OM651 timing setting while changing chain - advice please.

[JP79]

Hi all, hope someone can clarify something for me please.

Have a 2010 E220 cdi estate, 120k miles, which has a rattle at cold start, read loads about it and possible causes.
Tried the easiest one first, change the tensioner, didn't help much. maybe slightly better.

So decided to investigate further and go in for a change of chain and cam gears. - could be guides, but inspecting so far, they seem to be there, could be worn.
but can also see the chain been hitting the head on right hand side and chain is slack. Anyway, if this doesn't work next step might be pulling the engine out which I could potentially do with a friend helping.

But here's my question...
I've put the crank pulley on OT, and as per my photos, the line on the inlet cam lines with the mark on the cap, and at the gear end they also line up. Perfect.

but now I was thinking, if I remove the cams, to change the gears, then put them back with new gears only finger tight, put the cam locking tool on - I then have to feed the new chain using the old chain, doing this by turning the engine by hand.

How will I know I'm back where I started on the crank?
putting just on the OT line doesnt mean i'm at the same place? or does it?
saying that because with all connected as is now, lines all matching up, I do 1 revolution of the engine, back at OT and the cams are not at the same place.
I even tried a couple more full revolutions and the line on the cam closer to the front was still not in line when the OT mark was by the tab. I had a wooden chopstick through so I could see it coming up as piston comes to TDC, but... line was still not lining.
So, thats that one, the mark not lining up after I turned about 4 times (and I haven't undone anything)

and the other question is, with the cam gears loose to feed the chain, how will I know I have the crank in the place it should be?

thank you!
on a good note, the engine looks very clean inside, which means oil changes been done regularly. (car is new to me)

 

[pcthrillrider2]

ot mark lined up,camshafts marks lined up and both in and exh valves lobes up valves closed number 1 cyl

 

[JP79]

ot mark lined up,camshafts marks lined up and both in and exh valves lobes up valves closed number 1 cyl

just like that?
maybe I'm overthinking this from working on old engines and there's some electronics here that make everything match?

So, what you are saying is all I have to do is put that OT mark on the tab, put a chopstick on piston 1 to make sure it at TDC, and then drop the cams in with all the lines matching up...and that's it?

Second question, so how come, after I had everything lines up and kept turning the engine over, it didn't seem to all match up again? although I turned the engine about 4 times?
when the OT line was on the tab, the line on the inlet cam closer to the front wasn't at the line yet. and once that was lined up, the OT mark was past the tab..
that confused me why is happening. surely everything should have lined up again as its going around?

 

[Jobsworth]

Cams turn at half crank speed, so 2 turns of the crankshaft for camshafts to align again. I’m not surprised the camshafts are lagging a bit if you have enough stretch on the chain to be rubbing the cylinder head.

 

[JP79]

Cams turn at half crank speed, so 2 turns of the crankshaft for camshafts to align again. I’m not surprised the camshafts are lagging a bit if you have enough stretch on the chain to be rubbing the cylinder head.

So, what you are saying is, when it comes to the time of feeding the new chain, using the old chain, and cranking by hand, I'll have to be counting how many times I go past the OT mark?
so that I end up with a even number, for example 12..or 14..etc.. (no idea how many turns I'll need till the chain has come through), so that then I can drop the cams all lined up?
I'll have a friend holding the chain and putting tension on it.

my fear is, or what I'm getting confused/overthinking is, as you say if you do only 1 turn of the crank, the camshaft has not turned enough to line up, how will i know that Im not at that position of the crank when i finish feeding the chain, and I'll be dropping the cams lined up when they shouldn't be?

I might be really overthinking this! hahaha
old american V8s are a bit more simple, get piston on compression stroke, bring it to TDC, mark the pulley, turn the distributor...and off you go! haha

yes, think there's a bit of slack, but to be fair not as much as some youtube videos I seen. it's not like the chain is hanging down between the gears when engine at TDC.
Attached a photo with an arrow pointing to where there's a shave on the head.

 

[Jobsworth]

No, it won’t make any difference at all
Tdc is tdc whatever. It’s the cam position that determines whether it’s an intake stroke or an exhaust stroke. Look for a picture of the gearset on the back end if you are struggling to get your head round it. It’s very basic four stroke engine science. You need your head properly round it if you are going to attempt this job
Don’t worry, we’ll help you

 

[JP79]

No, it won’t make any difference at all
Tdc is tdc whatever. It’s the cam position that determines whether it’s an intake stroke or an exhaust stroke. Look for a picture of the gearset on the back end if you are struggling to get your head round it. It’s very basic four stroke engine science. You need your head properly round it if you are going to attempt this job
Don’t worry, we’ll help you

I edited my post as you were replying.
Yes I think i'm really overthinking this, I'm used to put a finger in a spark plug to check im on compression stroke!

Right then.. so is basically feed the chain, put that OT on the tab, drop the cams all lined up, put the locking tool on, tighten the gears and off we go!
thank you, fingers cross it resolves the rattling problem.
Engine runs sweet as a nut throughout rev range, not a slight noise, but those 2 secs of rattling at start really interfere with my mechanical heart that always needs everything working tip top. and the rattle hurts!