Author Topic: 6.9 engine seized while cranking  (Read 4473 times)

raueda1

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Re: 6.9 engine seized while cranking
« Reply #60 on: 27 September 2019, 06:36 PM »
Update:

The engine is now pretty well stripped apart from removing the crank.  Toady I made an interesting discovery after pulling the pistons for carbon removal and inspection.  The engine has indeed been rebuilt.  Maybe that's why it was so clean, though clearly it wasn't all that recent given the carbon on the pistons. 

The pistons are +0.5 oversize, code 75.  This corresponds to 8.4:1 compression instead of 8.8:1.  That makes it a demi-Euro engine in my mind, so I'm annoyed.  The main difference between the versions is mostly the depth of the cavity on top.  From what I make of the specs it looks like MB progressively reduced the euro engine's compression over time.  I wonder why.  Too many knocking issues?  Declining fuel quality at the time?  Who knows.  Maybe somebody can cheer me up with news that 8.4 is actually pretty close to 8.8, so no big deal.  ::) 

Haven't checked bearing journals to see if they messed with that (need a suitable micrometer).  There was an old mouse nest in the V between the heads and under the intake plenum.  Slowly progressing.......              Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Randys01

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Re: 6.9 engine seized while cranking
« Reply #61 on: 28 September 2019, 01:22 AM »
...not surprised....I thought the minimal scuff on the piston skirts suggested low mileage= rebuild.
When you pop the big end shells out you will see on the back if they are oversized or stds.
The 6.9 variant of the M100 saw dramatic modifications compared with the 6.3....As I recall there are 4 compress ratios and some of these also saw a change in gudgeon offset.
In Aust we got the so called 8 :1.  Introduct Down-under was towards the end of production. A mate of mine has a lively Euro import aka 9:1.no smog etc. Seat of the pants, there's nothing between them but I reckon I reckon mine goes very well for its spec. [ I have spent hours finessing it ]
So 8.4 or 8.8...if there ever was any discernible difference, the gap narrows as the old dears start to wear.

raueda1

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Re: 6.9 engine seized while cranking
« Reply #62 on: 28 September 2019, 09:01 AM »
...not surprised....I thought the minimal scuff on the piston skirts suggested low mileage= rebuild.
When you pop the big end shells out you will see on the back if they are oversized or stds.
The 6.9 variant of the M100 saw dramatic modifications compared with the 6.3....As I recall there are 4 compress ratios and some of these also saw a change in gudgeon offset.
In Aust we got the so called 8 :1.  Introduct Down-under was towards the end of production. A mate of mine has a lively Euro import aka 9:1.no smog etc. Seat of the pants, there's nothing between them but I reckon I reckon mine goes very well for its spec. [ I have spent hours finessing it ]
So 8.4 or 8.8...if there ever was any discernible difference, the gap narrows as the old dears start to wear.
Hmmm.  I can't make heads nor tails of the bearing designation "100 3110 KZ".  However, they're also stamped 11-75 which, per Mahle's system, suggests that they were manufactured in Nov 1975.  If so then perhaps they're original.  The car is #923 and was built in April 1976 but first licensed in the USA in 1977.  Engine is also original, matches the build card.  So, this chronology seems to make sense.   And if so, that suggests that somebody did a piston job at some point but left the big ends alone. 

Or maybe not?  I guess there's the possibility that they are oversized and were on the shelf for some time before the piston job.  The bearings are all in good shape.  The shop guy actually commented on how good they looked.  The other pistons all look good as well.  Obviously the piston job was done when pistons were still available - when was that?  Given low wear I'm guessing that the car got little use after that job.  Now I wonder what necessitated piston replacement.  I can't wait to see what surprises are lurking with the heads!  ::)

Well, all this stuff is fun I guess, but doesn't really impact the task at hand.  I'll measure the crank soon enough.  In the meantime there's a lot to inspect, clean, carbon to remove, stuff to repaint, plate, reassemble etc. 
Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

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Re: 6.9 engine seized while cranking
« Reply #63 on: 16 June 2020, 06:37 PM »
Today I hereby declare victory on this project, almost a year later.   The car is running well (though not perfectly, more below), seems drivable and looks stunning.  There was a lot of scope creep with this project.  You guys are entirely to blame!  "Well, while engine is out, blah blah blah," etc, etc.  But what a journey.  It was worth it.  I learned more about these car than I ever dreamed possible and relearned an unbelievable amount of stuff that was long forgotten.  The last engine I rebuilt was a 1966 230S back in 1979!  There were many times I thought I'd lost my mind and was in way over my head. But in the end it all seemed to work.

There are a few items still needing attention.  As noted elsewhere, the suspension light won't go out.  I'm having a hard time getting and keeping a smooth, steady idle.  The tranny control rod needs to get dialed in.  But now that all seems trivial and I'm sure I'll get it sorted out in due course.  I'd certainly be comfortable with a highway trip.

To all of you who helped me out, than you, thank you, thank you!  And to the readers, lurkers and "that's way beyond me" people:  you can do more than you think if you take your time and ask a lot of questions along the way.  Best wishes to all,

-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Jed

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Re: 6.9 engine seized while cranking
« Reply #64 on: 16 June 2020, 07:01 PM »
Well done Dave!  Congrats!

My parents live in SLC and I usually make it there once a year. maybe some day you'll take me for a drive. :)
1979 Mercedes 6.9 #5206 - restored
1979 Mercedes 6.9 #6424 - ongoing restoration
1976 Mercedes 6.9 #484 - restoration?

daantjie

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Re: 6.9 engine seized while cranking
« Reply #65 on: 16 June 2020, 07:11 PM »
Nice one Dave, mammoth effort, go and have that well deserved frosty ;)
Daniel
1977 450 SEL 6.9 - Astralsilber

TJ 450

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Re: 6.9 engine seized while cranking
« Reply #66 on: 16 June 2020, 11:39 PM »
Excellent news,

Yes, getting it to idle smoothly will be a mission.

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

raueda1

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Re: 6.9 engine seized while cranking
« Reply #67 on: 17 June 2020, 06:59 AM »
Excellent news,

Yes, getting it to idle smoothly will be a mission.

Tim
Understatement.  :P  Any and all suggestions welcome!
« Last Edit: 17 June 2020, 07:23 AM by raueda1 »
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

TJ 450

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Re: 6.9 engine seized while cranking
« Reply #68 on: 17 June 2020, 11:26 PM »
In my experience it’s all about getting the best compromise. Assuming the WUR and FD are in proper order it’s the idle mixture screw and idle air screw that need to be tweaked. Finding the sweet spot is going to involve a lot of trial and error. For example if you get it silky smooth on a cool, humid night it might be lumpy on a warm dry day etc.
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

Randys01

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Re: 6.9 engine seized while cranking
« Reply #69 on: 18 June 2020, 12:46 AM »
so how did the crank measure up?
...and congrats on getting it all back and going.!

The elusive smooth idle.  hehehe!!.........yeah..............I've spent a 100 hours on this if I've spent 2 minutes.
I've got mine pretty good across the entire temp spectrum but just be satisfied with hot idle in drive at 650 rpm.
The key is hot control pressure and evenness of fuel delivery at the injector nozzle.

I have designed and built my own fuel head and injector test bed.  It's a fascinating science but as these babies are getting older, the cast iron FD's are proving snarky in reliable and consistent fuel flow due to wear.  10000's litres of fuel washing thru them over 30 years is actually wearing them out.
Fuel deliv at idle is down to 6cc per min. max variation is 1 cc. that's on just the delivery. Then there are nuances of the injectors...dirty..cracking pressure.. leakage.
If we go back to the beginning. air flap clearance..idle fuel ratio..........these have little range and must be spot on.
All of these moments are truth are almost exclusive K jet considerations..but of course you still have the basic engine fundamentals that need to be correct....We  haven't come to air leaks yet..!   evenness of compressions.......accuracy of valve lift and timing.
As I said.......if you can achieve a reasonably smooth hot idle take a bow and unless you are OCD about it, be content with near enuff is good enuff.

raueda1

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Re: 6.9 engine seized while cranking
« Reply #70 on: 18 June 2020, 09:22 AM »
so how did the crank measure up?     ...and congrats on getting it all back and going.!
Thanks! Crank was fine.  I went through that last fall, can't recall details.  I didn't mess with the mains but replaced rod bearings.  Oil pressure is excellent, but possibly a function of 30 weight break-in oil.

The elusive smooth idle.  hehehe!!.........yeah..............I've spent a 100 hours on this if I've spent 2 minutes.
I've got mine pretty good across the entire temp spectrum but just be satisfied with hot idle in drive at 650 rpm.
The key is hot control pressure and evenness of fuel delivery at the injector nozzle.

I have designed and built my own fuel head and injector test bed.  It's a fascinating science but as these babies are getting older, the cast iron FD's are proving snarky in reliable and consistent fuel flow due to wear.  10000's litres of fuel washing thru them over 30 years is actually wearing them out.
Fuel deliv at idle is down to 6cc per min. max variation is 1 cc. that's on just the delivery. Then there are nuances of the injectors...dirty..cracking pressure.. leakage.
In hindsight I think the FD rebuild actually went well.  I had help from an unnamed collaborator on this board with mucho experience with the iron FDs.  The original diaphragm was quite deformed from wear and the metering ports uneven.  The polishing process fixed all that, which is key to even flow (I guess).

If we go back to the beginning. air flap clearance..idle fuel ratio..........these have little range and must be spot on.
All of these moments are truth are almost exclusive K jet considerations..but of course you still have the basic engine fundamentals that need to be correct....We  haven't come to air leaks yet..!   evenness of compressions.......accuracy of valve lift and timing.
As I said.......if you can achieve a reasonably smooth hot idle take a bow and unless you are OCD about it, be content with near enuff is good enuff.
Turns out my WUR, which had been rebuilt by the famous CIS Flowtech, was substantially out of whack.  It seemed ok before the rebuild, but no longer.  Maybe running the system without the FD metering piston toasted it, who knows.  Among other things cold pressure was close to zero.  Anyway, I've got a box of WURs, one of which was the high-altitude version out of a parts car.  I swapped and guess what? Everything instantly improved instantly. All the pressures are spot on.  Idle is much, much better.  And stable.  Before it would be fine, then go bad at the next traffic light, then ok again.  I got a Gunson CO meter in the mail and will play with that.  In the meantime the car is running well. Just gotta get the transmission rod right.  So tedious - it's close but not perfect.  Finally, I looked for vacuum leaks with a smoke tester.  No leaks, system seems to be tight.

Next will be checking lifters and cam timing, but I'm no big rush.  The car got a new chain, rails and sprockets.  During assembly timing was pretty close (way better than it had been), but not perfect.  Somebody had messed with the woodruff keys and done it backwards if I recall.  Anyway, I want to get some mileage on it first so it's settled in.  Small stuff remains.  One headlight wiper doesn't work and neither do headlight washers.  Cruise control is kaput.  AC needs recharging.  Suspension light problem needs diagnosis.  But none of that prevents motoring fun in the meantime.  Most of my friends have long questioned my sanity.  This removes all doubt.  ::)  And so it goes....
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

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Re: 6.9 engine seized while cranking
« Reply #71 on: 18 June 2020, 09:47 AM »
Dave, I have engine bay envy now ;D
Daniel
1977 450 SEL 6.9 - Astralsilber

ptashek

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Re: 6.9 engine seized while cranking
« Reply #72 on: 18 June 2020, 10:34 AM »
Nice job on that engine bay :)
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Randys01

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Re: 6.9 engine seized while cranking
« Reply #73 on: 18 June 2020, 11:35 PM »
all's well that ends well.    and that engine bay looks just sweet!

Mick74

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Re: 6.9 engine seized while cranking
« Reply #74 on: 21 June 2020, 02:46 PM »
That engine bay is amazing. Those rocker covers.....  8)