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Rough idle when cold

Started by raueda1, 01 November 2018, 10:03 AM

ramiro

I finaly got my bad idle fixed , as i got i the feeling that i got worse i started investigating more and found out that the header on cylinder 2 was always colder then the others so it was cylinder 2.
I took the valve covers off and found the hydraulic lifter completly compressed but the roker arm was tight for the exhaust valve on cylinder 2.
So i did this procedure https://handbook.w116.org/cd/Engine/107/M117_45/05-213.pdf and had to change the thrust piece from 4.75 to 4.05 and then the readig was fine , the same issue was at cylinder 8 i also had to change it from 4.75 to 4.05 at the exhaust valve.
After this the idle is perfect when cold and also got much better when warm before it was only really good when the engine was really hot.
So for anybody fighting a bad idle check your valve clearances , for 3 years i was always searching the cause and actually started to believe that a 6.9 just does not idle very good.

raueda1

#31
I've been meaning to do this for a long time.  Seems like a good project to combine with setting cam timing, which I know isn't spot on.  Did you get the measurement tool?  Pelican parts seems to sell one for $145, yikes.    Please share where!  Thanks,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

ramiro

I bought the Tool 2 years ago for 80 eur at Mercedes , did this procedure 1 time but did not understand that if you remove the roker arm the hydraulic lifter goes to the top and will stay there for at least 10 minutes even unter pressure , so you have to wait before measuring again or else the reading will show that need to use a thicker piece.

But i actually saw by eye even before using the tool that the lifter was bottomed out , you just have to compare the space between the roker arm and the cover of the lifter.

daantjie

With that much clearance error it must have been making a clacking noise?
Daniel
1977 450 SEL 6.9 - Astralsilber

ramiro

Noise wise there is no difference i think , also i dont see a reason for clacking when the valve play is to small because the Valve was not fully closing.
Tested all lifters with the hammer method because i have a slight ticking noise but i am not sure if it's even from the valve train , there was 1 that needed a thicker Shim but that also didn't change anything most were good.

But the Noise is nothing to the one you get when the Rocker arms ar fully worn on a M117 happened twice to me first time it was after driving fast on highway and comming to a stop i was thinking my engine blew up, but it was just a roker arm.

raueda1

    Quote from: ramiro on 23 February 2024, 03:52 AMI finaly got my bad idle fixed , as i got i the feeling that i got worse i started investigating more and found out that the header on cylinder 2 was always colder then the others so it was cylinder 2.
    I took the valve covers off and found the hydraulic lifter completly compressed but the roker arm was tight for the exhaust valve on cylinder 2.
    So i did this procedure https://handbook.w116.org/cd/Engine/107/M117_45/05-213.pdf and had to change the thrust piece from 4.75 to 4.05 and then the readig was fine , the same issue was at cylinder 8 i also had to change it from 4.75 to 4.05 at the exhaust valve.
    After this the idle is perfect when cold and also got much better when warm before it was only really good when the engine was really hot.
    So for anybody fighting a bad idle check your valve clearances , for 3 years i was always searching the cause and actually started to believe that a 6.9 just does not idle very good.
    This is an excellent topic. My tool is ordered. I'm amazed that it could make such a difference in idle.  So, to summarize, what I get from this is that the sequence is:
    • deactivate fuel pump
    • crank 30 seconds
    • check clearance on valve(s?)s with cam lobe pointing upwards
    • If out of spec substitute new thrust washer.  Wait 10 minutes and check again.
    • rotate cam for another valve(s), measure, repeat until all valves have been checked

    And this is done with cold engine?  And the 30 second crank is enough to keep the lifters pressurized for the whole process?  Seems like it wouldn't be bad to crank again at some point and then again at the end to recheck everything. Thanks for illuminating this stuff.  It reminds me again how "Nothing works until everything works."  This is kind of like the distributor story.  How many of us have gone nuts on the CIS when the issue turned out to be a sticky distributor?  I doubt it's only me.  Cheers,

    [/list]
    -Dave
    Now:  1976 6.9 Euro, 2015 GL550
    Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

    daantjie

    Dave, maybe start a new thread when you start your tests.  There have been numerous posts on this topic on many forums I am a member on and it always seems like everybody gets different outcomes on this little caper.  Randy "Randys01" has a lot of experience here too and I'm sure he'll chime in ;D
    Daniel
    1977 450 SEL 6.9 - Astralsilber

    ramiro

    The best scenario would be if the lifters are empty and just under the tension of the spring, i would not crank the the engine before because you don't the lifter under any tension from oil pressure.

    The main problem is as soon as you remove a rocker arm the lifter will go to the upper limit ,  and while doing that i will suck in oil from the small reservoir in the head.
    If you then put a the rooker arm back in it will stay there for a while because the oil valve is a one way valve so it won't allow the oil to get out again so you have to wait until it slowly leaks out before you can measure again.

    I actually rotated the engine so that the valve was open on the cylinder and when the lifter was collapsed i rotated the engine again to measure.
    You also will see the lifter go up when you do that , if it does not go up and the rocker arm is loose i would suspect the lifter is broken also when it collapses very quickly when the valve is open it is broken.

    In a german forum i even read that somebody removed the lifter and pressed all the oil out so he had no wait time between the measurments.


    rumb

    The manual isnt clear on cranking in between, but you could read it as the procedure for each valve. I think you should crank everytime you remove a rocker to refill the lifter or to do another valve. Otherwise after a few revs all the lifters have lost some oil.



    '68 250S
    '77 6.9 Euro
    '91 300SE,
    '98 SL500
    '14 CLS550,
    '16 AMG GTS
    '21 E450 Cabrio