Author Topic: 6.9 engine seized while cranking  (Read 1283 times)

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Re: 6.9 engine seized while cranking
« Reply #15 on: 08 August 2019, 01:11 PM »
I recently assisted a local main dealer with a 450SL kjet.  Someone had mad a mess of trying to fix the fuel distributor.  They had tried to install the metering barrel without any lube on the 8 orings that seal the metering slots.  This resulted in 7 of the 8 splitting.  This resulted in max unregulated delivery to those cylinders.  I advised a compression test as I was confident hydraulic lock had occurred... Three workshops had tried cranking the engine ad nauseum.  Any how, I rebuilt the fd, but we still really struggled to start the engine.  Short version of a long story

'76 6.9 Euro, '78 6.9 AMG, '80 280SE, '74 350SE, '82 500SEL euro full hydro, '83 500SEL euro full hydro , '81 500SL

s class

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Re: 6.9 engine seized while cranking
« Reply #16 on: 08 August 2019, 01:14 PM »
Short version of a long story is we then found that the left cam was timed 180 degrees out.  We corrected that, and I then got the engine to run fairly well, despite probable bent valves and probable bent rods.  The workshop manager and I were both pretty surprised to get it running that well.  But this is not the recommended way to treat an engine.

'76 6.9 Euro, '78 6.9 AMG, '80 280SE, '74 350SE, '82 500SEL euro full hydro, '83 500SEL euro full hydro , '81 500SL

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Re: 6.9 engine seized while cranking
« Reply #17 on: 08 August 2019, 01:17 PM »
I've Sen 450 motors survive unregulated fuel delivery a few times, but your situation is a bit different.  Running without the meter g piston would dump fuel directly I to the intake, not via the injectors.  Remember the pump can deliver approx 2 litres a minute.  The possibility of crank case lock did occur to me, but it would take quite some time to get enough fuel to full the crank case to pass through the rings. 

'76 6.9 Euro, '78 6.9 AMG, '80 280SE, '74 350SE, '82 500SEL euro full hydro, '83 500SEL euro full hydro , '81 500SL

s class

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Re: 6.9 engine seized while cranking
« Reply #18 on: 08 August 2019, 01:19 PM »
Have you tried depressing the air mass meter flap, and opening the throttle to see if there is fuel pooled up in the intake manifold?

'76 6.9 Euro, '78 6.9 AMG, '80 280SE, '74 350SE, '82 500SEL euro full hydro, '83 500SEL euro full hydro , '81 500SL

raueda1

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Re: 6.9 engine seized while cranking
« Reply #19 on: 08 August 2019, 03:17 PM »
For some findings to report:

> drained the oil.  There was a LOT in the sump but I'm not sure how much would be normal.  Oil stinks of gasoline.  It seemed to be thinned, to be sure, but not to the extent of "watery."  No metal chunks or anything came out.  I still couldn't move the crank after draining the oil.

> looked at valve timing.  The timing notches don't line up with the index lines on the post of course.  I made a little gauge to see how far offset they were from the index mark. Both sides were offset by the same amount, so it didn't look like their relationship with each other got changed.

> borescope: 
   *  looked in all the cylinders and saw nothing obvious amiss.  Stupidly I left the 90deg angle mirror at home so couldn't see everything or look at valves. I'll do that tomorrow.
   *  looked down the chain path as far as I could.  Nothing obvious - couldn't see broken teeth, metal chunks, anything like that.
   * ring gear:  poked as far as I could (which was pretty far) and couldn't see any damage.

So, it does look like there is some kind of mechanical blockage.  Or maybe hydrolock lead to something else?  The mystery continues. 

Next step, I guess, is to start >>really<< taking stuff apart.  Seems like 3 choices - from the rear (transmission), the bottom (oil sump) or top (heads).  Any further theories or suggestions are certainly welcome.  Seems like pulling the sump is probably less involved than the heads. 

Oddly, a sense of calm has overtaken me.  It's so baffling that I'm now philosophical about it.  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 #20 on: 08 August 2019, 05:39 PM »
So you only got a couple  of litres out of the sump. How full is the reservoir?
However, I think the journey now takes us to timing chain/tensioner/guide issues.
In order to narrow this down I would de-tension the main chain tensioner to relieve the tension on the banana tensioner rh  bank. With the chain slack I would try to turn the cam shafts [spanner on the cam sprocket] We don't need to wiggle it far to determine the cams will turn a bit. any rotation either way tells us the top of the motor is not the culprit inc the myriad of cogs/wheels/guides n the top timing chain entourage.
Now try turning the crank pulley a smidgeon..to date it has been locked solid but if you can now get a bit of action it would indicate something is binding in the timing chain department.
Report in!

rumb

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Re: 6.9 engine seized while cranking
« Reply #21 on: 08 August 2019, 06:03 PM »
Transmission in neutral? Though even in park I think you should still be able to turn crank.

Total oil in pan I would think would be about 10 quarts with probably 2 left in the filter and cooler.

Random ideas:
can you wiggle each cam a few degrees? Grab with vice grips to see if they each move at least a little bit.  If it moves and all your upper valve train looks normal -no loose rockers -  then that would reduce odds in that area.  You may need to remove chain tensioner to allow a little chain slack.

Have you run the scope in the oil pan?
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

raueda1

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Re: 6.9 engine seized while cranking
« Reply #22 on: 09 August 2019, 07:20 AM »
So you only got a couple  of litres out of the sump. How full is the reservoir?
Reservoir was full.  The gasoline thinning was very notable on the dipstick.

However, I think the journey now takes us to timing chain/tensioner/guide issues.
In order to narrow this down I would de-tension the main chain tensioner to relieve the tension on the banana tensioner rh  bank. With the chain slack I would try to turn the cam shafts [spanner on the cam sprocket] We don't need to wiggle it far to determine the cams will turn a bit. any rotation either way tells us the top of the motor is not the culprit inc the myriad of cogs/wheels/guides n the top timing chain entourage.
Now try turning the crank pulley a smidgeon..to date it has been locked solid but if you can now get a bit of action it would indicate something is binding in the timing chain department.
Report in!
This will be today's project, along with more thorough borescope exam. 
-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 #23 on: 09 August 2019, 08:07 AM »
Transmission in neutral? Though even in park I think you should still be able to turn crank.
Yes, in neutral.

Total oil in pan I would think would be about 10 quarts with probably 2 left in the filter and cooler.
Seemed like more than 10 quarts came out, more like 12.  Hard to measure exactly, but my 5 gallon oil drain tank was easily 2/3 full.

Random ideas:
can you wiggle each cam a few degrees? Grab with vice grips to see if they each move at least a little bit.  If it moves and all your upper valve train looks normal -no loose rockers -  then that would reduce odds in that area.  You may need to remove chain tensioner to allow a little chain slack.
Yes, Randys01 suggested similar.  Good suggestion, gentlemen.

Have you run the scope in the oil pan?
Since this is going in from the bottom I guess that's an automotive colonoscopy.  Will perform procedure today. 

All this now has me wondering about a different path.  I'm picking up the beater 6.9 early next week.  Then I could conceivably do an engine/tranny swap. Is a USA engine a simple bolt-in on a Euro chassis?  I think there are significant differences in how the oil and transmission cooling is set up.  AC might also be an issue.  I'd like to preserve the euro AC which is nicely charged with Freon 11.   USA engine would also need to be desmogged too I guess.  Anyway, I'd then have a running car to play with while the weather's still nice and sort out the original Euro engine in the meantime.  Maybe even rebuild to it's former Euro greatness.   It would also be an opportunity to redo some other stuff on the car that would otherwise be harder, like engine mounts.  This might sound kind of nuts but at some point the cumulative time & effort messing with the seized engine might exceed the effort of swapping.  And I'd eventually be pulling the donor car's engine anyway.  I haven't yet spent any time exploring this option.   Hmmmmm.
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

rumb

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Re: 6.9 engine seized while cranking
« Reply #24 on: 09 August 2019, 11:37 AM »
I think you are best with keeping/building a Euro engine. More horsepower from different pistons and no smog.  Additionally with your euro engine you can get if you dont already have an permanent EPA waiver. Putting smog crap on will only anger your emissions department and they might demand cats which have a different floor pan to make room for them. AFAIK the heads are the same. You could build a US engine to look like a euro from the outside.

I dont remember if the parts car is euro or not, but I have a spare euro engine that parts can be obtained from if needed.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

raueda1

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Re: 6.9 engine seized while cranking
« Reply #25 on: 09 August 2019, 01:56 PM »
More info!  Loosening the chain tensioner gave enough slack to move the cams a bit - they aren't frozen.  However, the chain slack did NOT translate to the crankshaft.  It"s still stuck.

I tried to do the sump colonoscopy but failed.  The 90deg mirror on the scope is crap, crappy reflective surface, so the LED illumination is diffused and totally clouds the image.  Terrible design.

I'm not sure where this leaves me, but I doubt it's good.  I guess it means either drop the sump or pull the engine.  I'm somewhat inclined to pull engine, especially if I can do it but still leave AC compressor etc in place.  Seems like there are various possibilities that would require pulling the engine anyway, so might as well bite the bullet.  If the concensus is "yes, pull engine," then I'll start another thread on that.  I expect I'll need so guidance.  :-\

Further thoughts welcome!  Thx,
-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 #26 on: 10 August 2019, 05:30 PM »
We gave it our best shot and whilst we didn't determine a positive diagnosis we eliminated all the soft options thus justifying a major project pulldown.  Good luck.   I have read the new thread.......

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Re: 6.9 engine seized while cranking
« Reply #27 on: 10 September 2019, 07:47 PM »
Mystery solved!  The problem was exactly as some of you surmised.  See picture.  The crank counterweight is jammed against piston #8.   I'm amazed at how little clearance there is so, it didn't take much of a bend to jam it up.  The rest of the rods look fine, at least visually.  No metal flakes, chunks, or any other obvious problems.  The sump was surprisingly clean.  It doesn't look like the failure event took anything else with it, like broken valves.  Still, any thoughts would be welcome.  For example - new vs used rod/piston?  Special tricks or things to be aware of?

It would also be great to get any comments or views on how far to take this now that the engine is out.  Barring any surprises my inclination is to replace the rod, piston and bearing and call it a day.  I'll do the timing chain too as I know it has a little stretch.  I also discovered an exhaust manifold crack, though it doesn't seem to actually leak.  Nevertheless, I'll replace manifold too.  What else?  Others might say redo the whole bottom end etc etc, so discussion of pros/cons would be welcome.  By way of context this engine didn't ever smoke, rattle or have any other fundamental problems that I know of.  My work on the car has mostly been along the lines of making sure it's working 100% and not compromised by WUR problems and other small stuff like that.  Of course that's what got me into this whole mess. :-[ 

At this point I'm actually pretty excited.  The job seems do-able and created an opportunity to do lots of other stuff that I'd probably have ignored, like those oil hoses, resealing AC, etc.  Thanks to all for the ongoing support and help on this thing. Cheers,
-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 #28 on: 10 September 2019, 10:50 PM »
So can we conclusively say this is as a result of hydro lock?
Daniel
1977 450 SEL 6.9 - Astralsilber

Randys01

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Re: 6.9 engine seized while cranking
« Reply #29 on: 11 September 2019, 01:22 AM »
Yep..the dreaded hydraulic lock...and we all know how this came about.
...and so to recovery. Without going back over the history can you confirm that you never got the engine started...that it jammed under starter motor conditions?
Hydro lock occasioned by kjet flooding usually fills all cylinders equally. When the engine is cranked the 1st cylinder to approach Top Dead Centre is the one that is going to lock. In most engines there are usually 2 cylinders at TDC. In this instance No8 rear lh bank] is the offender. Calculate which other cylinder was at TDC and give it extra forensic examination. All other cylinders cannot theoretically be impacted.
I am amazed at how clean that engine looks and in partic how little wear there is on the piston skirt. This is either a  remarkably low mileage motor that had the oil changed every fortnight or this engine has been apart before. I'll be interested to learn  if the piston is std bore.

Options

I'd be inclined to go with your suggestion...pull the piston.. rod.. and big end...replace. new gudgeon of course!
I'd pull another piston rod set so that the replacement assembly can be at least weight matched. The original is also a valid balance weight reference.
You will want to be dead certain you get the right piston /rod combo as there were a couple of production variations over the course of the motor.