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  #1  
Old 07-22-2012, 07:14 PM
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Das German Diesel Mann
 
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Question OM602 Timing - (Chain Stretch)

Using the MB service information found here I pulled the cover and lined up the camshaft sprocket with the mark on the camshaft bearing cap



Then I check the timing mark on the crankshaft pulley



Uh oh its clear my timing is more than 10 off and according to the above bulletin:

If the timing mark on the crankshaft pulley is off by 3 - 10 - The timing chain is stretched and should be replaced

If the timing mark on the crankshaft pulley is off by greater than 10 - Inspect the top of the pistons with a borescope to determine if any of the pistons have come in contact with the valves

The pointer that lays over the crankshaft pulley was removed earlier today to provide access for replacement of the water pump. Upon removal I discovered that the mounting hole is actually a slot.



Is the degree from 0 (TDC)?

How do I ensure the timing pointer is at the correct spot?
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Old 07-22-2012, 07:24 PM
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Can you take another picture of the cam timing marks so it looks more like this?



This is a convenient way to take a picture. In practice, I sight the slot on the cam flange through a hole in the sprocket and align it with the vertical rib on the cam tower. Then check the crank indicator. Repeat about a half dozen times, throw out the highest and lowest readings and average the remaining.

If there's a chance you repositioned the crank pulley indicator, the "right" thing to do is pull the #1 prechamber and use a dial gauge on the piston crown to find true TDC. I wouldn't trust the cam lift method on a chain with lots of someone else's miles on it. Or have you had this car since new?

Seeing as there isn't enough range in the slot to set the indicator at TDC, chances are you need a new chain.

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Old 07-22-2012, 08:32 PM
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When I laid a Straight Edge a crossed you pic the Timing Marks were not lined up; but were close.

On the 617s in the FSM to correct the Pointer it calls for removing the #1 Prechamber and inserting a Dial Indicator with a long tip on it and bringing up the #1 Piston to Top Dead Center.
Adjust the Pointer if needed.
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Old 07-22-2012, 10:19 PM
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sixto your photo was priceless, thank you!

Turns out I was lining up my cam with a nick (orange arrow) in the cap and not the correct mark (red arrow)



After properly aligning things my stretch looks good



FYI: The engine has 282,392 miles and the chain was last changed at 123,200.
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Old 07-23-2012, 12:21 PM
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The 606 also has this movable pointer and I also removed it without aligning the engine to TDC when doing the water pump (want to kick myself) I however did my best with a mirror and light to align the pointer back to the wear mark the screw made on it. But I know that the best way is to measure at TDC with a dial gauge.

In another car with a gas engine I have aligned such a pointer back to TDC with help of a round protractor on the crank and a stick in the plug hole.
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  #6  
Old 07-23-2012, 02:45 PM
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Quote:
Originally Posted by Zulfiqar View Post
In another car with a gas engine I have aligned such a pointer back to TDC with help of a round protractor on the crank and a stick in the plug hole.
For me that would have been a 69 Chevelle with a 350

Like you I presumed it had a hole when I removed it and didn't mark it's location. Luckily after all the grease was removed I was able to use the clean / wear mark to align the pointer, but is it at the factory position? That depends if the last mechanic set it properly.
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Old 07-23-2012, 06:22 PM
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Prior Arrangement of pointer alignment

If one "Locks" the Crankshaft against inadvertent movement.(@ TDC)
(Either at the Starter aperture,or the rubber plugged Oil Pan Opening)
AND then EXACTLY marks the point on the scale of the H.B. the Pointer
is set to...
When re-assembling (Unless New Timing chain components were installed)
re-aligning the pointer BACK at the exact same spot on the H.B. scale...
will yield exactly what you started with...

Howeveah,There is No guarantee that's ACTUALLY TDC since you're just
replacing everything AS YOU FOUND IT.
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Old 07-23-2012, 06:24 PM
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The problem with the FSM procedure is that you need a special tool to mount the dial gauge too. In other engines you just rotate backwards in MB you dont.
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Old 07-23-2012, 08:44 PM
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Quote:
Originally Posted by Zulfiqar View Post
The problem with the FSM procedure is that you need a special tool to mount the dial gauge too. In other engines you just rotate backwards in MB you dont.
If you speaking of re-alignment of the Pointer:
I don't see why any Dial Indicator with an extension on it could not be used. It could be the special tool is needed because the Head is Aluminum and you cannot stick a magnetic base on it.

That means you need to attach a Universal Dial Indicator Clamp; clamped to some place solid where you can position the indicator properly.

However, you need the Special Tools to remove the Prechamber.
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Old 07-23-2012, 09:31 PM
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Quote:
Originally Posted by Diesel911 View Post
However, you need the Special Tools to remove the Prechamber.
Diesel911 are you positive the prechamber has to be pulled? No chance of simply removing the injector and accessing the piston?
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Old 07-23-2012, 10:45 PM
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Nope. There isn't a line of sight since the combustion mixture is sprayed around the combustion chamber like a fire sprinkler rather than directly into the crown of the piston. Besides, you're talking about pinholes in the prechamber.

Here's a picture that shows the business end of a prechamber -



But who says you have to use a rigid rod? Use oil and a graduated cylinder to observe TDC.

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Last edited by sixto; 07-23-2012 at 10:59 PM.
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  #12  
Old 07-23-2012, 10:56 PM
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Quote:
Originally Posted by 300D-91 View Post
Diesel911 are you positive the prechamber has to be pulled? No chance of simply removing the injector and accessing the piston?
Below is a pic of the Prechamber and Retaining Collar installd on the Head without the Injector or Glow Plug.
R is the retaining Collar.
The part outlined in Red is the Prechamber.

C points to the nose of the Prechamber and notice except for some hole drilled into it the nose is solid.

Note this is not the Factory Method:
I don't know if it would work on this Engine but on the 617 Army described a method of removing the Valve Spring and retainers so that the Valve dropped down on the Piston Head. You would position the Dial Indicator over the top of the valve Stem and as the Piston moves so does the Valve.

It might be an O-ring or something else could be wrapped around the top of the Valve Stem so that it would not drop too far into the Engine by accident.
In theory if you are careful to have the Piston close to Top Dead Center (OT on the Damper) the Valve would not fall in too Far.

Dial indicators are most accurate when they move ecactly inline with the part to be measured; any angle to it throws it off.
That may not matter in this case as you only want to know when the Piston stops moving.
Attached Thumbnails
OM602 Timing - (Chain Stretch)-prechamber-602.jpg  
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Last edited by Diesel911; 07-23-2012 at 11:07 PM.
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  #13  
Old 07-23-2012, 11:14 PM
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sixto and Diesl911 thanks for explaining what I'm up against. The straight shot idea is the old gasser in me coming out mixed with a bit of lazy.

sixto I like the idea of filling the cylinder with oil to find TDC. Without direct line if sight how would I use a graduated cylinder? Screw it in place of the injector and watch the fluid level?
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Old 07-23-2012, 11:25 PM
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You might be keen enough to observe the oil level in the prechamber. If not, get a compression tester adapter and stick a clear hose on that. I've never done it. I'm only guessing it'll work.

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Old 07-24-2012, 12:22 AM
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Quote:
Originally Posted by 300D-91 View Post
sixto and Diesl911 thanks for explaining what I'm up against. The straight shot idea is the old gasser in me coming out mixed with a bit of lazy.

sixto I like the idea of filling the cylinder with oil to find TDC. Without direct line if sight how would I use a graduated cylinder? Screw it in place of the injector and watch the fluid level?
Yes, I still have a device some where that screws into the spark Plug Hole Hole of my Old BSA Motor Cycle that rested on the Piston for that purpose. It had scribed lines on it to oviate the need for a dial indcator. It also went in at an angle.

Concerning a liquid it is going to leak by the Piston Ring gaps and side clerences and it also seems that it would be hard to get an accurate reading.
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