6.9 Distributor Rotors

[TJ 450]

Good evening all,

I finally got my 6.9 running again (of sorts) today. However, it still has a big missfire and runs very roughly, there is a characteristic put-put sound of a very rhythmic nature suggesting that at least one cylinder is not firing correctly. Ignition timing appears to be way off (retarded), as the "0" mark is way down at the diagnostic sensor. The reference point is up the top just under the w/pump, is that correct?
Bill, I noticed in one of your tutorial pics, your distributor rotor. Is that offset? Someone has fitted the standard M117 rotor at some point, could this be part of my problem? The distributor was, and has been, advanced as far as possible.

By the way, for those who were unaware, this is the list of work required and items that have been replaced/checked so far relating to this.

*Compression test - all withing 5% (according to my gauge!).
*Ignition leads replaced with the correct part, distributor cap replaced with known working part.
*Spark plugs changed before ignition leads - potential problem, plugs were dark grey/black in appearance (not wet).
*Full set of injector nozzles, lubricate airflow meter, clean out fuel dist. with carb cleaner etc.
*Timing chain will need to be replaced as it is obviously worn (original).
*New exhaust system installed (OEM).
*Valve train looks good, oil pressure is excellent.

Tim

 

[s class]

The timing pin on the 6.9 is not directly above the damper. As you look at the car from the front, directly above the damper would be the 12 o'clock position. On the 6.9 motor, the timing pin is visible more between the 10 o'clock and 11 o'clock positions. Well from memory it seems to be this way - you see it by shining the timing light at an angle from the alternator side downwards.

 

[Styria]

HI Tim, that characteristic putt putt from the exhaust you are referring to is obviously not a good sign - to me, it indicates that you may well have a valve problem. Whilst you tell us that all cylinders are within 5% of each other compression wise, you haven't said what the readings are.

I just don't know how I could advise you properly - there are so many factors that influence and are instrumental in a well and properly running engine, and I suspect, and recommend, that you need a good Mechanical shop that has the knowledge to check out all fuel and electrical, as well as your valve components, such as hydraulic lifters etc. in order to determine what's right and what's wrong.

As far as the distributor rotor button is concerned, the position of the shaft may just be one segment out, but that should not affect the running of the engine as you can reposition the leads to suit the position of the shaft. When correct, and looking at the engine from the front, No. 1 lead should be roughly in the 12 o'clock position. Good luck with everything - keep us posted. Regards, Styria

 

[TJ 450]

I had a look at the timing light and realised that the electronic advance setting was set to about 40deg rather than 0, so it seems the timing isn't too far off. About the missfire, there certainly is a lot of possibilities.
Some of the lifters on the RH bank are very noisy. If they were completely collapsed, would the corresponding valve remain closed for longer? I'm thinking it is more than likely a mechanical problem, as it is a very regular miss. There is considerable movement of the engine from side-to-side.
Regarding the compression test, the results were around 145-150PSI or thereabouts.

Tim

P.S. Once I have everything back together, I'll definitely book the car in at "The Starshop" for a bit of a going over. At the moment the trial and error approach isn't working too well.

 

[Styria]

Hi Tim, there certainly is not a lot wrong with the compression of your cylinders - in fact, with those readings, the car should be a sparkling performer.

As far as the lifters are concerned, Mercedes recommend that the static setting should be checked at 40,000 kms. intervals as a routine service. For this, they recommend a special tool that not many people possess. I believe that there is an alternative method, by means of a dial gauge, that is a more precise means of measurements. I have never done this although I do wish how to !

Operation of the lifters, and to test their effectiveness requires removal of the lifter - at least, that is what I believe. Others may come in with different opinions.

Furthermore,I can also tell you that the setting of the fuel distributor and its association with the warm-up regulator are of significant importance. As an example, I fitted a fuel distributor that worked perfectly well to another engine, and one would swear that there are valve problems etc. with the manner in which the engine runs now. It misses slightly, spits and has an uneven beat. So, from that example, it is clearly a case of getting someone onto the job that know what they are doing and what to look for. Regards Styria

 

[WGB]

As regards the warm up regulator my 6.9 starts from cold with a reasonably low regular idle but my 450 is both rough and quite rapid and sounds like a couple of cylinders are not getting enough mixture. Within about 90 seconds it smooths out to a very smooth idle that the 6.9 could never hope for.

When you have checked your ignition and worked out what cylinder is not working why not let it run for a while and see if a thorough warm up doesn't make a difference - esp if a lifter is stuck.

If it doesn't settle remove that particular plug and have a look at it.If it is wet it is less likely to be too much wrong with the fuelling unless you have a very worn injector running too rich. If it is dry you probably have a fuelling problem to that cylinder.

Once fouled the plugs don't clear very easily and it might be worth trying a new plug in that cylinder.

I find the best thing is to shut the door to the shed in disgust and let the mind clear for few days - the answer is always there somewhere.

Bill

 

[TJ 450]

Sounds good, Bill. I'll start by inspecting the plugs. All the injectors are brand new (this was the first time that car has been started with them installed). I probably had the car running for somewhere between half and three-quarters of an hour, It was fully warmed up.
Tim

 

[Styria]

Hi Tim, have you actually driven the car at all, or perhaps just a short distance ? I take it that it is still unregistered and, if so, I can understand any reluctance you may have in 'testing' it on the road.

I don't recall ever seeing any pics of your car. What is it like and what are your plans for it ? Questions, questions, I know, but it would be interesting to get more details if you feel free to do so. Regards Styria

 

[TJ 450]

Re: 6.9 Distributor Rotors/TJ 450's 6.9

Hi Styria,

I have driven the car about 8km so far, a few laps around the block and up and down some right-of-ways behind where I live. It's still unregistered at this point.

Overall, I am quite impressed with the car, as it has minimal rust and is actually better than you would expect mechanically. Though, it has suffered a severe lack of maintenance over the last few years... I don't think it has been driven since 2003, as that was the last year of rego. The previous owners of the car inherited it and couldn't afford to run it, so they left it sitting in their front yard for the duration. They brought it over from Adelaide with them. Apparently they kept it for sentimental reasons.

Although the car is ADR compliant 1-78, the date of manufacture was mid 1976. Interior woodwork is Zebrano with black console, there is no fanfare horn option, the sunroof lacks a wind deflector and there is no evidence of one ever being there.
From what I can gather, the car was delivered in Europe in 1976 and the engine, etc. was retrofitted in 1978 officially. The details in the maintenance book state the owner as "Mercedes-Benz Aust.". There was no first service stamped in the book, but the pre-delivery inspection was done at Lane's. It was first registered in 1981, in Victoria, according to the books. There is a "European Delivery Program" badge on the grille.

Here's some pics

Tim

 

[s class]

Well TJ,

I'm impressed. That car looks rather good for something standing in a garden for 5 years.

 

[TJ 450]

Thanks, s class

Although I have done a lot of detailing and replacment of parts, most things you see are original. Some of the exceptions are the battery tray, rocker covers and radiator. They have been re-painted. The steering wheel was an ebay purchase, as there was no wheel on the car when I got it. The P.O. wanted to keep the Nardi wheel that was on there.
I have since replaced the grille with a good one I got from Nathan.

Tim

 

[Michel]

Very good looking Tim.

What colour is that blue? I like it..

I'm also impressed by the cleanliness of the well in the boot (trunk) area !

 

[B13]

This is going to sound rather irresponsible of me but 8km all told since you've bought it, no wonder its running so badly... it probably hasn't even reached proper operating temperature since you've bought it... I know the temp guage may read 80C, but i bet the oil remains cold-ish.

No, what you need is a PB-style italian tune up...

If the dist rotor really does point under lead #1 and the TDC marker is out by 40 degrees just remove the dizzy and fix it...

Get your permit and then get lost on a freeway on your way to a repairer, get angry and give it heaps.

The team116 #2 car I have ran really bad when I got it (still does if I prolong idle it). The I take it for a caning it just gets better and better.

Of course by all means get a 2nd opinion before going for an italian tuneup, I wouldn't want to be seen to be putting you up to it if there's a valve about to break or something...

I.

 

[TJ 450]

Hi Michel,
Thanks for the comments, I believe it is just blue, the non-metallic version of. It has been partially resprayed in a slightly lighter colour though. I will be having it restored to the original colour in due course. About the boot wells, I was very surprised with their overall condition, along with most other panels. Dents aside, the sills are original and very solid. Rust has started in the firewall as the car was sitting, though it is still very localised.

Hi B13,

That's true, I'll see how it goes after changing the plugs and getting the timing right. I still have a bit to do before I can get the permit though, such as replacing the front spheres and strut mounts, then I should be right. I certainly agree that it does need to be driven "properly" before reaching any conclusions, as these cars really need to be driven on a regular basis.

Tim

 

[TJ 450]

Well, I pulled the spark plugs tonight. #1 was dry carbon fouled, #2 was covered in what looks and smells like WD-40, obviously not firing. All the others are good. Perhaps that light oil is WD-40 from when I injected it into the cylinders and it was not firing due to the previous dodgy ignition leads. Obviously the plug is still fouled so even though the leads are new, it's still not firing.
I'll find out on the weekend when I get a new set of plugs and my hydro fluid/filter/o-rings.

Tim

 

[Styria]

Hi Tim, that's a nice enough looking car to encourage you to perservere, and to effect steady improvements as you go along. With the prevailing compression readings and what appears to be a high compression engine,, this girl should fly.

Believe me, new spark plugs can make a hell of difference. I once had a 6.3 that gave untold problems for ages - it drove everyone aound the bend and there was a lot of money involved in getting things right. In the end, a new set of plugs completely transformed that car. I am not saying that was 'the end all and be all' solution, but by God it certainly finished what had been a totally traumatic and troublesome period.

Yes, you need to drive that car - constant starting and fiddling will not make it run better - also, from my 6.3 experience, plugs don't seem to clean themselves particularly well, no matter how much you rev the engine. Good luck with it. Regards, Styria

 

[B13]

I've heard people remark that the 6.3/6.9 when cold are rough, noisy and basically very un-Mercedes-like... I have to say I've found this the case with both of mine and to a lesser extent the M117 engine as well. Takes a few km with my 6.9 each morning for it to settle down to the refined smooth V8 burble you'd expect from an MB, esp. if your car as an elevated cold-idle speed.

 

[TJ 450]

Heres a video showing how the car was running a few months ago.
I have a new set of plugs ready to go in this weekend, so hopefully that will get all cylinders firing properly.



Tim

 

[Michel]

Tim,

Is that a Metropolitan in front of your 6.9 ?

 

[TJ 450]

That is indeed a Metropolitan.
The other is a 1932 Nash 1090.

Tim