Which mark do I check to determine T-chain stretch - PeachParts Mercedes-Benz Forum

#1 07-26-2003, 03:24 PM

Sorry for another timing chain question, I did perform a search.
I performed my first valve adjustment today, went without a hitch (lots of tight valves

). I went to check the stretch on the chain and got a bit confused.
Do you line up the notch on the cam washer with the pointer on the cam tower? If this is the case I have about one degree of stretch.
Or, do you line up the tiny dimple on the cam sprocket with the pointer. In this case I have about 7-1/2 degrees of stretch.

I'm just a bit confused and worried about possibly driving around with a chain stretched 8 degrees.

Thanks all for the great info (thomaspin's website really made the task at hand easy)

Stevo · #2 07-27-2003, 03:14 PM

What engine do you have? Assuming you talking 617/616. What you do is clean off your harmonic balancer so can see the marks good. I use a ratchet and socket on the P/S pump and go only clockwise. As the mark on the cam comes up slow way down and line them up. Now look down at your timing marks ( use the "knife edge" not the one with the hole) and you will be able to determine the difference which is your stretch. Go around a few times and you,l get the hang of it. The more accrete way is to use a dial indicator on a valve. It sounds like you have the idea and have found the marks.
Hope this helps

#3 07-27-2003, 08:42 PM

I thought this one was going to go unanswered.
I maight not have been clear. My confusion is which timing mark to use. I'm not quite sure what you mean by "Knife edge". Are you talking about the dimple on the cam sprocket?

Once again thanks

mplafleur · #4 07-27-2003, 10:16 PM

I think he means the little angled piece of metal thingamajig hanging over the harmonic balancer that you use to check timing with. One side of it should be straight and perpendicular to the block face. That is the "knife edge".

On a gasser, you would be looking at it with a timing light.

Stevo · #5 07-27-2003, 10:58 PM

Sorry for not being more clear. When you have the valve cover off crane your neck around and look at the big washer on the cam on the aft side of the fwd cam tower. The notch in that lines up with the mark. The crank timing marks will go around twice and the cam once so when your timing marks on the crank are at TDC and the notch in the cam washer are now where to be seen then your 180 out and the cam marks will show up next time around. The cam marks are not easy to see till you know where to look.

Thomaspin · #6 07-28-2003, 10:31 AM

Here's the way the cam marks align and here's the 'knife edge' on the crank pulley.

You align the cam marks and read the degree of chain stretch at the knife edge.

Stevo · #7 07-28-2003, 11:02 AM

Thomaspin

Wow...Good pics. That about says it

Very nice

Steve

#8 07-28-2003, 11:14 AM

That's exactly the info I needed. Accordingly to this method, I have slightly less than one degree stretch. Would any of you recommend using the dial indicator approach?

mplafleur · #9 07-28-2003, 11:58 AM

Yeah, that's the thingamajig hanging over the harmonic balancer.

R Leo · #10 07-28-2003, 12:06 PM

Quote:

Would any of you recommend using the dial indicator approach?

I wouldn't recommend using the 'pointer and mark' method mentioned above since it is only for use during engine assembly and not a reliable means of determining chain elongation.

just my .02

#11 07-28-2003, 01:08 PM

be sure to verify that someone hasn't already used an offset Woodruff key to correct the cam timing for stretch -- otherwise you may be reading that the cam is almost right on but in fact several degrees of stretch have been adjusted away by the offset key.

blloyd7 · #12 07-28-2003, 02:50 PM

How do you do it on a 603 engine.
Anyone have picks of this?
Thanks in advance.

leathermang · #13 07-28-2003, 03:08 PM

"Would any of you recommend using the dial indicator approach?
"
The factory shop manual says what RLeo said... the method you are using is for assembling the engine...

The manual says if ANY performance complaints are extant to use the dial indicator on the number one intake valve as the way of measureing.

If someone has used an offset key then you can just read from there... the offset keys are called for in the manual for fixing the elongation up to about 8.5 or 10 degrees... I forget which.... and is a perfectly legit method of getting your valve in synch with your crank.. according to the Factory Shop Manual...

gsxr · #14 07-28-2003, 04:49 PM

blloyd7, here's the photo of the OM603 camshaft marks (note they are NOT lined up in the photo). The factory service manuals specify replacement on OM61x chains at 5 degrees stretch or more, and OM60x engines at 4 degrees stretch or more. OM60x engines have NO provision for offset keys/pins. Here's two PDF's related to the OM60x timing chains:

http://www.meimann.com/docs/mercedes/OM60x_Timing_Chain_TSB.pdf

http://www.meimann.com/docs/mercedes/OM60x_Timing_Chain.pdf

Thomaspin · #15 07-28-2003, 05:14 PM

One especially interesting thing about gsxr's factory attachments is the statement in the first one, as follows:

"In order to check basic engine timing, turn the engine
slowly (in normal rotation) using the crankshaft pulley bolt
until the mark on camshaft sprocket aligns with the mark
on the camshaft bearing cap (arrows, Figure 1)."

If that is a valid procedure for the OM60x motors, why does it not apply to the earlier OM616/7 which, I keep reading on this forum, require the use of a dial indicator?

Could it be that the dial indicator approach, which I understand allows for cam/follower wear, is obsolete, mistaking precision for accuracy?