6.9 valve timing sorted out

[WGB]

Thanks for that level of detail and exprience.

I too have a similar 2 year old assistant but he never just sits and plays with the little things - always the biggest spanners and screwdrivers.

Bill

 

[s class]

During this process a couple of small 3/8" drive sockets have gone missing. I'm having nightmares about the fact that he was playing near the car when I had the valve covers off, and I just hope that he didn't put them in somewhere they shouldn't be. I'm hoping they're just buried in the garden or something harmnless

 

[s class]

I've also been meaning to mention that since sorting out the valve timing, the quality of my transmission's shifting has also improved considerably. I attribute this to proper vacuum being dependent on, among other things, proper valve timing.

Bill, you will not be disapointed with your new chain.

 

[Styria]

Hi S-Class, I have re-read the whole thread as I had obviously missed some of your posts in the hurly burly of keeping up with all the goings-on on the discussion board. What you are telling us now is smashingly good news, but in summary it arouses my curiosity on two counts:

1. How did you measure the inlet valve lift of 2mm on cylinders 1 and 6, and

2. Did you fit off-set keys to BOTH camshafts ?

The performance comparison with your W140 is rather interesting - think about this...what would a 4 or 5 speed box do to the performance of the 6.9. I wonder if it could also be 'explosive' like your 140 ? When you think about it, the gear ratios on all 116 - 3 speeders are widely spaced and hardly the recipe for violent acceleration.

Anyway, thanks for sharing with us all the work you're doing - plus, your new assistant - gorgeous looking little boy and it takes my mind back at least thirty years to a life full of rich experiences with three boys growing up and finding their way in life. Thank you, Styria

 

[s class]

OK, yes I ended up with offset keys on both camshafts, and if you think about it it makes sense as follows :

There are two potential causes for valve timing error :

a) chain stretch
b) sprocket wear

Now obviously a) affects the right hand camshaft more than the left, because of the greater length of chain from the right cam to the crank compared to the left cam to the crank.

In my case now, the new chain essentially eliminates this effect a), leaving me only with effect b). It makes sense that both cam sprockets are equally worn, and they are both equally affected by the wear in the crank sprocket, and thus exhibit the same timing error.

Measurement of the valve lift is achieved with a dial guage. If you look at the 6.9 heads just above the #1 and #6 exhaust ports, there are threaded M6 holes provided specifically for the purpose of mounting the dial guage. I think these holes are visible even with the valve covers in place.

The strictly correct way to do it is to replace the #1 and #6 inlet valve hydraulic tappets with solid tappets, and adjust them to have zero clearance between the rocker and the heel of the corresponding camshaft lobe. I did do this because I don't have the special solid substitution tappet, and I didin't like the idea of messing with the rockers. I convinced myself that what I was doing was acceptable because my tappets were not leaking down, and so still met the criterion of zero rocker to camshaft heel clearance.

Note that in general this 'cheat' will not work on all engines, because the tappets tend to seep away pressure once the engine is shut off, and particularly if the engine has been standing some time since last running, clearance may have developed between the rocker and heel of the corrseponding camshaft lobe.

OK then on to performance issues. I think the only reason the W140 has the better of the 6.9 in some circumstances is the sophistication of its transmission. My car is an early one with 4 speed (later ones were 5 speed). The shift quality is considerably better than the 70's benzes, and it is aided by the engine management. Specifically, under full throttle acceleration, at the instant the transmission shifts, the engine management retards the engine timing for a very very brief moment to ease the torque on the gearbox and allow super-quick changes without slurring or harshness. Very clever, and it works very well. Add to that a fairly low ratio in 1st gear, available on demand, both from stand still and in kickdown.

Its also worth mentioning that the W140 transmission will, if appropriate, drop down 2 gears during a kickdown. So, one can be trickling along at 80km/h in 4th gear, and then stamping the gas in anger gives you 2nd gear instantly with no 'gathering up its skirts' as a 70's benz transmission does when kicking down. It is spectacular. Never ceases to gobsmack passengers.

Perhaps this is why S500's eat flex discs for breakfast?

Further, also realise that the M119 in the s500 is much more free revving than the 70's engine, and it spins to 6000 rpm with no complaints or harshness.

So after all these ramblings, I think the 6.9 has a fairly relaxed behavior for a car of that engine displacement, and I think its all down to transmission and final drive.

 

[Styria]

Hi S-Class, did you use a dial gauge to measure the 2mm lift on Nos. 1 & 6 inlet valves ? I take it that basically what you are advocating is that the left hand camshaft needs to be times as well, and not just the one on the right hand side ? Is that correct ?

I really appreciated the thoroughness and information contained in your posting - there is just always so much to learn. You did mention also that you had some fuel issues and you thought that may have explained your AMG's lacklustre performance. I guess that has all been eliminated now, has it ? Thanks again, regards Styria

 

[s class]

Yes I used the dial guage to measure lift on #1 and #6 inlet valves. I think it is more thorough to check timing on both cams. Usually, I imagine that if the right hand cam is timed correctly, most likely the left one will too. However, these cars are old and have had long lifes before we come to own them, and one is never quite sure what may have been done before - so yes I advocate thoroughness and checking everything.

Yes I believe I have fuelling issues - the consumption is very heavy (OK no jokes, we know its a 6.9), - it is much heavier than the blue car. The exhaust also smells very strongly of unburnt gas, and is has difficulty with hot starting. So when I get a chance, I will be checking fuel pressures and flows.

I also discovered that the system is not holding pressure - within half an hour of turning off the engine, the air metering plate flaps loosely - so either the injectors are dribbling or the accumulator is leaking.

The next problem is that #2 cylinder is not running properly. I checked its compression and that's fine, so its not a basic mechanical issue. Ignition is fine - I swapped spark plugs, ignition leads, and that all made no difference.
This leaves two possibilites - collapsed hydraulic tappet, and fuel supply problems, with the latter being the most likely. With that in mind, I removed the #1 and #2 injectors. Trying to clean them with carb cleaner caused them both to emit a thich brown sludge, so definately the injectors are not up to scratch.

When I get a chance, I'll send in all 8 injectors with my next job lot of ultrasonic cleaning. If they don't come up to scratch, they will have to be replaced.

 

[Styria]

Hi S-Class, I know you will be away for a few days - hope you have a safe and enjoyable trip. Just a couple of comments on my part. I have reason to believe that these injectors cannot be cleaned on account of their design and you may well find that your engine running characteristics will remain the same.

Secondly, your comment in relation to No. 2 cylinder is interesting - you refer to erratic mechanical behaviour. I have a similar problem with No. 6 on my 'Gleaming Beauty'. When idling, there is a distinct puff-puff audible from the exhaust system, yet this "seems" to disappear as soon as one revs the engine. I pulled the plugs after prolonged idling (about ten minutes) and all plugs had good colour except No. 6 which was wet with petrol - obviously not firing. I have also pulled all plugs after normal outer suburban running, and there was no evidence of any firing issues on that cylinder. Therefore, I suspect that I am faced with a 'lazy' hydraulic lifter or, alternatively, with a valve that may need to have the shim thickness adjusted. I am yet to try an alternative high tension lead and/or substitute distributor just in case it is an electrical fault. Anyone else have any opinions on this subject matter as well ? I would be interested to hear. Regards Styria

 

[John S]

For sticky hydraulic valves I have found nothing better than a cup of Automatic Transmission fluid in the engine (may need 2 for a 6.9 because of the large oil reserve), cleans noisy hydraulic tappets in most cars within 3 minutes, worked wonders on XA and XB Falcons many many years ago!

I also started adding "Lucas" fuel cleaner regularly to my 450 and the motor slowly got smoother and smoother.

 

[Styria]

Hi JohnS, I might give that a try aftyer I have finished checking the electrics. It is quite peculiar that this should have started quite suddenly - there was no prior warning or indication. So it will be interesting to see what happens or what the likely remedy will be. Regards Styria

 

[John S]

I hate to say this styria, while a sticky exhaust valve can give a light "puff puff" sound from the exhaust, it can also be an indication of a (don't read further) burnt valve too.

 

[koan]

Anyone else have any opinions on this subject matter as well ? I would be interested to hear.

Not directly related but while investigating my low compression I came across a leaking exhaust gasket.

Noticed a warm pulsing air current on my fingers. Probing around with a listening tube confirmed it to be #2 cylinder. The manifold bolts were barely finger tight.

After tightening, the leak is gone and the tick-tick sound too, the tick-tick of what I thought was a noisy hydraulic lash adjuster.

So if anyone thinks they have a noisy "tappet" it might be worth a few minutes looking for manifold leaks.

koan

 

[Styria]

Hi JohnS, I am only too aware that a burnt valve could be the culprit. It is fairly easy to establish this by performing a leak-down test, but as you would understand, I am leaving this to last - for obvious reasons.

Under normal driving, and once on the move, it takes a 'very fine feel' to pick up the irregularity - if at all. If a valve was burnt, the symptoms would be fairly obvious and be present at all times. As I said, I'll go with the electrics first, then the ATF, compression test and after that , the leak down test.

After that, it may be 'heads off, and a lot of time and pain. Right at this moment, I'd prefer not to think about the last option - luckily enough, I have had two reconditioned heads on stand by for about two to three years. Regards Styria

 

[s class]

styria, my symptoms are very similar to what you describe. Puffing at the exhaust, and weak combustion on #2 at idle. In my case, the investigating I did seems to point towards injectors. I know it is said that they can't be cleaned, but I must admit its not clear to me why this is the case. In any case, if the injectors are the same as the 280/450, as they appear to be, they are not terribly expensive.

 

[Styria]

Hi S-Class, the injectors are indeed the same and, as you said, they are inexpensive. A friend of mine cross-cut a spare injector, and they were his findings - cannot be cleaned on account of their design. This confirmed what I had been told by other sources. At best, you can run a cleaning fluid through them, but that's about it.

It may be of interest to you that I have replaced the four injectors on Nos. 5 to 8, and it made no difference to the 'puff-puff'. Furthermore, No. 6 had been wet with petrol, so one would assume that fuel was not an issue. I also 'cracked' all connecting pipes on the fuel distributor, and that part of the system seemed to be okay. Regards Styria

 

[s class]

In my case, the #2 spark plug looks fine, and no wetness even after idling, so I think spark is fine - I'm suspecting fuel starvation on that cylinder - well at least at idle. My attempts to clean the injectors brought forth such filth from them, I was happy to accept they may all be blocked, to a greater or lesser degree - obviously greater in the case of cyl 2.

I replaced the 6 injectors on my 280SE some 5 years and 150 000km ago, and at the time, I was very pleasantly surprised at the useful performance increase that this brought about.

Why did you decide to replace 4 of the 8 injectors - and were the replacements new?

 

[Styria]

Hi S-Class, routine maintenance more than anything else, and I only did the left bank as that was all the time I had. Besides, I initially suspected N0. 7 after a 20 km drive, but No. 6 only became evident after some ten minutes of idling.

Anyway, replacing thgose injectors have made no difference and, yes, they are new ones. Regards, Styria