Author Topic: Understanding valve train specs (quantitative & tedious)  (Read 4350 times)

raueda1

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Understanding valve train specs (quantitative & tedious)
« on: 17 October 2019, 11:29 AM »
OK, I've moved forward a bit - lots of measurement and inspection to see where I'm really at.
[Sidebar remark:  I used to work with an extremely excitable German doktordoctor scientist who was constantly being bullsh*ted by the sales and marketing guys.  When they made a claim he didn't believe - which was most of them - he'd leap to his feet, slam his fist down on table, and scream, "I vill see ze data!  You vill put ze data on ze table!!"  This reaction was 100% predictable.  Hysterical!]
Anyway, the point is, one data point is worth 100 opinions.  So here goes.

> Valve stem wear:  All were measured meticulously all along the stem as well as around the diameter.  Every single valve was in spec.  I was quite amazed how consistent the measurements were. 
     Specs:                                   Actual:
     Intake:     8.95 - 8.97mm        8.95 - 8.965mm (every single valve fell within this range. 
                                                 The majority clustered on the high side)
     Exhaust:  10.93 - 10.95mm    10.935 - 10.945mm (same as above)
So, it looks like that's all fine.

> Valve springs:  All I can measure is length.  See below.   
    Specs:                   Actual:
    Large:   53mm       49.33mm average, range 0.42mm
    Small:   45mm       44.53mm average, range 0.13mm
I'm a surprised that valve-to-valve variation seems so small.  The large springs are clearly shortened a bit.  Does this matter?  And is it worth it get the force tested?  Also, the manual says that the springs should be installed so that "the close coils are seated against the rotocap."  I can't see any difference on my springs, the coil seems symmetrical.  ???

> Valve guide wear:   This is the topic we all love to hate.  I haven't measure valve guide bores yet, but will.  In the meantime I did make a few calculations:

Guide and valve specs:   
    1. Exhaust guide ID:           11.000 -> 11.018mm
    2. Exhaust valve stem OD:   10.93 -> 10.95mm
    ---------------------------------------------------
    Theoretical max allowable clearance = (1) - (2) =  11.018-10.93=0.088mm

    1. Intake guide ID:           9.000 -> 9.015mm
    2. Intake valve stem OD:  8.95  -> 8.97 mm
    ---------------------------------------------------
    Theoretical max allowable clearance = (1) - (2) = 9.015-8.95=0.065mm

I took a look at some valve guide play numbers per various generalist auto & hot rod sites:
    Allowable exhaust valve stem play: 0.076 -> 0.13mm (sodium filled)
    Allowable intake valve stem play:    0.025 -> 0.076mm
From this it looks like the MB spec may be a bit tighter, but is generally in line.  However, in section 05-280 the manual states "Permissible concentric runout vertical to valve seat when mounted at valve stem 0.03mm" and "Permissible axial runout vertical to valve seat when mounted at valve stem 0.02mm."  These sound like the values for the 'stem wiggle test.'  Am I reading this right?  Seems like I can't be OR they differ from the limits derived from the respective guide ID and stem OD specs.  There's something i don't understand here.  Any clarification would be welcome.

Regardless of that, I noted that with oil-lubed stems what small wiggle there was disappeared.  This seems to be a commonly used poor man's valve guide test.  I haven't yet tested all the guides in this way, but will.  I'll also look at dry runout with a dial gauge.  Anyway, let's assume for a moment that the wet-wiggle test is OK all around and actual bore measurements check out.  By definition, that should mean that the guides are OK. Again, for those just tuning in, the car did not burn oil and did not smoke going down steep grades and did not make noises, ticks, tocks, clicks, clacks etc.   Obviously I'm trying to build a case against the "just do it while it's easy to do" school, cause I don't want to do it.  I'm not averse to changing guides, but only if the data supports it.  Doing so opens other cans of worms.

There's also the matter of replacement guide size should that be necessary.  All the replacement guides I've found indicate "0.001 oversize."  What's that mean and does it matter?

As a matter of interest I also measured the thrust pieces.  Wear was extremely small in all cases (measuring thickness on the side vs center where it contacts valve stem), maybe 0.005mm, hard to measure.  The sizes used were a cocktail.  9 were 4.75mm, 5 were 4.40mm and 2 were 4.05mm.  Presumably somebody set them up at some point and this isn't just random.  Are they still right?  Who knows.  I'll assume so for the time being and recheck when car is running.

Finally, I took a closer look at the differences between Euro and USA heads.  Interestingly and inexplicably the molded part numbers are the same.  In the case of the left head they do indeed seem to be the same.  The right USA head has a long, shallow plenum on the exhaust side.  There are small bores connecting the plenum to the respective exhaust valve chambers.  The plenum goes to a fitting and tube feeding the smog system (EGR?).  The Euro head lacks all this.

Any comments on this stuff would be great.  Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

TJ 450

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Re: Understanding valve train specs (quantitative & tedious)
« Reply #1 on: 17 October 2019, 01:34 PM »
It sounds like it's all in surpringly good order. Play during the wiggle test on some of the exhaust valves during my engines head refurb was in the order of mm +/- (several). That results in a loud clacking sound.

Aus cars have the US heads with the channels for the air injection too.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

raueda1

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Re: Understanding valve train specs (quantitative & tedious)
« Reply #2 on: 17 October 2019, 02:48 PM »
It sounds like it's all in surpringly good order. Play during the wiggle test on some of the exhaust valves during my engines head refurb was in the order of mm +/- (several). That results in a loud clacking sound.

Aus cars have the US heads with the channels for the air injection too.

Tim
Just finished the oiled-stem-wiggle-test on the rest of the guides. All are good!  Nothing makes my day better than a post like yours.  +/- in mm's!!!  Happily mine is nothing remotely like that, and that means the end is in sight.  No Frankenmotor, no USA head swap, no guides, hopefully no more surprises.  Looks like now it's mostly just clean up and reassembly.  Sorry that you had a clacker though.  Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

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Re: Understanding valve train specs (quantitative & tedious)
« Reply #3 on: 17 October 2019, 02:55 PM »
Dave can you maybe post a pic of this plenum setup on the RHS head?
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

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Re: Understanding valve train specs (quantitative & tedious)
« Reply #4 on: 17 October 2019, 04:15 PM »
Dave can you maybe post a pic of this plenum setup on the RHS head?
Will do.
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Randys01

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Re: Understanding valve train specs (quantitative & tedious)
« Reply #5 on: 18 October 2019, 03:42 AM »
All sounds good to me. I'd only be replacing the valve stem seals.

"There's also the matter of replacement guide size should that be necessary.  All the replacement guides I've found indicate "0.001 oversize."  What's that mean and does it matter?"

Replacement 1st service sized guides are 1 thou of a mm less ID. you won't be needing them  so forget it.

As a matter of interest I also measured the thrust pieces.  Wear was extremely small in all cases (measuring thickness on the side vs center where it contacts valve stem), maybe 0.005mm, hard to measure.  The sizes used were a cocktail.  9 were 4.75mm, 5 were 4.40mm and 2 were 4.05mm.  Presumably somebody set them up at some point and this isn't just random.  Are they still right?  Who knows.  I'll assume so for the time being and recheck when car is running.

So long as you put them back exactly as they came out she'll be right. if you alter any component of the valve train you will need to test and adjust.

The large springs are clearly shortened a bit.  Does this matter?  And is it worth it get the force tested?  Also, the manual says that the springs should be installed so that "the close coils are seated against the rotocap."  I can't see any difference on my springs, the coil seems symmetrical.  ???

Don't fiddle with the springs. they have compressed a tad over the years.As the car was running fine before, don't worry about having the springs tension tested....you won't be pulling 6 grand in top gear down Route 66. ;)


So far the ods are smiling...........

raueda1

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Re: Understanding valve train specs (quantitative & tedious)
« Reply #6 on: 26 October 2019, 11:34 AM »
All sounds good to me. I'd only be replacing the valve stem seals.

>>>snip<<<

don't worry about having the springs tension tested....you won't be pulling 6 grand in top gear down Route 66. ;)

So far the gods are smiling...........
Thanks for the info super helpful/reassuring.  That still looks like the plan.  Just got heads back from the shop.  The heads are absolutely flat, so that's nice.  They commented that the guides were indeed worn but also very far from terrible.  Valves and valve seats are all good.  They also did some port polishing just for fun but the machinist said it was really just cosmetic.  Springs and rotors are fine.

We discussed my usage of the car, which is basically a fair weather, low annual mileage road tripper.  They agreed that it made sense to just put it all back together.  In an ideal world they'd replace guides but they're still serviceable, especially since they weren't the original problem anyway and not causing obvious issues. 

And so, the reassembly will now commence.   :)

ps - I'm in Route 66 territory and I WILL be pulling in top gear!  Just not at 6000 rpm.  4500 rpm is plenty fast.   ;D
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

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Re: Understanding valve train specs (quantitative & tedious)
« Reply #7 on: 31 October 2019, 07:24 PM »
While recovering from lung surgery I returned to the valve guide issue.  Surgery went great, I was out in record time and now back to the car project.   I doubt this info will be of much practical use to anybody.  But who knows? If nothing else it adds to my own understanding.  OTOH it may be old news to the old timers.  Anyway, here's what I did.

Valve Guide Wear - procedure:
I more-or-less mapped my valve guide wear to see what I might see.  The object was to see how wear differs along the length of the valve guide (taper wear) and to see if the wear differs around the circumference of the guide (ovality).  Here's how I did it:

    1.  Measured bore width in the axis of the cylinder head along the length of the head.
    2.  Measured bore width at a 90° angle from (1), i.e., across the head
    3.  This was done at the top of the guide, at the guide midpoint and at the bottom (valve side)
    4.  A ball gauge was used to size the bore and measured with a caliper micrometer (accurate to 0.01mm).

Results:
It quickly became clear that my measurements were quite precise (repeatable) but possibly not entirely accurate.  For purposes here that's probably OK, certainly better than the reverse.  After all, we know what the specs are supposed to be, so it would be possible to apply a correction factor.

Cyl head axis
       Top         Middle   Bottom   Average    Range (max to min)   Spec
Intake valve ID:     9.02mm   9.01      9.03       9.02         0.02                         9.000-9.015
Exhaust valve ID:  11.02      11.02    11.08      11.04       0.06                         11.000-11.02


Cross axis
           Top         Middle   Bottom   Average    Range (max to min)   Spec
Intake valve ID:     9.03mm   9.02      9.06       9.03         0.04                         9.000-9.015
Exhaust valve ID:  11.05      11.01    11.14      11.07       0.13                         11.000-11.02

This suggests several things. 
  > Wear is greater across the head, i.e, the guide wears in a very slightly oval cross section.
  > The most wear, by far, occurs at the bottom of the guide.  I looked at this more closely.   All the wear seems to occur in the bottom 10mm of the guide.  So, in a macro sense it's right to say that the guides become tapered.  But it isn't really a true taper, more like a step change in ID at the very bottom of the guide.
  > Maybe the "wiggle test" needs to be done with valve almost seated (e.g., 0.5mm off the seat) and open, say, 10mm.  Maybe that's the right way anyhow, I don't know.   
  > I don't know the dimensions of the MB wear gauges (would love to know if anybody has the specs), but it seems like a simple, cylindrical wear gauge would miss some of the subtleties.  Or maybe it doesn't matter?
  > I'm definitely outside the specs, at least as I read them. 

Well, that's it.  Does it mean anything?  Probably, but i don't quite know what.  Regardless, it was a fun little project.  Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

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Re: Understanding valve train specs (quantitative & tedious)
« Reply #8 on: 01 November 2019, 09:09 AM »
Here is one for sale from the Argentinian outfit, not sure if it is the right one but looking at the specs it might be.  I have bought stuff from them before, good service and quick shipping:

https://www.ebay.com/itm/Mercedes-Benz-go-no-go-gauge-for-inlet-valve-guide-6365890021-tool-OEM-NOS/183778371345?hash=item2aca0b6711:g:SoEAAOSwq8BZbusb

I have often wondered why there is such a treasure trove of Benz parts in Argentina.  Could it be related to the Nazi's having fled there after WWII and they wanted to keep driving their Benzo's..?
Daniel
1977 450 SEL 6.9 - Astralsilber

rumb

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Re: Understanding valve train specs (quantitative & tedious)
« Reply #9 on: 01 November 2019, 10:53 AM »
If the spec is x.015 then you are pretty much there.  If my engine I would just go ahead and put all new guides in.  Not likely that you will ever be in there again and would just eliminate any and all future issues. 

besides genuine MB parts your machine shop may well be able to find reliable high quality guides.  There is is an entire industry that supplies them.

what is the pn's of the guides?


'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

UTn_boy

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Re: Understanding valve train specs (quantitative & tedious)
« Reply #10 on: 08 November 2019, 09:23 PM »
If the spec is x.015 then you are pretty much there.  If my engine I would just go ahead and put all new guides in.  Not likely that you will ever be in there again and would just eliminate any and all future issues. 

besides genuine MB parts your machine shop may well be able to find reliable high quality guides.  There is is an entire industry that supplies them.

what is the pn's of the guides?

Standard size intake: 100-050-47-24 (replaced by 100-050-48-24)    No longer available
First repair size intake: 100-050-48-24 (14.043-14.050mm)              Still available
Second repair size intake: 100-050-49-24 (14.2mm)                         No longer available
Third repair size intake: 100-050-50-24 (14.4mm)                            No longer available

Standard size Exhaust: 100-050-55-24 (replaced by 100-050-56-24) No longer available
First repair size exhaust: 100-050-56-24 (15.043-15.050mm)           No longer available
Second repair size exhaust: 100-050-57-24 (15.20mm)                    Still available
Third repair size exhaust: 100-050-58-24 (15.40)                             No longer available

The measurements given refer to the outside diameter.  Also,bear in mind that if new guides are installed that the valves will have to be re-cut/re-seated, as installing new guides disturbs the valve seat to valve face alignment.  If the aforementioned takes place the installed height of the valve stems must be reset.  Otherwise the valve lash will have to be reset.

1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex
1978 450sel 6.9 Euro, Anthr/velour