2nd Gen R56 Cooper S Need help performing a compression test

Before computers were running cars, I had no problems with compression testing. Still have most of the equipment. My concern is the way the engine starts when the start button is pushed --- it cranks until it starts.
Does it have a timer, to quit cranking if it doesn't start?
Is there a special test fixture to plug into the starter?
Remove all plugs before testing?

I'm afraid to just connect the compression gauge and hit the starter, not knowing what will happen, and don't want to just start experimenting with different possibilities. Had a dealer test it for me a couple years ago - good results, but an hours worth of labor charges. No explanation on how they performed the test.

So much to learn about the '07 R56 ---

All helpful inputs / links appreciated!

 

Thanx for the info. I'll post my readings and any other helpful hints I come across --- hopefully today or tomorrow.

 

That didn't take long! Pulled plugs then the fuel pump fuse and cranked it for 10 - 15 seconds to clear fuel from the system. Found out that after the start button is pushed, it cranks for 17 secs before stopping by itself. Also discovered that while it's cranking, it can be stopped by pushing the button again. Seems obvious, but I was afraid to try it before prepping for this test. Still running the original battery - 62K miles and car was built in 9/07.

Compression gauge with spark plug adaptor is about 2' long. I believe this long length causes readings to be low - at least I hope so.
#1 = 105psi
#2 = 105psi
#3 = 115psi
#4 = 115psi
Dealer check 2 years ago was between 168 - 171psi. Not concerned about actuals, just variance. I'm happy with the results, but I'm also open for criticism ---

 

Month or so ago, I had the rear PCV hose connection blocked off --- BSH OCC installed on the driver side hose. This caused serious oil consumption --- crankcase pressure blocking the turbo oil drain line, so oil leaked thru the turbo seals into the turbo air inlet chamber, and mixed with the air. Totally defeating the purpose of OCC! Anyhow, I'm still seeing occasional smoky exhaust and wanted to ensure it wasn't rings / pistons, but residue in the air hoses / FMIC. So far, I'm convinced it's residue. The puddle inside the turbo inlet chamber is gone, after routing the rear PCV thru a "Tee" connection at the OCC.

Lotsa opinions on the subject of OCC connections. I'm planning on a lengthy summary of my OCC installation by next month. Should be of interest to those with sudden high oil consumption. Will be a new thread.

As for these low readings, I'm looking around locally for a shorter hose for my compression gauge. Maybe cut and splice my existing one. While shopping for a gauge, I saw some kits had short, metal adapters, instead of a hose. Didn't look like they would fit inside our spark plug well, so I opted for a hose.

 

Shortened the compression gauge hose length with a splice from 23" to 16" and tested the low cylinder again, twice --- once hot then cold. Was expecting significant differences, but the cold (sat overnight) was 100psi and the hot was 95psi. Both down from the 105psi a couple days ago. I probably screwed up the splice, and have a small leak.

Now that the leak down test has been explained, I'll bet thats what the dealer did for me a couple years ago. I can't believe my gauge is that far off, or that it's worn that much --- dealers 168 - 171 to my 105 - 115.

Anyone have experience with the two different tests and their results --- on the same engine, in the same time frame?

 

Bought a whole new gauge kit, just to get the correct hose size. First set of readings (post #5) was with the new hose and my old gauge --- it has better resolution between numbers. Tried it again last week with the new gauge (just one cylinder) --- no significant difference!

Obvious conclusion, after squirting a little oil in the cylinder and getting an increase of about 20lbs --- shot rings. Still runs nice, but time to start considering the bottom end upgrades.

 

Like Dave says --- nothing in the manual! However, when a dealer checked my '07S, at my request, they documented the following --- "All cylinders are within 5% of each other and between 160-180 PSI. Checked OK." Don't know where they got these numbers, maybe a manual not available to the general public? I put a lot of faith in this dealership's service dept. Can't say the same for all of them.