What is the magic number for compression? - PeachParts Mercedes-Benz Forum

Ian White · #1 08-24-2009, 02:53 PM

Give me an idea on what good compression will yield in terms of relative psi. Fair compression? Poor compression? Thanks

Brian Carlton · #2 08-24-2009, 02:57 PM

Due to the variability of the gauging, an absolute number is somewhat meaningless.

If all cylinders checkout within 10% of each other, you're probably good to go. I doubt that you'll find that all of them have worn equally down to 220 psi...............

300 psi is considered typical for a good engine (20.5:1 compression).

barry123400 · #3 08-24-2009, 02:59 PM

You will be doing a cold compression check so about 300 pounds or higher would be nice across the board. Compression check is prefferably done with an engine at operational temperatures.

Junkman · #4 08-24-2009, 03:25 PM

I haven't had to run compression check on a diesel. Is it easier to access via glow plug or injector holes? Is a leak down test as useful as on a gasser for diagnosing the problem before dis-assembly?

barry123400 · #5 08-24-2009, 03:43 PM

Quote:

Originally Posted by Junkman

I haven't had to run compression check on a diesel. Is it easier to access via glow plug or injector holes? Is a leak down test as useful as on a gasser for diagnosing the problem before dis-assembly?

Mandatory in my opinion. You really want to have a real indication of where the problem actually lays if possible before taking things apart.

winmutt · #6 08-24-2009, 03:52 PM

Quote:

Originally Posted by Junkman

I haven't had to run compression check on a diesel. Is it easier to access via glow plug or injector holes? Is a leak down test as useful as on a gasser for diagnosing the problem before dis-assembly?

To each their own. Most will say GP is easier, however if you haven't inspected your prechambers or cleaned your injectors now is an excellent time to do both.

Ian White · #7 08-24-2009, 06:34 PM

How do you remov the pre chamber?

barry123400 · #8 08-24-2009, 07:28 PM

Quote:

Originally Posted by Ian White

How do you remov the pre chamber?

You should keep us informed as you go along. It seems very early to ask about removal of prechambers. Or you have already moved way ahead of where we think you are. Have you done any tests yet? We all should be on the same page.

winmutt · #9 08-24-2009, 09:14 PM

No he misunderstood me. You don't pull the prechambers unless you have to. You do inspect for the atomizer ball. You do this when the injectors are out.

Ian White · #10 08-24-2009, 09:22 PM

Quote:

Originally Posted by winmutt

No he misunderstood me. You don't pull the prechambers unless you have to. You do inspect for the atomizer ball. You do this when the injectors are out.

I see it ( the atomizer ball) in there what should I be looking for?

winmutt · #11 08-24-2009, 09:39 PM

Mostly that it is still there. They have a nasty habit of breaking off and ruining your valve train. One of the few Achilles heels of this car.

Ian White · #12 08-25-2009, 12:13 AM

Okay did a compression test and wow someone sold me a worn engine. Comp test #'s: cyl 1: 76 psi, cyl2: 49 psi, cyl 3: 111 psi, cyl 4: 145 psi, cyl 5: 151 psi. So now I am going back to talk to him about a refund. The funny thing is when i had the pickup and pan off there wasnt a spec of junk down there just look like a normal oil pan with 215k. I am pissed, I am thinking about ceasing to own my benz. Its turning into a money pit uhh!