Chain Tensioner Tour

[ja17]

The chain tensioner on the W113 engines is a mechanical/hydraulic unit. It is mounted directly below the thermostat housing. A piston protrudes into an oil pool in the chain gallery of the head, where it contacts the chain tensioning sprocket arm.


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An opening in the end of the piston draws oil into the hydraulic cylinder and a check valve prevents the oil from escaping. Normal engine operation and chain sprocket movements provide a pumping action which keeps the tensioner and chain tight by filling the piston and housing with engine oil.

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A spring inside the tensioner provides some tension, however the real work is done by the hydraulic pressure. This spring is also critical in the operation of the oil check valve of the tensioner. This check valve involves the ball, the cap and the spring.

A plastic or metal spacer is located in the tensioner spring and limits inward travel of the piston.


The "oil pool" is an area built into the chain gallery of the head which collects oil as it splashes inside the engine. The opening in the chain tensioner piston retrieves oil from this "oil pool". A 6mm socket head bolt is also located in this oil pool. This bolt must be in place or a severe exterior engine oil leak can result. The threaded hole for this bolt can emerge on the exterior of the block behind the water pump. If the bolt is left our during repairs, a mysterious oil leak may result.




The chain tensioner provides chain tension until the chain wears or stretches beyound the tensioners outer limit at which point the timing chain would need replacement. These tensioners are very reliable and durable and normally last the life of the engine. There are no seals invoved in the hydraulics. Very, very tight tolereance between the piston and its housing (cylinder) insure good seal and long life. Instances of tensioner failure on these engines is very rare.

 An aluminum seal is located uder the "cap". Also large rubber "O" ring is seated in a groove at the tensioner/head parting surface. These two seals prevent oil from leaking but are not involved in the tensioner hydraulics.

Removal of the chain tensioner is accomplished by removing the thermostat housing and removal of the two nuts at the tensioner. If the car has factory AC the complex compressor brakcet must be removed. It is not necessary to remove the chain tensioner sprocket and arm in the chain gallery when removing the tensioner.




Joe Alexander
Blacklick, Ohio

[knirk]

Excellent tour, Joe.
I did an engine rebuild last year and cannot remember seeing the little ball. Hopefully it’s still in the piston. Is there any way of checking it’s hydraulic operation without removing the hole tensioner (and AC bracket)?


Per G. Birkeland
69 280 sl aut 834
Norway

[ja17]

Hello Knirk,

The chain tensioner will not work without the ball. You can check to see if the tensioner is working once installed and primed by taking a large screwdriver and push downward on the tensioner sprocket. It should remain firm. With a lot of firm steady force the tensioner sprocket will eventually begin to move slowly downward.

Joe Alexander
Blacklick, Ohio

[knirk]

Thanks Joe, I will check.

Per G. Birkeland
69 280 sl aut 834
Norway

[Ricardo]

Great explaination Joe and good pics as usual, but you better get your wife's cookie sheet back in the kitchen before she finds out.[:p]
Ricardo

[Malc]

Thank you Joe now I know how that works.
Do you think that in Naj's case that the following is possible?
THe spring has lost some of its "springy-ness" Ie its gone soft or something. Could he check the free length?

Could the ball be damaged or not seating properly, causing the problems??
Malc

[113gray]

Hi Joe. Thanks for another really nice contribution. This is familiar ground since I visited this area when replacing the head gasket on my Ponton several weeks ago. The mechanism is similar (?idenical) in both cars. The bolt you mention beneath the oil pool is the one with the washer that I stupidly dropped into the chain gallery to the right in your photo, a painful memory that I mention only as a caution to others. It was eventually recovered with a magnet after a couple of anxious days. Regards,     -JP-

[ja17]

Hello Jim,
Yes this design was the same as on almost all the engines 1955 through 1972. The length of the piston varied depending on the application. The design worked very well. Mercedes came out with a new design after this time. These new "improved units" did wear and did not last nearly as long as our older version.



Joe Alexander
Blacklick, Ohio

[saygold]

I am (slowly) rebuilding my 230SL's cylinder head and looked at this topic on chain tensioners.  After looking at the dissassembled tensioner and comparing it to what I had, my tensioner did not include the small ball that makes it work.  

I ordered a new one.  The part I received was marked as no. 130 050 03 01; however, the small ball that operates the tensioner is not included.  

Could anybody tell me if this was the correct part, and if so, was the ball supposed to be included?  If not, what is the part no. for this missing ball?

Thanks in advance for your help.

Ken Deter
'66 230SL (euro)

[ja17]

Hello Ken,
Did you order the whole tensioner or just an internal part?

Joe Alexander
Blacklick, Ohio

[saygold]

I bought the whole tensioner assembly.

Ken Deter
Gig Harbor, WA

[ja17]

Hello Ken,
This is a mystery> Mercedes could have changed the design in later years. Do the rest of the parts look the same? Take a flashlight and make sure the ball is not hidding in the plastic cup or in the tensioner.  I will try to check this number also.

Joe Alexander
Blacklick, Ohio

[saygold]

Joe

Thanks for your suggestion.  I disassembled the original tensioner and flushed the piston out with WD40.  Bingo!  The missing ball showed up.  

Now knowing exactly what I was looking for, I found out that the new tensioner was also correct.  Boy, am I embarrassed!

Thanks for your help.

Ken Deter
Gig Harbor, WA

[ja17]

Hello Ken,
Good deal! Just a bump in the road along the road to understanding!

Joe Alexander
Blacklick, Ohio

[Ziggy]

Does anyone happen to know whether a chain tensioner from the m121 can be used in the m130 engine?

[Naj ✝︎]

quote:Originally posted by Ziggy

Does anyone happen to know whether a chain tensioner from the m121 can be used in the m130 engine?

Probly not:

M130 tensioner 130 050 0311
M121 (one of them...) 115 050 1011

naj

[Ziggy]

You are right. This piston and spring have a different length.
I put in a new ball and cap and with warm engine, the tensioner remains firm.
The sound is fainter, but it is still there.  :twisted:
How much play is allowed in the chain between the right chain guide and the chain with the tensioner firm? It was almost 1 cm, which seems like a lot.
Still, I did not have this problem before I put in the new cam. The new bearings must be slightly lower or something.