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  #1  
Old 03-05-2012, 02:57 PM
Shadetree
 
Join Date: Jan 2010
Location: Back in SC upstate
Posts: 1,835
380SE 116.xxx engine chain tensioner question.

This engine has only run for a few minutes in the last several years. I started it last week with a new fuel distributor. I ran it such a short time due to fear of chain rails breaking because of their age.

Today when I took the left valve cover off to change the chain guides in that head I found the chain very loose. Is this normal? Does this indicate its time for a new tensioner? Please elaborate.

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380SE 116.xxx engine chain tensioner question.-dscn0559.jpg  
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  #2  
Old 03-06-2012, 09:30 AM
Senior Member
 
Join Date: Nov 2002
Posts: 829
you don't mention how many miles and if the odometer works.

to check for chain stretch, pull both valve covers and with a 24mm socket and ratchet, turn motor clock wise as you face the engine and look for line up marks on cam towers. the d/s cam might line up and pass before the p/s. this is not critical, unless it is quite a bit. when the mark on the p/s cam is on, look at the crank pulley. all 3 marks should be close to 0. if the crank is 0 to 5 degrees past, don't worry about it. 6 degrees or more, the chain should be replaced. always replace the chain and tensioner together. good luck, chuck.
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  #3  
Old 03-06-2012, 10:41 AM
Shadetree
 
Join Date: Jan 2010
Location: Back in SC upstate
Posts: 1,835
The odometer was broken when I got the car. It jumped timing and I put a piston in it with a handful of valves. I replaced the chain and all the rails and guides when that happened six or seven years ago. They probably have about 5 to 10 thousand miles on them. I didn't replace the tensioner. I guess I'm have guilt complex from no doing so.

I will check the chain stretch today.

Thanks
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  #4  
Old 03-07-2012, 01:53 PM
Shadetree
 
Join Date: Jan 2010
Location: Back in SC upstate
Posts: 1,835
Am I doing the 'chain stretch test,' right?

The p/s side cam is zeroed out, the driver's side mark is just past the reference point and the crank timing mark is past zero somewhere in the 7 to 8 degrees location.

Actually, it looks closer to 9.
Attached Thumbnails
380SE 116.xxx engine chain tensioner question.-rightcamtiming.jpg   380SE 116.xxx engine chain tensioner question.-leftcamtiming.jpg   380SE 116.xxx engine chain tensioner question.-cranktiming.jpg  

Last edited by Clemson88; 03-07-2012 at 01:55 PM. Reason: reevaluation of last thumbnail
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  #5  
Old 03-08-2012, 10:06 AM
Senior Member
 
Join Date: Nov 2002
Posts: 829
you got me. 10k should not stretch a chain. maybe a cheap 1? i've never checked a new chain against an old tensioner. always installed a new chain with old tens. installed, then replaced with new. i'd replace the tensioner and check again. after that, i don't know. good luck, chuck.
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  #6  
Old 03-08-2012, 12:52 PM
Shadetree
 
Join Date: Jan 2010
Location: Back in SC upstate
Posts: 1,835
I really appreciate your input. I ordered a new Iwis chain and tensioner from PParts this morning.

This was the first MB I had ever worked on and the first engine I had torn into in 25 years. It is likely that I found the cheapest chain on the market. Its been seven or eight years.

Last edited by Clemson88; 03-08-2012 at 12:57 PM. Reason: Deleted a question which exposed my ignorance
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  #7  
Old 03-08-2012, 01:48 PM
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Join Date: Nov 2002
Posts: 829
when you do the job, the marks SHOULD line up real close to 0tdc at all 3 places. the cams may not be PERFECT but will be very close if not. and this is right after it's installed, not even started. and you can see if 1 cam gear is off a tooth. it does happen on a chain install, just go slow. curious about the results. good luck, chuck.
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  #8  
Old 03-08-2012, 02:30 PM
Shadetree
 
Join Date: Jan 2010
Location: Back in SC upstate
Posts: 1,835
I have rolled the engine over a couple times using the crank bolt. The plugs were not removed from the engine and it was a little tough. I didn't feel enough resistance to believe a valve and piston had made contact.

The MB CD on this auto says each cam gear tooth is worth 18 degrees of rotation. I deduce from that, that it has not jumped a tooth on either cam or it has jumped a tooth on both.

I couldn't find where it listed the crank gear but they have 18 teeth according to the photo offered by PeachParts. I'm sure it is not advisable to bank on that. Although, if it happens to be accurate one tooth on the cam gear should be worth 20 degrees rotation.

If this engine is screwed up now its because I rolled it over without the chain tensioner in place. It purred like a kitten when the new fuel distributor was installed.


Last edited by Clemson88; 03-08-2012 at 02:40 PM. Reason: it needed editing
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