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  #1  
Old 10-23-2008, 08:49 PM
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'81 300 TD- apart, needs rings, I need advice!

hello All, I have a chance to buy a very clean '81 wagon for 1,500 that has had the head and sump removed as the PO was advised that the rings were badly worn. My question is, easy to pull pistons and re-ring with correct ring size? The car had the head redone to the tune of 3,000 dollars plus so this car has seen some love and this work was recent. I think the PO just got it in his head that the car needed rings based on a mechanic's advice (?) The engine has 189,000 on it which is low mileage. The PO paid 5,000 for the car last year - I am going to offer 900 and hope to get it running this winter. This will be my first ring job - I will also reseal motor and take care of other work in and around the engine. All comments are welcome! Car has been stored in a garage here in California

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Old 10-23-2008, 09:16 PM
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Being able to re-ringing an engine depends on much much taper an out of round exist on the cylinder walls.
Next is if the Piston Ring Grooves are worn or the out side of the pistons are worn.

If either of the above is in bad condition/out of spec it is better to rebore the cylinders and replace the pistons with (ones of the same type and weight) good used or new oversized ones.
Another way is if the Pistons are OK but the cylinders are worn is to have the block bored and new cylinder Sleeves installend and bored to your old good pistons (the Cylinder Sleeves cost way less than new Pistons).

Sometimes it is cheaper just to get a good used engine.
It seems like low mileage but why is the head off in the first place???
Low mileage does not mean much if the engine was over heated, a Oil Cooler Hose leaked and starved the engine for oil, or the prior owner never changed the oil regularly.
It is better to buy a running vehicle as you have a better idea what you are paying for.

Last question how does the owner know it needs new rings? Were the Cylinder Bores measured, was a compression test done, or did the car have a history of burning oil?
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  #3  
Old 10-23-2008, 10:47 PM
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No it is not easy to re ring. Usually there will be other major wear in the block if the rings are shot as well. You have to pull the engine if it was just rings anyways. The oil pan is two piece and the major portion cannot be practically removed with the engine in the car. The present owner has had it for only a year. The odometer indicated milage on many 123s is not accurate for many reasons.

That said a good used engine could be aquired for it's short block. The head is station wagon specific as it has the rear suspension pump in the head. At least his head is rebuilt. Make sure it is the right head.

. You might be advised to take a guy with you to examine the car carefully before making a decision. He should be really experienced on the old 123 mercedes diesel types. Of course it is a fair price if the car is really good otherwise and overall milage as represented. Or previous owners have spent a small fortune on it if a higher milage example.

If the drivers seat has any major wear you might be better to take a walk. The experienced guy will know what to look for. In my opinion a somewhat dangerous situation for someone not experienced with 123s to buy on his own.
Some things about these cars you only learn by owning and working on a few of them yourself. This develops an educated feel for what you are looking at in another example. . It is too late to change your mind after you buy it and find out yourself sometimes.

There is nothing wrong with taking on a decent project. You do have to pretty well know what you are starting with though. These cars are just a little harder to judge the condition than most even when running with no experience. With a reasonable amount of prior experience you kind of know exactly where to look for possible problems.

Just so you do not think the above is all doom and gloom. An experienced guy may tell you it is a really good buy after doing a few checks and having a look. You do not want to buy a potential money pit in this state. If the present owner paid five grand and in the first year has paid 3k to rebuild the head and is faced with other problems he wants out of his money pit. Only he knows if there are other expensive problems lurking. Things like the automatic transmission, rear automatic self leveling suspension, air conditioning, Front end components, shocks, brakes, cracked flex disks, tires, the list can be extensive.

I only wish I had taken someone really experienced along on my first 123 diesel purchase. The car started easily, transmission shifted well, Brakes seemed a little hard , heater blower would not activate,etc, simple stuff to fix on most cars. Body was really good and so was the interior.

The list of what I had to repair became almost endless. The car when new and under warranty things were fixed I hope. After that the owners just drove it. If something actually stopped the car from moving it was dealt with. . If non essential the past owners kind of did crazy things sometimes to get around it. Otherwise nothing was repaired.

If at that time there were not good parts cars around The bills to repair it myself would have been astronomical. Remember I started with a good engine and transmission. I never tallied up the total repair hours. They were substantial as well. I have purchased three more 123ds since that time.

I actually enjoy spinning wrenches etc as a general stress relief when I find the time. That first 123 diesel car was just excessive. I still own it. The upside was it did teach me a lot and familiarized me well with many aspects of the 123d type.
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Old 10-24-2008, 02:16 PM
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excellent advice! I have done alot of work over the years on gassers and diesels, and I assumed that I could do rings with engine in the car -sounds like this is not so! I have a mercedes guild mechanic friend who I will take with me so that we can make some educated assessments. I think buying a running motor as a donor is an excellent idea, unless I try to rebuild existing motor once pulled -
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Old 10-24-2008, 02:45 PM
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Another way to look at it is, a well kept, rust free TD even without an engine is worth 1500.
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  #6  
Old 12-15-2008, 07:17 PM
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Quote:
Originally Posted by warmblood58 View Post
excellent advice! I have done alot of work over the years on gassers and diesels, and I assumed that I could do rings with engine in the car -sounds like this is not so! I have a mercedes guild mechanic friend who I will take with me so that we can make some educated assessments. I think buying a running motor as a donor is an excellent idea, unless I try to rebuild existing motor once pulled -
you said: The car had the head redone to the tune of 3,000 dollars plus" wow! I wonder what they did? maybe it needed a new head from the dealer? a head rebuild with the original valves would run about $350 to $400. Uninstalled of course.
I re-ringed my '87 at 220K miles, because I had the head off and knew little about the history on the engine. I did it with the engine in the car. Turns out several rings were worn significantly but the cyl walls were not in need of replacement (liners that is). I considered myself lucky to have bought the car sans head (not running) for $475 so it was something I could invest some money in to bring it up to spec. Now its a daily driver.
If the cyl walls had been worn badly I would have been not so lucky but it wasn't a real high miler so the cylinders were still fairly round. If you look back in the archives I posted the brand of rings and headgasket I suggest using (I remember the gasket was a Victor Reinz). That engine uses about 1 qt of oil every 1000 miles maybe a few more miles depending on how hard I drive and that's not bad for an old diesel on its second life! After I broke it in carefully I took it out on a desert road and easily got it up to 105 MPH (but its an '87 6-cyl turbo, not the 617 you have).
Your car is running, right? then what is the oil consumption?
Do you have a lot of blowby? If yes to these q's then you might have worn rings and it might be worthwhile pulling the head and inspecting the rings. Hey the car sounds ike its in good shape otherwise and if you like it and want to keep it a long time then the plan to restor the engine is justifiable.
I used to drove a '79 diesel with ring problems. I even drove it cross country and had more blowby than you can believe. It was a junk it or fix it proposition. I pulled the engine and had it bored and new pistons etc. Still got it, its got a turbo engine out of an '85 300TD now though. Retrofitting that turbo into the non turbo chgassis was a exercise I would not go through now. Especially with the sour economy, it takes a lot of stuff to convert to the turbo. I believe your '81 is NA (non turbo) also, right? that was a transision year as I recall.

In the 123, to remove a piston you need to remove the entire oil pan, the upper part of it that is (there is a upper main pan and smaller lower pan on the 123). I believe the suspension blocks the upper pan in some early 123's.
Have the mechanic look at the cross hatching on the cyl walls, that needs to be there to assure your new rings will seat properly otherwise they will wear prematurely. And of course he needs to carry a cyl measuring device and a strong light to see what hes doing to measure the amount of wear.
At the mileage you reported its possible the cylinders are still round enough to accept new rings.
You can also pull a piston to see what kind of wear they have accrued, if you have the pan off and shop time. I would suggest if you have the opportunity to replace the rings by all means do so.
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Last edited by dieseldiehard; 12-15-2008 at 07:25 PM.
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  #7  
Old 12-15-2008, 09:39 PM
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I cannot remember if the 81 is a turbo. If its not I have a perfect na block that I used the crank out of that I will sell cheaply. I may have five good pistons too.

Most likely your crank and bearings are good.

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