OM617.952 Help - PeachParts Mercedes-Benz Forum

phatfj · #1 11-19-2011, 10:28 PM

Hi all, I am doing an engine swap with a motor out of a 1985 300CD. I will be putting this motor into a 1970 Toyota FJ-40 which now has an 5.7L & a SM465 4spd. I picked up the motor at a local parts yard and got a 90 day warranty with it. I was told that this motor had aprox. 148K on it and it sat out in a yard for over 2 years. Well, I got the motor home and put on a stand, checked the oil (black as all diesels are) level was good and did not smell bad, someone had pulled parts off it at some time so I have been identifying and making sure I have all necessary parts. I did a compression test today and the results were as follows C1= 280, C2=80, C3=90, C4=120 and C5=190, I double checked C2 twice, all tests were done through the glow plug with the exception of C2 when I double checked it I put the glow plug back in and pulled the injector, the test result was still only about 80psi. My question is, (some say that a motor that has sat for an extended time needs to run again before the compression will come back) do you think it is worth trying to get it running and do another comp. test? Or, should I just take it back and try and get another motor? I do not know if I can even get it started with this low of a compression. Thanks in a advance for the help!!

piccolovic · #2 11-19-2011, 10:35 PM

YIKES . . . . compression all over the place!!!! If it were only one cylinder . . . but it's 2 and the range is wide. I'd take it back and look for another motor!!!!

t walgamuth · #3 11-20-2011, 05:30 AM

My old Chiltons says you need 220 minimum for reliable starting. ON the other hand with readings so low I don't know how it would even run. I suspect that running some penetrating oil into the cylinders and cranking it over a bit might lubricate it enough to get a more truthful test of the compression.

vstech · #4 11-20-2011, 07:39 AM

it all depends on WHAT parts were removed, and if water got into the motor, seized rings from rust might be freed up with some penetrating oil. I'd also adjust all the valves.
does the block heater work? try getting some coolant in the motor, and plugging it in, and getting the block warm, then fill the bad holes with marvel mystery oil, and letting it sit for a day. then empty that out, and spray in some pb blaster, and cranking it over a bit, then put a teaspoon of motor oil in each cylinder, THEN crank it up to pressure...

phatfj · #5 11-20-2011, 09:42 AM

Quote:

Originally Posted by vstech

it all depends on WHAT parts were removed, and if water got into the motor, seized rings from rust might be freed up with some penetrating oil. I'd also adjust all the valves.
does the block heater work? try getting some coolant in the motor, and plugging it in, and getting the block warm, then fill the bad holes with marvel mystery oil, and letting it sit for a day. then empty that out, and spray in some pb blaster, and cranking it over a bit, then put a teaspoon of motor oil in each cylinder, THEN crank it up to pressure...

All excellent ideas!! I thought about the valves last night, had not thought about the block heater though. Thanks, I think I will also do a leak down and see if I can get some indication of where the pressure is going..

phatfj · #6 11-21-2011, 12:56 PM

Well, I adjusted the valves, did another compression test with no change. I did a leak down test as well, seems the air is escaping past the rings into the case as the leak sounded loudest through the timing chain valley. I will contact the yard today in hopes of getting another motor. Thanks for all you help, I appreciate it!!

kerry · #7 11-21-2011, 01:40 PM

Take it back. I wouldn't pay money for a motor with those kind of compression numbers.

Zacharias · #8 11-21-2011, 04:11 PM

Short answer: what Kerry said. Those values are so far out of line I would be suspecting my compression tester or using this motor as a boat anchor.

My longwinded and somewhat speculative answer: The only way that I can see it should have compression values of 80-90-120 is either partly seized rings, which would make me suspect polymerization due to use of unheated/untreated waste vegetable oil, or possibly a problem with seriously carbonized valves (also apparently possible due to same cause).

IF the cause is polymerization, and I am just throwing darts at a board in suggesting that, then you can't do anything short of pulling the pistons -- so it would be time to exchange that motor.

On the other hand: I generally take whatever a yard-rat tells me at about 50 percent of its face value. So, in this case, I would immediately assume the engine has been sitting for 4-5 years and has 280-300k on it

(My friend who runs a shop once had a diesel engine shipped to him that the yard owner verbally "guaranteed to run great... tested it myself when it came in." When it arrived, two of the glow plugs were broken off in the head and had been that way for some time. The others were all nearly dead.)

BUT, if you are at the point where you have nothing to lose and want to give it one last shot, I have rescued two motors (and a trashed lawn mower) this way:

1. Pour coca-cola or pepsi into each cylinder. Keep filled if it drains down, for 48 hrs.

2. After 48 hrs have passed, pour in marvel mystery oil. Leave for 24 hrs.

3. Retest compression (but obviously don't attempt to start with that cr*p in the oil pan).

If you do go the exchange route, I just hope this wasn't their best used Mercedes diesel they sold you....

Good luck with it.

piccolovic · #9 11-21-2011, 04:40 PM

Another reason for compression that low . . . burned exhaust valves!!!! Best to return it for another, cut your losses now . . .after all, time IS $$.