Valve Adjustment Clarification - Page 4 - PeachParts Mercedes-Benz Forum

funola · #46 08-21-2014, 10:30 AM

My 83 240D @ 200k and 83 300D @240K had tight valves when I acquired them, the 85 @ 157k had properly adjusted valves. None had uneven cam base circle wear.

mach4 · #47 08-21-2014, 10:47 AM

Quote:

Originally Posted by funola

.... None had uneven cam base circle wear.

How could they? It would take something pretty bizarre like variable tension springs, or variable length valves or little creatures with microscopic dremels to create uneven wear on the base circle. And if they were uneven any contact would tend to even the base circle, not make it uneven.

funola · #48 08-21-2014, 10:58 AM

Quote:

Originally Posted by mach4

How could they? It would take something pretty bizarre like variable tension springs, or variable length valves or little creatures with microscopic dremels to create uneven wear on the base circle. And if they were uneven any contact would tend to even the base circle, not make it uneven.

Well, some people are saying they do wear unevenly. I didn't think so and my observations agree with what I think.

leathermang · #49 08-21-2014, 11:33 AM

To others who do not understand the object of this base circle discussion....

It only makes a difference to people who ARE TRYING to TAKE a shortcut in terms of setting the valves. If you follow the FSM instructions this does not affect you.

AND I would suggest that trying to accurately determine if the base circle IS ROUND... with any meaningful accuracy.... would take more time than actually setting the valves according to the instructions in the FSM...

leathermang · #50 08-21-2014, 11:40 AM

Quote:

Originally Posted by funola

Well, some people are saying they do wear unevenly. I didn't think so and my observations agree with what I think.

The ' N ' in your ' survey' is too small to have statistical relevance.... therefor it is by definition ' anecdotal '.... and can not be trusted for generalizing.
But it is nice that you agree with what you see... otherwise I might have to offer you some more help....

interzonearts · #51 08-21-2014, 11:42 AM

The (allegedly

) uneven wear may or may not be negligible. But PO says that he's doing the adjustment for the first time. And regardless it being a pretty simple task, it may be a bit confusing in the beginning. Tight spaces, odd angles, various lines and links in the way.
I'd suggest that the first adjustment needs to be done exactly by the book. And then when the correct procedure gets embedded in the muscle memory, like in case of you guys who's done a lot of them, you can decide which corners to cut.
My two centavos.

vstech · #52 08-21-2014, 12:56 PM

I was under the impression the FSM was unclear in the process. .. does it specify lobe pointing position?

Quote:

Originally Posted by leathermang

To others who do not understand the object of this base circle discussion....

It only makes a difference to people who ARE TRYING to TAKE a shortcut in terms of setting the valves. If you follow the FSM instructions this does not affect you.

AND I would suggest that trying to accurately determine if the base circle IS ROUND... with any meaningful accuracy.... would take more time than actually setting the valves according to the instructions in the FSM...

funola · #53 08-21-2014, 01:08 PM

Quote:

Originally Posted by vstech

I was under the impression the FSM was unclear in the process. .. does it specify lobe pointing position?

FSM has just a pic of lobe pointing position, no words. It also specifies turning the engine by either the crankshaft nut or a remote starter via the wheel well terminal block so you are following the FSM.

If the base circle does wear unevenly, we have a big problem with valve adjustments on these old engines depending how it wears.

leathermang · #54 08-21-2014, 01:37 PM

Quote:

Originally Posted by vstech

I was under the impression the FSM was unclear in the process. .. does it specify lobe pointing position?

As Funola said... it has a picture of the lobe position which I would feel confident as describing as ' one o'clock ' position.

The actual words are ' the cam peak must be perpendicular to the rocker arm'.

mach4 · #55 08-21-2014, 01:47 PM

We need to remember that the FSM is written for the lowest common denominator technician - the kind of person I think we've all come across in dealings with repair shops, dealerships...and even forums. Mercedes, and other manufacturers, have to do everything possible to provide a "cook book", "follow the bouncing ball" kind of procedure that even the aforementioned kind of person can follow. There is no assumption of logic, understanding or intelligence only a step-by-step procedure that can ensure that a job gets done successfully the maximum percentage of the time.

In this context, doing a valve adjustment with the cam lobe pointing the same direction for every process makes complete sense - no thinking involved, just one rote procedure that meets the implied goal of getting the job done successfully regardless the expertise and intelligence of the person doing the job.

Now if we actually understand the design of a camshaft and realize that the manufacturer would have no reason to introduce other than a circle to the non-lobe portion of the camshaft (as this would functionally be a double-lobe cam), it's intuitively obvious that we, as thinking and intelligent and inquisitive human beings, can set the valve lash anywhere in the base circle, because we understand the operating principle and can recognize what is and is not within the base circle.

Clearly the FSM way is a safe way to proceed (provided it wasn't written by the designer of the evil servo, the air cleaner mount or other examples of German engineering) but not necessarily the "only way".

And until I twist off the nut on the PS pump, I'll continue to rotate the engine that way too.

leathermang · #56 08-21-2014, 02:04 PM

Mach4,
I wish I could agree with that description of the FSM.... I find they assume all sorts of things and it was not written by a native English speaker...
The photos are pretty much terrible also..
I think even with the FSM that the Haynes manual is a great help to understanding what needs to be done to do it correctly...
BUT you can not use JUST the Haynes manual because LOT OF WARNINGS are in the FSM which are not in the Haynes...

I would like to also suggest that their is a possibility that by doing it exactly one valve at a time that variable wear in other items in the equation might be negated.
That is just a theory .... but if true is an endorsement for the FSM method.

The FSM is far from a ' cookbook'.... The Idiot's Guide to VW maintenance ' by Muir IS a cookbook style instruction... I WISH the FSM was anywhere near that...
Which brings me to ask you.... do you own a paper copy of the FSM ? and if so.. have you read it ?

sokoloff · #57 08-21-2014, 06:30 PM

When I do the valves on my ponton, I jack up one of the rear wheels, release the parking brake and turn the tire to get the valves where I want them. I haven't done my 240D in a long time, but that will work for it too (manual transmission). Not sure it works with an automatic?

Not necessarily applicable to everything here, but some might find it interesting:

Mercedes-Benz Ponton Type 220S Valve Adjustment © www.mbzponton.org

Mölyapina · #58 08-21-2014, 06:51 PM

Quote:

Originally Posted by sokoloff

When I do the valves on my ponton, I jack up one of the rear wheels, release the parking brake and turn the tire to get the valves where I want them. I haven't done my 240D in a long time, but that will work for it too (manual transmission). Not sure it works with an automatic?

Not necessarily applicable to everything here, but some might find it interesting:

Mercedes-Benz Ponton Type 220S Valve Adjustment © www.mbzponton.org

Definitely wouldn't work with an automatic, but that's a nifty trick for a stick-shift.

Graham · #59 08-23-2014, 08:33 PM

Quote:

Originally Posted by mach4

And until I twist off the nut on the PS pump, I'll continue to rotate the engine that way too.

Just got back from a roadtrip. While driving I was daydreaming about this issue. What I wondered, was - what is the FSM spec for the PS pump drive shaft nut?

When I got home, I looked this up in my manual. It said 50Nm. Which I think is about 37 ft.lbs.

So how much torque does it take to turn the engine over (using the PS nut)? If more than 37ft.lbs then nut would tighten. If less, then no affect on nut tightness.

Because of an obstruction, I could not fit my torque wrench. Instead, I used a 1ft long wrench on the PS nut and pushed on it. I had no way to measure the force, but I don't believe it was as high as 37 lb., and this is an engine with excellent compression. But how would I really determine the number? Maybe if I had a fish scale?

Not trying to stir the pot - just trying to put some numbers against what some think may be an issue. Anybody like to do a more scientific test

leathermang · #60 08-23-2014, 09:51 PM

Graham, you are not stirring the pot...
I have seen FSM's which stated how many Ft/lbs a newly rebuilt engine should require to turn over... meaning that if you got to that number and it was not moving you should check for something binding...

With something like 21 to 1 compression.... I am betting that spec you found is exceeded in turning over the engine..

Anyone thought of this from the other end ? Why did the Mercedes people writing the FSM SPECIFY using the crank bolt ? Why would they have not mentioned...given its handy location... using the ps nut ?

UNLESS there was some physics reason not to...
if it were not a taper fitting...there would be no good reason not to use it...

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