Hello Jeff,
When the crankshaft is at 0 (zero) the alignment marks on the cam bearing and camshaft should be lined-up as close as possible. It is normal for the cam marks to be a little late since chain stretch and head work can cause the cam timing to become late. Always turn the engine in the normal direction of rotation (clockwise as you stand in front of the car looking rearward). Turn the engine and note when the crankshft reaches TDC as you described. The cam mark can be a little late but NEVER NEVER EVER even a bit EEARLY!!!!!!!!! After tampering with valve timing always turn the engine at least one revolution to double check the cam timing.
One chain link equates to about 18 degrees of cam timing. So for instance; if your camsahft mark is 20 degrees late, reseting the cam one chain link forward will get you from 20 ATDC to 2ATDC (this would be fine). However if your cam is 15 degrees late your cam timing will go from 15ATDC to 3 BTDC (will damage engine)!!
Mercedes has "offset" camshaft woodruff keys available to make adjustments from 4 to 10 degrees (see BBB 00-93 for part numbers and more informtion).
Before you go to all the trouble off installing off-set woodruff keys, Mercedes states that it will probably make no "noticable difference".
You have nothing to be concerned about until your cam timing gets over 10 degrees late. At this point I would consider looking into the cause. My first concern would be that your chain may be worn enough to need replacement.This is the biggest cause of late cam timing. If you have records with your car look through the service orders to see if a new chain has ever been installed. If you are unfamiliar with making that judgement on chain stretch, the 100,000 mile rule for a timing chain is good insurance. Installing a new timing chain will automatically make your cam timing closer to specs.
When a cylinder head is "milled" or "re-surfaced" the head becomes shorter and the timing chain becomes longer, in a sense. Since the chain travels through the head twice (once up then down), Milling the head one millimeter will give the chain TWO millimeters more slack. So this also makes cam timing a bit later.
I have done quite a bit experimenting with cam timing over the years. Difference in performance can hardly be felt until cam timing becomes later than twelve or fifteen degrees. If the cam timing is more than a link late the loss of power, fuel economy and running quality will become very very noticable.
Advancing (early) cam timing, to just a degree or two before TDC, will immediately cause the piston to come in contact with the valves!! (not good). As stated never time the camshaft early even a little bit!
Don't confuse this with ignition timing which deals with spark delivery to the engine. We are talking crankshaft, camshaft and chain here no distributors yet.
As far as injection timing, yes the injection pump is installed at 20 degrees ATDC. Normal chain stretch will NOT noticalby effectt injection timing and performance.
Now Mercedes changed engine crankshaft timing pointers around 1968. The pointer actually changed shape and position on the block so as to become more visible. The early pointer was positioned at two o'clock and was rectangular in shape with one corner clipped. The latter pointer was positioned at one o'clock and was triangular in shape. Now the factory had a large supply of vibration dampners already made for the early pointers, so they just added a second degree scale on the vibration dampner for the new triangular pointer! Later engines with the "triangular " pointer always use the inside scale (closest to the block). Eventually when stock of these vibration dampners (two scale) depleated new versions were supplied with only the one correct scale!
Refer to BBB p. 00-7/2 for some photos and more information.
Joe Alexander
Blacklick, Ohio
