Leak down test...... Question

[Amelio]

My car has been running great...... I have been having issues with traction lol!

I have also noticed the car huffing a Lil more than usual. It very well could be valve guide seals but they are fairly new.

I freshened the engine up about 3 years ago new seals gaskets, rings and bearing (due to blown head gasket)

Any way it looks like I have cyl2 burning some oil as it shows more so on the plugs than any other cylinder.

I wanted to do a leak down test to make sure the rings are ok. I plan to run the car in a few weeks. I don't mind if the car smokes a little and as I said it runs really good so I can't see it being a ring but I wanna make sure.

With all thy being said I have a differential gauge my uncle uses for the airplane engines he works on. Those engines have a 6" bore and I believe the valving in the gauge may be bigger than something I would buy for a car.

I have never done a leak down test...... But I was wondering if the valving was different would it cause an issue with the reading?

In other words.... If the gauge is made for a 6" bore would the volume of air be too much for a 4" bore?

Also do I test the cylinder TDC or BDC or does it not matter as long as both valves are shut ?

Thanks


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[TexasT]

I wouldn't think the gauge size would matter(they measure pressure). The accuracy of the gauge would be what I would be concerned with. I always run the cylinder to tdc as that is where the "bang" occurs or near there anyway. That is where both valves are closed. You might need to keep the engine from turning. A good compressor with some volume so you don't have to wait. I have a little hot dog speedaire since my 33 gallon craftsman quit. I fill it with the hot dog to get volume. I usually run a dry test then add a squirt of oil for a wet test. Record them in my note book with a date and a temp. Helps to see what is happening over time.

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[earlbrown]

The bore doesn't matter. The leak down test reads in percentages so it's all relative. As far as the actual testing you have to be either at TDC or BDC as the compressed air will blow the cylinder down if you're not at TDC dwell.


If you have a nick/scratch/gouge on the middle of the cylinder wall, the leakdown test won't show it unless the rings are straddling the compromised spot.

 

[cruzn57]

leak down will only test compression rings, it will NOT tell you if the oil rings are doing their job,
if dry and wet tests are the same, it means you have oil already in the cyl, (usually from the oil scraper rings)

 

[Amelio]

So I should be able to test at BDC and TDC and if my readings are the same then most likely my rings are good correct?

Now that is not to say I have an oil ring that is not doing its job..........

I will let the car sit a week or so to ensure that the cylinder is not real wet.......I have a feeling its most likely the valve stem seals since most of the smoke I see is just after startup.........

Again I don't mind a little smoke.......most fast cars do smoke LOL and I don't think I have a broken or leaking ring....the car runs too strong....but I am not ruling it out just yet.

Thanks for the replys

 

[earlbrown]

If ti's startup smoke only, odds are it's not your ring seal. If it was rings or cylinder wall problems, it would smoke at startup and get worse at the temp comes up.

If you had a broken ring, you'd know it without having to run a leakdown test

 

[Amelio]

Thanks Earl.......

that's why I think its just valve seals......it does go away after start up.......sometimes I see a slight puff when laying into it but it is really difficult to tell and its very light.

 

[earlbrown]

Or worn exhaust guides. If you're heads have never been worked, you don't have any seals on the exhausts. All it takes is one little drop to run down the valve stem overnight.

 

[Buick Mark]

If you don't have seals on the exhaust guides, I'd look there

 

[Amelio]

My heads have been worked by Champion and I do have the nylon comp seals on both intake and exhaust side.

However it has been 12 years or so since the heads were worked......I did put a new set of seals on a few years ago when I had the engine apart for a refresh after the head gasket let go.

However it could be the valve guides themselves ....I did not think about that...................

 

[getdowngranny]

My heads have been worked by Champion and I do have the nylon comp seals on both intake and exhaust side.

However it has been 12 years or so since the heads were worked......I did put a new set of seals on a few years ago when I had the engine apart for a refresh after the head gasket let go.

However it could be the valve guides themselves ....I did not think about that...................

I've been chasing a plug that has been fouling for a while and it turned out to be a valve seal that popped off. You might want to remove the valve cover and take a look.


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[Amelio]

Fortunately I don't have a plug fouling issue. It's just a little oil getting in...... The plugs look pretty good across the board except #2 it's pretty clean on the tip and ground strap but it has some build up at the base.

I just had the covers off a few months ago replacing the gaskets. Everything looked good but that's not to say one has jumped off since then.

I am wanting to replace the stock covers anyway I am sick and tires of the leaky breather on the driver side.

I will check the seals when I swap out my covers for new ones.


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[Buick Mark]

Fortunately I don't have a plug fouling issue. It's just a little oil getting in...... The plugs look pretty good across the board except #2 it's pretty clean on the tip and ground strap but it has some build up at the base.

I just had the covers off a few months ago replacing the gaskets. Everything looked good but that's not to say one has jumped off since then.

I am wanting to replace the stock covers anyway I am sick and tires of the leaky breather on the driver side.

I will check the seals when I swap out my covers for new ones.


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If no plugs show signs of oil fouling, Im betting its an exhaust guide seal, the oil weeps past the guide and into the exhaust stream and burns, it (the oil) never makes it into the combustion chamber.