Just completed a compression test. After reading a few posts and finding that several out there feel a compression test is less than perfect, I thought I would run my situation by everyone and get some input.
Mileage: 190k
model: 82 300TD
Symptoms: rough idle warm, cold, otherwise; smoke that doesn't go away; loosening injector #3 has no effect on idle, but does reduce smoke; excessive blowby? plugging valve cover vent causes engine to die in 5-10 sec
Compression numbers (psi):
#1- 400
#2- 375
#3- 180
#4- 370
#5- 380
Now, I suppose something is amiss with the rings in #3, but I would like any input on what things I should check before pulling the engine and checking for broken rings.
Thanks
Baja

It's not necessarily the rings. Now that you know what hole is the culprit you need to do a cylinder leak down test on that hole and listen for where the air is escaping. If you hear it through the oil filler hole, it is ring/cylinder related, if through the tail pipe it is an exhaust valve, and if through the intake it is an intake valve.

Since diesels rarely burn valves it is likely ring/cylinder related, but you just don't know until you check. You should DEFINITELY check so that you know what to plan on doing next.

Good luck,

larrys post.

what units are u measureing with? that is too high for psi., imo.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

The air is definately going into the crankcase. The air compressor could barely keep up with the rate air was escaping the cylinder. Does this mean that there is a gaping gouge or hole in that cylinder. I really hope that rings is all this thing needs.

You could have stuck or broken rings...a holed piston...and or a chewed up cylinder....at this point it would take a borescope to look into it with the head on...or pull the head and see what you have...

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

A good diesel will indeed give PSI compression this high.

Bajaman,

Regardless of the cause, it will have to come apart. You should plan on boring cylinders and using oversized pistons. There are MANY here on the site who prefer to replace sleeves and go back to standard bore with the original pistons. I am definitely NOT a fan of that approach on a diesel engine due to the high stress that a diesel piston deals with.

In addtion to that, you may very well have a broken piston ring land or a failed piston. I have one such piston in my box of momentos.

Good luck,

Awwww man!

Check out my 300TD smoking saga thread. I had one cylinder that read much lower than the others kind of like yours but #1.

I tried all kinds of engine washes and the leakdown test just sent air whooshing out the oil filler. I've finally given up on that namby pamby stuff and I'm pulling the head tomorrow. Got my brand new cherry picker from the local parts supply and I'm dangerous!

Mutual wish of luck to us. I'm hoping I have a cracked ring that has done virtually no damage to the bore!

Reality, I'm probably going to find that thing nuked inside. Look for photos on the smoking saga thread.

Cheers,
Ykobayashi

As a charter member of the 300TD smoking club I will be watching for your thread, and can't wait for pics.
I have good even compression, mine is more of an injection timing issue I believe, but I'm still interested in what's going on with yalls diesels. My '85 has so much blowby I'll probably be there some day.

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

Larry, I am not sure I see how changing the cylinder bore will decrease the amount of stress on the piston? If the forces excerted on the piston are related the the cross-sectional area, won't increasing this number exert more force (stress) on the rod and related components?
Yes, I will be taking the engine out this week. I am borrowing a hoist from a friend of a friend and should have it out this week. (I hope the DIYer Nazi in my nieghborhood does not get wind of this, Yes there is a local ordinance that says I cannot work on my vehicle in my own garage )
Baja

__________________
For Sale: 1982 MB 300TD
1995 Chevrolet Suburban 6.5TD

Sold: 1980 IH Scout Traveler- Nissan SD33T Diesel

i think larry just meant he did not like reusing used pistons.

and while that is a valid position, i have used the old ones on at least three mb diesels and know of a couple more with success. the pistons have to be examined and measured for excessive wear by someone who knows what they are doing (not me, my machinist). on some of my engines we had a piston or two that did not measure up and had to find other pistons. we used pistons from another engine or two that i have laying about that did measure up.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Bajaman; I am not very far away and have some free time this week. Especially if you are working at it during the day. I would be happy to give you a hand.


"If it was easy everybody would do it!"


Junqueyardjim

How is this possible? You can't work on the vehicle in your own driveway and you can't work on it in your own garage??

How do they possibly get away with this $hit? Is this a condominium or a coop of some sort?

Simply amazing.

I'm with you on this Brian. I went back and looked at his location and it is indeed in the USA. Amazing!

It's time to find another place to live.

Have a great day,

Did I say that changing cylinder bore changes stress on the piston? I said that I don't reuse pistons in a diesel engine due to the high stress that they deal with. Some people sleeve back to original bore size and reuse their pistons. It costs more to buy new pistons, but there is some savings in simply boring to the next oversize rather than replacing the sleeves. I personally will not go to all the work and expense of rebuilding one of these engines and then put in used pistons.

Have a great day,

I can't have an unregistered vehicle on my property here in this village. But, to prevent a person from working on his own vehicle? I'd move faster than you could find a moving truck.