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Old 03-16-2002, 10:22 PM
pmizell's Avatar
Benz Zealot
Join Date: Jun 2001
Location: Houston, Texas
Posts: 838
Thumbs down Lost timing relation between cam and crank

This move might qualify me for the bonehead of the year award!

Today, with timing cover off and no tension on timing chain, I decided to turn the crank a couple of times. When I did, I got about 1/2 turn before the engine locked (pistons hitting valves) -- turned it back the other way and same result. Did this about 4 or 5 times before I realized what I just did.... threw the timing waay off. Maybe 2 links, maybe 5 I'm not sure. I had no idea there was that much slack down beneath the bottom timing sprocket

While no one thread addressed this issue, I gleaned from various posts that I essentially have to:

1. close all valves by removing rocker holders
2. set crank to TDC (do I need to put the balancer back on or can
I assume that the woodruff key in 12 position is TDC?)
3. remove cam sprocket and set cam to TDC, put cam and chain
back on
4. quickly seal timing cover on with chain tensioner in place

:p :p

If this is all I have to do, then I'll call it even and chalk it up as a lesson and more knowledge learned about my car.

Please advise.

TIA as always guys!

'91 300E, 208k miles

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Old 03-17-2002, 12:32 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Well that will do it, one time out of two.

I sure would start by removing the rocker assemblies so that the valves will stay closed. Then figuring that you have only moved it a small amount I would go to TDC. Guestimate it from the key but eventually you will need to be accurate when you correct the gear. Now you must decide whether you are slightly off from number 1 cylinder or #6 by the orietation of the valves. On older motors you would just set the cam to number one but ignition is created off the crank sensor's reading of the flywheel and there is only one number one on it, so you can't set the cam up right if the engine is wrong..

If you get it wrong turn the motor 360 degrees and take the cam gear back off and it will look like six. take the gear off and move the cam to one and reassemble.

I could be all wrong about this but I am pretty sure this is the way it will work.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 03-17-2002, 02:28 AM
Mike Murrell's Avatar
Registered User
Join Date: Feb 2000
Posts: 2,580
Paul - in a previous post you showed a photo of a timing chain cover with an arrow pointing to a hole. Benzmac indicated that's where the timing chain guide went and appeared to be missing.
Is this maybe why you have so much slack in the chain as you mentioned in this post? Just a thought.
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
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Old 03-17-2002, 09:16 AM
pmizell's Avatar
Benz Zealot
Join Date: Jun 2001
Location: Houston, Texas
Posts: 838

According to the shop manual, the aluminum piece that used to stick out there is the "timing chain protector". As far as the timing chain tensioner guide and tensioner itself goes there is absolutely no problem with slack, when the tensioner is in place and fully ratcheted out. That piece probably would've prevented my timing mishap as there would've been less slack in chain with tensioner out (I think the chain hangs over that piece with tensioner out to prevent what happened to me), but after I fix the problem I'm not going to let any slack in chain, and replace the cover ASAP.

BTW, I cold welded (JB Weld) that hole up. I'm crossing my fingers it holds when put back in action.


'91 300E, 208k miles

Last edited by pmizell; 03-17-2002 at 09:22 AM.
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Old 03-17-2002, 06:20 PM
pmizell's Avatar
Benz Zealot
Join Date: Jun 2001
Location: Houston, Texas
Posts: 838
Well I yanked the rocker arms off and 3 valves on the right side facing windshield won't close completely, thus I still get piston/valve contact with cam and crank both at TDC and rocker arms off. I just had new guides and seals replaced a week ago. Are these valves "sticking" because the guides are new or did I more likely bend them? As I understand it, the rocker arm should always be in contact with the cam lobe.

If I have to pull the head again to have valves replaced I'm gonna cry.

What a nightmare

Thanks for any insight available...


'91 300E, 208k miles
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Old 03-17-2002, 10:28 PM
Live to Learn
Join Date: Mar 2002
Location: Raleigh NC
Posts: 145

Sorry......But it sounds like ya bent em to me.Even if the're just sticking,the heads got to come back off.I would also replace that timing cover.That is not just a hole.There is a tab that sticks out from there to keep the chain against the crank gear.JB weld is just too risky.
Mercedes Benz Master Tech
ASE Master Technician
Diagnostic Technician
Owner of "Behind the Star Inc."
Raleigh NC.
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Old 03-18-2002, 07:16 AM
Posts: n/a
The valves won't "stick" with the springs in place. I feel your pain.

It's time for the heads to come off.

Best of luck,
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Old 03-18-2002, 10:45 AM
pmizell's Avatar
Benz Zealot
Join Date: Jun 2001
Location: Houston, Texas
Posts: 838
Thanks all for the help

'Nuff said. Praise the lord no piston damage. Head came off with no pain having the front covers off. Someone give BWBenzTech moderator status.


'91 300E, 208k miles w/only a crankcase

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