How to perform a leak down test. In this video I revisit the cylinder leak down test. Just to give us all confidence (including myself) in the direction we a…
How to perform a leak down test. In this video I revisit the cylinder leak down test. Just to give us all confidence (including myself) in the direction we a…
You must be logged in to post a comment.
 Leak down test revisited')){kind=link}
I’ve seen leakdown testing done with different incoming pressures (usually
lower). Is there an optimum intake pressure for the most accurate test?
Presumably doing it with lower pressures might be a little safer….
That leakdown tester is wack… on the one that I use, I can connect the
hose to the cylinder and then add air to whatever level I want without the
worry of sudden crank rotation. Keeping the tranny in gear also helps
prevent crank rotation… obviously doesn’t work with automatics. Would
love to see a cranking map waveform with one of the spark plugs removed (as
someone else already mentioned in one of the prior videos).
Always great content Scanner Danner appreciate the time and energy you put
out. If you guys want to save money and learn how to build a leak down
tester watch my “MAKING A CYLINDER LEAK DOWN TESTER AND CHECKING ENGINE
INTEGRITY, PISTON RINGS, VALVE & SEAT SEALING” its simple.
In this video I revisit the cylinder leak down test. Just to give us all
confidence (including myself) in the direction we are going with this
misfire case study. I also covered some key points missed the first time
around, thanks to your comments and suggestions.
Just for giggles when you pull the head fill the runners with water and see
how bad they leak. Thanks for the vid.
what percentage of leak down will be aceptable, I know comparing cylinder
and highest will be the bad, but wear off even engine ??
what was the fix ? with this one
More good stuff that TDC trick works on boxer style engines also. I’m a old
vw guy. Porsche and Subaru
Good stuff as always man. I was actually surprised at how much controversy
there was about a leak down test during this series lol. Back when I was a
second year apprentice at trade school (here in BC, Canada, second year is
focused on engines, rebuilding, diag, maintenance etc etc) we were taught
to always do a leak down test at TDC for more accurate results and safety,
but to do it at BDC after just as a secondary test to reveal any issues
with a head gasket that might have been missed due to the piston covering
the sealing surface at TDC. I always thought this was a pretty “textbook”
test lol 🙂 For better or worse, we learn new stuff everyday thanks to the
internet :)
Hi Paul, well I think what ever kind of engine it is the con rod and crank
will all be in line at TDC, just one comment, when you do this with a
Manual Transmission car you can put it in top gear with parking brake on to
stop engine moving, I guess a lower reading at tdc prob means the bore is
worn a bit at the top, I don’t think valve overlap would come into it for
quite a lot of crank travel, with the old distributor cars you can see what
cylinder you are on by checking where the rotor arm is pointing
roughly..cheers good video, I think you would only need to put oil down the
bore if you were getting pressure out the oil cap – Fred in England
Scanner and Students:
I hope we get to see the dis-assembly and repair of this Hummer engine.
I wonder what a smoke machine test would reveal….
Good stuff- I do like the use of the MAP wave form and look forward to pico
pressure transducer wave form, since the two are so much different it would
be interesting if we could view the WPS500 wave form and be able to
interpret the MAP wave form consistently.
Man you’ve got bigger balls than I do, hanging onto that wrench is asking
for a broken wrist or something. TDC works for V type engines as well, all
you have to do is get the connecting rod/piston within the “dwell” period
at TDC and you’re good. Imagine you did but man I hope you made it clear
to your students not to hold onto that wrench (or have it on the crank at
all) when you apply the air pressure to the cylinder.
Part 4? I understand it’s a great learning experience for your students
but compared to all of your past videos it seems like you’re going
overboard on your leak down results. Yeah it’s the company vehicle and you
want to ensure you’re diagnosis is correct but you were correct in the
first video. You’re on TDC, timing is good and mechanically sound (no
broken cam), you have air in the intake, that’s it, done. Time for a valve
job.
You are a good teacher…keep it coming master..
how long does your class last as in weeks?
Glad you liked my tip! That works on all motors, and the more centered you
are on piston dwell at TDC, the safer you are against the crank suddenly
rotating on you. I try to estimate the middle of dwell, and that IPA TDC
finder helps me to a bit.
Bore wear is usually greater near TDC, so measuring at the top can be
important. Head gaskets are above the piston, so there is no concern about
blocking the air pressure from escaping out the head gasket at TDC.
The ideal air pressure is 100 psi, because it makes the math easy. The left
gage reads how much air pressure goes into the bore. The right gage
measures the pressure remaining in the cylinder. So that right gage is only
dead accurate if the left gage reads 100%. Otherwise it’s reading a
percentage of a percentage!
The OTC leak down tester has two gages that both read psi, and it includes
a chart that converts the leak down % when using lower air pressures. That
snap on gage is nuts if it thinks a 40% leakage rate is anywhere near
acceptable. 15% would definitely indicate a problem!! At 40%, you have
major blowby or valve sealing issues.
You might also want to start the test at 0 psi on the regulator, and slowly
increase the air pressure to 100. Much safer and less likely to rotate the
engine suddenly. Otherwise, you had better be at true TDC in the middle of
piston dwell. Engine should be warm as well, so rings seal correctly and
cylinder bore is oiled up. FYI, piston dwells for probably 6 to 8 degrees
at TDC… but the rod is still swinging side to side except when it’s right
near the middle of piston dwell. Visualize the piston, rod and crank as the
rod rotates from one side of the bore to the other.
Would it be true to say that running the compression test at TDC and then
lower in the bore at different points be a good indication of bore taper
wear ?
Never ever put air in with the damn wrench on. Especially don’t hold it.
Good way to brake your dang arm. Low pressure applyed slow saved u.
Just curious as to how much shop air pressure you actually need to make the
test accurate? Would be a lot easier to control the crank with 40 psi than
120 psi for example.
Here is instruction on a harbor fright compression leak down tester:
“NOTE: Set the air compressor’s regulator
to 7 to 100 PSI. Never operate this
tester with air pressure set higher than
100 PSI, which can damage this tool.”
Not sure if 7 psi is enough to even move the crank.
Latex or rubber glove over intake.
Pretty ballsy touching that wrench on the crank with compressed air in the
cylinder.
GMC TSB# PIP4013C: In-line Truck Engine Misfire at Idle.
Important: Before replacing the cylinder head, review the latest version of
PIP3940, I forgot to mention this is a recall. you must change the entire
cylinder head, what is bad are valve spring. the new head got this fix.
I need to review d leak-down procedure. Haven’t done it in awhile. Look
like a good tool u got there
I’d like to see a secondary ignition wave form and look for hash on the
spark line which would indicate valve sealing issues. Would this be
possible?
THANX
I usually have the leak down tester set at around 25psi input and around
the same on the reg so when I turn the crank to find TDC when the hold down
gauge begins to rise it’s coming to the top.
The lower pressure makes it easier to turn the crank,TDC is easy to
judge,if it’s not then it spins the crank.
Then dial up 100 psi on the input,
Saves all the screwdriver down the plug hole process.
Dan you one crazy sob.
I like to turn into tdc by hand and hold it while noting force… Built in
torque wrench on arm.. bionic mechanic man…
Why didn’t any of the valves open at BDC because of valve lead or lag,
depending which way the engine rotated? I don’t know cam spec for that
engine but I assume the exhaust valve would have opened before BDC. Did you
not allow the piston to go all the way down to BDC with the wrench? Great
videos by the way.
11:15
I dont think a V type engine would be any different. As long as the
connecting rod is perpendicular within the cylinder to the crankshaft it
should stay.
Great videos, in my experience doing leak out tests I have found that
normal engines that have average wear are always about 10 to 20%….. 25%
is a borderline time to overhaul, and 30% is need to repair now and usually
a misfire or poor driveability issue has brought the car in for diagnosis.
Good information. Are you going to show any video with the cylinder head
removed? Just curious
a timing chain, guides and tensioner can give you that problem with poor
sealing valves, timing correlation, misfire, lean condition are also
symptom related to a loose timing chain. great videos, keep it up.
I need to review d leak-down procedure. Haven’t done it in awhile. Look
like a good tool u got there