Need help interpreting leak down sound
 

I did a leak down test on my engine, and while three of the cylinders were solid (2-5% leakage), I got three others with 15-25% leakage. The bad cylinders were 2, 4, & 5, so one on the left side of engine and two on the right side. For all three of these bad cylinders I heard kind of a pulsing, gurgling sound coming from the upper, LEFT side of the engine. Hard to make out but close to the top valve covers on the left side. No significant sound from anywhere else. What could this mean?

JW... typically one listens to the exhaust pipe (for leaking exhaust valves), intake (for leaking intake valves), and case breather (for leaking rings.) A pulse and gurgle... that sounds organic!

I don't think pulse/gurgle is significant, the point is the sound is coming from one place, which is near the top left of the engine, near top valve covers but below the intake manifold. I wasn't sure exactly where in intake valve leak would be heard.

Have you checked the head studs?

Head studs were recently replaced as part of a top end rebuild. What part of the intake would one listen to for leaking intake valves? I haven't adjusted the valves since the rebuild and thinking I might have valve leakage but don't know where the air would escape if the throttle is closed?

Intake valve can be heard through the intake, try near the air cleaner.
Exhaust valve through the exhaust, put your ear at the muffler tail pipe.
Rings through the oil fill.
Head studs usually through the alt fan.

Who did the work? You or a shop? If it was done by a shop let them figure it out, if it was you, your out of luck.

If this was just done, did you rering it and hone the cylinders or replace them?

You should re-torque the head studs and adjust the valves too, then check the leak down again.

I had a reputable shop do it and will be taking it back to them but wanted to get as much info as possible and possibly avoid a trip down there.

Every set of instructions I've read says leak down test is supposed to be on a COLD engine.

I could have sworn Wayne's 101 book said leak down should be done on a cold engine but maybe that was for the valve adjustment. I'll look again. The logic is that the clearance specs are set for cold, not hot.

You have 3 good and 3 no so good, you have a problem. Hot or cold you should have similar readings across the board.

45 years of having fun in Motorsport

since 911's don't have wings id consider that the tried & true method of leakdown with a cold motor should be the choice. I realize a hot motor should make for higher numbers due to components expanding, but those may be skewed if previous efforts were done cold.

im not an aircraft mechanic, or a Porsche mechanic, but do spend a bunch of time a local shops as I have no life.

There is a big difference between hot and cold.
I like it hot.
Next- drive it around the block and try it again.
Make sure you are at TDC or close as possible
An AC engine only ask about 1/2 HP per a cubic inch. ( Way derated )
Plus -
They are loose and wore out day one by auto standards.

I don't know where you guys are getting it should be done on a cold engine. Directions I have seen say 'warm engine' and as to Wayne, he says:
However, if the leak-down test is performed on an engine that isn’t warmed up, then the test may not give accurate results.
Tech Article by Wayne: Pelican Technical Article: Time to Rebuild? - Part II

Like Mr. Boom noted, a leak down test on a cold engine is an inaccurate way to measure cylinder pressure loss regardless of the vehicle the engine operates in. You can get a wildassed guess measurement that way, but if something doesn't seem right, then the next thing you do is repeat the test warm, so might as well do it correctly in the first place.

I may have only made it partially clear that however you set your baseline numbers, cold, warm or smoking hot that commits you to that method moving forward. if you base a healthy motor on a warm reading it should be stated as to how warm. most shops do it cold so they do not have to burn knuckles or explain where exactly the number are derived. a cold motor may not tell you what you want to hear, but it's a good, solid basis to set an even playing field, without numbers skewed by a warm, hot, or somewhere in between motor when tested.

You have this backwards. If you want skewed numbers, start with a cold engine. Then, progressively warm the engine to get less skewed numbers. The least skewed and most predictive will be those test results when the engine is at operating temp.

And you are a legend in your own mind, I want to see you do a HOT engine leak down on a 930 engine instead of your B&S lawnmower engine or a Lycoming Cessna engine with flip up cowls.

My bad, after going back to my references I realize the cold engine requirement is for valve adjustment, not the leak down test. I will go back and redo the leak down on a warm engine and see what happens.

I see this place is disintegrating to that of other forums where people are trying to trump each other rather than just explain fcts.
I suggest some of you take some time and learn decorum.
Review post from five years ago please.
The real geniuses on here are dying, dead Or at least retiring.
Please bring up the bar to where it should be.Used to be.
You can disagree, agree.But please with fact.
We do not need to carry on like 14olds olds or PARF below.
Thanx.
Now on point
A AC engine standard is loose compared to most any other vehicle engine and it has to be .
A Porsche engine is jewelry in comparison.As in a rolex.
Hell Porsche made a A/C engine .
The Nerds with papers did not understand it and it never became viable .

yes, and I said as much earlier in the thread.

it may be that a warm motor is going to give the more favorable numbers, an accurate idea of the motor's health in a single snapshot in time. what I am trying to say is that if you want a repeatable baseline number that can be referenced and compared accurately time after time the only way is to have the motor to be in the same exact state each time the test is preformed. the same motor somewhat warm will give a different numbers as the motor gets hotter, I understand this completely. what im trying to state is that if you test a motor this week with it "warm", and again next week and it's a bit "warmer" you will likely get different numbers.

a cold motor will have higher numbers, yes, but the test conditions can be repeated over the lifetime of a motor to chart it's health over a number of years. warm, hot, somewhat warm, kinda warm, kinda cool is not accurately repeatable so long term observation with even the slightest variation is not going to show how wear is occurring over time.

now, should we get into differing gauge calibration factors? like a dyno, jose's gauge may not read the same as jos-b's.

that's all, carry on.

.

I'd put my faith in an A/P mechanic's advice any day. No other mechanics on earth have more to lose if they make a mistake.

David

A couple things]
A - A&P is a remove and replace guy. They are not allowed to do work, as the parts that need machining etc have to be sent to a proper licensed station.
Most have not, and could not reface valves or replace a simple valve guide.
They are not allowed NO ROOM for adjustment / or modification other than STD or AD...and that depends on what it is.
It is pretty much nazi town.

One has to realise a A/C engine is at least 50 years , maybe a 100 years now behind the rest of the IC engine world.
Pretty archaic .
Single cam.- non over head
low RPM
magneto
low low CR ratio
big bore
Etc Etc
The are purrfect for what they do ..but caveman compared to a variable ratio cam and etc.
Go peer into a F1 platform.
It is day and night in differences.
Walk up to a A& P ask him about Volumetric efficiency , piston speed, static VS dynamic CR values,
You will get the Duhhhhhhhh, with a "which way did he go george" look and deer in headlights stare.
They are still arguing over detergent VS non-detergent oils !
They are great mechanics, and can safety wire a live kangaroo dwn , but as far as being in the pits of a race track ..you will not find them there.

Show me.
What do you know about me?( that is or is not surprising?)
I was not meaning to be offensive
Just explaining the facts .
A A&P is allowed to find TDC and that about it.
They are pretty low on the totem pole of technology .
It is not their fault. It is big govt.
They will not let them do too much.
Feel free to critique me.

my high school girlfriend's pops was a jet mechanic for TWA at the west coast hub up in so san Francisco after serving in the same capacity in the navy. he was a very cool guy with three cute daughters who's workshop seemed to have everything in place and everything in it's place. im sure id appreciate it much more today being more familiar with what tools are what by sight and how they might help in a project ive got planned.

he used to hang out in the shop hosting his girls' current or past boyfriends helping with our cars like we were the sons he never had. he had a chain hoist, a lathe, large drill press and a noisy old compressor before you could get one at sears that he'd take exceptional joy in us being startled when it kicked on. he was that kinda guy.

he'd often share his thoughts on a number of things including planes, which were his passion. I was never a model plane sort of kid but I do remember something he said more than once over the time I spent with him. he would say, "boys" cause he never remembered our names, "boys, don't aim to fix planes, aim to fly them". he said that every guy working on a plane he ever met was a guy not smart enough to fly them and were mostly angry. he on the other hand was fine with that.

im gunna call his daughter to check up on my old friend robert lee as they are all in Idaho now. I hope he is well.

t

Reno air races?
LOL
Those planes are not the planes most people work on.
They might not be planes at all! (by most definitions)
They have bonafide engineer Crew chiefs, Like the dragster folks .
AFAIK they are all Experimental and not under the conspiracy of govt regulation.
They are not regulated as far as every nut bolt and screw..

Someone and their 22000 hundred hours of classroom training and a hubris problem does not want to explain?
Ohhh where did you go?
I was just having a conversation about A&P mechanics and what they are and are not capable of...
You deleted all your post?
Why?
Like I stated -
Walk up to a A&P and ask about CC and volumes,
What size valve seat width for what application, valve size and ETC
Or
Which type piston rings?
A little thing like deck height
Perhaps squish chamber ?
You see what i mean?
A A&P is GREAT at what they do .
They do a -very very standard practice with no allowances for variation.
They are VERY concerned about FOD, picking up after themselves, the fasteners tied dwn, all paperwork and log book entries.
They are very confined as to what they can not do.
You will NEVER hear a A&P explaining port sizes and shapes.
Or piston styles , configurations, and metallurgy .
So your illustration of a A/C mechanic is more qualified here is not at all true.
A Porsche engine would completely baffle most aircraft mechanics that work on a common recip engine .
No cam timing marks? Most would loose their mind over that one.
In fact, most muscle car mechanics would be bafled.

You are a sad sad troll. You never served, nor retired, for the simple reason, you would have been fragged. I reviewed you previous posts and it became clear that I had foolishly engaged a troll. To the other posters I apologize, it was a rainy day and I thought a little discourse would be entertaining and possibly enlightening, I was wrong.
Wonder where the people 549 mentioned went? Elsewhere, which he and it's ilk hastened.

WTF are you talking about?
You deleted all your post!
Engines or the Military?
You can not support your argument so you want to pick on my military service?
This your version of LOONY Tunes?
How could you possibly ascertain anything from post here?(Military Service)
Like I said. A- A&P is a very bad rendition to compare to a high-performance modern IC engine be it Porsche or otherwise.
At present, I own 3 helicopters....I do know A&P crap from very high tech stuff.
Transparently you do not,


You truly owe me an apology for your discourse and accusations here.
I never asked YOU OR ACCUSE you about your military service.
You never asked about mine,yet you know something?
I think I know what and who a troll is.

Vietnam 162 AHC , C troop
D Troop 3/5
MOS 67N20, 67Y20
USAAVS, VSM, RVNCM, 2 O/S BARS2, 2 AM (AIR MEDALS )

that is a few things I just copied off my DD 214
Now, you want to talk engines or Military Service?

first, thank you for your service to our country.

second, it would appear CCB was ashamed of his know it all trumpeting in this thread so with moderator help had all evidence of his douchery removed. that I feel reeks more of troll than anything typed here thus far. I wonder if his post count was appropriate adjusted?:rolleyes:

Thanx
I never brought my service up..Not sure what his problems are .
Like you said he was trying to use a A&P as a trump Card.
They are great mechanics but hardly performance minded .
That was the point of the whole discussion for a sunday afternoon.
Anyway..Up aft and away! LOL
and thanx again

Does being a rotor head in country count? :)

So, bottom line, a leak down at operating temp is the only way to get viable numbers?

Hay, I did not know you are a fellow rotor head!
Congrats! ( I would like to know more)
I always wanted to make a home version of the 540......
Anyway back on que here-
I think that was the argument.
But perhaps we all presume too much
In my part of the world it is 10 above zero as of right now...LOL
I think that would be hard to duplicate in July !
I would think that at least get the engine up to operating temp or as close as possible woud give real world results
Even if it had to cool dwn some to get at it.
Rings pistons cylinders all change a bunch from cold to hot...
My opinion.

No, I was an 11B in country with the 25th, just bustin' your chops. Believe me, hearing the whop whop only a Huey makes was a sound we loved to hear on log day or exfil.

Good info on the leak down stuff and I learned about AC mechanics....it's all good.

To this day this day I dont know who had it better or worse ..In the end I think the 11B guys did!
They were tougher then a keg of nails .
We would insert, than come get what was left..not always EZ, not always pretty.
You guys lost a few , we lost a few.
At the end of the day I could usually get a hot shower..you guys were still out in the slime !
I do not believe i was tough enough for 11B
Congrats !

https://www.youtube.com/watch?v=fq0vFuIcOac

Good vid.
I got medevac'd with one of my guys (I was a shake n' bake buck Sgt.) You never forget even the littlest thing.
He was much worse off then I, he'd taken a 7.62 in the thigh and lost 4 inches of his femur. I'd been hit in the shoulder and right hand. You get that metallic taste in your mouth. You are in your own world because of the noise. Mike B was in tremendous pain and flailing and the Medic just smothered him with his body.
In triage I remember this....vividly...from the Docs/nurses while they worked me over.
"Right shoulder entry no exit..right hand thru and thru...then they kept flipping me over and back, over and back....I found out later Mike had bled on me so much they thought I'd been hit elsewhere.
Honestly, I'd not trade any of it for anything...the guys you know.
I stayed in for 33 years lol.....got to do the medevac gig again later, years later but am peachy today, all my parts work.

Way off topic here........LOL
In no way am picking on a A&P mechanic. But auto and airplane recips are just alike, only different. LOL
A lot different.
The two shall never ever trespass each other in the Certified A/C world.

Next
One, I am so happy you made it out.
For us it was a lot of inserts, bring water, lead and the like .
Bring a few soldiers back
I even had a to bring 4 of our own back . Pilots crew chiefs and door gunners .
When i say bring them back..........you know.
Some days were diamonds, some stones.
We had a lot of EZ missions too lots of what we called ash and trash .
Towards the end we were inserting arvens
.I never thought they would win the war,sorry-
They did not have the verve that the Americans had ..
They were a get it done bunch!
Now! now meant now ! ............Not in 5 min.

I deleted my stuff because I realized that it was wasted effort, between the armchair commandos and expert computer geeks, it became evident that it was devolving into a baiting contest. :rolleyes:
The stuff 549 is posting is available anywhere the interwebz reach, and as far a douchery, you and 549 are the leaders of the pack between your lack of understanding(self admitted) and his ability to bait, you guys should get a room.
I supported everything I said with supported documentation, the inability to read and comprehend the info supplied is not my problem.
549 has been baiting on these forums for a whopping 3 months with some of the most inflammatory waste posted on a website.
He posted a series of supposed units in his signature line to provide him some legitimacy, but 20 pages of posting history shows him to be a troll.
3 helicopters, puleeze, unless they are RC I am calling BS.

There is something wrong with you clickyboom
Some kind of roaring jealosy.
You may come see my helicopters anytime you like.
You know NOTHING about me except what you are making up.