help with leak down testing

[1Gina2G]

okay so I've read this a few times

http://www.dsmtuners.com/forums/articles-engine-fuel/338152-compression-leak-down-testing.html

this part of the article I don't understand, so it may or may not be causing me to miss something during the testing.

Note: In our engines, cylinders one and four and two and three are at TDC at the same time, but you need to be sure the one you are testing is on the compression stroke; in other words... make sure all the valves are closed for the cylinder being tested.

so far, it looks like 2 of my cylinders are leaking out the exhaust valves, when I belive the piston to be at TDC for each. have not fully checked to see if anything was also coming out of the intake side or not but I moved the TB with nothing coming out of the elbow...also nothing out of the dipstick or oil feed.

1 of the clyinders that were leaking out of the exhaust manifold was also leaking through an adjacent cylinder hole. so if the testing was done right I think this indicates a blown headgasket and exhaust valves..

I also put the trans in 5th with the ebrake up hard to hold the timing once in place..i stopped turning the crank as soon as I saw the screwdriver stop moving up, and for 1 @ 4 I just parked the crank at the TDC line on the cover, which is why I was wondering about cylinder 4s relation to #1.

thanks all..

 

[black97spyder]

#4 and #1 will be in the exact same place at the same time. So if #1 was at TDC then so is #4. Same with #3 & #2 they are in the same position at the same time.

A leak down test will show a blown headgasket through bubbles in the radiator. That Is def not the case.

I'm Almost 100% certain It's your valve seals. BogusSVO is the guy to ask about ANY engine questions such as What symptoms would mean.

Take your exhaust mani off like I stated before and look through each port and at each valve stem where it goes into the head. It should be a yellowish-white color (indicates proper combustion) and if there are any that are black or oil then that is where your problem is.

You can do the same to your intake as well but just requires more stuff to be taken apart to look at the valves

 

[1Gina2G]

okay well I belive I have multiple major problems here...all of which if confirmed will make it to where I have to give up on this new build....

cylinder #1- air leaking through oil feed cap hole and dipstick
#2- air coming through number 4 cylinder & TB elbow, just more air out the TB if you opened up the TB
#3- air through the oil feed and dipstick
#4- all air through exhaust manifold

so it doesn't look like I have anything holding up in this new build....I'm almost positive that the pistons were at TDC, and I locked up the ebrake with the trans engaged in 5th so nothing would move..

is there any chance in hell that things are leaking because the engines cold? I think im screwed honestly

 

[bryanwheat]

#4 and #1 will be in the exact same place at the same time. So if #1 was at TDC then so is #4. Same with #3 & #2 they are in the same position at the same time.

A leak down test will show a blown headgasket through bubbles in the radiator. That Is def not the case.

I'm Almost 100% certain It's your valve seals. BogusSVO is the guy to ask about ANY engine questions such as What symptoms would mean.

Take your exhaust mani off like I stated before and look through each port and at each valve stem where it goes into the head. It should be a yellowish-white color (indicates proper combustion) and if there are any that are black or oil then that is where your problem is.

You can do the same to your intake as well but just requires more stuff to be taken apart to look at the valves

If the valves are sealing than the valve seal will never see any pressure during a leakdown test. If air is leaking into the intake or exhaust manifolds than it is coming thru the valves. The valve seals the combustion chamber. My advise it to turn the engine over to the next stroke to see if it is still leaking out the valves. You will have to turn the engine over a bit to do each cylinder.

 

[1Gina2G]

What do you mean by the next stroke? As long as the piston is at tdc shouldnt both valves be closed? If there's anything i can double check before i take the engine out ill look into it.

 

[black97spyder]

What do you mean by the next stroke? As long as the piston is at tdc shouldnt both valves be closed? If there's anything i can double check before i take the engine out ill look into it.

No only one of the two pistons that are on TDC at the same time will have the valves closed.

By next stroke he means rotating it 180* so that the piston is in the same spot as It was, only performing a different stroke (letting air In or exhaust out).

Also if you warm the car up some It will give you better sealing results on the leak down test.

 

[luv2rallye]

All 4 cycle engines (no matter how many cylinders) have 4 strokes on each cylinder which repeats: intake, compression, power, exhaust. However each cylinder is on a different stroke from the others. At TDC the piston that is between the compression and power stroke will have all valves closed (which is the one you do the leak down test on). The other piston at TDC at this time is between the exhaust and intake stroke and both valves will be slightly open due to valve overlap (exhaust is almost closed while intake just started opening).

 

[1Gina2G]

All 4 cycle engines (no matter how many cylinders) have 4 strokes on each cylinder which repeats: intake, compression, power, exhaust. However each cylinder is on a different stroke from the others. At TDC the piston that is between the compression and power stroke will have all valves closed (which is the one you do the leak down test on). The other piston at TDC at this time is between the exhaust and intake stroke and both valves will be slightly open due to valve overlap (exhaust is almost closed while intake just started opening).

thanks a lot for the explanation. this may very well have caused me to have bad results..may I ask how one would go about getting each cylinder to the right spot?

so each pistion should be at TDC of the compression stroke...how do you tell?

 

[boost97gst]

#1 cylinder at TDC mark should be on its compression stroke i.e. all valves closed

 

[1Gina2G]

#1 cylinder at TDC mark should be on its compression stroke i.e. all valves closed

what I don't understand is how number 4 is not also in a compression stroke while number 1 is at TDC at compression. how can it be a different stroke? I know I'm missing something here so I'd like to know.

so with the number 1 at TDC of compression (all timing marks lined up right?) the number 4 will also be at TDC but not on the compression stroke? but rotating the crank 180* clockwise will bring number 4 to tdc of compression?

just trying to figure this out. thanks everyone

okay so doing a little research I see that the piston pushes air up while going up and you can use the spark plug hose tool to make it easy to feel assuming the cams are timed in place, and that with number 1 at tdc of compression #4 will be at tdc of exhaust. so I will be going out to do a retest right now, hopefully atleast my valves are good. apparently I can also take the VC off to get to something to make sure all the valves stay shut.

So what I'm really stressing about is my headgasket and piston rings. I used an oem composite gasket by itself without any special spray, maybe I should've used the copper on it afterall.

 

[boost97gst]

Think about it: If both 4 and 1 were on compression strokes and ran esactly the same (and 2/3 did the same thing but like 180* out) you would basically have a "parallel 2" it would sound like an older parallel twin motorcycle. It would mean 2 cylinders igniting at the same time, then 180* later(?) the other 2 igniting at the same time. Would seriously imbalance things and produce way less hp.

here: This explains it better than i can. [ame=http://www.youtube.com/watch?v=M1h9eU9YH5o]4 STROKE ENGINE ANIMATION Pt. 2 - YouTube[/ame]

 

[BogusSVO]

When cyl #1 is on compression, cyl#4 will be on the exhaust stroke.

Cyl 1,

Compression= Both sets of valves closed, piston moves up to compress air/ fuel

Power= Both sets valves closed, spark plug fires igniting air/fuel mix, pushing piston down

Exhaust = Exhaust valves open, Int valves closed, piston moves up pushing spent air/fuel charge into the exhaust system

Intake= Intake valves open, exhaust valves close, piston move down filling the cylinder with air/fuel mix.


Repeat...

At any given time, any cylinder will be on one of the 4 strokes, no two cylinders will be on the same stoke.

Cross over from one stroke to the next will happen at either TDC or BDC

compression to power happens at TDC

Power to exhaust happens at BDC

Exhaust to intake at TDC

Intake to compression at BDC


The simplest way to run a leak down test, for a person just leaning will be with the valve cover off.

When on the true compression stroke, the fat circle of the cam, called the heel, will be on the follower, closest to the valve spring.

If the valve is fully open, the point of the cam lobe, called the toe, will be on the follower, the valve spring will be compressed.

The follower is the bridge under the cam, that one end is on the valve tip, the other end is on the HLA.

 

[1Gina2G]

okay so this time my results are slightly different this time but still looking really bad for the piston rings.

#1- leaks out oil cap & dipstick
#2- leaks out oil cap & dipstick
#3- leaks out oil cap & dipstick
#4- leaks out exhaust manifold only


this time no air came from one cylinder to another but number 4 still has air coming from the manifold. on a hunch I decided to turn the psi all the way down on the tester to where I could barely hear / feel air from the manifold and proceeded to turn the timing after taking off the ebrake. was hoping to hear the air seal off at some small point but it never did, just got worse and then back to how it was. does this mean my #4 exhaust valves are definitely bad?

is there any chance my rings can still be getting broken in at this point or are they ruined? I currently have the turbo and I/C completely off so there's a lot of stuff that has to go back on for me to start the engine up.

 

[BogusSVO]

Yes, you have a chance of the rings still taking a seat, a small one, but a chance.

Before you claim bent exhaust valves in #4, remove the followers, retest, and see if they seal.

You may just have to bleed down the HLAs for those valves.

Before you junk the rings, get the engine fired up, and check for blue smoke out the tail pipe.

 

[1Gina2G]

okay can someone tell me if my gauge is working correctly? I can tell the inlet pressure / adjustable pressure valve on the tester works, but I think the cylinder leakage gauge may be off / wrong

this is what it looks like with no air pressure / before you put any pressure to the tester:

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it basically starts off a little under 20 as it shows, then once air pressure starts going in the needle goes all the way to the right, getting stopped by the needle stopper, which to me looks like the wrong way.

would I be wrong in seeing what happens if I move the needle passed the stopper? or is it just a bad gauge? thanks

also proceeding to take the valve cover right now...I'll post a pic so I can ask specifically what I need to check out for the exhaust valves.
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okay so I got the valve cover off, and took some close pics of the head on the exhaust side of #4 I belive. so does the entire cam have to get unbolted for the valve check? I really have not done this before and could use some tips...unless its really not recommended. I'll try the best I can.

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