Timing Chain Stretch Issue

[stepper]

Hello,
I'm fairly new here. I'm in the process of winter maintenance on my 240D 616 engine. I'm attempting to check my timing chain stretch. I've already used the matching of the cam shaft alignment mark with the crank shaft TDC mark and they match well. The issue I'm having is with cylinder 1 intake valve .080" dial indicator movement. The procedure I've read mentions "to remove all valve lash" with cam lobe perpendicular to rocker arm. Not sure what that mean, but I'm assuming it mean to remove the clearance between the rocker arm and the cam lobe. So with the peak of the cam lobe pointing perpendicular to the rocker arm I tightened the valve adjustment nut (finger tight) to the rocker arm. Zero'd out my dial indicator and began to rotate the crankshaft. What I noticed was the dial indicator moved .003" (valve more closed) with the peak of the cam lobe at the 3 o'clock position then as I continued to rotate the engine the dial indicator started moving in the direction of the valve being opened. Once I reached a dial movement of .080" I checked the balancer marks and I was at 15 degrees after TDC. What I don't understand is why the dial indicator changed the .003" prior to heading the other direction, and why the alignment mark procedure indicated nicely, but the dial indicator tells me my chain stretch is outside the acceptable limits. Can anyone give me so clarification as to whether I'm doing the procedure correctly?

I'd appreciate any help. Steve

[stepper]

Continued:

One item of notice is since the engine has sat for awhile the chain tensioner, having lack of oil, keep popping in and out while rotating the engine. How can this be avoided while performing timing chain checks. See; https://www.youtube.com/watch?v=ekMAW3tKWPk

[Sugar Bear]

How many miles on the engine and if you know on the chain. I've seen a few 240D chains break and cause damage. If the car is a long term keeper consider replacing the chain stretched or not. Another step is to replace the vacuum pump or better yet eliminate it to prevent chain damage.

[Sugar Bear]

How many miles on the engine and if you know on the chain. I've seen a few 240D chains break and cause damage. If the car is a long term keeper consider replacing the chain stretched or not. Another step is to replace the vacuum pump or better yet eliminate it to prevent chain damage.

[stepper]

The engine was rebuilt 30,757 miles ago. Work order indicates timing chain was replaced. This is a completely restored inside & outside vehicle, definitely a keeper. I'll crank the engine over today to reestablish oil pressure. I'm still curious as to why is see more valve movement (opening) when the cam lobe peak is rotated from perpendicular (1 o'clock position) to the 3 o'clock position. The procedure I've read say's set the dial indicator when the cam lobe peak is perpendicular to the rocker arm.

[stepper]

Here’s what I found;
Cranking the motor for approximately 10 seconds, twice, corrected the chain tensioner issue, thanks!

What brought me to checking the timing stretch was the injector pump was set @ 18 degrees BTDC after the engine was overhauled, instead of the 24 degrees BTDC as per shop manual 07.1-110.

Checking the timing chain stretch using the valve cam/crank indicator marks placed the crank shaft pointer at 4 degrees ATDC.

Checking the 0.080” cylinder 1 intake valve opening (as per multiple website procedures) showed a 15 degree ATDC mark, not the 13.5 degree as indicated in the shop manual page 05-215.

Doing the conversion of inches to mm (2mm = 0.078”) cylinder 1 intake valve opening showed a 11 degree ATDC mark at 0.078”, which is within an eyeball calibration on the crankshaft balancer as per the shop manual page 05-215 of 11.5 degrees with new timing chain.

As I mentioned in my previous remarks the engine has 30,757 miles on the engine since a complete engine overhaul. From the information above would it be valid to consider the timing chain to be in worthy shape? Reason I question is the stretch indication of 4 degrees using the cam/balancer alignment marks and the fact that the injector pump was set at 18 degrees not the 24 degrees.
I’m enjoying learning about the 616 engine and finding the mechanical engineering of this engine amazing.

I’m a retire electronics technician and I’m always amazed as to how thing were accomplished before the reliance on electronic precision.

[Sugar Bear]

The chain should be excellent at 30,XXX miles up through 100,XXX miles. I'd be looking to confirm a properly aligned crankshaft pointer that indicates exactly zero degrees when the piston is perfectly at TDC and that the camshaft woodruff key isn't an offset version to correct for chain stretch when there isn't any stretch.

Can you post a picture of the camshaft gear teeth?

[engatwork]

As SB said. I would not even be looking at the timing chain on a 30k mile engine.

How did it run before you started work on it? If it is running ok I'd button it up.

[stepper]

Without taking the head off, what method is there of telling whether the #1 piston is TDC?

[Sugar Bear]

By dropping the lower oil pan and putting a dial indicator up to the rod is all I can think of. That pointer being accurate matters.

[cth350]

I don't know beans about the OM616. Is there any equivalent to the old gasser technique of putting a long, thin screwdriver down a spark plug hole and the watching it bob up and down?

>> was the injector pump was set @ 18 degrees BTDC after the engine was overhauled, instead of the 24 degrees BTDC

When you say "was set", you're using the cute little drip tube to figure out the start of fuel delivery?

-CTH

[stepper]

After the engine was overhauled I shipped it from Alaska to Seattle. After several weeks of driving I notice the engine running rough, so I pulled into a Mercedes shop in Bakersfield, CA and had them look at the engine. I know they replaced a couple of injectors, but not sure it they set the timing to 18 degrees, or if the shop that rebuilt the engine set the timing. Yes, I am using the drip tube method of checking the timing.

I'm attempting to learn the engine and how to improve its performance. It seems to be getting sluggish when pulling into traffic. I've cleaned and checked the injectors, patterns and pressures are good. I've set the valve clearances. Then, reading an article led me to check the injector timing, that led me to question chain stretch.

Chain stretch show 15° ATDC for .078" valve movement. The shop manual indicates 13.5° for a chain from 20,000 miles. I guess my stumping questions to myself is 1.5° beyond the 13.5° telling me I need to replace the chain, and would that be why the injector pump was set at 18°? And, how do I replace a timing chain?

Cam sprocket pictures as requested. Also notice the cam shaft doesn't have any code stamped on the back, but does have these number on the shaft; 616051 22VV B4

[Sugar Bear]

Replacing the chain is done by splitting the old chain and connecting it to the new one, an assistant rotates the engine by hand "rolling" in the new chain as the old one is pulled out. Once the new chain is all the way in its two ends are connected via a master link that is crimped into place. It isn't difficult but can get ugly in a hurry if the chain is dropped during the process, it must be kept taught on both ends every second until it is crimped. If it falls it gets jammed and can break plastic guides and rails.

I can't over emphasize how important knowing that when the balancer is at zero that the piston is perfectly at top center. However much it is off in degrees will transfer to all of your other adjustments. It is the foundation for all the other steps, think of it as trying to build a house on a foundation that isn't level.

From the picture the cam gear looks good. Try to post another picture of the cam gear looking at it straight on showing as many teeth as you can.

Is there a reasonable chance that the injection pump moved since the rebuild? Although never a powerhouse, those motors run really well when all adjustments are dialed in.

CTH, I can't think of how to gain access to put something in to touch the piston on that motor to find TDC.

To the OP, TDC is best found using a dial indicator then zeroing the indicator to the balancer.

[engatwork]

Thanks for explanation, now I understand where you are at with it.

improve its performance.

Running rough means at idle or all the time? If during idle open hood and look at engine. Is it moving around any/much? To make sure it is not a single cylinder, while idling loosen an injector line at the injector and see if "roughness" changes any. if it does not then it is an issue with that cylinder.

How is fuel quality?

[stepper]

@Sugar Bear, unfortunately I don't know what the acronym CTH, nor OP means?

The engine is far from being able to start at this time. I have all injectors, and injector lines removed. It's dead of winter here 2° outside, no way I can start it in the garage and smell the whole house up. The engine ran good, but since I'm spending this winter tweeking and learning the engine I want to get my alignments correct. I'm getting along in age and I'm not sure I'll be able to enjoy working on the engine in a few more years.

At this point I'm leaning more toward installing a offset woodruff key rather than pulling a new chain. From what I've read a 4° offset key should put my time back in alignment. I've loosened the cam gear/shaft bolt, ty wrapped the chain to two ports on the cam gear. Not sure what the next step is to be. Do I need to remove the tensioner and the chain guide on the right side? Will the cam gear slide enough to expose the woodruff key to allow removing and replacing the key without the cam gear coming off the cam shaft? Is there a written procedure? Which, in the long run, is the easiest task; new chain, or woodruff key replacement?