For all of you with 240D idle woes - PeachParts Mercedes-Benz Forum

mabbonizio · #1 12-01-2017, 04:26 PM

Speaking with a long time MB mechanic I asked him why my 240D might idle SO rough, especially when its warmed up.

I went through the laundry list of things I've done to the car including filters, lines, motor mounts, valve adjustments.

He then said at what clearance did you adjust the intake valves and I told him factory spec. He replied that its best to adjust them at .006" instead of .004" and to give it a try.

He also explained not to adjust the valves with the cam lobe directly pointed up- rather it should be cocked to the side slightly.

Well - Perhaps everyone else knew this information but I have to say upon firing up the 240D the idle is SO MUCH SMOOTHER in drive. I mean, its actually bearable. Prior to this the entire car would shake like a jack hammer at a stoplight in drive. The motor also has better pickup and trans shifts better.

Now I feel bad I drove the car 15k miles like that and god knows how long the previous owner drive it like that!

Just thought I'd pass this along!

pj67coll · #2 12-01-2017, 06:05 PM

Interesting. Mine has a severe shake/buzz/vibration at idle. I mean so bad it feels like a massage seat option. And I can watch the entire hood vibrating like in a comic book or something. I've recently done a valve adjustment which has had some effect both on smoke and smoothing out the shutoff for some reason but no noticeable difference in idle. So I've had to increase the idle speed permanently to make it bearable. I had heard of the cam lobes being pointed to the 13:00 position rather than 12:00. But I think when I did mine I mostly had them at 12:00. I'd not heard of the .006" setting. Might try that and see if it has any effect if I do another one soon.

- Peter.

mabbonizio · #3 12-02-2017, 07:24 AM

Quote:

Originally Posted by pj67coll

Interesting. Mine has a severe shake/buzz/vibration at idle. I mean so bad it feels like a massage seat option. And I can watch the entire hood vibrating like in a comic book or something. I've recently done a valve adjustment which has had some effect both on smoke and smoothing out the shutoff for some reason but no noticeable difference in idle. So I've had to increase the idle speed permanently to make it bearable. I had heard of the cam lobes being pointed to the 13:00 position rather than 12:00. But I think when I did mine I mostly had them at 12:00. I'd not heard of the .006" setting. Might try that and see if it has any effect if I do another one soon.

- Peter.

I would say give it a try. This is very much how my car used to idle as well.

He basically said that the way the Mercedes cam is shaped + the way that most people incorrectly adjust the valves with he lobe pointing straight up + the extremely tight tolerance of the intake valves means that most times the intake valves are adjusted too tight.

240Dee · #4 12-02-2017, 08:17 AM

Quote:

Originally Posted by pj67coll

Interesting. Mine has a severe shake/buzz/vibration at idle. I mean so bad it feels like a massage seat option. And I can watch the entire hood vibrating like in a comic book or something. I've recently done a valve adjustment which has had some effect both on smoke and smoothing out the shutoff for some reason but no noticeable difference in idle. So I've had to increase the idle speed permanently to make it bearable. I had heard of the cam lobes being pointed to the 13:00 position rather than 12:00. But I think when I did mine I mostly had them at 12:00. I'd not heard of the .006" setting. Might try that and see if it has any effect if I do another one soon.

- Peter.

I’d like to try this next spring - but by 13:00 do you mean 1:00? As in roughly 1/12 rotation clockwise past 12:00? Thanks for the tip! My 240D idles well (I think) but I can see a little vibration in the hood and the steering wheel vibrates as well, so I’ll probably give this a shot and report back!

Sent from my iPhone using Tapatalk

pj67coll · #5 12-02-2017, 12:25 PM

Quote:

Originally Posted by 240Dee

I’d like to try this next spring - but by 13:00 do you mean 1:00? As in roughly 1/12 rotation clockwise past 12:00? Thanks for the tip! My 240D idles well (I think) but I can see a little vibration in the hood and the steering wheel vibrates as well, so I’ll probably give this a shot and report back!

Sent from my iPhone using Tapatalk

Yes, that's what I meant.

- Peter.

leathermang · #6 12-02-2017, 04:52 PM

Quote:

Originally Posted by mabbonizio

.......He also explained not to adjust the valves with the cam lobe directly pointed up- rather it should be cocked to the side slightly......

There were people on this forum who were trying to convince everyone to use 12 O'clock ....and why I do not know.....and I finally gave up arguing with them....

but all I was doing was quoting the Factory Shop Manual... which has a picture of the cam lobe pointing to the ONE O"CLOCK position for setting that valve.

Why they thought our DIY members were not smart enough to find the one o'clock position......and could only find TWELVE o' clock I do not know to this day.

They swore that the bottom of the cam was round... thus it made no difference... REALLY ? Then why was the Factory Shop Manual so specific ?

SonnyMorrow · #7 12-03-2017, 11:34 PM

I will for sure try this out on my next valve adjustment. I'll post an update in the coming months hopefully. I'm also curious why the rumor is only to use the 12 o'clock position?

Shern · #8 11-15-2018, 06:29 PM

Anyone ever try this?

ROLLGUY · #9 11-15-2018, 07:07 PM

I can see adjusting the valves a little on the loose side (.006), but I can't understand why someone suggests to adjust the valve with the lobe at 1:00 and not 12:00. Either one will work. I personally put both lobes on each cylinder facing up, adjust both, and then rotate the crank till the next cylinder in the firing order has the lobes facing up. It really does not make a difference where along the "base circle" of the cam the follower is for measuring the clearance. The cam is in fact round approximately 240 degrees (I say approximately- it could be at least 200, or as much as 250). Point being, there is quite a bit of area that the cam can be to get an accurate clearance. One can test this by using the feeler gauge at any place within the base circle, and it will be the same measurement.

math · #10 11-15-2018, 08:46 PM

Quote:

Originally Posted by ROLLGUY

I can see adjusting the valves a little on the loose side (.006), but I can't understand why someone suggests to adjust the valve with the lobe at 1:00 and not 12:00. Either one will work. I personally put both lobes on each cylinder facing up, adjust both, and then rotate the crank till the next cylinder in the firing order has the lobes facing up. It really does not make a difference where along the "base circle" of the cam the follower is for measuring the clearance. The cam is in fact round approximately 240 degrees (I say approximately- it could be at least 200, or as much as 250). Point being, there is quite a bit of area that the cam can be to get an accurate clearance. One can test this by using the feeler gauge at any place within the base circle, and it will be the same measurement.

Hey, I've been doing it at 1o'clock for a long time ever since an older german guy with much more w123 experience showed me.

If you look at the holders for the camshaft assembly, you'll see there is a mark at the 1'oclock position.

Also, when the cam lobe rotates, the 1 o'clock position is where the cam lobe is 180 degrees away from the maximum valve opening point where the lobe pushes down on the spring.

you see, conventional wisdom would say straight up and down, however, with the little arms between the cam lobes and the spring/valves this makes an offset. It's hard to explain without pictures, next time your valve covers are open, take a look, there's a little circle mark on the cam assembly at the 1 o'clock position

ROLLGUY · #11 11-15-2018, 10:02 PM

Quote:

Originally Posted by math

Hey, I've been doing it at 1o'clock for a long time ever since an older german guy with much more w123 experience showed me.

If you look at the holders for the camshaft assembly, you'll see there is a mark at the 1'oclock position.

Also, when the cam lobe rotates, the 1 o'clock position is where the cam lobe is 180 degrees away from the maximum valve opening point where the lobe pushes down on the spring.

you see, conventional wisdom would say straight up and down, however, with the little arms between the cam lobes and the spring/valves this makes an offset. It's hard to explain without pictures, next time your valve covers are open, take a look, there's a little circle mark on the cam assembly at the 1 o'clock position

I believe you, and yes the tip of the cam is in fact 180 degrees from the contact point of the follower at 1 o'clock. However, the cam is still round at that point, and also round at least 100 degrees on either side.

JHZR2 · #12 11-15-2018, 11:59 PM

My 240 exhibits much of the same vibration. May try this adjustment.

rocky raccoon · #13 11-16-2018, 06:28 AM

On OM627,true that anywhere on the base circle works but I find it easier and more accurate to have the cam lobe pointing at the cam oiler tube, hence about 1 o'clock.

IRT clearance, I use the factory specified settings. I used to sometimes introduce error when manipulating a short feeler gauge. I obtained a pair of 8" long feeler gauge leaves from a machinist supply house and no more problem.

JHZR2 · #14 11-16-2018, 08:16 AM

Quote:

Originally Posted by rocky raccoon

On OM627,true that anywhere on the base circle works but I find it easier and more accurate to have the cam lobe pointing at the cam oiler tube, hence about 1 o'clock.

IRT clearance, I use the factory specified settings. I used to sometimes introduce error when manipulating a short feeler gauge. I obtained a pair of 8" long feeler gauge leaves from a machinist supply house and no more problem.

What was the cause of the error that longer gauges fixed?

Junkman · #15 11-16-2018, 09:27 AM

The diagram of the cam lobe shows the bottom to be round. This allows multiple valves to be adjusted with the cam in 1 position - on OTHER vehicles. I've found that it doesn't work on a 617. Cam pointed at the oiler per FSM seems to be the most accurate.