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  #1  
Old 10-19-2009, 06:35 PM
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Chain tensioner rail bolt

Can anyone please help me identify the chain tensioner rail bolt. From what I've read, I need to remove a cover plug to access the rail pin. The attached pictures show in red what I believe is the correct bolt, but confirmation would be nice before I remove anything.


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Chain tensioner rail bolt-tensioner-003.jpg

Chain tensioner rail bolt-tensioner-004.jpg

Thanks all.
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Last edited by 450slcguy; 10-19-2009 at 09:09 PM.
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  #2  
Old 10-19-2009, 08:23 PM
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I'm not sure what the bolt is that you have circled in your top picture, but I don't think it's the rail bolt. In your second picture, I can see one of the pins at the 11 o'clock position above that bolt. It is recessed into the block and requires a special tool to extract. As I recall, there are four or five of those pins that hold the various rails in place.
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'95 C280 - 174,000
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  #3  
Old 10-19-2009, 08:57 PM
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Quote:
Originally Posted by sublettd View Post
I'm not sure what the bolt is that you have circled in your top picture, but I don't think it's the rail bolt. In your second picture, I can see one of the pins at the 11 o'clock position above that bolt. It is recessed into the block and requires a special tool to extract. As I recall, there are four or five of those pins that hold the various rails in place.
The tensioning rail is the one I'm speaking of, not one of the 3 guide rails that have already been replaced.

From what I understand, the pin hide behind a plug. It's that plug that I'm trying to identify the location of. I'm fairly sure the one the one circled is it, but not certain. Anyone?
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Old 10-19-2009, 09:00 PM
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sorry I cannot work out from your pics exactly what i am looking at. here is a picture of the front of my M117 stripped down in a rebuild. The rail pins are pulled and sticking out of the heads about 1 inch. they are hidden behind the alternator housing and power steering pump. hope this is some help
cheers
barri

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  #5  
Old 10-19-2009, 09:07 PM
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Originally Posted by Gurunutkins View Post
sorry I cannot work out from your pics exactly what i am looking at. here is a picture of the front of my M117 stripped down in a rebuild. The rail pins are pulled and sticking out of the heads about 1 inch. they are hidden behind the alternator housing and power steering pump. hope this is some help
cheers
barri

Yes, I know the chain rails, they've been all replaced.

I'm talking about the tensioner rail. The top end is spring loaded via the chain tensioner, the bottom end is held in by a pin similar to the chain rail pins. Access to that pin is beneath a plug on the timing chain cover, that's what I'm looking for.
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Old 10-19-2009, 09:07 PM
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That is an excellent shot of the two pins which hold that rail in place.
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'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000
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Old 10-19-2009, 09:14 PM
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Maybe the 450 SL engine is different, but in the picture above those two pins hold the rail in place. Tightening the chain tensioner puts the required amount of tension on the chain...assuming the other rails are properly in place.
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'95 C280 - 174,000
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Old 10-19-2009, 09:22 PM
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Thanks sublettd
I think we are both missing his point which is the pin which holds in the bottom of the tensioner shoe itself rather than the static rail. in the picture i posted you can see the pin at the lower end of the tensioner shoe at the end of the 45 degree turn. undo the big nut on the side of the engine and withdraw all of the springs and holders and the pin. then drop down to the front of the timing cover and the bolt covering the tensioner shoe lower pin is opposite the second bolt down the side of the timing cover that holds the timing cover on. I am pretty sure its the bolt you have marked but its too close up for me to be sure
cheers
barri
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61 Austin mini
67 Lotus 7
74 450sl
76 Cadillac 8.2l (501 ci)

some new cars

megasquirt conversion on:
djet 74 450sl http://www.mercdjetmegasquirt.britautorepair.com/
cis 76 450sl http://www.merccismegasquirt.britautorepair.com/

the best view is always from the point of no return
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  #9  
Old 10-19-2009, 09:37 PM
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Originally Posted by Gurunutkins View Post
Thanks sublettd
I think we are both missing his point which is the pin which holds in the bottom of the tensioner shoe itself rather than the static rail. in the picture i posted you can see the pin at the lower end of the tensioner shoe at the end of the 45 degree turn. undo the big nut on the side of the engine and withdraw all of the springs and holders and the pin. then drop down to the front of the timing cover and the bolt covering the tensioner shoe lower pin is opposite the second bolt down the side of the timing cover that holds the timing cover on. I am pretty sure its the bolt you have marked but its too close up for me to be sure
cheers
barri
Thanks, appreciate the advice.

The chain tensioner has been removed from the engine as a unit, no need to mess with the internals. I will proceed tomorrow and remove the plug I have circled.
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Old 10-20-2009, 10:31 AM
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Yes, that is the TC tensioner pin cover. Remove it and the pin slides out easily.
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Old 10-20-2009, 11:48 AM
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Yes, that is the TC tensioner pin cover. Remove it and the pin slides out easily.
Removed it this morning, thanks.
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Old 10-21-2009, 08:03 PM
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Your thread came in the right time for me. I am doing the exact procedure with my '74 450sl.
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Old 10-21-2009, 10:57 PM
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Originally Posted by Genbiltstein View Post
Your thread came in the right time for me. I am doing the exact procedure with my '74 450sl.
The pin pulls right out. You don't really need to do the puller thing , unlike the chain guides. Simply screw the 6mm bolt into the pin and it slides right out without any resistance.

I did have a hard time mating up the pin with the new tensioner rail when reinstalling. When you insert the tensioner rail in the head, you'll be working blind trying to get the pin to line up with that damn hole in the rail. After 2 very frustrating hours, the pin finally slipped in on my last attempt of the day.

Patience surely is a virtue.
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Last edited by 450slcguy; 10-21-2009 at 11:25 PM.
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  #14  
Old 10-22-2009, 05:58 AM
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Yep I can understand the frustration. I have been in the maintenance field since the early eighties and I am still learning. This is the first time I owned a Mercedes though.
The weapon of choice is going to be a snap-on camera that I can get into tight places and have a look see if I have any problems lining it up.
There designs I admire and some I don't. The power steering pump bracket is one I don't love too well.
The chain started slapping when I would go under moderate load but no chain guides broke.
The chain tensioner is known to wear out and the new one I have has needed tension. Tho old tensioner will not resist fully rearward in travel like the new one. The old one is getting laid to rest.
I am sure that #1 these chain tensioners can be rebuilt. #2 if neglected in the state this tensioner is in then the timing chain will wear out very quickly.
I am going to replace the tensiner first and then the chain guides and then the chain and sprockets. Its hard to pass up on sprockets at 25 bucks a pop.
I will probably make a table lamp out of the old sprockets and chain and use the tensioner as the push button.

Last edited by Genbiltstein; 10-22-2009 at 06:07 AM.
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  #15  
Old 10-22-2009, 05:22 PM
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Quote:
Originally Posted by Genbiltstein View Post
The weapon of choice is going to be a snap-on camera that I can get into tight places and have a look see if I have any problems lining it up.
I have found that inserting something much smaller than the diameter of the hole (thin drift punch or small screw driver) and then moving it about the hole circularly will line things up fairly close.
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