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W116 6.9 (6632) engine rebuild

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

HPC

Hi Everyone,

Some advice and/or parts needed please. My 6.9 #6632 is need of an engine rebuild... I bought it as a project, in decent condition with 71k mi on the clock, except for an engine with blown head gasket/ possible overheating issue.  After removing the heads we discovered the valves are worn past factory specs, excessive for the miles. Which puts doubt on the integrity of the block (and the accuracy of the odometer).  How robust are the engines? Any way to tell if the block (and bearings) are still good without opening up, or move on and try to source a complete running engine?

To rebuild the heads - intake valves are NLA from MB classic center - any other sources to try?

Thanks
Manie

daantjie

It would be unusual for a 6.9 engine to have suffered such a fate but of course anything is possible.  Any idiot can ignore an engine temp gauge and run an overheated engine to failure of course.  As a rule the 6.9 engine is very robust and probably the most overbuilt engine Benz has ever made.

Having said all that, if indeed the motor has been severely overheated we must assume that it is now compromised and thus personally I would not try and drag a dead horse over the finish line.  You can usually find used 6.9 motors on ebay and such.  Likely some forum members here might have a spare motor kicking around.

You can usually find NOS parts on ebay.  There is a seller in Canada selling NOS valves for the 6.9 if you still want to go down that route.

Cheers
Daniel
1977 450 SEL 6.9 - Astralsilber

HPC

Thank you Daantjie.  I am a bit weary of purchasing an engine out of a car, not knowing if it runs or not, I don't want to end up with 2 non-runners  :o   But if my block is OK, then doing a rebuild on the heads should is workable, if I can locate valves. I do have some part already like full gasket set, chain, guides, etc.

Randys01

When you say valves are beyond spec are we talking valve stem dimensions OR we talking valve face/valve seat?

In order to assess how worn this motor is, what are the rocker arm pads like? No 7 and 8 usually have a story to tell.

By now most of these motors clap out the valves guides if they have been neglected...........is the wear in the valves more to do with wear on the guides?

What is then running clearance in the camshaft bearing towers?  Take 2 measurments of both.

What do the cyl bores look like?.scouring?..excessive lip at the  top.  partic No5?

What condit were the head gaskets? Blown around No 5?

I look fwd to your findings.


HPC

Valve stem dimensions... my mechanic says valves and guides needs replacing.

Not sure on the camshaft bearing towers

The cyl bores look OK, no scouring or lip.

I could not see any particular point of failure on the gaskets. I'm attaching pics that I have during dismantling, maybe you can spot something.

HPC

Here are some pics of the right side camshaft and rocker pads

Randys01

All looks pretty good to me..
cam lobes AOK 
cam bearings LOOK OK.

WHAT ABOUT ROCKER ARM TO CAM LOBE?

BUT.......how rich has this thing been running?.and not for a little while either?!!

So valves and springs huh?  with all due respect from 10000 miles a way I'd say not a problem.
They will have to be dismantled of course but to write them off arbitrarily  is a bit premature.
The springs can be measured for length/crush etc . and compression strength. I reckon they will scrub up ok.

The valves should be removed and clearance with the guide carefully measured. If the guide is worn -as these are prone to do-, the valve- once removed of springs etc- will wobble in the guide.
Take an observation of the valve stem at its end/tip and inserting the valve stem partially, see how wobble/play/wear you have. ie unswept area
I think you will find if there is anything worn, it wont be the valve but the guide. All pretty simple stuff. 

Love to hear your findings.



HPC

OK, so, the history that I have on the car...
1st owner in Oklahoma City had it for 10 years (1979-1989) and 32,000 miles, regular oil changes
2nd owner in Fort Wayne, Indiana, drove it for 3 years (1989-1992) and another 11,000 miles,
  total 43,000 miles with regular oil changes
then a dark period with 2nd owner, with no oil change records available, next oil change on record 10 years later in 2002 at 67,000 miles ( at MB dealer)
after this the car went into storage with 71,000 miles, and got pulled out by the son of the 2nd owner in 2013 who then discovered coolant in the oil.
Something must have happened between 2002-2005-ish and 4,000 miles to cause the issue
Between 2013 and 2022 the engine was periodically started to keep it turning over, with no coolant to get mixed into the oil. Maybe this cause the evidence of rich running, and maybe excessive wear?

When I got it, it would fire up easily (with a small puff out the exhaust) and drive a short distance to move it.

I found the radiator and coolant cavities filled with oil, thinking heads reconditioned and new gaskets would get it back on the road..

I may be in way deeper than expected...

Randys01

nice looking bus.
Yes.a bit of an interesting history.
Id say there is nothing major to this point with the motor.
The head galleries look fine.no major corrosion.
Anyway, I look fwd to your responses to my questions at 10pm.

HPC

Thank you for your observations, makes me feel more positive again.
I will take another look at the heads and valves and report back accordingly :)

daantjie

On a side note looking at the green puddle in the valley that is the wrong type of antifreeze for a Benz.

Once you button it up flush completely and refill with Zerex G-05 (Valvoline) diluted 50/50 with distilled water.
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

This project is stroll down memory lane. ::)   Agree with Randys01 assessment (but lesten to him, not me, he's far more knowledgeable).  My question is, how far do you want to take it?  Engine needs head gaskets, not doubt.  And it's half taken apart.  You could do a head rebuild job, new gaskets and call it a day.  OTOH, you could pull the engine and do a more thorough job, such as replace all the chain guides, maybe crankshaft seals, replace the old and probably brittle wiring harness, rehone cylinders, inspect pistons etc.  I discovered that my engine had been rebuilt (+1 pistons) but chain gears hadn't been replace and were quite worn so those got replaced.  And do a nice repaint/restoration of the engine compartment while you're at it.  That's the rabbit hole I got sucked down, but in the end I'm glad I did.  Cheers,

ps - be sure to replace the valve springs in the right orientation.  They have an up and down that is not at all obvious!
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

As well, if you do not need to pass smog testing, then now is the time to yank all that smog garbage off the motor and block off all the ports.  Once the engine is assembled it's a lot more difficult to plug all the ports. Especially the connection and piping at the throttle body, it's pretty much impossible to pull the recirc piping with the intake in place.
Daniel
1977 450 SEL 6.9 - Astralsilber

HPC

Quote from: raueda1 on 24 January 2023, 10:25 AMThis project is stroll down memory lane. ::)  Agree with Randys01 assessment (but lesten to him, not me, he's far more knowledgeable).  My question is, how far do you want to take it?  Engine needs head gaskets, not doubt.  And it's half taken apart.  You could do a head rebuild job, new gaskets and call it a day.  OTOH, you could pull the engine and do a more thorough job, such as replace all the chain guides, maybe crankshaft seals, replace the old and probably brittle wiring harness, rehone cylinders, inspect pistons etc.  I discovered that my engine had been rebuilt (+1 pistons) but chain gears hadn't been replace and were quite worn so those got replaced.  And do a nice repaint/restoration of the engine compartment while you're at it.  That's the rabbit hole I got sucked down, but in the end I'm glad I did.  Cheers,

ps - be sure to replace the valve springs in the right orientation.  They have an up and down that is not at all obvious!

Thanks for the advice, this is quite the big rabbit hole! 

I planned on doing the chain and guides along with the head job, gaskets, the rubber parts on the intake manifold and vacuum lines. 

The wiring harness is bit stiff towards the front of the engine but not bad.
There is some surface rust under the brake master and on the other side that needs treatment. not a complete repaint, a touch up of the affected areas.
I didn't think it would need new valves - but I will recheck that on the weekend and get a second opinion.
And the crankshaft seals I have heard needs doing at some point too...

I would also need to do the brakes, suspension and steering. So need to be careful how deep down the hole I go ;D

I need more hands to help

HPC

Quote from: daantjie on 24 January 2023, 12:30 PMAs well, if you do not need to pass smog testing, then now is the time to yank all that smog garbage off the motor and block off all the ports.  Once the engine is assembled it's a lot more difficult to plug all the ports. Especially the connection and piping at the throttle body, it's pretty much impossible to pull the recirc piping with the intake in place.

Yes the smog stuff will not find its way back into the engine bay...