Hi all,

My '93 190 2.3 is at a local shop, getting it's head gasket replaced after finding oil in the coolant.

I've used the mechanic before, and he's competent, but not a Mercedes mechanic per se.

After buttoning things up, mechanic ran and test drove - and the CAM BROKE!

He replaced it, and the replacement CAM BROKE!

What would cause this? I looked at the head and Cams with him, and nothing looks awry ( of course, I am NOT a mechanic ) but he's a bit stumped.

Any help much appreciated, as at this point I'm soliciting expert advice from people experienced w/ Mercedes in particuler.

Thanks in advance,
Mark
markl@aracnet.com

Ask if he had to shave the head....

sounds like the timing chain may be too tight. maybe hr forgot to reset the chain tensioner.
paul

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Paul Roberts
Mercedes Centrum Inc.
Bellevue,WA.

I would guess the cam timing is way off (two teeth or more).

however, if the head was warped and it was machined to flatten it, the cam is now running crooked and the head is toast unless it can be align bored straight through the cam bearings. The cam will NOT flex as it turns.

If the head exceeds the warp limit, it must be bent back into shape, it cannot be machined flat unless the cam bearings are also bored and a cam with oversize bearings fitted. Failing that, replace the head.

Peter

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1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
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If the head was resurfaced because it was warped, chances are the cam bearigs are now way out of line. Top of head where cam bearings mount still has the identical 'warp' that was removed by resurfacing the head--causing the cam to bendwhen rotating and possible seize in the bearings.

Continual bending will cause it to break.

Paul was correct!!

ON the M102 engine & most other MB's the timing chain tensioner MUST be dis-assembled & reset before re-installing back into the engine. IF not there is too much tension & the cam will break as it is hollow! Have seen that problem at least 4-5 times when the "mechanic" doesn't have MB engine knowledge!

IT was his fault for not reading correct info on removing & installing the tensioner!

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ASE Master Technician
Mercedes Benz Star Technician (2 times)
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27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

First, thanks for the reviews.

The head was not resurfaced, as it was deemed fine.

I saw the mechanic lay a heavy duty straight edge along the cam bore and it appeared fine.

Makes sense to me that if the tension from timing chain is too tight the torq could break the cam. The break was within inches of the cam gear end in both cases ( if that detail corroborates the supposition ? ) .


I DON'T believe he dissassembled the chain tensioner and reset ( although I'm not sure ). I'm headed there RIGHT NOW to show him these posts to advise him.

Hi,

I hate to be the middle man in these discussions but:

Can someone point me to explicit instructions re: the timing chain and tensioner readjustment.

Mechanic saying ( in broken English to me , mind you so this is what I'm understanding ): tensioner is just a spring and he's not understanding how it is to be adjusted, retensioned during reinstallation.

I'm stopping him from doing anything to the head, as I don't think it's warped or needs shaving, or has any problem with the cam bore - and from the sounds of things: that will just complicate matters if they're not really the problem.


Thanks again ,
Mark
markl@aracnet.com


Mechani

The basic point you want to tell him is that these tensioners are not like the old spring/oil pressure ones .
These have a ratchet device that , as the chain wear/streaches. the tensioner ratchet locks at each step it extends.
The reason for this is that the old ones would leak pressure if the car sat for a while , and then when you started the engine , there would be too much slack until the oil pressure pushed the tension back onto the chain.. The ratchet locks the tensioner in its last extended position and it can not go back [..so, if you put in a new chain or do a repair, you have to take the tensioner apart , pull the rod out past the locks and re-install it from the back side so it starts off anew.
Otherwise, just putting the tensioner back in a cranking the bolts down will put extreme tension on the chain and cam , as the tensioner is preset to the LAST locked setting.

Here is a link that has a couple of points on BOTH styles , and this may help you if you can print it out.

http://www.peachparts.com/shopforum/showthread.php?t=58536&highlight=tensioner+ratchet

Thanks very much Arthur!

I'll ferry your comments to the mechanic and even try to take off some time for work and go to the shop to take a look.

Will follow up with the prognosis.

Hi,

I just visited the mechanic after advising him of comments re: Resetting the tensioner.

I'd like to take pictures of the tensioner and send 'em to

as it does just appear to be a large hollow nut that screw into the block from the side, and inside of it is a spring and a rod that push against a crescent shaped tensioner against the chain.

There does not appear to be any ratchet locks to affect the spring or rod - that can be 'reset'

It's a 1993 190e 2.3 4 cylinder.

I'm off to take pictures now and if anyone can - please send me your email address so I can send you pictures when I get back.

My email is: markl@aracnet.com

Thanks!

Mark you remove the COMPLETE tensioner from the block! Then the inner "nose" part that pushes the tensioner rail comes out thru the front of the tensioner. THEN you slide that nose piece back thru the opening where the spring was removed from. That will reset the "ratchet". then the tensioner BODY is reinstalled, the inner nut is tightened & THEN the spring can be re-installed!!

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Photos attached.

I have to drive back to the shop to futz with the tensioner components, but as tension_2.jpg shows, is the nose piece on the right actually TWO pieces, and the dull grey tip is to be reset within the chromed/shinY piece?

Thanks for your patience,
Mark

Attached Thumbnails

     

After reviewing photos with Arthur, and looking at the tensioner represented on FastLane for the 190e 2.6 ( which IS a ratcheting tensioner),

it does not appear that this is a tensioner that resets. This 'nose' component at the right end of the spring looks like 2 pieces ( chrome sleeve and grey tip ), but they are solid as one piece.

- Mark

Hi Mark
I've been reading this and reading the posts, which seem to be drying up.
Here's my take: I think there is still part of the tensioner that screws into the timing case, you have just the "outside" part (plus the shiny part).
The shiny part, opposite of the gray dull part, has a groove in it, there is supposed to be what would be described as as a wire clip in it. The wire clip allows one way movement (ratcheting) of the shiny part in towards the timing chain. I don't know if Mr Broken English lost it, broke it, tossed it or what, but it NEEDS to be there. The tensioner is reset by removing the ENTIRE tensioner (not just the outer cap), then the shiny part is shoved through in the direction it is SUPPOSED to go (towards the chain if it were still installed in the engine). Then the inner screw in part is screwed in a torqued to the timing case. THEN the shiny part is pushed into the bore as hard as possible (ratchets in and stays in the bore), then the spring and outer cap is screwed in and torqued. You have triple redundancy with this system. The spring of course will hold SOME tension. The main source of tension is oil pressure in this bore. And third this circlip will prevent the tensioner from loosing too much tension in the event the spring breaks and oil pressure is lost. The spring and ratcheting clip also hold sufficient tension when the engine is started (before oil pressure builds up).
I don't know if parts are available for the chain tensioner or not, may need a whole new one now.
I would also like to add another possible cause for the breakage; what if the cam bearing caps (rocker arm brackets) were put back on in the wrong order? Could this cause binding and breakage?
Gilly

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