Can't install timing chain
 

I just put the head back on my car and have a problem where there isn't enough slack in the timing chain to reattach the exhaust cam sprocket with chain on it! Everything was marked and put back in the same position. The tensioner side guide rail was swung back, but it isn't enough. Why don't I have enough slack?

It sounds like the chain may have gotten a bit "bunched up" at the crank sprocket. No big deal. You may need an extra set of hands to get it free though. Have a helper hold the chain tight on both sides while you turn the crankshaft SLIGHTLY in either direction. If you meet stiff resistance, don't force it. It may take a few tries, but it will free up. This is a common occurence and is nothing to worry about. With the chain free, you'll have plenty of slack on the tensioner side when you re-install the cam sprocket. Good luck and keep us posted.

Thanks, your answer is a time-saver. I figured it was something like that. I noticed I can turn the crank about 50° before I get interference. I'll just have to iterate between turning the crank and turning the cams until the chain slips into position.

Fixed!
 

The problem wasn't slack at all. The tensioner needed to be removed and reinstalled per instructions in the manual. I thought the tensioner was preloaded by a simple spring design. Turns out the tensioner has an internal ratcheting mechanism that needs to be dealt with.

Yeah, the spring keeps the tension constant, while the circlip prevents the tensioner from backing out. I'm glad you got it straightened out. Let us know how the rest of the job goes.

What do the instructions say about reinstallation
of the tensioner?
William Rogers.........

Mine is the design where it goes through the passenger side of the timing cover. The tensioner has a circlip that acts as a ratchet, only allowing the plunger to index toward the pressure direction. It can't go backward. Basically, if the timing chain goes slack for any reason, you're supposed to remove the tensioner (after moving the air pump out of the way) from timing cover, then take it apart by pulling the plunger all the way through in the pressure direction. Then put it together by inserting the plunger from the other end, but only after the timing chain and guides are in place and the chain is ready for tension.

There are more tips I can give you if you need detail. I wasted three hours on something that should take 30 minutes. I'm still at the steep part of the learning curve for this vehicle.

Kestas, That is very interesting thank you. I did a cover off timing chain job on my 86 Euro 500SE that has a Euro 420 engine in it . I experienced that the chain would go slack for just a brief second and then re tighten as I rotated engine by hand as I checked out timing marks. As I was working with out a manual (very dumb trick) I thought this was caused buy the lack of oil pressure on a non running engine, I have driven the car several thousand miles since chain change but maybe I should go back and do something with the tensinor? would you or any one else know if this is nessary on a 420 engine..... Thank you...
William Rogers.......

William,

The 116/117 engines do not use a ratcheting tensioner. The tensioner has a heavy spring and is then pumped up by oil pressure. When you did your timing chain and upper/lower rails you should have replaced the tensioner, even if on nothing more than principal.

Mike, yes I put a new tensioner on plus a new oil pump chain and bottom rails the bolt on the big bottom rail right side had backed out till it could go no farther as it came in contact with front cover ,that rail was worn thin enough to see light through so am glad I did a cover off instead of a roll in job.......
William Rogers.......