LEAKDOWN TEST ? - air leaking out cam sensor hole

[PaulRV6]

I have the engine out and decided to check the leakdown (I know it should be done warm) but why am I feeling air leaking out the cam sensor hole (cam sensor is also removed)? If I shouldn't then what would cause this?
Would this have anything to do with having oil on top of the intake manifold floor?
This has got me wondering.

paul

 

[TurboTR]

Well the air is probably getting past the headgasket or even the rings and into the crankcase. If it's alot you may have a blown hg, worn or broken rings or piston, etc.

TurboTR

 

[Chuck Leeper]

Air ??

Could be several possibilities.
1. The rings are gone, allowing test air into the crankcase.
2. Broken or burned piston " " ' " ' "
3. Head gasket blown into the lifter valley.
Broken or worn out rings, broken/burned piston will cause high crankcase pressure, which in turn will blow oil above the rings and thru a PCV valve..
A faulty PCV could also cause the oil in the intake, as could bad turbo seals.
The leakdown test air coming thru the cam sensor hole may have no connection to the oil in the intake.

When you did the leak test, what were the results??

HTH,

 

[equalizer442]

put alittle oil in each piston and then do a leak down test again, if its the rings the oil will seal them and stop the leaking but if it keeps leaking air you should pull the heads and take a peak at the head gasket.

if its the head gasket its not going to be that big of a deal but if the oil stops the leaking and its the rings then the engine is due for a rebuild.

 

[PaulRV6]

Well this engine was just rebuilt with no more than 200 miles (easy ones at that). I pulled it to find an oil leak (intake gasket and add an oil pump spacer plate).
The results were 12% (best) and 18% (worst) and I could feel the air out the cam sensor hole on all cyl. Keep in mind this is on a cold engine.

Chuck, it is not oil in the intake, it is oil laying on the top of the manifold base (where the pcv grommet goes into).

Could this just be because things are not warmed up to temp and therefore not sealing? I will try the oil and see if it improves. Any other suggestions? Thanks for the replies.

paul

 

[salvageV6]

Could it get past a valve?

 

[PaulRV6]

That's a good question, how do I check?

paul

 

[Chuck Leeper]

LEAKZ??

IMO, 12 to 18% on a new engine is too high. This is most likely why U R seeing the air coming out of the cam sensor hole.. too much of the test air is getting into the crankcase..
Given the engine has 200 miles, it may be the rings are not seated yet and the % may go down w/ some more use.[I doubt it].
IE: we run engines on the dyno for about an hour at part load to break things in.. After a check, it's BALLS to the WALL!! No thousand mile breakins needed...
Another trick is to rap the valve w/ a plastic hammer while the test air is on.. the valve will snap shut, possibly improving the seal. It'll sound like a rifle shot when you do it...
If you are doing the intake, redo the test w/ it off and that will tell you how well the intake valves are sealing.. Same w/ exh valves.
What was the end gap set on the rings??

Oil externally on the intake is most likely being blown past the seal at the PVC.. Does the PVC fit tite? Is the seal new? Is the intake on w/ a gasket that has a pan under the intake??

Perhaps you need to talk to the engine guy..

 

[Tony sy2356]

What pistons are in the motor?

In my sy motor I run trw's, very similar to the buick design. When I leak the motor down cold i've seen as high as 24% leakage into the crankcase. When the engine is even a little bit warm the leakage goes down to 6%. I've duplicated this several times.

The TRW's have a large piston to wall clearance causing that issue. Perhaps you have a similar issue.


HTH

Tony

 

[PaulRV6]

Chuck, the end gap was set at .021 on both top and middle rings and by the way I am the engine guy (for all the assembly).

The intake manifold gasket is the Fel-Pro stock type. The PCV valve and grommet are new so they are a tight fit.

Tony, the pistons are .030 over stock GM. That is encouraging about the difference from cold to a warmed engine! The piston to wall clearance ranges from .0024 to .0033 between the cyl.

I hope that it is just a matter of either the rings are not seated or because the engine is cold and things are not expaned as when the engine is warmed up.

Thanks for the help.
paul

 

[salvageV6]

I agree with tapping safely on the valves although I am not an expert on leakdown testing.

 

[Bobtempest]

I use a long oak dowel to tap on the valves. Works.

 

[Lee Thompson]

leakdown test

IMO, the #s for your COLD leakdown test are about right.
I have leaked an eng. warm---0-2 percent leakage
Leak the same eng. cold and get --8-12 percent.
When you think about it---why do you have a gap on your ring ends????
Also I have made a few leakdown testers. There is a .060 hole in between the 2 gages. 10 percent of a .060 hole is not much.

 

[Bobtempest]

I have seen a real cold engine with forged Ross pistons and don't forget that ring gap. Also not being at TDC, it read 40% down in a leakdown. It also may have been some rust or carbon on the valves. Engine was fine.

Run it hard and test it warm as possible for a leakdown test. Take the rockers off and have someone hold it at TDC on each test.