1982 300 SD Compression Test

[nyko46]

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]

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]

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]

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]

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]

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.

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

[Diesel911]

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]

You may want to adjust the valves first.

[nyko46]

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]

Correctly set valves will give you an accurate compression reading.

[nyko46]

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]

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]

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.