Bad news -- 603 engine -- now what? - PeachParts Mercedes-Benz Forum

Jeremy5848 · #1 01-17-2008, 04:18 PM

Just got the bad news from my mechanic.

Our '87 300DT has a bad #2 cylinder in its 603 engine.

The numbers look like this:

#1 compression 400, leakdown 0
#2 compression 300, leakdown 20%
#3 compression 460, leakdown 0
#4 compression 410, leakdown 0
#5 compression 420, leakdown 0
#6 compression 380, leakdown 0

Thus, it's likely that the car's oil smoke is a result of damaged rings in the #2 bore. This is a far more serious and expensive problem than the valve stem guides that I was hoping it might be. Let that be a lesson to all of you: don't do dumb things like buying cars with no pre-inspection and no service records.

The mechanic reported that the glow plugs and injectors are all good. I've spent a lot of money on the suspension and a lot of my own time fixing the bits and pieces of the interior, so the car is otherwise in pretty good shape. I've considered keeping it and just driving it but it's a "third car" that we really don't need.

The car is currently drivable, in fact it runs pretty well. The bad cylinder is not a complete killer, clearly, but I could not possibly get more than a small fraction of the money I've spent out of the car. Swapping in a known good engine would cost another thousand or more, I suppose, on top of the cost of the engine. With a good engine it would be worth keeping, I just hate to keep dumping money into the car (yes, I should have said that a year ago).

People, what is your advice?

Jeremy

Hatterasguy · #2 01-17-2008, 06:42 PM

I'd put a borascope down cylinder 2 and see if the walls are scored. If not and the rings are leaking you may be able to get away cheap just re ringing that cylinder.

networkboy · #3 01-17-2008, 06:51 PM

My two cents:
If the piston looks Ok, re-sleeve it. Not trivial though and beyond my skills ATM...
Edit: or what Hatty said while I was posting this...

How much you got into it? I'd honestly be a little interested in it (pending the spouse's approval).
-nB

dieseldiehard · #4 01-17-2008, 07:39 PM

Jeremy, as I read your signature line it says only 137K miles on the car? Makes one wonder if it ran low on oil or had the wrong kind of oil in it or PO's failure to change oil frequently? (I suspect the last possibility)
If that is true then I am really surprised the rings would be worn at that mileage.
I had the opportunity to replace the rings in one of my '87s when I had the head off. It showed some vertical scratch marks on a couple of the cylinder walls so we pulled the pistons and saw the rings were real thin. The base metal was gone on a couple of the rings, they definitely needed to be replaced.
I never had an opportunity to perform a leakdown test because the car came to me sans-head (its a long story) but I had the pleasure of cleaning the grooves in the pistons, a job I'd never done before, and my friend reinstalled the pistons. We lightly honed the cylinder walls with the engine still in the car. I sort of did my apprenticeship on the car, I call it the blue bomb. Greasybenz has driven it and can attest to it running like a champ now!
I don't need a divorce (my wife would probably leave me if I bought another car!) o/w I would buy it as another project.

If you are interested in having my friend replace the rings I can ask what the shop wants. It's something I recommend whenever a diesel owner has the head off for any reason (especially the 603) its not much more labor and little money for a set of rings but what a great way to restore an engine and add lots of miles to its future! As long as you have a car that allows you to drop the upper oil pan completely you then push the pistons out the bottom and therefore you don't need to remove the engine! That alone will save you 8 or 10 hours (equal to over a thousand $$ at today's shop rates)

I wish I had been so lucky on my 617 engine in the '79 300TD. It needed new pistons and 1st oversize bore because the walls were scored badly, thanks to a cracked ring.
DDH

babymog · #5 01-17-2008, 07:48 PM

Rings might not have worn due to bad lubrication.

Could have been carbon, carbon fouls rings and they stick, which can crack the rings or the pistons, or both.

Idling is bad, running bad fuel is bad, and running a wide-open thermostat is bad, all can carbon the rings (to the point where there is no clearance in the land, they will bind).

Jeremy5848 · #6 01-17-2008, 09:22 PM

Thanks for all the good ideas! I suspect that the car has more than 137,000 miles (the odometer was slipping for awhile) but probably not a great deal more unless the Carfax numbers were completely off.

My mechanic's current guess is that the engine was overheated, damaging the head (and who knows what else). This is based in part on observing that the head was removed sometime in the year or so before I bought the car. One might speculate that the person who damaged the front end then tried to drive home (no police report per Carfax!) with a damaged cooling system. We don't know how much damage was done in this supposed collision but it clearly took a hit to the left headlight area. Not enough to do structural damage that would affect handling, fortunately.

The borescope idea is interesting, let me ask. Since the other cylinders test OK, it would be great if this one cylinder could be repaired with the block still in the car.

DDH, if you have the head off, doesn't the piston come out that way? Dropping it out the bottom would require removing the crankshaft, or am I completely misunderstanding you?

NB, my investment has to be at least $10,000 by now, probably more. Yes, I'm an idiot. What can I say, out of 3 M-Bs bought I got two great ones and this, which could be great if it were fixed. If I could get this thing running properly for less than another million dollars or so, I'd keep it and sell the '85.

Jeremy

Bio300TDTdriver · #7 01-18-2008, 01:16 AM

Quote:

Originally Posted by Jeremy5848

Thanks for all the good ideas! I suspect that the car has more than 137,000 miles (the odometer was slipping for awhile) but probably not a great deal more unless the Carfax numbers were completely off.

My mechanic's current guess is that the engine was overheated, damaging the head (and who knows what else). This is based in part on observing that the head was removed sometime in the year or so before I bought the car. One might speculate that the person who damaged the front end then tried to drive home (no police report per Carfax!) with a damaged cooling system. We don't know how much damage was done in this supposed collision but it clearly took a hit to the left headlight area. Not enough to do structural damage that would affect handling, fortunately.

The borescope idea is interesting, let me ask. Since the other cylinders test OK, it would be great if this one cylinder could be repaired with the block still in the car.

DDH, if you have the head off, doesn't the piston come out that way? Dropping it out the bottom would require removing the crankshaft, or am I completely misunderstanding you?

NB, my investment has to be at least $10,000 by now, probably more. Yes, I'm an idiot. What can I say, out of 3 M-Bs bought I got two great ones and this, which could be great if it were fixed. If I could get this thing running properly for less than another million dollars or so, I'd keep it and sell the '85.

Jeremy

Jeremy,

I'll make you feel better and less stupid. We are up to $24,000 (talk about stupid) in our 300TD. Heck at $10,000 we were just getting started.

Chris

t walgamuth · #8 01-18-2008, 07:25 AM

Mr. obvious here......are you sure it is not a valve leaking?

Tom W

rick surgent · #9 01-18-2008, 07:41 AM

One of the points of doing a leakdown test with compressed air is to find where it is leaking. I'd sugest you redo the test. First make sure the engine is warm, as close to operating temp as possible, piston must be at tdc of its cyl for this to really be a valid test, otherwise the air pressure will knock it to the bottom of the bore, or at best you wont be testing each cyl the same. Thirdl when you get leakage remove oil cap or breather, listen for air coming thru the exhaust, intake or crankcase to help pinpoint the leak.

Hatterasguy · #10 01-18-2008, 11:40 AM

Quote:

Originally Posted by t walgamuth

Mr. obvious here......are you sure it is not a valve leaking?

Tom W

X2. Did he do a leak down test?

Since the head was recently off, I would suspect a bad valve. As is proven again and again very few machine shops can get these heads right.

Knightrider966 · #11 01-18-2008, 12:31 PM

I suspect a bad valve here too. If you can get a scope into this cylinder, do so and see if the walls are scored. If not proceed to step 2. Get some Cello-Solve and spray or pour a little into this cylinder and let it sit for a day or 2. Don't worry, cello-solve will burn.

It dissolves the carbon buildup in between the rings and breaks it loose.

After a day or two, start the engine and take a dishwashing detergent bottle, rinse it well and fill it with clean water. After your engine has warmed up for a minute or two, remove your air cleaner and direct a fairly strong stream of water into the intake throat with the engine about 1750 RPM and use all the water in the bottle, but DON"T flood or stall the motor!!!!

Take another compression test and/ leak down test. If compression is worse, you have bad rings in that cylinder.

If compression is better, that cylinder has an overly rich condition carbonising the rings.

If there is no change or very little, you have a bad valve.

But it's better than a re-ring job.

If it turns out that you have an overly rich condition creating carbon from too much unburned fuel, get your injectors tested for spray and volume or this condition will repeat itself and get worse!

Or you could switch to Biodiesel for awhile and experience a 56% reduction in operating costs and twice the engine life and clean emissions that smell like doughnuts!

P.S. This may not be good for the diet plan.

Jeremy5848 · #12 01-18-2008, 01:00 PM

A leak-down test was done (go back and read my first post).

If there had been a bad valve, the mechanic would have heard compressed air whistling past the bad valve into the intake or exhaust manifolds. He did not. The air was leaking past the rings into the crankcase.

These tests are expensive and I do not choose to repeat them. I trust my mechanic to know his job. I will gladly allow you to come to my home and do your own tests.

So let's move on to fixing the problem. I will look into borescoping the cylinder. I see three possibilities:

(a) No cylinder wall scoring -- problem is stuck rings
(b) Slight cylinder wall scoring -- remove head, remove #2 piston, hone cylinder, replace piston with new rings
(c) Bad cylinder wall scoring -- engine must be removed/rebuilt/replaced.

Jeremy

Knightrider966 · #13 01-18-2008, 01:10 PM

Quote:

Originally Posted by Jeremy5848

A leak-down test was done (go back and read my first post).

If there had been a bad valve, the mechanic would have heard compressed air whistling past the bad valve into the intake or exhaust manifolds. He did not. The air was leaking past the rings into the crankcase.

These tests are expensive and I do not choose to repeat them. I trust my mechanic to know his job. I will gladly allow you to come to my home and do your own tests.

So let's move on to fixing the problem. I will look into borescoping the cylinder. I see three possibilities:

(a) No cylinder wall scoring -- problem is stuck rings
(b) Slight cylinder wall scoring -- remove head, remove #2 piston, hone cylinder, replace piston with new rings
(c) Bad cylinder wall scoring -- engine must be removed/rebuilt/replaced.

Jeremy

Sorry! I guess I often wrongly assume that everyone does a lot of their own work like me.

Still the cello solve is a good idea to loosen stuck rings! All your assumptions are correct except for "c". Engine can be resleeved in that cylinder, but it would require removal to do so, yes.

I was suggesting another leakdown test after the cello-solve test, but then I do my own stuff! I might be interested in this should you choose to sell it.
I would come over to help you, but Santa Rosa is a long way to go! I just noticed your a registered Biodiesel user. Are you burning biodiesel in this now and at what %?

Jeremy5848 · #14 01-18-2008, 02:03 PM

Quote:

Originally Posted by Knightrider966

Sorry! I guess I often wrongly assume that everyone does a lot of their own work like me.

Still the cello solve is a good idea to loosen stuck rings! .....
I just noticed your a registered Biodiesel user. Are you burning biodiesel in this now and at what %?

I do a lot of my own work, especially electrical stuff, but don't have much in the way of specialized diesel tools and have never done a compression/leakdown test. I'd prefer to at least see someone else do a job like that before attempting it myself. (In the next couple of weeks I'll get to pull a glowplug on a 606, first time for me, that's how new I am to diesels.)

Yes, the "stuck ring" theory is very attractive. I'll look into it as one of the options when the borescoping is done -- I'll ask the mechanic today about that.

As shown in my signature line, this car has been on commercial B100 for the past year.

Jeremy

Hatterasguy · #15 01-18-2008, 02:14 PM

B and C are the same. If the cylinder wall is damaged you replace the liner, doesnt matter how much.

Anyway a rebuild is going to be expensive to do right, so a used engine would be the most economical solution.