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Testing Valve Stem Seals

MBS206

By MBS206,
in Engines & Forced Induction

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MBS206 Grand Master

MBS206

Posted
Posted

Hey guys,

I'm probably going to be pulling my head off again within the next few months, and would like to know, how do you test the valve stem seals properly when the head is off.

I read a post where Trent was saying that when they change them, they have to pressure test them (which you can't do when you leave the head on and do them with the special tool) so I'd like to know, how you do test them?

I want to pull the head to put an oil restrictor in, and also to change the valve springs (I know I can do it with head on, but I want to put the restrictor in too)

at the same time, I'd like to pressure test the valve stem seals in case they're shot...

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https://www.sau.com.au/forums/topic/305260-testing-valve-stem-seals/
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Warpspeed Experienced

Warpspeed

Posted
Posted
at the same time, I'd like to pressure test the valve stem seals in case they're shot...

If you are not blowing exhaust smoke, your seals are fine.

Leaky inlet valve seals will suck oil under high manifold vacuum, mainly idle and backing off at high rpm.

Crook exhaust valve seals usually show up as smoke when you first start the engine up cold. Oil drains down the stems.

While the engine s running, especially under boost, there is usually enough exhaust back pressure to blow oil up OUT of the valve stems.

Unless you are seeing smoke, there is no problem to worry about.

MBS206 Grand Master

MBS206

Posted
  • Author
Posted
If you are not blowing exhaust smoke, your seals are fine.

Leaky inlet valve seals will suck oil under high manifold vacuum, mainly idle and backing off at high rpm.

Crook exhaust valve seals usually show up as smoke when you first start the engine up cold. Oil drains down the stems.

While the engine s running, especially under boost, there is usually enough exhaust back pressure to blow oil up OUT of the valve stems.

Unless you are seeing smoke, there is no problem to worry about.

I'm seeing LOTS of smoke...

At the moment the turbo is, and it all appears fine... That's the problem...

I'm seeing a SHITLOAD of smoke once I boost up for 2 - 3 seconds, and a shitload if I pump it back to 3rd gear at around 130 - 140KM/H with closed throttle.

SECURITY Grand Master

SECURITY

Posted
Posted

these are the things you do while youve got the head off just to save yourself a headache later;

- service the head.. get it cleaned, get the valve guides checked and the valve stem seals replaced.

- machine all surfaces (head + exhaust side at least as well as the exhaust manifold - get the inlet manifold done if you wish, not as important though).

- get your valves checked for any bends

- clean/check lifters (submerge them in diesel/mineral oil the entire time theyre out)

- replace both front cam seals (same part number as the crank seal).

do these things as a minimum to save yourself a headache later on. well worth the time+money.

MBS206 Grand Master

MBS206

Posted
  • Author
Posted
cold start the engine, hold rev at 2000RPM. If steam seals are gone you will notice some blue smoke. once the car warms up the smoke goes away.

Can't rev the engine whilst cold.

It's not perfectly tuned yet for cold starts etc, it will only idle.

The head is coming off, I've heard there is a proper way to pressure test them. I want to know how so I can. Heads being pulled no matter what soon, not because of the Valve Stem Seals.

  • 4 weeks later...
ascenion24 Enthusiast

ascenion24

Posted
Posted

First you have to make sure your valves are sealing properly (all valves leak to some degree straight out of the factory)

Then you have to block of your inlet and do a leak down style test, if you know your valve only leaks 1%, but your getting a reading of say 5% then the other 4% must be going through the only other leak path, your valve stems.

But of course all this means nothing unless you have the factory specs to compare too.

I guess different work shops could have different ways of testing this, best to just ring around and see what they say.

MBS you said "I'm seeing a SHITLOAD of smoke once I boost up for 2 - 3 seconds, and a shitload if I pump it back to 3rd gear at around 130 - 140KM/H with closed throttle."

Is this constantly or only at start up? if its a dodgy valve stem seal after start up all the smoke is burnt away because it can only burn off the oil that could seep through while the car was off, unless you have a massive leak path here but thats rare.

It sounds more like a turbo seal possibly?

Also the smoke, is it whitish smoke? or a darker bluish colour?

MBS206 Grand Master

MBS206

Posted
  • Author
Posted
First you have to make sure your valves are sealing properly (all valves leak to some degree straight out of the factory)

Then you have to block of your inlet and do a leak down style test, if you know your valve only leaks 1%, but your getting a reading of say 5% then the other 4% must be going through the only other leak path, your valve stems.

But of course all this means nothing unless you have the factory specs to compare too.

I guess different work shops could have different ways of testing this, best to just ring around and see what they say.

MBS you said "I'm seeing a SHITLOAD of smoke once I boost up for 2 - 3 seconds, and a shitload if I pump it back to 3rd gear at around 130 - 140KM/H with closed throttle."

Is this constantly or only at start up? if its a dodgy valve stem seal after start up all the smoke is burnt away because it can only burn off the oil that could seep through while the car was off, unless you have a massive leak path here but thats rare.

It sounds more like a turbo seal possibly?

Also the smoke, is it whitish smoke? or a darker bluish colour?

It's a very whitish smoke.

And no, nothing at all at startup or idling around. Only when I'm giving the motor a bit of a work out after a few seconds.

Then it pumps a whole heap of smoke, take it easy on it, let it clear up, give it another hit and it goes again.

I had the turbo apart the other day, but I have no idea what I'm looking for with spotting a dodgy seal (When I saw apart, I mean I have the VBand un done and the rear housing off)

MBS206 Grand Master

MBS206

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Are you running a restrictor on the turbo oil feed?
Bush bearing, so I was told not too... But I'm going to grab an oil pressure regulator (as have been discussed in another thread where someone runs an actual pressure regulator) and fit that to see if it stops.

My problem is, I'm at the point for a new bottom end to go in now... So I have to decide how I want to attack it to set the car up for track work... High Comp N/A that revs its guts out, or buy a whole nwe turbo/mani setup and stick with the bottom ends how I have been...

PCV is hooked up and working properly.

MBS206 Grand Master

MBS206

Posted
  • Author
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Coolant doesn't move. I've been told by numerous people it's oil. When it does any one standing around smells burning oil.

It's blue but not super blue like when a magna/excel takes off with stuffed rings.

  • 3 years later...
B-rice Mentor

B-rice

Posted
Posted

reopening closed thread. i did a cold compression test my results were within 120 -128 or so across the board. Seems like the rings are fine. I also have smoke on deceleration or when i give it gas it puffs for a bit. MBS did you find the cause to the problem. Willling to try and change them without removing the head aswell for the added costs of machining it and getting new gasket.

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