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 6.9 strut overhaul
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WGB

Australia
252 Posts

Posted - 01/08/2012 :  19:33:44  Show Profile  Reply with Quote
I have opened my right front strut and fitted one of my two seal kits.

The drama was in getting the strut apart - 18 inch pipe wrench with a 6 foot length of two inch galvanised pipe - to break the (presumed) red loctite used at both ends.

The seals were a cinch once I stopped overcomplicating the whole procedure and I will perform a full pictorial when I have time in the next few days.

My question is concerning the very glazed bore.



This picture is a view down the bore of the cylinder from the top and what it shows is a matt unused upper section and a very shiny lower section. This strut did not leak externally to any great extent but it was always the first to go down and also tended to "collapse" in a hard LH turn.

My feeling is that this bore needs to be honed - or at least de-glazed with emery - before being re-assembled to allow the piston ring to seal more effectively and I would appreciate knowledgeable comments from RonB or other persons before I do what my instincts tell me.

Bill



1979 Euro 6.9 with AMG modifications #5554
1979 450SEL plus another 1979 for spares

Ron B

Australia
11633 Posts

Posted - 01/09/2012 :  06:06:31  Show Profile  Visit Ron B's Homepage  Reply with Quote
Unlike an engines bore hydraulic cylinders don't need a honed finish to hold oil for lubrication purposes. (shafts are hard chromed and polished on rams etc ) and if the bore is out of round or worn in the center it could be hard chromed and honed back down to size. The matt finish you describe is the surface that results from cold drawn tube . There is a lot of info here about the surface requirements of hydraulic cylinders.
http://www.hallite.com/upload/surface.pdf

quote:
12-14-2004, 11:49 PM #8
Tom Hanson
MBCA Member

What the heck, try to stuff a MB 6.9 liter V8 in it. What a machine that would be..
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Tom Hanson
Orange County Section
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etmerritt33

USA
1415 Posts

Posted - 01/09/2012 :  07:48:41  Show Profile  Reply with Quote
Cool!!! Please take the time to take some good pics of the process and post for the group!!

- Tom
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Ron B

Australia
11633 Posts

Posted - 01/09/2012 :  16:57:45  Show Profile  Visit Ron B's Homepage  Reply with Quote
looks like this...



quote:
12-14-2004, 11:49 PM #8
Tom Hanson
MBCA Member

What the heck, try to stuff a MB 6.9 liter V8 in it. What a machine that would be..
__________________
Tom Hanson
Orange County Section
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WGB

Australia
252 Posts

Posted - 01/09/2012 :  19:34:32  Show Profile  Reply with Quote
My 6.9 has always had a weak right front strut although it never particularly leaked externally.

The struts are no longer procurable new but I purchased two kits of seals of US E-bay last year



The individual measurements of the O rings and teflon seals are given in this posting. They were also posted at this site but I can't find them easily.

http://forum.w116.org/mechanicals/as-rare-as-rocking-horse-poo/msg90765/#msg90765]http://forum.w116.org/mechanicals/as-rare-as-rocking-horse-poo/msg90765/#msg90765

The previous owner had also fitted wider than normal 140 Eight slot wheels and these had rubbed the right front hydraulic hose but have held up over the four years I have had the car.

In-situ with frayed hose - I have a new pair of hoses for the fronts.



Strut removed and sitting in the open air after removal of upper mount and a de-grease



Bottom ball joint removed with a 22mm slim spanner



Markings on this strut before being attacked with a pipe spanner



Top mounting clamped in vise and 18 inch pipe wrench attached to other cast end - unscrewed the top cover with some degree of difficulty - conventional wisdom received after the event is to heat the joint to break the loctite seal but the bottom bump stop is very close to teh bottom joint.



Here is a picture of the top cast cover still in the vise and showing the O ring in that cover



The next bit was the difficult bit strut reversed and bottom cast end clamped in vise ( with the piston removed through the top) using the bleed take-off point as a method of preventing it turning and after an hour of heaving with the pipe wrench I had only succeeded to turn the tube about 1 turn and then it was jammed even tighter and would not tighten or untighten.

Penetrating oil (probably irrelevant) - left overnight - and another 30 minutes heaving later not one skerrick of movement. At the point of "repair-despair" I remembered I had a 6 foot length of galvanised steel pipe which I placed over the end of the pipe wrench and with about 5 to 6 foot of leverage and my not insubstantial weight it started to give with a lot of graunches and moans.

They appear to use something like red-loctite to prevent the cylinder from turning and probably as an extra sealant and it is very effective and the reason it is so hard to undo. Once the threads are cleaned of the stuff the cylinder can be spun into the housings very freely by hand.

Here is the bottom teflon seal tensioned by the thick O ring in the cast end with with the bump stop - this is after the bleed off point so it is really the "seal of last resort".



Here is the real shaft seal that is a push fit into the end of the cylinder and is held in place by the lower cap.



Here is a view of it from the lower side with a new seal and O ring fitted



Here is the piston complete with piston ring surrounding the valving.



Here is a collection of the bits laid out - the cylinder has been reversed and should be the other way around.



After a bit of overcomplicated stuffing around due to inexperience in the end the seal change is a walk in the park.

Lower cast end shaft seal (hat section teflon and fat o-ring) just pushes into the cast end by hand after removal of old seal



External O ring as well as old teflon seal and o-ring hidden under plain teflon seal are fished out with a small hook and replaced quite easily in the mainlower cylinder seal.



The new O ring is placed in the slot and then the teflon seal fed in over the top of it. The teflon seals against the shaft at the inner edge and the small o-ring on it's outer edge.



And of course a new O ring is placed in the upper cap



Here is a picture of the new parts waiting for "Cylinder rehabilitation" prior to assembly.



I am actually inclined to think that the poor performance of this strut has more to do with the glazing of the cylinder bore than the state of the seals . This picture shows the upper part of the bore which is quite matte in colour vs the very shiny lower bore.



Opinions on how I should deglaze the bore are still being gratefully accepted.

This sort of hydraulic equipment is very common in the earthmoving and agricultural industries and I have had one opinion that says a 60 degree crosshatch finish with a small set of honing stones and I am awaiting on a couple more who I will be telephoning today.

Bill



1979 Euro 6.9 with AMG modifications #5554
1979 450SEL plus another 1979 for spares
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Ron B

Australia
11633 Posts

Posted - 01/09/2012 :  21:47:06  Show Profile  Visit Ron B's Homepage  Reply with Quote
The hoses can be rebuilt too, the fittings can unscrewed and reused.

quote:
12-14-2004, 11:49 PM #8
Tom Hanson
MBCA Member

What the heck, try to stuff a MB 6.9 liter V8 in it. What a machine that would be..
__________________
Tom Hanson
Orange County Section
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WGB

Australia
252 Posts

Posted - 01/09/2012 :  23:07:21  Show Profile  Reply with Quote
I'll hang onto my old ones but the new ones are only $75 each and they look nice and shiny.

Not sure what ENZED et al would charge to change the hose.

Bill

1979 Euro 6.9 with AMG modifications #5554
1979 450SEL plus another 1979 for spares
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mirafioriman

United Kingdom
193 Posts

Posted - 01/10/2012 :  16:45:34  Show Profile  Visit mirafioriman's Homepage  Reply with Quote
Nice job and a great write up. All we need to do now is find a job lot of strut rebuild kits

Mercedes W116 450 SEL 6.9, W109 300 SEL 6.3, W126 420 SEL, Fiat 131 Supermirafiori, Fiat 131 Panorama, Fiat 130 saloon, Fiat 132 2000, Fiat Argenta and a Citroen Xantia 1.9D!
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Ron B

Australia
11633 Posts

Posted - 01/10/2012 :  16:55:08  Show Profile  Visit Ron B's Homepage  Reply with Quote
You can do it yourself,compared with pulling a strut down it's a POP. .
ENZED would charge too much to do a job like that plus ruin the fittings in the process.
re the tube surface ;
You are right about the smooth surface though,it is too smooth to allow a decent seal.
Do you have access to anyone in WA who has a surface reader? you could get a reading of the surface above the wear mark and have the tube resurfaced to the same degree, as in the Pdf,.01-.04 micron surface. You wont achieve this with a hone in a drill or emory cloth.


quote:
12-14-2004, 11:49 PM #8
Tom Hanson
MBCA Member

What the heck, try to stuff a MB 6.9 liter V8 in it. What a machine that would be..
__________________
Tom Hanson
Orange County Section
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WGB

Australia
252 Posts

Posted - 01/10/2012 :  21:07:02  Show Profile  Reply with Quote
I hear your perfectionism Ron and if this was to be a career decision I might go down that path but I am just a broken down old country doctor with an interest in cars.

I have harangued several of my patients over the past two days.

1) Heavy duty fitter in the mining industry - light hone with 60 degree cross hatch.
2) Mechanic - light hone with 60 degree cross hatch
3) 2 x agricultural engineers - light hone with 60 degree cross hatch

I have one very experienced agricultural engineer who I am trying to track down and I guess it is likely to be a light hone.

As regards opening a strut all seem to say judicious heat is an advantage to break down the vicious thread sealant used.
This is easy enough on the top cap as there is only a replaceable O ring to damage but at the lower end there is close proximity to the bump stop.

As regards the hoses - you say "unscrew" - is that what is done. I would have thought the compression fittings over the hose rendered them unrepairable.

Bill

1979 Euro 6.9 with AMG modifications #5554
1979 450SEL plus another 1979 for spares
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Ron B

Australia
11633 Posts

Posted - 01/11/2012 :  17:09:22  Show Profile  Visit Ron B's Homepage  Reply with Quote
It's not actually a compression fitting, it is a tube which is gripped in a device which is held in a vice (basically two halves of steel with a hole in the middle where the round pipe ferule fits).
you then undo the nut which unscrews out of the hose. Once that is out,undo the hose by twisting it from the ferule.
You aren't the doctor with a 6.9 in the bush either, there was/is one in Country NSW at Cobar which had done a lot of fast hard mileage out there.


quote:
12-14-2004, 11:49 PM #8
Tom Hanson
MBCA Member

What the heck, try to stuff a MB 6.9 liter V8 in it. What a machine that would be..
__________________
Tom Hanson
Orange County Section
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etmerritt33

USA
1415 Posts

Posted - 01/12/2012 :  15:30:35  Show Profile  Reply with Quote
Bill,

Thanks a bunch for taking the time to take and to post these pics. They are very helpful in understanding the internals. I am compiling a folder with all the pics and info for reference purposes.

Please continue to keep us posted.

- Tom
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WGB

Australia
252 Posts

Posted - 01/13/2012 :  02:04:21  Show Profile  Reply with Quote
I finally contacted my most trustworthy and experienced agricultural engineer who looked it all over and said that there was nothing particularly surprising about the ram - except for the use of a secondary seal after the bleed off point.

He suggested some gentle and evenly distributed heat if possible to break the loctite - this is easy on the upper housing but a bit more problematic on the lower one unless after the piston is withdrawn the tube is heated rather than the end housing.

He also suggested using a chain pipe wrench instead of a stillson and I have spent a fruitless lunchtime trying to find one for sale but I have a tool shop I will go to in the morning before I dismantle my left side.

He again emphasised the 60 degree cross hatch hone and gave specific instructions on drill speed - 1000 rpm as well as using kerosine with 2 squirts of oil in it - and gave me a lend of his specific hone he normally uses for the job.

He also emphasised taking the shine off the face of the ring by putting 3-400 emery on a glass surface and rotating the ring.
He also said the rings were quite readily available if I broke it but as I am not prepared to try to remove it from the piston I hope this will not be a problem.

I will post more photos when I do the other side and finish this side.

Bill

1979 Euro 6.9 with AMG modifications #5554
1979 450SEL plus another 1979 for spares
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Ron B

Australia
11633 Posts

Posted - 01/13/2012 :  20:51:51  Show Profile  Visit Ron B's Homepage  Reply with Quote
But these guys are talking about slow moving rams in machinery, totally unlike the speeds and service life of a shock absorber which is expected to run through thousands of cycles in just one drive.. I maintain that this business of 60 degree crosshatching may be OK for quicky repair on a ram on a machine but tottally unsuited to the shock struts. The finish you need (as described in the Pdf above ) is the one that you can see in the unworn part. Rubbing with emory is not what is done.

quote:
12-14-2004, 11:49 PM #8
Tom Hanson
MBCA Member

What the heck, try to stuff a MB 6.9 liter V8 in it. What a machine that would be..
__________________
Tom Hanson
Orange County Section
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WGB

Australia
252 Posts

Posted - 01/14/2012 :  00:49:08  Show Profile  Reply with Quote
So why is it used in engine cylinder bores?

Bill

1979 Euro 6.9 with AMG modifications #5554
1979 450SEL plus another 1979 for spares
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Ron B

Australia
11633 Posts

Posted - 01/14/2012 :  17:28:09  Show Profile  Visit Ron B's Homepage  Reply with Quote
Engine cylinder bores are not lubricated ,as in "filled with oil under compression". The cross hatch is required to keep a microfilm of oil in place to lubricate the piston rings which have to tolerate high surface speeds and temps ranging from 80C to 900C on firing ..I have some very old Mercedes blocks here with massive mileages on them and the cross hatch is still in place. Once an engine is allowed to run rich and the oil is washed off,the bores wear rapidly ,as do the rings. The glazed bore can no longer lube the rings and the engine begins to exhibit blowby and smoke. .A certain amount of initial wear is allowed to get the rings to match the surface of the bore and this will work for the life of the car as long as the engine is maintained .
With hydraulic cylinders running a synthetic type of seal, the idea of crosshatching doesn't provide a sealing surface but a means for fluid to escape under pressure .Via the scratches .
A tight seal will only seal as long as the seals surface against the cylinder wall is maintained. Eventually the edge of the scratches destroys the seal as it acts as a cutting edge. Admittedly this takes a period of time but as plenty of folks have found when honing brake cylinders it does happen before the bore shows signs of glazing again.
Modern Mercedes Engines with Nikasil bores are etched to provide the same surface with Acid after boring .


quote:
12-14-2004, 11:49 PM #8
Tom Hanson
MBCA Member

What the heck, try to stuff a MB 6.9 liter V8 in it. What a machine that would be..
__________________
Tom Hanson
Orange County Section
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