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+--- Thread: Compression test on 617A; readings too low to be belivable? (/showthread.php?tid=6186)
Compression test on 617A; readings too low to be belivable? - ErikT - 01-30-2015
Have MB G with 617A which have problems starting in the cold. it starts down to about 0 deg. at minus 1 - its rough and below no start unless the engine heater is used.
Suspected compression problems so had a shop test it. The method they used is removing the injectors and measuring it that way.
The readings they got:
Cyl 1: no apparent compression
Cyl 2: 12 bar (175psi)
Cyl 3: approx 11 bar (160psi)
Cyl 4: 12 bar (measured twice)
Cyl 5: 12 bar
All which are of course too low. Specs are, I believe 200 psi minimum and 340-400something for "normal"
But are they too low for a engine which does start? Read somewhere and there the opinion was that a diesel probably wouldn't start but I dont know.
Have you guys even heard of a 0 compression cylinder? ( I suppose it may be just too low for the measuring tools so it says 0)
RE: Compression test on 617A; readings too low to be belivable? - barrote - 01-30-2015
yep those values are quite normal for a worn engine. they do make sense with the fact that the engine has problems starting.
nr one is dead , stick rings, or valves are not sealing.
if the engine is in bad shape regarding rings (compression) after start there should be a huge withe smog comming from exaust. one or more cylinders may be failing, after getting hot all cyliders will come to life. when at normal temp it may quit smoking in white.
nevertheless it wont have much power.
if the head gasket is burned u should have oil or pressure in the cooling system. check valves , operate the lifters with a screw driver make sure there´s no problema with the valves.
BTW have u been running VEG oil?
specs for this type of engo«ine is between 18and 30BAR below 18 engine should be repaired. (values for hot engine)
regards
RE: Compression test on 617A; readings too low to be belivable? - Volker407 - 01-30-2015
(01-30-2015, 02:32 PM)ErikT Have MB G with 617A which have problems starting in the cold. it starts down to about 0 deg. at minus 1 - its rough and below no start unless the engine heater is used.
Suspected compression problems so had a shop test it. The method they used is removing the injectors and measuring it that way.
The readings they got:
Cyl 1: no apparent compression
Cyl 2: 12 bar (175psi)
Cyl 3: approx 11 bar (160psi)
Cyl 4: 12 bar (measured twice)
Cyl 5: 12 bar
...
When was the last time you did set your valves?
Valve settings should be checked every 5000-10000km as the correct valve play is crucial on those engines!
I guess after setting your valves everything will be ok.
http://www.w123-forum.net/phorum/read.php?1,1413058,1413059
Gruß
Volker
RE: Compression test on 617A; readings too low to be belivable? - ErikT - 01-30-2015
Thank you both.
Valve were adjusted last Saturday, only drove approx 70km after that before the test.
used normal diesel only
Will also check the valves as Barrote mentions
Got some white smoke after start which disappears after a short while.
will pull it apart when I get the chance
RE: Compression test on 617A; readings too low to be belivable? - Volker407 - 01-31-2015
Does the compression change/get better if you put a little engine oil on the piston/cylinder before measurement?
Gruß
Volker
RE: Compression test on 617A; readings too low to be belivable? - ErikT - 01-31-2015
Don't know.
I don't have the testing equipment and there had a shop/mechanic do the test.
RE: Compression test on 617A; readings too low to be belivable? - barrote - 01-31-2015
it is just worn out , have a set of rings inside, u´ll see it alive again.
regards