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1986 300SL - would appreciate advice

8K views 40 replies 18 participants last post by  stradivari1689 
#1 ·
Hi

Last week, I was given (yes, given) a non running 1986 300SL. The donor even paid for it to be towed to my place. Here are some images of the car as it was delivered to me. Please read down further.









The vehicle has about 98000 miles on it. The cloth top, windshield, tires were replaced about 2 years ago when it got a new paint job. The interior looks about as nice as the outside. The hard top (he delivered it in his pickup) is on a dolly and matches the car. This being said, it was a very generous gift and I feel it deserves a mechanical renewing.

Whilst driving back from the beach, traveling about 75mph, he experienced a sudden gush of steam from the hood (bonnet) and he pulled over as soon as he could. The car stalled on the side of the road. Opening the hood, he found the fitting on the upper right of the radiator had broken loose. See picture of what I found and note how the line can be freely moved in and out. The "nut" was found, by the PO, on the ground where the car came to rest.









It appears the radiator had a catastrophic failure and vented all coolant in just a few seconds. I would think I would have to replace the radiator. Is there a recommended source?

Surveying the rest of the engine compartment, I found the cover for the distributor was loose. Removing it, I found that parts of it were melted - the guides for attaching it for example. Interior molding were also warped by (I suppose) heat. Look at the pictures to see the damaged cover AND the melting of part of the distributor cap. It was very hot in the engine compartment. Could the venting nearby steam have done this, OR, was this most likely the engine itself heating up?









The oil smells burnt. The engine compartment has what I can only describe as a "cooked" smell.

I attempted to start the car. Battery was good, all lights on the dash seemed to be in order but the car did not start. Only the sound of what I presume to be the starter trying to turn things. Please look and listen to the video. This is the one and only time I attempted to start the car.

http://www.replications.com/r107/uhoh.mp4

So, what does the collective think about the engine??

If it is just electrical, do I even think of trusting the engine, now?

If it is the engine, do I rebuild this engine? Can I trust it?

If it is the engine, do I swap in a known good engine? If so, what type? I noted (from looking at some web sites) it uses a m 103.982 Are the other potential 3.0 inline 6 engines going to go right in? Has anyone done this to a 300L?

I live near Gettysburg, PA, USA. As most of you probably already know, the 300L was not officially imported here and I'm not finding many resources (yet) for this primarily European model. Ex. I will not find a donor 300SL the next town over . . .

I am totally new to Mercedes - never owned or worked on one. I would welcome any and all advice on how I might proceed in an economical but thorough manner.

Thank you for your time and kind attention,

Regards,

John+
 
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#2 · (Edited)
The person who donated it to you said: "he pulled over as soon as he could". That could mean anything from a few seconds, to until the car simply stopped running (which I suspect given the "cooked" smell.)

The video seems to show the engine turning over. If not, time for another engine. If, in fact, it did turn over, you can probably salvage it. Parts are expensive - but if the block, cylinders, pistons and rings are okay, you're probably in luck.

Good luck. The Benz in-line 6 is one of the most bullet proof engines they ever built.
 
#3 ·
The good news is that the engine appears to be turning with aid of the starter.


However , you can do some simple tests before you decide which direction to go in.

First thing would be a compression test.

I'm not very familiar with that particular engine but if I recall.......it is a great engine but is prone to eating head gaskets.

The melted stuff might be related to overheating or something else entirely.

I would seriously do a compression test before all else.

Any coolant in the oil?
 
#4 ·
Thank you both for your replies.

The oil does not seem to have any coolant in it - no milky goo at least. Oil level is normal.

I will try a compression test. At least we will know the status of the current engine.

Thank you again.

John+
 
#5 ·
I fear this does not end well... From the video, I can not detect any hint of compression. Sounds like the engine is spinning freely. Any number of reasons from hole(s) in pistons to stuck/bent valves, to, well, you get the idea. I concur with the advice to do a compression test.
 
#6 · (Edited)
John+

Please read this comment with the understanding that I have no mechanical ability whatsoever so I usually stay clear of offering any views on matters mechanical.

My response relates to your question concerning a potential replacement engine for your car and the fact that the 300SL was a grey import into the US and therefore that there will not be a ready source of donor 300SLs lining up to source a replacement engine for your gift horse.

However, Mercedes Benz made approaching one million M103 in-line six three litre engines using it in no fewer than six different MB models many of which were sold in the US as official imports.

So whilst there may be a dearth of 300SLs there almost certainly will be no shortage of W124 300Es or 300CEs fitted with the M103 found in your car.

My only caveat is that each of those might have a slight difference of set up and if you do end up having to replace the engine it would obviously make sense to take advice.

That said the M103 is an extremely robust engine so fingers crossed it won't come to that.
 
#8 ·
Dear Friends,

Thank you for your advice so far.

I need to look at a parts book to figure out what is what. (online source?)

I had not traced the loose line. Transmission line? Now that expands the issues. What in the heck happened here?

I will run a compression test later this week but I don't have much hope there.

Best Regards,

John+
 
#12 ·
Dear Friends,

Thank you for your advice so far.

I need to look at a parts book to figure out what is what. (online source?)

I had not traced the loose line. Transmission line? Now that expands the issues. What in the heck happened here?

I will run a compression test later this week but I don't have much hope there.

Best Regards,

John+


From the General Tech section of the EGv107.
 
#9 ·
Dear Friends,

Please pardon the length of time in following up to my post.

We ran a compression test . . . nada . . .zip . . . zero . . . It seems the chain has jumped the gears. It was suggested the tensioner may have failed.

I am really hesitant about reworking this engine given many components have heat failed. I *think* the best route is to swap an engine in from some nice 300E.

What does the collective hive mind think?

Thank you in advance,

John+
 
#13 ·
no compression - the real reason

Dear Friends,

With things beginning to warm up again, it was time to return to our 300SL project.

Timing chain was NOT the culprit it seems. At least not at first. Overheating was . . . the head warped from the extreme heat. This opened a gap and resulted in no compression. The engine reached a sufficient temperature for a plastic part mounted on top to *slide* down the slope of the cover. The plastic chain tensioner was somewhat malformed as well.

I had an experienced Mercedes mechanic take a look (without telling him what I thought might be wrong). It was both satisfying and sad to hear the same diagnosis. Nice that we figured out what was wrong but not so nice that the engine would be suspect for any further use.

As some of the plastic bits were melted around the distributor (and else where) I wonder if other electrical parts - those on the firewall for example - would be suspect as well.

We found a 300E donor sedan, rear ended, having 109K on the odometer so not far off from the chassis.

Would any of you, experienced with such things, care to offer any advice on what else I might be aware of?

John+
 
#14 ·
Here the overheated engine has been removed. When the oil was drained it smelled so badly it would make one retch. Note the discoloured dizzy plate - it's brown now (was a bright yellow). Also, the sensor on top was so hot it melted enough to allow the sensor to be slid off of it's base a bit. Head cover has lost black paint where it used to be pristine. Head is definitely warped.



Engine from the 300E in place. I'm glad MB put this engine in a "common car." Finding a model specific engine for a ROTW car would have been a challenge. Engine went in fine, manifold hooked up easy. Old (SL) hoses were replaced including those in the heater core circuit. Side benefit of fooling around with the heater core and adjacent areas was the pleasant discovery that there was no rust.



Observation: All the necessary parts were found at MB. Few engine/model specific parts could be found from domestic aftermarket sources. MB USA distribution even had THREE of the radiators in stock. Mind you, these radiators seem to be specific to this engine fitment in an SL. Curious that they would stock them. Not that I'm complaining . . .



To the "hive mind" of the group, "from your collective experience, have you encountered issues with the engine electrics after a heat episode?"

(I am wondering about sensors and ECU . . . not those mounted on the engine, but those on fenders and bulk head).
 
#15 ·
Nice work. You should have a nice and desirable SL when done.
 
#16 ·
5 bad engines ??

Dear Friends,

Well, the "new" engine was in, everything hooked up and it started right up. It roared to life and had a bad knocking sound from deep within. Something wrong with "new" engine. <sigh>

Soooo . . . out it went. Fortunately, the recycling coop had several other m103s. They would bring one, it was tested for compression first ... and failed. Four engines later we are running out of local "door stops" to run tests on.

Engine number "2" looked pretty clean and, unlike the rest, had oil still in the crankcase and spurted oil very nicely over the important bits in the head. OFF WITH ITS HEAD! Iron block looks real good. Someone did something right with this one. Head is being sent out to machine shop for them to restore it to it's (almost) former glory. All new bits are being ordered for the head. Barring the shop finding something amiss with the head we should start reassembling next week.

Any thoughts to share at this point?
 
#17 ·
You are going to be an expert and installing this engine:)

Curious, how difficult was it to remove the Bell Housing bolts?
Any other tips you can share with us on removing/installing this engine?
 
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#18 ·
The car was typically only driven on nice, dry, days. There is little rust or other corrosion on the car. The nuts came right off and the engine separated from the bell housing with no difficulty. Removing the engine was text book simple.

In removing the head we discovered a fair amount of carbon build up which probably caused the valves to stay open a hair resulting in low and irregular compression. We found the cylinder walls had original factory cross hatching with no rim ring at all. With little apparent wear and good evidence of oiling the block is probably just fine.
 
#19 ·
Dear Friends,

The head was sent out to the machine shop. They pressure tested it first to determine that the head was usable. Then it was taken apart and parts were measured for tolerances. The valves were virtually unworn. Valve guides were replaced as a matter of course. A few areas were touched up and then the unit was reassembled and pressure tested again. Here it is back on block.

I hope some of these pictures are of use to those that may never have seen their engine torn down in this way.

Regards,

John+
 

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#24 ·
Hello Friends,

Yesterday, with everything in place, we fired up the new old engine. Started right up but felt like it was running a little rough. Almost like it was misfiring. After warming up a few minutes we took it out it and it really seemed to do well. The roughness disappeared for the most part. Returning to the garage, it was running a bit rough again. It seems to be fine under load but rough when idling without load.

On a hunch, my Merc guru friend pulled one of the injectors he was suspect about. It looks ok. Put a new seal on it and . . . most of the roughness went away. It would seem that air was getting into the wrong place. We are going to replace all those particular seals tomorrow when they arrive.

Question(s) for the collective mind:

Have the injector seals been an issue for you? perhaps age related? Or, could they have broken down due to the heat event which started this whole procedure?

Thank you and best regards

John+
 
#26 ·
Have the injector seals been an issue for you? perhaps age related? Or, could they have broken down due to the heat event which started this whole procedure?
Yes, yes, and yes. Injector seals leaking air is a common issue, it's usually age related, and overheating badly enough to melt plastic parts could cause injector seal degradation.
 
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#28 ·
The injector seals were seemingly a fault for most of the "roughness." For the most part, it idles well, however, it every now and again seems to hit a "rough" spot. I have a spare set of Berus. If things were hot enough to harden and ruin the seals (two seals had to be "wapped" and they cracked apart) it would not surprise me the plug wires might have been compromised as well.

SinSL . . . I, too, have been thinking about the injectors. If it was hot enough to effect the metallurgy what might it have done to the injectors as well?

I am going to try swapping some plug wires and see what happens before we get a new set of injectors. We have tried to use the injection system as it was before the thermal event. The car was, reportedly, running well. Given the condition of the vehicle, it seems the PO took good care of it and probably gave the mechanicals similar care. . .

To those whom have been posting: thank you for your collective input. I appreciate the time and kind consideration you have taken in reading about my project, thinking about it and offering your advice.

Regards,

John+
 
#29 ·
Dear Friends,

We put another set of Beru plug wires on, used, but look good - no green oxidation inside - dated 12/12. Fuel was at 1/2 tank (since last August) added Lucas injector cleaner and filled up tank with 93 Sunoco. Perhaps it will kick loose any clod that may have been in gas or injectors (?)

Hooray!

Car took first run ok. Then took on 40 mile run.

Observations (remember this is the inline 6 cylinder M103):

Still rough at idle. Idles at about 600 when warmed up.

Smooths out at speed. Very smooth comfortable ride. Handles well. Seems to have plenty of power. I would not call it a rocket ship but I got to 60 fast enough.

Temp runs about 85.

Suggestions on rough idle? (and thank you!)

Regards,

John+
 
#30 ·
@verg

you need to check and see if your OVP relay is good. It has a fuse on top of it that may have blown. This relay is located behind the battery and has a red top. It's good practice just to replace this anyway as they tend to go bad.

After that you need to check the duty cycle at the X11 socket. This can be done with a common multi-meter. See W124 forum for more info.
 
#32 ·
Good post John keep us informed on you little baby wont you .You have the same engine as my 260e . I am just abput to takle the injectors .I have all the bits and bobs to do the job only short of injectors .But am thinking of cleaning them up in my sonic cleaning tank .Just need fluid to break all the carbon up inside them.
 
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