leak down test

[Charlie V]

I use a single gauge tester for the last several years - some 50,000kms. I follow the same procedure each winter when doing annual maintenance.

I have been tracking the numbers and it "gives me a feel" for how the engine is doing. Close enough for me. This was the primary reason for getting the tester........to understand the engine wear over time.

And yup, the engine is slowly wearing as the numbers inch upwards. Nothing drastic or of concern, so I continue to exercise the engine through the full rpm range.

Buried deep down here is wanting the engine to wear quicker to justify a big bore short stroke build. At the current rate of wear, this will be a few more years out.

[r-mm]

Originally Posted by john walker's workshop

hot, with the rings oiled.

This is a very interesting thread.
Can anyone comment on the value of a leakdown test done cold? We have established that LD and Comp tests are ordinal / comparative not absolute and cross reference-able from different testers, conditions etc. But is the test meaningful on a cold (aircooled) motor?

I ask because I LD'd my 3.2, which is on a stand and therefore cold, and heard leakage thru the breather on all cylinders even those that measured 1-2% @ 50psi. Rings seat from the pressure of combustion and pistons expand - therefore wondering if some leakage past the rings is inevitable on a cold, air cooled motor. Especially one with 100k miles.

[docrodg]

IMHO a leakdown cold will still be valid within the uncertainty of measurement of the test process. I have not done the sadistics (statistics) but the "feeling" is that the uncertainties from cold to hot are much smaller than the rest. You hear leaking but the important thing is how much... 2% is nothing. I personally would use higher pressure to ensure the rings perform as intended; a good example of a larger uncertainty.

[MConn]

I decided to buy a leakdown tester, and do some online learning here at PP mechanics school. I read here not to do a cold LD, so I did cold and hot. Here’s the results:

Conditions-
Air cleaner off
Throttle open
MAF open
Oil filler cap off
All spark plugs out
80 PSI Supply pressure

Cylinder---------Cold---------------------Hot
1-----------6%----(75 PSI)----------6%--(75 PSI)
6-----------2.5%--(78 PSI)----------5%--(76 PSI)
2-----------4%----(77 PSI)----------5%--(76 PSI)
4-----------2.5%--(78 PSI)----------0%--(80 PSI)
3-----------4%----(77 PSI)----------4%--(77 PSI)
5-----------2.5%--(78 PSI)----------5%--(75 PSI)


The leakdown tester was a brand new OTC 5609. I measured the orifice to be 0.040" –

http://www.summitracing.com/parts/otc-5609/overview/

The cold results seem better but the hot results were more consistant. I’m guessing that this is due to oil that has seeped into the chamber and sealed the rings a little better during the week it was sitting cold, and the hot numbers are a truer indication of engine condition, but overall not much difference. The 0% for cylinder #4 is bugging me so I connected the tester to a flow meter.



LD----Flow
0%----3
5%----6
10%---7
I ‘m not sure of the units on the flow meter, but it is designed for gas. It seems that any leak smaller than the orifice size will show 0% leakdown. Also, that LD is not linear – so that as the cylinder leakage grows a little, the LD % grows more. Alan L makes a good argument in post #32, that 0.040 orifice is too big for 911 engines.

Is it normal to see 0% on a leakdown using a 0.040" orifice, or am i making some rookie mistakes?

If a Porsche dealership does a PPI, is there a standard orifice size used?

Mike

[lvporschepilot]

I highly doubt a Porsche tech uses a 'Porsche certified' leak tester, if such a thing exists. A .040" orifice is an FAA mandated size which is per FAA regs to be used at 80psi, and not more than 15% leakage is the max amount per FAA regs thus such an orifice is by default the standard. A larger orifice tester yields a more obtuse leakage %, so these tests must be taken in context of the tester.

[cgarr]

It's good practice to rock the engine crank to seat the rings while the pressure is applied to get a more accurate reading too.

[jackmech]

Sorry to revive a VERY old thread. But this was the first post I found that actually took the time to assess the function and accuracy of leakdown testers. I came across it while educating myself about the quality (or lack of) for the Harbor Freight 94190 Leakdown Tester.

The HF 94109 tester has a >2.5mm orifice and is completely unsuitable for use. It can be 'fixed' by disassembling the unit, filling the orifice and redrilling to 1mm/0.040".

Hopefully this will get passed around. I see a lot of posts asking if the HF leakdown tester is accurate.