leak down test
 

what are good numbers and what numbers would it be time to rebuild ?

IMO even across all cyl is more important

You can also listen to where the air is leaking from to determine exhast intake or ring leaks to narrow it down.

I would also do it with the engine at operating temp

a cylinder with 20% leakage needs attention,its true that it may seem to be running fine,but power is being lost,and it will not get better,ie,it wont fix itself.

so if boat is winterized in building that is only 40 should i wait till spring

no,even a cold reading can give you a heads up if you have a serious problem,if you wait until spring,and then find a problem,you will be working on the boat,instead of enjoying it.

1 cyl,,,,or alll 8 ?

I see anywere between 8-15%,w/ not much residue in the puke tank on my blower motor.

Gapless will give ya false reading,but like above if one is out of line,start looking.

all 8 willl be tested

fixx
 

time for some total seal rings,,i see 2 to 4 % on the engines i have done..

Copied this from a blown alky site.

"The only thing I use leakdown for is a comparison to the rest of the cylinders. Not a condition of the motor itself. If you have 20% leakage, I would say that's good, as long as the rest of them are comparable. Gapless rings create their own set of issues. Besides, you don't race with the engine not running. And I guarantee, the rings will seal better with cylinder pressure. Gapless rings have a tendancy of trapping blowby between the top and second ring. When this happens, it unseats the top ring (bad) and you lose ring seal and power. But the leakdown number look great, who cares."


"Forgot something. One time I was told to try something, so I did. I did a compression test with our standard ringset, hellfire dykes top, cast 2nd and 3 piece oil ring. All the plugs out, throttle wide open, gauge read about 200PSI after the 4th pump. Pulled no. 1 piston out, changed the 2nd ring to a gapless ring and put it back together. No other changes, everything was the same. After the 4th pump on the gauge, 145PSI. After advancing the cam a total of 6 degrees, I finally reached 160PSI. I know what your thinking, yes, the ring was put together the right way, it wasn't upside down. Went back to the cast 2nd ring and ran the compression test again. It escapes me now what the gauge read with the cam advanced, but after putting the cam back to where it was, it read 200PSI again. After that, I threw all the gapless rings we had in the shop into the trash."

iim not suprised the compression reading was down,he claimed he put a new,unseated ring in a cylinder that has who knows how much run time it has,of course the already seated ring will show better numbers.it is a proven fact that total seal 0 gap top ring seals way better than a standard ring,but to each there own.

Looks like he actually was talking about running a gapless second ring. So kind of moot of me even posting it.

While a gapless ring will give very good leakdown numbers, and if I saw 15% leakdown using gapless, then Id be alarmed. 15% on a convential ring with a few hundred hours, Id think that's normal.

As we know theres more to how the ring actually seals when running then when doing a leakdown test. Just because one engine leaks down at 3% with gapless, and the other at 13% using convential rings, I'd be owing someone some cash if that identical engine made 10% more HP on a dyno. Heck, why would anyone, even the automakers run anything other than gapless when in the quest for MPG, power, and meeting EPA regulations. The cost isn't that drastic between them.

Ive seen several buddies running gapless rings. And after several miles of wot running, still have a little bit of oil mist from the breathers, just like the conventional rings.

I think we need to call robby. Id be in for some total seals if I can pick up 80HP. :bunnydance:

i think it was patrick swazey in road house when he said OPINIONS vary,interesting reading..

joe,as far as the big 3 not useing gapless top rings,i think from a cost standpoint,at app 125 bucks a car,and millions of cars produced,well,you do the math,with the materials and coatings on todays rings,a production engine just does not need them,imo.i put them in my 588s in the fountain,and in joes engines,i think it is money well spent in a supercharged,or high compression engine.dont get me wrong,im not saying conventional rings are bad,just not as good as the gapless top ring sets.

maybe eddie young will chime in,id love to get his take on this.

Im not disagreeing with ya. :party-smiley-004:My response was more towards strippoker's. He mentioned his leakdown numbers, and how little blowby he had, and he had conventional rings with whipples, which served him well. He mentioned how the leakdown results using gapless rings can be misleading.

I think what he was getting at, is gapless will always show better leakdown numbers. But, doesn't necessarily mean the cylinder is sealing 10% better when running than a non gapless setup. Leakdown % is simply a measure of what air is lost when doing a static diagnostic test. It doesn't tell the entire story of whats going on inside the engine at 6000RPM with say a 300 shot of nitrous , or 10-15lbs of boost. Theres way more to a good cylinder seal than what a leakdown tester will tell you, on a cold cylinder, with no combustion pressure, etc. Now, a blowby tester/meter, will give a better idea of how things are sealing up when the engine is in real world operating conditions.

Gas porting designs, ring flutter, standard tension, low tension, vaccum pumps, pressure differentials above and below the ring, thermal expansion, and so on come into play. A standard ring needs combustion pressure on the top side of the ring to aid in sealing. We have a set ring gap to follow, to allow for thermal expansion when running when using a conventional ring. It does not have any of this going on during a leakdown test.

But, with that being said, I would absolutely agree to have used the gapless top ring in your build, joes build, and even in my engines. I am fine with the old fashioned speed pro plasma moly rings, mainly because they just work for your typical low boost low hp marine engine like I have. Been around for ever. But, to the original poster who has a 454 420HP, its not needed, and if he sees 12-15% leakage, or even a little more, leaking past his rings with a few hundred hours, and the valves are sealing well, I would tell him to run it. Just my opinion.


Would also love to hear some insight from Eddie or one of the other pro's. I think we'll find that it boils down to personal preference. While gapless rings are great, theres still a million builders using non gapless with good results. Whether it be a 500HP engine or 2000HP engine. A 400 dollar set of rings with a improper honing/finishing process is no better than a 80 dollar set of rings.

I agree with Onoxus. For the average hobbyist a leakdown test should be used like a compression test, to check for consistency, and listen to where the air is getting out. There are many variables as Mild mentioned above. Another huge variable is the test equipment, and how the test is performed. A leak down tester is a differential gauge. There is a specific control orifice in the middle that I believe is supposed to be .040". If you change the "set" pressure by a few pounds, or the cheap, mass produced orifice is actually .038", or .042", it will change the leak percentage readings. So it's hard to compare numbers from one engine to another. If you know what your gauge reads on your engine and test regularly using the same procedure every time, you'll be able to easily spot any decline in sealing.

As far as the ring debate... As I have posted in the past, I strongly believe running a gapless second ring, especially in a blown marine app, is a bad idea. Gapless top rings work great in certain applications, and a properly gapped conventional ring works great also. There are many variables here as well.
* This is not a bash: Eddie is the only builder I know that uses gapless second rings, and seems to have excellent results. Maybe he can chime in on why, and how he makes these work.

is i have a guy doing my motor work seance i am new to the bigger motors and just got the new to me boat this year. now he called me today to let me know about the the leak down and compreshion tests. port leak down where at mostly at 10% with a few around 20% and the compreshion test where all in good range. now on the starboard motor is where it gets weird. when i would start it there was alway a strong smell of raw full, then a few months in of me running the boat i started to notes that after going out the starboard motor oil presher would be down around 20psi from the port. :eek: now he sad that the leak down was the same as the port with most in the 10% range with a few around the 20 mark. now with the compreshion test all where good but one. one was at 5.....yes 5 psi :eek: now i heard some stuff he sad it might be but he sed he need to get the valve cover off and do some more tests. just wondering what u all would be thinking about my big OH NO :eek:

i cant see how 1 cylinder could have 5 lbs on compression test but a max of 20% leakage on that cylinder,it does not add up,that cylinder should be near 100% cyl leakage.

Listen to where its coming from like I was saying earlier,,,,,intake ,,,,exhaust,,,,will indicate one valve or the other,,,,, 5 PSI is a big problem and should be easy to find. Years ago I had a keeper pop off and held a valve open and the motor still made 50 psi !!!

know anyone with a scope you can stick in the spark plug hole ???

+ 1 :poopoo:

Bent intake pushrod, or intake rocker backed off can still show a good leak number but no comp 'cause the valve's not opening to let any air in. A really flat cam lobe will do the same..

ya i dont know much yet.... but it didnt sound right to me eather. with only 5psi that is like a dead cylinder witch can be the ression for the oil presher and gas smell with it not fireing and gas dumping in to the oil. but i never heard knocking or any thing and seamed like they both where running good. now it is hard for me to tell right now whats running good and whats not. went from a single 454 to twin 500 hp efis. when i was only able to get 50/55 out of my 27 to running top/only once but it was 82. 70s all day.

a bent rod is one of the things he sead might be the problem.

Good point,,,, I didnt think of that sernario

that makes sence but i would think the owner ,or his mechanic would hear the noise from the xtra clearance,unless the rocker is not moving at all.

where i have the work being done i dropped it off after the final pull out and had them winterize it this time and they didn't hear any thing at that time ether. and like i sad be for 500 efis sound a lot better then my 454. even on 7 instead of 8.

Broken top piston ring could also have good leakdown #s

also if I remember correctly a broken valve spring once gave us a good leakdown # but very low comp readings. putting the 100 psi air into the cylinder closed the valve against the seat.

Also other factors that can give you good leakdown #'s is high valve spring pressure's when in fact a problem can be taking place in that area.

I would like to hear more about the negitives of leakdown testers. Neither comp test nor leakdown down tests are 100 % full proof. I know alot of people live by a comp test along with a lot of people live by leakdown testing.

IMO both are helpful for testing and I would do both but neither are a 100 % for problem solving. So far some really good points up here. thanks

this is some good reading and advice im having both test done leak down and compression
thanks for all advice will post results

+1
If there is no air gettting into the cylinder you will not get any compression readings, but leak down will be fine. You will not hear much difference in the way it runs either, other than it won't have the power that it use to have. I've seen this many times and has always been due to bent push rod or loose rocker. Your mechanic will find it most likely by pulling the valve covers, and the good news is that it's an easy fix.
Good luck!

Hopefully a roller lifter didn't come apart

Makes cool grooves in the cam,,,,,,wanna see !!!!??

on your boat share...... on mine NOOOOOOO. lol lets hope it is some thing on the top end thats causing it because was planing to do them any way.... bought the boat with 345 hours and on about 15 or 20. didnt run as much trying to recoupe form buying the boat. with having near 20% leak down on some cylinders should i just go ahead and have them pull the heads any way and have them checked and new head gaskets a car guy told me that if the leak down is good just do the springs.

i will and i will take a camera with me this weekend when i go up to meet with him. and am going to have him save all parts changed. i am that guy that saves all the $hit and puts it on walls and what not :lolhit:.

Im glad that me takeing it from behind is helping you...:hitfan:
i might be rollin a canoe this year. lol maby some one can give me a pull to kelleys

See what you find out this weekend. At 345 hours that motor should have a lot of life left in it. The leak downs at 20% when cold are not that accurate, but a good indication of no major problems. If you do anything with the heads, because you are half way into it, I would pull them to change head gaskets and do a quick valve job and springs to start off fresh.

i mainly wanted to do the top end becouse merc has it to be done every 300 to 350 hours. pluse with buying used its better to be safe then sorry. u never know how the outher guy drove the boat, he keept it mint and only put 324 (now that i looked back) hours on it in 11 years. but thouse could be hard hours.

ok did both test
compression 145-150 on all
leakdown all good but 1 leaking air below number 2 plug
could be this be a head gasket or a cracked head?

what was the leakdown #'s especially on # 2 just wondering since you hear air leaking around the head area.