What to look for when doing a leak down test?

kingtigg

kingtigg

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Nov 21, 2005
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Location
Winnipeg, Manitoba
I'm about to use my new leak down tester on my machines and was wondering what I should look for!

MrViper you've mentioned that this type of test is far superior to a simple compression test.
Specifically how so?

What kind of numbers should I see for % leakage that indicate a good or bad engine? and at what pressure?
How will those numbers tell me anything more than just the state of my rings?
Should I perform the test on a hot engine or cold?

Thanks in advance!!!
 
Do a search lota of info on this...

you do it on a fully warmed up motor, with piston at TDC, you want to be
with in 10% of each cyl. so using 100psi you don't want to be any lower
than 90% on a given cyl.

like i said lots on this subject try a search..
 
partly it tells you if you are loosing compression after it is built, if you have 145 lbs but it leaks out then it is useless. it shows that it holds the compression in.
 
Right, it shows the ability of a piston and rings to hold pressure,any piston and rings can make compression but can it hold it?? that's what you want to find out.
 
I know the purpose is to check to see if it holds pressure...but when should I be looking at chaning rings?...10%...15%?
Additionally, can I perform other tests that would diagnose the piston or any other components?

Thanks!
(BTW - I've already searched a lot and can't seem to find anything on this!)
 
kingtigg said:
I know the purpose is to check to see if it holds pressure...but when should I be looking at chaning rings?...10%...15%?
Additionally, can I perform other tests that would diagnose the piston or any other components?

Thanks!
(BTW - I've already searched a lot and can't seem to find anything on this!)
Click to expand...
Thats funny myself have posted on this before as others did and nothing
shows..

anyway myself i wouldn't want go lower than 6-7%..

not that i know of a L/D test is the best.
 
the leakdown test give you the true condition of the engine inside. Its all about holding onto the compression, a compression guage simply shows you what the cylinder can build rapidly, but on its way up tp TDC it doesnt tell you the amount of compression that bleeds off between the rings and the cylinder.

Another couple ways to see is either remove the head and inspect the amount of play the piston has when trying to rock it back and forth in the bore. You can also remove the reedblock and peer intot he intake side of the engine, a engine with alot of blow by will have black skirts and if the pistons are worn there will be a small alum. shiny spot and rest of skirt will be all black. The black is blow by from poor sealing rings letting exh. get by the rings and contaminating the fresh fuel/air charge below in the case.

With the leak test anyhting over 10% I would reccoment you change the rings. When you pull the cylinders you should always mic the pistons to keep them in spec. Running worn rings makes the piston lose its stabilty in the bore, will then rock back and forth and this will eventually break off the skirt of the piston and cause major engine damage.
 
go to dynotechresearch.com & spend $20. for a 1 yr. membership. the best $20. you ever spent.
jim covered leak down in a 11/1/2004 test on a hard ridden 600 skidoo. this sled had 50% leakage on one cylinder & 30% on the other. the total loss throughout the power band was only 2.5%. it had 114 hp with all that leakage & 117 hp after re-ringing & new pistons.
this test & more are there for your perusal if you join.

bob
 
much cheaper in the long run to keep good rings in the sled, good rings keep the pistons from being ruined with rocking back and forth in the bore. Pistons are a $100 each, rings $16 a set, do the math....
 
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