1971 250 2.8L Chain Tensioner Arm bolt.

[FreddMersaid]

 On a 1971 M.B. 250 Base,
Vin#114.011
 Eng# 130 923-12 
2.8

I'm missing the bolt that goes in the hole that leads to the end of the Timing chain tensioner arm shaft.
I've never built one of these engines. I have no information on it.

Is this  bolt to keep the shaft in position ?

Does this bolt have a special point on it ? 

If you look in this bolt hole, you can see the end of the shaft has a divit that looks like the bolt may have a special point on it to keep the shaft in position.

Anyone who has built one of these engines or replaced a top end on this engine, your communication will be appreciated.

[Tyler S]

This bolt is also used to hold the injector hard line bracket in place. If you have the bracket the bolt may be stashed with it. The bolt is nothing special, there is no special point on it.  The tensioner arm pin is threaded inside to facilitate removal during teardown.

[clunker]

This is an M12x1.5 bolt that thread into the head, but must not drive up against the chain tensioner pivot (which is withdrawn by thread an M6 bolt into it if necessary.) So measure carefully. If you use too long a bolt you will damage the head and not have a decent seal for the opening. This threaded opening is a source of oil leaks, and at Tyler says, the bolt also mounts the injector line bracket.

See https://www.sl113.org/forums/index.php?topic=26807 for my recent dealings with this particular bolt.

[FreddMersaid]

This car had an A/C bracket bolted to the  front of this engine. One of the bolts went in this hole in the front of the head. I then discovered this issue when I had to remove the bracket to repair a oil leak from the timing chain tensioner o ring.
But I have not reinstalled the A/C bracket as of yet, so I need to put back a bolt in its place that is not as long.

Since I don't know how this tensioner arm installs, my concern is:

How does this tensioner arm shaft install or stay in place ?

If it does not require a special bolt coming in from front, what holds the shaft in place ?

Will it move or come out of position without a bolt in the end of it ?

If I was to take this timing chain tensioner arm out, I know I would then understand if there was an issue or not, but I'm not interested in that much work to make this discovery if I can get some answers from my fellow enthusiast. 
But at the same time I don't want to drive it and worry about a timing chain failure.

More explanations please will be appreciated.

[Tyler S]

FreddMersaid, The tensioner arm pin "floats" in its bore. It bottoms out in the back of the bore and is kept from moving foreward with the bolt acting as a stop. You have 2 choices. Use a bolt that is shorter the thickness of the AC bracket, or use the original bolt and add washers to compensate for the length. The second option may result in an oil leak if not sealed properly as this area opens to the Crankcase. Be sure you use the correct sealing washers/rings.

[FreddMersaid]

Tyler, I've discovered the bolt I have, that goes though the A/C bracket then into then head stops about a 1/4" short of the shaft end.
My next question is: What keeps this shaft from wandering towards the bolt and coming out of position at the opposite end ?
 
If I'm understanding you correctly, this shaft trapped between a countersunk hole at one end and the bolt at the other ?

Is the shaft  installed by going though this threaded hole from the outside of the  head ?

Any idea what the purpose of the shaft having a tapered hollow hole at the end facing the outside bolt ?

Does anybody out there reading this have any photo's of the inside of this head without the tensioner arm and  shaft installed ?

Any technical installation information (such as a factory manual) that explains this stall would help.
As it is I'm not comfortable to drive this car at distance until I'm confident I understand this install and I'm not going to have a valve train failure.

For those wondering, I've got plenty of engine building experience and never had a failure, but this text based communication is a real learning curve that's new to me.

All assistance is appreciated.

[clunker]

Here are a couple of pics from the forums, shows the M6 bolt installed to install/remove the pivot. Also a pic I posted showing measurements on my 280SL head - I did not remove pivot, and I was not able to drive it in any further, so left as it at 9mm depth. These may help.

[Tyler S]

The shaft is hollow and threaded to aid in removal during engine teardown, as seen in Clunker's last pic. A M6 bolt is threaded into the shaft and then pulled out with pliers or the sort.
If you have 1/4 inch play then its possible the original bolt was not replaced with a longer bolt when the a/c bracket was installed.
If you are worried about the depth of the pin and if it could potentially back out enough of the rear bore, then you may want to use a longer bolt. You can also remove the pin and tensioner arm. You can then reinstall just the pin and stip bolt to verify the pin will not travel foreward out of its rear bore.

[FreddMersaid]

Ok, the last two photos Clunker posted look very much like my head and tensioner assembly.

So, if I'm understanding all comments on this subject correctly, the bolt should stop short of the end of the shaft with X amount of tolerance between the end of the bolt and end of the shaft ?

1. What is X from the factory ? 

2.  Then the shaft will float between the end bore at the  back and the threaded install bore at the front ? 

Anyone know ?

[gordon]

Mine did not float around, it was a tight fit and it had to be drawn out with a threaded bolt and a piece of tube and was a snug fit when driven back in again using the threaded bolt. I think you will find that the tentioner sprocket can float on the spindle and will move as it is constantly lubricated, perhaps others will correct it I'm wrong

[FreddMersaid]

BTW, my bolt is a 12x1.25