6.9 valve timing sorted out

[s class]

My 6.9 AMG had a valve timing error of about 9.5 degrees at the right hand camshaft. Last weekend I fitted a new chain and tensioner, and found that the error had come down to about 4 degrees (of crank) - based on the angle at which 2mm of intake valve lift is achieved on cyl 1 and 6. Not satisfied with this I purchased the mildest available woodruff keys, and fitted them yesterday. Fiddly to be sure, but its gratifying to see the timing of the cams spot-on now.

 

[WGB]

I will be interested to hear about the performance improvement.

Bill

 

[Styria]

Well Bill, I am just as curious as you are. I have fitted new chains to both of my 6.9's and , quite frankly, the expected improvement did not eventuate. Now, in my case, fitting the new chains resulted in the camshaft marks to be perfectly in line on both cams when looking at the marks on the crankshaft damper.

Now, I understand that lining up the marks on the camshaft bosses does not necessarily guarantee 100% accurate valve timing, so therefore is there a more accurate way of determining the accuracy of the valve timing ?

In S-Class' case, what could have been the reason for fitting off-set keys. a 'cluey' mate of mine with a 6.9 also, steadfastly maintains that fitting a new chain should be the beginning and end of the work required and he further maintains that 'worn' camshaft wheels WILL NOT cause the valve timing to be incorrect. Looking for clues and explanations. Regards Styria

 

[s class]

Well styria I'm not sure about the worth or otherwise of woodruff keys.

Before I did any work, the right cam was about 9.5 degrees behind and the left cam about 6 degrees - the difference indicating chian stretch. The new chain brought both cams to about 4 degrees behind - the fact that they were then the same indicated that chain stretch was eliminated, and the remaining difference was due to some other cause.

I verified my readings by the both the quick method of lining up the cam marks on the towers and reading the damper angles, and the 'proper' method of looking at valve lift.

I figured it like this. With these woodruff keys, the timing is now spot on, albeit 4 degrees more advanced than had I left the standard keys in. This way, after a few tens of thousands of km, when the chain has reached 4 degrees of stretch, we will be back where we started.

I have also put a new chain into my 450SL, and with that, new sprockets. The right cam is about 2.5 degrees behind, not significant, but I'm not sure why it isn't zero.

When it comes to chains, it is my W140 that really puzzles me. It has 4 cams, with variable valve timing. There are no marks on the cams or cam towers, because they would be meaningless with the variable valve timing. There is a fairly fiddly procedure for assessing the timing based on valve lift. What I found, about a year ago when it had 285 000km or so, was that all 4 cams were timed to within a degree of spec. I cannot explain how they are still so good, with apparently still the original chain. I am still baffled by it.

 

[s class]

This also raises an interesting theoretical question. Suppose the valve timing is out by just a few degrees - what is preferable - a few degrees too advanced, or a few degrees too retarded?

 

[Styria]

So S-Class, do you yet know if the fitting of the off-set keys has improved performance or changed engine running characteristics ? Regards, Styria N.B. See thread on Air Pressure cells.

 

[s class]

No I don't know yet I haven't driven it. The performance was so sad before it can only be better now. I had always blamed the performance on 2 things - valve timing and k-jet pressure issues. I have yet to address the second item.

The car hasn't run yet because it lacks a 5th suspension sphere. After the right front failed, I replaced it with the 5th sphere, thinking that this way the two front spheres are still of the same age and from the same production batch. The 5th one can be the odd one. I might install a used item there for now, or else try a warranty claim with AutohausAZ.

 

[WGB]

I know when I did my 450 chain some years ago that the level of subjective driveability was improved as well as the feeling of noticeably more power.

The chain had 11 degrees of stretch before changing and 2 degrees after change and new sprockets.

Bill

 

[s class]

Its just come to me - I think I may have an explanation why I still had a timing lag after changing the chain on the AMG - I believe the heads have been off before and skimmed - which fractionally reduces the distance between the crank sprocket and cam sprockets.

 

[Styria]

Hi S-Class - you have made it quite clear on a couple of occasions that your 'old crusty rusty' (have I got that right ?), is a much better performer. Have you changed chain and tensioner on it as well and if you have, how did it compare wear wise originally with your AMG car and are the valve timing settings similar on both cars now ?

As far as head removal and subsequent skimming are concerned - yes, that will alter the valve timing but it usually should only occur if that process has been carried out on more than one occasion. Bit hard to imagine that one skim would give you that problem, unless it was done indiscriminately. The Technical Data Manual does specify a minimum deck height, but the heads would have to be off to take that measurement. Regards Styria

 

[s class]

styria, yes trusty rusty's engine is more lusty, and I did check the chain stretch. It is the original chain, and the right hand cam is 2 degrees too early. What I take this to mean is that the chain actually has 16 degrees of stretch, and the sprocket has been advanced by one tooth (equivalent to 18 degrees) by way of some compensation. The tensioner is visibly greatly extended. The following pictures hopefully illustrate the situation :





As to other differences between the cars, I know that the AMG has fuelling issues (its running VERY rich, and has hot-start problems), so until that is sorted out I will not be too judgemental of it. The AMG has 5kohm ignition supressors, trusty rusty has 1kohm units. Which is correct for the 6.9?

For what its worth, the AMG indicates 195 000km, and I'm inclined to believe it. Trusty Rusty shows 148 000km, which I stongly doubt.

 

[John S]

You stated: The performance was so sad before it can only be better now. I had always blamed the performance on 2 things - valve timing and k-jet pressure issues. I have yet to address the second item.

Have you checked the ignition timing? Sounds as though it may be retarded!

 

[s class]

Yes John, the ignition timing is good, and it seems to advance properly as the revs pick up.

 

[WGB]

Did the ignition timing need to be re-set by much when the chain was replaced?

Bill

 

[s class]

Bill, what I meant was the iginition timing was good before I started on the chain job. I haven't reset it yet because I haven't finished putting back the valve covers etc, so the car has not run since chain change, and it wont until I get a new 5th sphere in.

 

[s class]

Finally I can report back on the performance of the AMG now with its new chain and corrected valve timing. THis weekend I completed the assembly (reffiting valve covers, spark plugs etc), refitted the small fitting to the base of the suspension distribution valve, replaced the 5th sphere, and went for a test drive.

To get the timing right I ended up with the mildest offset key (2 degrees of camshaft / 4 degrees of crank) on each of the sprockets. Valve timing is now perfect on spec (based on the angle of crank at which #1 and #6 inlet valves achieve 2mm of lift).

Performance is nothing short of spectacular now. Its in a different league - even a leap ahead of trusty rusty. To put it bluntly, before the AMG stood no chance of breaking traction of the rear wheels (admittedly they are sticky Bridgestones) - now one can spin the rears at will.

My faith in this 6.9 myth has been restored. Frankly I had found the 2 cars a bit of a let-down after all the hype - now I think the hype is true!. Its tough to really compare the car to the W140, but I would perhaps say that they are similarly powerful, but in a different way. The W140 is brutal, gut-wrenching, but not very refined in its power delivery. The 6.9 is turbine smooth, and would be better described as having 'thrust' than power or torque. At speed (110km/h plus), I would have to say the 6.9 is now more eager and lusty to accelerate than the W140.

The red 6.9 is now white-knuckle stuff. 120 km/h feels stupidly fast, whereas it feels like walking in the W140. Love them both!

 

[s class]

Sorry, forgot the pictures :



And VERY important, while my wife has been away, I've had a very curious and willing assistant :







He entertained himself for hours with items out of my bolts-nuts-washers-brackets container......

 

[Michel]

Great news on finally sorting out the AMG.

I have followed your odysseys with both the AMG and Trusty Rusty and I am heartened by the fact that the AMG is responding and has all the get up and go of a 6.9...

Hopefully it will make the trip down under with you and your family when you emigrate to Australia

 

[WGB]

I have my new chain and tensioner and as I am waiting for my new receiver dryer I will probably have it in before the A-C and CV joints are done.

I know the order in putting the 6.9 tensioner in but is there any particular order when it comes to removing it, also was is the torque setting on the two hex head bolts.

I will be interested to see if there is a performance difference with my 6.9 as well.

Bill

 

[s class]

Bill I sugest you first remove the closing plug on the tensioner - be aware that there is quite a stiff spring inside that will make it want to shoot off when you get to the end of the thread. Then release the lock ring. Next you will have to prise off the flange as the tensioner will not pass through it. I found it quite tricky to clean up the gasket face of the head, as access is limited behind the alternator. Considering the propensity for these flanges to leak, I thought it imperative to get a perfect surface, so I removed the alternator and its bracket - all in all only 15 minutes of work and well worth it.

Al has been complaining on the M100 forum of tensioner leaks, but I decided to do it by the book, with no gasket sealant - I was afraid it might work its way into the oil way. I couldn't find a torque spec for the flange bolts - I think I used 20 or 25nm - 25nm is pushing your luck with that diameter bolt into aluminium - certainly 25 must be the max.

I must also point out that in Al's thread on the M100 forum, someone suggests 40Nm for the locking ring - as I read the technical manual, that is WRONG - it should be only 30Nm, and this may be partly why they are getting leaks. The closing plug is 50Nm, and you will need a new copper/aluminium seal ring (not supplied in the tensioner kit).