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W116 6.9 (6632) engine rebuild

Started by HPC, 23 January 2023, 04:39 PM

raueda1

Quote from: HPC on 14 February 2023, 12:57 AM
Quote from: daantjie on 13 February 2023, 10:02 PMFor 6.9 parts check out

oldbenz.co

They're in Canada but I'm sure they'll ship to US.


I did speak to Arsen, he may have had some valves but no luck. He does have an almost complete motor :) We should be able to get it to Texas :)
Dude, I keep telling you I got a set of good used valves.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

HPC

Im so sorry I misread your post :o
Thats awesome. I'll send PM.

HPC

Update on bore inspections..
stuck an iphone and light in each one to take pics in all directions.  a carbon buildup ring/discoloration on top of each bore. No 7 is the worst, the grey area is probably where water sat on top of the piston for a while, you can feel the roughness with fingernail. the rest feels ok. the diagonal dark line possibly where it leaked in from the head gasket.

Randy, there was no wet and dry involved in cleaning, just pb blaster and a shop rag. mostly to get the carbon off piston and the ring on the top of the bore.

Randys01

So it's a matter of how much can we sand away the water damage in no7. The tracking I reckon you can get out with wet n dry.

However we hit a show stopper with the actual corrosion. This is typical of what you have described. Do you know, it doesn't take long.? For all the oil that is supposedly left on a bore after the piston has swept by, they corrode in a matter of months.
And not what's clear is why the gasket went in the 1st place.  and No7?.it's usually no 8.

Well we've arrived at the crossroads my friend.

In the perfect world we would pull her all down and back to Tours............7/10 thousand dollars.
Rebore..  no 1 o/s pistons /rings/bearings bla bla.
 
The problem here is that you cannot restore one cylinder without doing them all.
 So the way ahead is to restore No7 as best as possible and accept that she'll be as good as gold even with that blemish on the bore.
If it's done properly, you won't know.
I doubt that there will be any measurable drop in compression.
 I doubt that it will blow any smoke.
I doubt that it will use any more discernible oil.

So long as that corrosion is sanded back to the bore diam . ie the corrosion has not thrown a teeny weeny crust.

In your contemplation  just remember that another motor you might chance upon has probably the same issue...a benign leaking head gasket.

HPC

The corrosion spot is a valley not a peak... the engine is able to turn freely.

When I examined the head again, there is some corrosion on the head that formed a peak that could have caused the leak into the cylinder.  I still have not seen definitive proof of where the oil and coolant have mixed. I will get the  heads pressure tested to rule that out.

The PO provided me with compression test numbers if that is worth anything.
1 - 155
2 - 150
3 - 150
4 - 150
5 - 145
6 - 150
7 - 150
8 - 155

daantjie

#50
Those compression numbers are not bad but not great either.  I would say at this juncture you need to ask yourself what you want out of the car.  Just a fun occasional cruiser, which most of these are now, or a very reliable daily driver.  Likely a 6.9 is not the best choice as a daily for mulitple reasons, so really if you want a Sunday cruiser, then it makes no sense to drop big coin on this motor.

If I were you and just wanted a fun type fair day driver, then just do the bare minimum to get it buttoned up again, maybe just hone the cylinders and get the heads done and call it a day.  The bottom end on these motors is very stout so unlikely you would need to do bearings I would think.
Daniel
1977 450 SEL 6.9 - Astralsilber

Gpapaniko

The fact that the compression ratios are roughly the same across the whole block is a good outcome.  I have much greater variability in compression across my 6 cylinder block and it serves me well as a Sunday cruiser.  I have more work to do on on vacuum leaks and the fuels system before I even consider doing the engine even if it is up to 400k kms.  If I keep the car for ever and do about 3000 to 4000ks per year, i will not add 100k kms to the motor. I agree with daantjie that align you strategy with the use case for car and the more time you have to enjoy the better value the purchase.
Never stop loving
1980 280SEL

Randys01

OK.compressions are pretty good.
Considering one or more is supposed to have a compression leak some where, it isn't showing up is it?
As matter of intertest the manual states that an 8.8:1 CR Euro motor pumps out 147 to 176 psi...so you are well with in range.
So there is no reason to abandon the  motor on this aspect.
If you have not scoured the bores, why is there so much evidence of cross hatching but in a random pattern?
By 100 K miles, the factory finish is pretty well gone.............?

By way of intertest I pulled the head off a Nissan Navara recently that had a blown head gasket......oh dear the head had to be thrown away but the point of interest is the water had sat in one of the cylinder for not a long time but it had a series of wave like marks in the bore.  From a cost effective point of view there was only one way to go. Clean her up using every trick in the book.. nail her up and away we go. Not a problem..cripes it stood every chance of blowing smoke but nary a drop.

rumb

I've seen cross hatch on bores of MB engines over 100K several times.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS

HPC

My plan is not for a daily driver - I have a W124 400E for that. I would like to be able to do a little road trip now and again... 3000mi annually should cover it... 
The car shows 71k miles on the odo and I verified it is the original engine number. No evidence of it being opened before, so those must be the factory honing marks.
Should I take the oil pan off to inspect the bottom?
Is there a good way to flush out the oil and coolant cavities to remove any leftover sludge?

raueda1

Quote from: HPC on 23 February 2023, 11:51 AMMy plan is not for a daily driver - I have a W124 400E for that. I would like to be able to do a little road trip now and again... 3000mi annually should cover it... 
The car shows 71k miles on the odo and I verified it is the original engine number. No evidence of it being opened before, so those must be the factory honing marks.
Should I take the oil pan off to inspect the bottom?
Is there a good way to flush out the oil and coolant cavities to remove any leftover sludge?
Not sure how to flush oiling system without actually running the engine.  Probably somebody else knows.  But something to think about is this - By the time you've undone everything enough to remove the pan you've done the worst part of  the work needed to pull it entirely.  And much of that is accessible from the top of the engine compartment.  If it were me I'd just pull it and clean up some other stuff too. And pulling it will greatly speed up a lot of other stuff that becomes easy if engine is out of the car.  Obviously I'm assuming that you access to big hoist etc.  Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Randys01

.Dave's pretty well covered it. Use compressed air to blow out the various holes,pull down and clean what you can get to.eg oil filter/oil resevoir/oil lines./oil cooler.

Flush/ purge/ heater/radiator hoses/therm etc

poss send radiator to specialistt for clean out.

When the engine is all back together leave the cam boxes off........new oil and filter..remove plugs/pull the coil etc and with plenty of rags at the ready crank the motor until you have oil pressure and can see all the old grungy oil coming out of the cam area. Do this a couple of times.  Mop up. These are a wet motor and the camboxes fill with oil quick smart.
After this purging exercise, close up .and run at idle for 10 minutes.
Drop the oil and filter and reload with new filter and oil.
In the meantime use your favourite coolant cleaner as per manuf reccos.

Make sure the engine is well oiled with an oil can used liberally over the valve gear.

Special note: hydraulic valve lifters. These are due for clean up. Remove from cyl head and crush them to expunge the oil within. They will need to be reloaded with fresh oil. This is a job no one ever does and perhaps best left to the workshop. You may of course choose to replace them all with new  ones.
You now have one very clean engine.

Randys01


HPC

Update!
Found a good euro motor base - thanks Rumb! Bores and heads seem to check out good. 
I think this is a much better base to start from.
guess it is time to get my old block out of the car...

rumb

My spare engine turned out to be in great shape! Valves and guides and bores all within spec. Glad it found a new home!

BTW this engine was out of 1976 with VIN serial number of 162.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS