping compound is thicker and could indeed show full banding.
the bluing will be thinner and will be a more positive test,

edit he lapped them I am really surprised it leaked.

jokem59 · Aug 21, 2020

Street said:
If you pull the heads and do the petrol test down the port...thats a basic mechanic test, check if it leaks between the valve and seat.

However if your a machinist you pull the valve and blue the valve, do the contact test, blue the seat do the contact test this checks concentricity of valve to seat and seat to valve.. if it is a nice contact seat and you can see it with the blue all is good...this is the ultimate test.
don't use too much bearing blue only a small amount.

Modern seat machines cut the seats and testing is done with a vacuum gauge to check the seat if it passes this it is generally reasonable.
If you want it spot on just grind the seat and blue test it so it lines up perfectly if gets it that little bit better. More labour involved to do this.

As any liquid is thicker than air if it leaks with a liquid it is a bad seat so needs to be fixed.

Leakdown does not identify which area is at fault, you need to eliminate a few things before you can pin it down to bad bore ring seal or bad seats so will need to pull the heads.
Ideally you need to check items before you assemble them when you do things in the future, cheers.

Thanks for the tips. I might go ahead and pick up some Prussian Blue and run that test for my warm and fuzzy. It sounds like as long as this test passes, then I don't have to worry about a leakdown test.

I did a before leakdown test as well and all cylinder that didn't have the burnt valve returned good numbers (~5% loss). I didn't do any work to the piston rings and don't note any air leaking from PCV or oil fill tube. Air is definitely leaking from the intake/exhaust ports as well.

Street · Aug 21, 2020

1953chevB said:
the lapping compound is thicker and could indeed show full banding.
the bluing will be thinner and will be a more positive test,

edit he lapped them I am really surprised it leaked.

You are correct it may show full banding...however blue test it best.

anyhow modern seats are really hard so material is hard to remove by lapping and your just wasting your time when grinding can be done if you want it perfect.
Cutting seats is cost effective so most do it that way thats why its done this way.

jokem59 · Aug 21, 2020

dalmatiangirl61 said:
Friend does lots of Subies, iirc the starter mounts thru the trans. He needs to mount flywheel and figure a way to lock it against case, friend uses a properly placed prybar, I think someone makes a bolt on tool too.

What I've been doing is holding the crankshaft stationary with a wrench. "Good" results is if I can no longer hold the crankshaft stationary. "Bad" results is when there's leaking and insufficient pressure to push the piston down.

jokem59 · Aug 21, 2020

Thanks for all the replies!

I guess the question I'm trying to get answered is: Can a good valve job result in a bad leakdown test BEFORE the engine is run? Does running the engine help the final seating of the valve/valve seat assuming everything was cut and lapped correctly?

I'm just hesitant to install the engine with 3 out of 4 cylinders leaking from the intake/exhaust ports.

1953chevB · Aug 21, 2020

Street said:
You are correct it may show full banding...however blue test it best.

anyhow modern seats are really hard so material is hard to remove by lapping and your just wasting your time when grinding can be done if you want it perfect.
Cutting seats is cost effective so most do it that way thats why its done this way.

Hi Street

correct I do a combination of grind and then lap, grind a nice smooth finish then give them a lap, but I do it with a power drill
there is an old school wood shank with a suction cup at the end, and place over the valve head, and spin it. takes patience.

1953chevB · Aug 21, 2020

jokem59 said:
Thanks for all the replies!

I guess the question I'm trying to get answered is: Can a good valve job result in a bad leakdown test BEFORE the engine is run? Does running the engine help the final seating of the valve/valve seat assuming everything was cut and lapped correctly?

I'm just hesitant to install the engine with 3 out of 4 cylinders leaking from the intake/exhaust ports.

I believe it will get worse
and here is my rational, the reason valves get toast is from high temperature, as the valve starts to distort it starts to leak, now the extreme heat effects
the valve seats and it's toast.

1953chevB · Aug 21, 2020

I wondering if the valve guides were replaced. edit improperly installed valve guides causing the valves not to seat correctly, every body right or wrong.
if that is the case running would wear and would self seat, but that would be a different issue,

Bobw · Aug 21, 2020

1953chevB said:
Hi Street

correct I do a combination of grind and then lap, grind a nice smooth finish then give them a lap, but I do it with a power drill
there is an old school wood shank with a suction cup at the end, and place over the valve head, and spin it. takes patience.

Those stupid suction cup tools are just crap. Has anybody every successfully used one in the history of mankind. They suck.

Grab the shank in a cordless and pull. Done.

Thanks for the tips. I might go ahead and pick up some Prussian Blue

Smurf hand.

Street · Aug 21, 2020

I have a set of those suction cup tools new and handy if required, they are no good to lap seats only use if required for the blue test.
Most of the time you can do it by hand so they not needed. I bought the set i have on clearance you don't want to pay too much for them.

Valves can be torched if the seat is no good, ie a groove is cut in the valve face or seat- just like using a oxy acet torch on it.. best to get it right before you run it.

Yes valve guides need to be good, they should have been checked...too loose and your wasting your time with all the other steps.

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