1982 300 SD Compression Test - PeachParts Mercedes-Benz Forum

nyko46 · #1 05-25-2009, 09:28 PM

I will go to test compression of all five cylinders of my MB 1982 300SD.
I need to know if heat shield must be removed or not when attaching compression tester adapter to engine block. I already removed the injectors, heat shields and tubes from pump to injectors. Any idea about how to void diesel spillage from injection pump while testing compression?
Thanks

sixto · #2 05-25-2009, 11:39 PM

I'd use an old heat shield with the adapter.

Hold/tie down the engine shutoff lever so there's no fuel flow out of the pump.

Sixto
87 300D

toomany MBZ · #3 05-26-2009, 10:43 AM

If you have a mity-vac, hook it up to the shut off valve under hood and pull some vac, this will ensure no fuel gets delivered.

nyko46 · #4 05-26-2009, 01:39 PM

Thanks for the great ideas.
After getting the results I will post here.
I am sending all removed injectors for cleaning and necessary adjustments.
I believe it will make my old car to run better.
Thanks again.

brownrice78 · #5 05-26-2009, 02:56 PM

I have tried to test compression with and without the heat shields and got the same reading, so I don't think it makes much of a difference. Make sure to use new shields when the injectors come back from the shop. Holding back the "stop engine" lever also is a good idea

..hope your numbers are good!

nyko46 · #6 05-26-2009, 03:57 PM

Thank you for your post.
The reason because I am doing this test is because I have no idea how is my engine compression and how good or bad are my injectors performing.
How much will be a good compression on a 1982 300 SD with 243K miles?
I am planning to check with cold engine.

#7 05-26-2009, 04:11 PM

Anything above 300 is good, 350+ is very good.

Diesel911 · #8 05-26-2009, 04:13 PM

Quote:

Originally Posted by nyko46

Thank you for your post.
The reason because I am doing this test is because I have no idea how is my engine compression and how good or bad are my injectors performing.
How much will be a good compression on a 1982 300 SD with 243K miles?
I am planning to check with cold engine.

These values are from 1978. 300SD Turbo Diesel Service Manual, Engines 917.910/12

Test Values are with the Engine at operating Temperature:

Normal Compression bar- 22-24, psi- 319-348
Lowest Compression bar- 15, psi- 218
Permissable differance between individual Cylinders, max bar 3, max psi- 44

Ceck the DIY section for how may rpm to crank and other specifics.

toomany MBZ · #9 05-26-2009, 06:33 PM

You may want to adjust the valves first.

nyko46 · #10 05-27-2009, 01:50 PM

Valve adjustment is included on my plan but I did not put it in first plan.
Really I don't know if it will make difference on compression readings.
Per sure without injectors will be easier to turn the engine by hand to adjust valves.
Thanks for share your thoughts.

toomany MBZ · #11 05-27-2009, 02:09 PM

Correctly set valves will give you an accurate compression reading.

nyko46 · #12 05-29-2009, 10:32 PM

Today I adjusted all valves and I found three exhaust valves gap too small.
It was less than .35 mm with cold engine. After all ten valves adjusted properly I performed the compression test with engine at room temperature.
Just to have an idea the outside temperature today was around F 85.
I used heat shield between adapter and cylinder block and crank the engine for a complete eight turns as suggested by Mercedes Benz manual.
Here is the numbers that I got:

Cylinder #1: 330 PSI Cylinder #2: 320 PSI Cylinder #3: 330 PSI
Cylinder #4: 400 PSI Cylinder #5: 300 PSI

As cylinder #4 gave me number higher than all others I retest it after finish cylinder #5 and I got the same reading than before; 400 PSI
Then I put back in place clean and tested injectors, tubing's from IP to injectors and start bleeding air from tubing's before have it complete tighten at injector. When I start cranking my engine to bleed air my battery was week and then I let it charging to finish tomorrow.
I will appreciate if someone have some observation or correction on the job performed.

Old Dies · #13 05-29-2009, 10:45 PM

If you get an unusually hi reading on just one hole, it is likely you got some fuel in there, or maybe the valve guides are leaking a little fresh oil down onto the piston. Does'nt take much to seal up the rings and raise the reading to 400+.

nyko46 · #14 05-29-2009, 11:34 PM

Thanks for your comment's.
About fuel in the hole I don't think it can be because I crank the engine several times without injectors before starting checking compression. It helped to clean injector seating on the block. I do believe about the oil from valve because my engine previously had some smoke. If there was oil from valve, it should not be visible at the adapter?
I didn't pay attention to see if there was some oil.
Anyway, your comment was great and if you have some another info to share it will be good and appreciated.