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PROJECT DRIVEWAY 1: 1982 Mercedes 123 300D Sedan Restoration

NOTE: Latest Update December 31, 2008

FROM THE AUTHOR:

For a couple years now I have been looking for a good example of a 123 chassis 300D turbo to restore. These cars have become one of the most popular and highly regarded diesel passenger cars of all time. I believe documenting the steps of its restoration on our website would be beneficial to many of our customers. Periodic maintenance updates could be made on a weekly or bi-weekly basis. The car has finally arrived! I hope you enjoy following along on its process and benefit from the things you will learn along the way.

Kent Bergsma

Phase 1: THE SEARCH

My goal was to find a 1982 to 1985 300D sedan in good solid condition. I did not want to find one so nice that it did not need much work, nor did I want to find one that was such a dog that it would become a time and money pit.  It needed to have just the right amount of things wrong to make it an effective learning project for our readers. It had to have absolutely no rust or accident damage and under 250,000 total chassis miles. From my experience of working on hundreds of 123 chassis I have learned that a Mercedes exposed to road salt is just not worth dealing with and one with more than 250,000 miles may leave you fixing many more things than you ever imagined. I was not afraid of an engine transplant as I have a good low mileage engine as well as a completely rebuilt 617 turbo hiding away in my shop. A good color combination was highly desirable.  It had to have a good interior.  Of course I wanted to find one with excellent paint, but a repaint was not out of the question as long as the body was not covered with dings and dents. The search has finally ended.  The car was located and purchased out of Poulsbo, Washington for $600 and trailered by the owner to Bellingham on September 10, 2008.

Phase 2: INITIAL VISUAL INSPECTION

Although normally against my principles I did buy the car sight unseen.  I was able to obtain a detailed description from the owner along with numerous pictures.  Others have already learned that buying an old diesel sight unseen can be very hazardous to your pocket book. If you are considering purchasing a Mercedes diesel I HIGHLY recommend you first obtain and read my Mercedes Diesel Buyers Survival Guide. This guide will show you many of the pitfalls to avoid and direct you on which models are least troublesome. I have received many emails from our customers wishing they had read this guide before they purchased their diesel.

CLICK HERE to order / read more about this buyers guide.

The owner expressed to me that the car was straight and rust free but needed paint. The main reason he was selling it was that it would not go any faster than 30 mph. I figured that if the engine was shot that would be ok for this project. On the other hand I have had some pretty amazing things happen when buying old Mercedes diesels that would not produce any power. Of the dozen or so I have purchased with those symptoms over 80 percent turned out to only need a simple fix. Maybe I would even luck out again this time.  In the end I had to calculate my risk of buying sight unseen.  If the car turned out to be a total mistake I could at least get my money back in parts....

When the car arrived Sunday on the trailer it proved to be exactly as my mind pictured. A quick two minute walk around showed that the body was good, chrome was good, glass was excellent and interior (except for cracked dashed) was above average (except for the misty smell inside the car). The engine fired right up without hesitation and the car was driven off the trailer. With title in hand I waved goodbye to the seller and decided this diesel just might be the right candidate. It would take a closer inspection though, before my decision would be finalized.



The next day I showed the car to my Angels - Kaia, Kiana and Kristin.  As you can see in the pictures they were excited about the find.  They thought that it maybe even had some potential but absolutely did not appreciate the mold and smell inside the car.  It was obvious the car had sat for quite some time without being driven.  The peeling clear coat was also a turn-off during their initial inspection. At least they did not think I was crazy.

With the visuals out the way it was time to dig into the reasons the engine was running so poorly.

Phase 3: INITIAL MECHANICAL INSPECTION

It was time to get in the car and drive.  Once again I was impressed with how well the engine started and quickly shut off. These are good signs of strong compression. My first goal was to find out why the car had no power. Sure enough I got out on the road and floored it.  It hit its max 30 miles per hour and felt like it was dragging an anchor! These symptoms can be classic signs of plugged filters, improperly adjusted throttle linkage, poor fuel delivery, and plugged air intake or exhaust.



All these procedures and checks are covered in my manual - Mercedes Diesel Performance Tuning and Repair.  CLICK HERE to order / read more.

Back at the shop I went to work checking the simple things first. You will be amazed at what I found!  Check back for the next installment...

 

 

 

October 25 update:

The first thing I looked at was the throttle linkage. You would not believe the number of diesels I have seen that were not getting full throttle at the injection pump. Linkage appeared out of adjustment but I found it was getting full deflection to the wide open stop. Next I pulled the ALDA fitting at the rear of the intake manifold. Sure enough - it was plugged solid with soot.  I cleaned the banjo fitting and was feeling confident this would give me a good boost in power.  Before I drove it again I pulled the top of the air cleaner to check the filter.  Filter was only slightly dirty and no signs of any obstruction in the intake elbow to the turbo. Fired the engine up again and hit the road. I floored it thinking I was going to feel some normal acceleration, but I was only able to get to about 35 mph before the car topped out. At this point I figured it had to be a fuel restriction somewhere - either at the tank outlet screen or the main fuel filter. Plastic pre-filter looked ok. 

As I was getting ready to pull the car back into the shop I kept thinking there had to be something else I was missing. Then it dawned on me.  Considering the condition of the car and the musty smell inside it was obvious that the car had not been driven for quite some time.  How long was anyones guess! Just how old was the diesel fuel in the tank! There was less than a quarter of a tank but any amount of old diesel fuel (older than one year) can raise havoc with engine power. Ran down to the local gas station and picked up a 5 gallons of new diesel.  Poured it into the tank and hit the road again. This time after a few moments of coughing and sputtering the old diesel accelerated right up to 55 mph. How is that one for a simple fix!

From the sound and feel of the engine I could tell there was still more work to do. The engine was running real rough and smoking right at startup. Transmission was not shifting properly and the water pump was making some bad noises and leaking water  (this was probably why the car was pulled off the road in the first place). The first thing on the list would be to determined the health of the engine.  The next installments will include the results along with other things I discover on a close engine inspection in the shop and on the lift.

For a complete detailed guide on how to determine your engines condition and causes please refer to my Advanced Diesel Fault Diagnostic Manual

This guide will cover starting, shut-off, performance, fluid leak, and noise issues. Each fault is discussed in detail along with possible causes and how to troubleshoot each one. A must have for any Mercedes diesel owner / enthusiast.

 

                                                                                 Or CLICK HERE to order my illustrated diesel compression test guide.

 

 

Phase 4: THOROUGH ENGINE INSPECTION

November 1 update:

During this phase I will evaluate the internal condition of the engine and determine if it is worth saving or in need of replacing. If you are wondering why I am starting here let me explain. In any old Mercedes diesel, the engine is the most important and valuable asset of the vehicle. In many cases the value of the engine can be more than what an owner paid for the entire car. Properly rebuilding a diesel engine can range anywhere from $4000 to $8000 (and up) if you have it professionally done. That has proven to be a real shock to many who are faced with a dying engine.

We regularly receive emails from our customers who have spent hundreds of dollars on their Benz only to find out later that the engine is worn out. I know the temptation. After spending weeks or months searching, you find and acquire your diesel and are immediately inspired to fix all the cosmetic and minor mechanical flaws. Then winter comes and the temperature drops. You discover the engine is very slow to start on those cold mornings. You decide take it in to your local shop for a check up. When the report comes back you are shocked and dismayed to learn your engine needs a complete rebuild.  This happens more often than you would think. Avoid the temptation to put ANY money in your diesel until you determine the condition of the engine.  In some cases what you find will encourage you to immediately sell the car and look for another.

There are a number of things you can do to help you evaluate your engines health. Sight, sound and smell can all help, but the single most important inspection item is a cranking compression test when the engine is cold. Diesel engines require very high compression to heat and ignite the diesel fuel properly. When the piston rings and cylinder walls wear, the compression will drop resulting in poor starting, loss of power, excess fuel consumption and poor fuel economy. AND there is NO quick easy fix for this condition.  You can not just -throw in a set of piston rings - like you could on a gas engine. A lasting fix will require complete disassembly of the engine - installation of new pistons and/or cylinder wall liners and rings - as well as bearings, gaskets, head rebuild, etc.

This next week I am pulling the 300D into the shop and will perform this important test along with an inspection of all external engine components, seals, gaskets and hardware. Check back later in the week to see my results. This will be my critical - Engine GO or NO GO decision...........

November 6 update:

On the 15 minute drive to the shop I had my first opportunity to see the engine good and hot and to get an overall feel of the condition of the chassis and suspension. What I noted was encouraging. There are a few simple visual checks one can make when inspection a diesel engine. These can all be considered guages to the internal health of the engine.  Here is a quick list and the corresponding results:

 

  • 1. Hot engine idle oil pressure. This can give you a good indication of the condition of the lower end of the engine (main bearings, rod bearings, pump gears, etc). To perform this test you want to drive the car for at least 10 minutes. The engine should be idling at 600 to 700 rpm (fast idle will not give you are accurate indication. On this 300D pressure gauge held a steady reading a just under 2 as shown in the picture. That is a good sign.  I do not like to see it drop below 1 - although Mercedes literature says that is acceptable.  If it drops below 1/2 at hot idle then you may have problems. NOTE: Other problems to attend to later:  Fuel guage intermittent and engine temp running below norms (indicating faulty thermostat)
  • 2. Condition of air filter. A visual inspection of the air filter and air filter housing can give you a good idea of just how much blow by the engine is producing. Excessive crankcase blow by will blow oil into the air filter and housing and will show up as a oily filter element or oil pooling in the metal housing. This does not necessarily mean your engine is toast, but it is another important gauge of its overall condition and expected life. On this engine the air filter was free of oil and the housing only had minor oil staining. Another good sign.
  • Amount of crankcase pressure (blow-by) pressure at breather.  All older diesels will have some blow-by so do not panic if you find yours does.  It is the amount and coloring of the blow-by that you must look at closely. My manual Diesel Performance and Tuning goes into this in more detail and will expain another test you can do. If it is blowing a hurricane out of the tube (when removed from the air filter) and/ or the color is smokey grey then you may have a problem! On this engine only average clean blow by was found for an engine of this age.  One more encouraging sign.

On the next installment I will post the results of the valve adjustment and compression test.

November 8 Update:

Engine Go... or no GO...

First step was to remove the valve cover.  Upon removal I took the time to check the condition of the camshaft lobes. These will often give you an indication of how well the engine has been taken care of.  A camshaft with scored lobes and rockers arms often indicates the engine did not receive frequent oil changes and is a sign there will be other excessive wear inside the engine. In this case the camshaft and lobes looked like new with absolutely no sign of wear. At the same time I also checed for timing chain stretch (refer to may manual Diesel Performance Turning and Repair) and that also looked excellent. Now these were good signs...

 

Next step was to do a valve adjustment.  We found 3 exhaust valves loose and two intake valves that had absolutely no clearance. This could explain why the engine ran rough for 2 to 3 minutes at startup. Most of the other valves checked out ok and with damage to the threads on the adjusting nuts. My custom valve adjusting wrenches include complete instructions and worksheets so you can do this job yourself. This was another good sign...

 

Then it was time to hook up the compression tester.  Injectors were removed and inspected.  Only minimal tip wear on the injector nozzles was noted. Compression tester hooked up to 1 cylinder and engine cranked over with starter. Glow plugs and fuel source plugged off for engine cranking. Whoops.... Compression only came up to 180 pounds on the guage.  There must be some thing wrong with the gauge!.  So we hooked up the compression tester to #2 cylinder and cranked again.  Compression came right up to 365 pounds. Now I was beginning to worry. Checked valve clearances again on No. 1 and redid cranking compression test.  Once again compression only came up to 180 pounds.  Ughh.  This is not an acceptable reading.  Remaining cylinders tested and all checked out at 350 to 375 pounds (now that is acceptable!).  Note:  The compression tester we offer for sale comes with my manual of how to read compression test results.

It was suddenly engine decision time.  With low compression on one cylinder, the engine could conceivably run for a very long time - but would likely not run well and in my mind this would not be acceptable for a restoration project. The problem could be a leaking intake or exhuast valve, but 90 percent of the time, low compression such as this indicates damaged piston/piston rings. I just don't have a good feeling about this engine. I have been around these long enough to know when it is time to bail....

Final decision: Engine will have to go . I will transplant another good used engine from a 1985 300SD. Before pulling this SD engine, I had good opportunity to run the engine and drive the car (minor rear end accident), With less than 120,000 miles it is one of the better used engines I have come across. Since this engine is out of a 126 chassis it will not be a direct drop in. There will be a number of things I will have to swap out before installation. I will go over these in the engine restoration section. Click on the ENGINE RESTORATION / TRANSPLANT link below to see how I am going to handle this transplant.

For those of you faced with the prospect of purchasing a diesel or who have just purchased one I would highly recommend you do a complete engine physical exam.  I have just put together a PHYSICAL EXAM KIT for 615 616 and 617 four and five cylinder diesel engines.  This  kit includes everything you will need to do this important exam yourself. ClICK HERE to view these kits.

November 21, 2008:

Besides the engine, I will be working on a number of other mechanical and cosmetic areas at the same time. It is becoming obvious if I post the full restoration details to this one story line it is going to get VERY long. So I have decided it would be a good idea the break up the restoration project into the following subcategories;  If the subject line is highlighted in blue then you can click on that link to continue to that category. If the line is not highlighted it means there have been no posts to that category (work not yet begun).  :-)

 

 

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