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Another cam timing question

Started by raueda1, 08 September 2018, 06:51 PM

raueda1

My valve covers are gross looking, paint is flaking off and they look cheesy.  So, off they came for bead blasting and repainting.  This is also the time to check cam timing.  Here's what I found:

With right cam set to the notch (Plate 1, right passenger side)  the left cam (Plate 2) was offset by just a tiny amount, almost impossible to see.  The corresponding offset on the crank is about 7°.  I guess the good news is that the respective cams are very close to each other.  But please help me understand the crank offset.  Does 7° off at the crank mean the cams are actually off by 14°?  Or is it the opposite, i.e., cams only off by 3.5°?  For some reason the logic here eludes me.

Regardless, my understanding is that the chain needs to be replaced if the cams are off by 14° or more.  If it's actually 3.5° then is that enough to warrant installing offset keys to get down to zero?  Thanks and cheers,

ps - there is a very small amount of black sludgy stuff in places.  It's very thin, it isn't hardened and can be easily wiped off.  I'll do a flush/oil change after putting it all back together, hopefully that will clean it up.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Randys01

Something unusual going on here.
Generally as the chain wears and stretches, the valve timing slowly retards. That is, the mark in the cam flange falls "behind" the datum line on the cam bearing tower.
Your chain shows signs of good honest wear yet the valves are at TDC whilst the the crank is 7 degrees before top dead centre.
If you bring the crank timing to TDC, you will observe that your valves are now in advance. viz the scribe line in cam flange is now well past the datum line on the tower.
How can this be?
One scenario suggests some one has previously put in over valued offset keys to the cam sprockets [possibly of differing offset values ] ie too much offset.
Bring the engine to TDC on the crank pulley and see that it so: the cams are ahead of the play.

btw...check the wear on your rocker pads.  In the glimpse of the rh cam you can just see the chrome pad under the cam lobe -and from here [10 thous miles away,!! ] -it looks as tho there is some heat/wear scoring. Might be an illusion but I'd just double check that-  coz if the chrome is about to lift, a stitch in time etc. No 1 is a good one to check the general health of rocker pad wear.

ptashek

Quote from: raueda1 on 08 September 2018, 06:51 PMThere is a very small amount of black sludgy stuff in places.  It's very thin, it isn't hardened and can be easily wiped off.  I'll do a flush/oil change after putting it all back together, hopefully that will clean it up.

I can recommend "Engine Flush" from Liqui Moly based on own experience. Pop-it in onto the block, let the engine idle for 10-20 minutes, change oil.
Might need two or three applications to get everything out, depending on how much crud is in the oil passages.

https://products.liqui-moly.com/engine-flush-plus-3.html

1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE

raueda1

Quote from: Randys01 on 09 September 2018, 12:28 AM
Something unusual going on here.
Generally as the chain wears and stretches, the valve timing slowly retards. That is, the mark in the cam flange falls "behind" the datum line on the cam bearing tower.
Your chain shows signs of good honest wear yet the valves are at TDC whilst the the crank is 7 degrees before top dead centre.
If you bring the crank timing to TDC, you will observe that your valves are now in advance. viz the scribe line in cam flange is now well past the datum line on the tower.
How can this be?
One scenario suggests some one has previously put in over valued offset keys to the cam sprockets [possibly of differing offset values ] ie too much offset.
Bring the engine to TDC on the crank pulley and see that it so: the cams are ahead of the play.

btw...check the wear on your rocker pads.  In the glimpse of the rh cam you can just see the chrome pad under the cam lobe -and from here [10 thous miles away,!! ] -it looks as tho there is some heat/wear scoring. Might be an illusion but I'd just double check that-  coz if the chrome is about to lift, a stitch in time etc. No 1 is a good one to check the general health of rocker pad wear.
Many thanks, super helpful.  This is both illuminating and vexing!  Let me summarize/replay it and see if I can put the story together right.  Here's how I understand it:

For whatever odd reason the cams are advanced by 7° on the crank.  This equates to 3.5° of actual cam advance.  Chain stretch goes in the opposite direction.  Therefore,
    1. Somebody deliberately advanced cam timing (which sometimes
        tuners do for various reasons) or,
    2. the car exists in a space-time anomaly wherein the laws of physics
        are distorted such that the chain shrinks with age. 
I vote for scenario 1.  It seems like a very odd thing for somebody to do.  Maybe precompensating for chain stretch?  But who would go to the trouble of doing that?

Anyway, is my understanding correct?  And then, if it is, what to do about it (if anything)?  I was browsing around some of the racing and V8 forums (Corvette, etc).  From these I learned that advancing the cam timing shifts the torque curve lower, i.e., better low end torque but at the expense of high speed HP.  Fiddling with this stuff is why they have adjustable timing gears and advancing 4° seems to be a pretty common thing in the hot rod world.  Maybe whoever advanced it was an old school hot rodder?  Anyway, if what I'm saying is correct then I'm inclined to just leave it alone.  Thoughts?  Thanks again and cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

Dave if it were me, and I had the time/money, I would go back to basics and replace the chain and tensioner, and at the same time look at the offset key situation.  As most folks here know, I am a fan of the baseline approach, and unless you know for sure what you are working with as a baseline, trying to correct issues is pretty  much pointless IMHO.
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

Quote from: daantjie on 09 September 2018, 12:04 PM
Dave if it were me, and I had the time/money, I would go back to basics and replace the chain and tensioner, and at the same time look at the offset key situation.  As most folks here know, I am a fan of the baseline approach, and unless you know for sure what you are working with as a baseline, trying to correct issues is pretty  much pointless IMHO.
Yeah, I think you're right.   I have the time and the car is apart now so in principal this would be the time.  However, $$ is tight at the moment and I'm in a local car show next weekend, probably not enough time to get the parts and do the job.  And.....   The car seems to run damn well (just did a 1500 mile trip mostly in tractless wastelands at high speed).  The distributor cleanup improved matters further.  Finally, I don't see how this situation carries any real risk.  So, I'm inclined to put this onto my "winter jobs" list for the time being.

All that aside, am I right that [7° at the crank] = [3.5° at the cam] ?  3.5° doesn't seem like a whole lot of error and might even help low end torque.  Obviously I'm clutching at straws here....  :P   Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

rumb

Since the two cam marks pretty much line up, I'm inclined to think the chain is not stretched. I would suspect offest keys.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio

raueda1

Quote from: rumb on 09 September 2018, 02:29 PM
Since the two cam marks pretty much line up, I'm inclined to think the chain is not stretched. I would suspect offest keys.
Well, OK.  But what would you do if you were me?  Get rid of offset keys (and maybe a little top end)?  Or leave it alone (and maybe benefit a little in the bottom end)?
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Randys01

I wouldn't worry about the valve timing. Somewhere down the track you can address it when you do a general top overhaul...replace chain..possibly the banana  tensioner..check cam lobes etc. With the passage of time, the chain will stretch even more and one day it will be spot on!
She's going like a rocket so leave it alone.
Different folk have different success with  additives /desludgers etc.  I've never had much joy but the Moly sounds as good as any.

The crank rotates twice to make the 4 cycles....the camshaft turns once for the 4 cycles. The relationship is theoretically 2 :1. 
Therefore every degree the crank turns the cams turn half a degree.
In a perfect world, the crank at TDC =cams at TDC.

It's a fair assumption that if the cam and crank are at variance, then 7 degrees at the crank =3.5 degrees at the cam.

In your case, when the crank is at TDC, your cams should be a few degrees retarded....[normal wear ] but they are a few degrees advanced. :o

This takes one hellava  offset key to adjust minus 2-3 degrees to plus 3.5?

As an exercise, measure the diameter of the camshaft thrust washer that has the timing mark in it, then accurately measure the difference between the 2 timing marks and divide the  difference into the calculated circumference. Convert this value to degrees and you should get about 3 to 4 degrees.

Cheers






daantjie

If I can make a little segue into a related topic ::)
One piece of advice which blew my mind at first (does not take much ;D) I received way back was to identify either top or bottom end noises by the frequency of the noise.  Top end noise is @ 1/2 engine speed, thus 5 taps per second @ 600 rpm.  Bottom end noise will be = engine speed, thus 10 taps per second @ 600 rpm.  Boom, drop the mike ;)
Daniel
1977 450 SEL 6.9 - Astralsilber

daantjie

Randy and others. one more thing which is puzzling me now looking at Dave's cam marks in relation to the marks on the cam tower...
My understanding is/was that when you stand in front of the car, looking at the motor, the marks on the cam washer should "come into" (moving from "left" to "right") the mark on the cam tower, thus denoting cam/valve advance and not retard :o?  Thus if you have the crank perfectly aligned with the pointer @ 0, then you want to have the marks either lined up spot on on the cams, or slightly "before", no?
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

Quote from: daantjie on 10 September 2018, 10:57 AM
Randy and others. one more thing which is puzzling me now looking at Dave's cam marks in relation to the marks on the cam tower...
My understanding is/was that when you stand in front of the car, looking at the motor, the marks on the cam washer should "come into" (moving from "left" to "right") the mark on the cam tower, thus denoting cam/valve advance and not retard :o?  Thus if you have the crank perfectly aligned with the pointer @ 0, then you want to have the marks either lined up spot on on the cams, or slightly "before", no?
Yeah, based on this thread and digging deeper it's apparent that my cam timing is indeed advanced - the opposite of what you'd expect.  When everything is perfect and new all the indexing should align.  Stretch retards it over time so the cam scribes should become progressively shifted counterclockwise on the cams with crank at TDC.

It remains a mystery how it got that way and what somebody's reasoning was.  Regardless, I'm going to leave it alone.  As Randy points out, it will get closer to spec as the chain stretches further.  It's odd but from my point of view it's a lot better than a must-change-chain-immediatley scenario.  It's also clear that there's little or no potential performance gain waiting to be unleashed, unlike the distributor cleaning project.  So I'm gonna leave it alone.

BTW, I'm having my valve covers polished for a local show this weekend.  It isn't original but WOW does it look great.  Squiggle gets credit for this idea.  His valve cover is polished and it's stunning.  Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

rumb

Here is the page from the data book regarding timing. Interesting that they predict retardation of 2 degrees over 20K km.  That would be 10 degrees at 100k km or 66K miles. They also start out with each bank different to account for chain stretch that affect each bank differently.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio

daantjie

Quote from: raueda1 on 10 September 2018, 03:25 PM
Quote from: daantjie on 10 September 2018, 10:57 AM
Randy and others. one more thing which is puzzling me now looking at Dave's cam marks in relation to the marks on the cam tower...
My understanding is/was that when you stand in front of the car, looking at the motor, the marks on the cam washer should "come into" (moving from "left" to "right") the mark on the cam tower, thus denoting cam/valve advance and not retard :o?  Thus if you have the crank perfectly aligned with the pointer @ 0, then you want to have the marks either lined up spot on on the cams, or slightly "before", no?
Yeah, based on this thread and digging deeper it's apparent that my cam timing is indeed advanced - the opposite of what you'd expect.  When everything is perfect and new all the indexing should align.  Stretch retards it over time so the cam scribes should become progressively shifted counterclockwise on the cams with crank at TDC.

It remains a mystery how it got that way and what somebody's reasoning was.  Regardless, I'm going to leave it alone.  As Randy points out, it will get closer to spec as the chain stretches further.  It's odd but from my point of view it's a lot better than a must-change-chain-immediatley scenario.  It's also clear that there's little or no potential performance gain waiting to be unleashed, unlike the distributor cleaning project.  So I'm gonna leave it alone.

BTW, I'm having my valve covers polished for a local show this weekend.  It isn't original but WOW does it look great.  Squiggle gets credit for this idea.  His valve cover is polished and it's stunning.  Cheers,

I'm still confused ::)

By my estimation, if you bring the marker to 0, you will see that your cam marks are "after" the mark on the cam tower, thus valve timing is retarded and not advanced?  Unless I have the whole thing ass - backwards :o?  Please snap a pic of your cam marks with marker @ 0 (#1 Cylinder @ TDC).
Daniel
1977 450 SEL 6.9 - Astralsilber

rumb

Daniel,

His earlier picture of the pointer show @7BTDC, turning the crank 7 more degrees will then turn the cams that much further past (advanced or ahead of) where they should be.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio