So I'm preparing for multiple projects on my 2020 C43 this Fall/Winter. One of which is re-sealing and replacing the cam magnets on the timing cover (spotted an oil leak at 56,000 miles both sides). Since I will have this timing cover off, it makes sense to check/replace the tensioner. My cold starts don't show signs of these rattles I've seen shared around but I'm willing to bet it starts soon at my mileage so why not just replace it?
I understand that I'll need to pull the intercooler to get to the crank bolt to rotate the engine for timing alignment. I'm trying to understand how critical my alignment needs to be to replace the tensioner? What if I'm off by a tooth for some reason and I pull and replace the tensioner? Its not like I'm replacing the cam phaser where the physical chain comes out from the cam teeth. I'm trying to understand why it needs TDC and the exact alignment for replacement. Is it more just so the chain doesn't come loose when tensioner is removed and potentially come off the lower teeth(yikes!)? Weighing in my risk to do this job.

Any other feedback or suggestions why I have the timing cover off?
Is it overkill to replace the tensioner at my millage even when I don't experience rattle on cold start? Maybe I'll record my cold start and post it for a "rate my cold start" score

 

Excellent reasoning about your timing alignment
-- I can confirm what you understood already... You do not need to align any timing marks to swap the limp chain tensioners. (Crankshaft alignment is only required when dealing with VVT phasers).
WIS shows a crank alignment procedure that is not necessary.

-- FYI: new hydraulic tensioners are weak enough to be compressed with two fingers only. They depend on oil pressure seal.

-- Tensioners plastic shaft seal increasingly leaks out oil pressure to become ineffective at holding chain slack. It's a cheap maintenance item not to overlook. Else the resulting low oil pressure waste the VVT lock-pin faster.

-- To ensure your 4x VVT don't get wasted, you can consider enabling "normal" oil pump pressure solenoid MOD.


> Magnets vs. CPS:
-- Double check what you call "magnets" (solenoids) are working perfectly well.

-- The plastic camshaft sensors (CPS) are the parts that get roasted by engine extreme heat soaks, not the "magnets".

-- Do replace CPS + Pigtails (not "magnets").

Note you can disable the extreme heat stored in dry pistons by spray cooling them at normal driving speed. Cooled pistons prevent extreme heat related issues.

 

So this means I don't have to set TDC if I'm just replacing the tensioners. Why would they put this in the WIS? This also means I don't need to undo my intercooler to get to the crank bolt.

I've read up on this and actually tried to get to and unplug it. I got as far as unclipping the fastener with a pick. For the life of me, I can't get my hands in there to actually pinch it and remove it. Probably a M276 TT space issue because of the intercooler. Any tricks to this?

By spray cooling do you mean doing the solenoid mod?

One other thing that I noticed people talking about is installing an oil check valve behind the tensioner. I don't think this relates to me on my 2020 C43, right? Meaning it should already be there.

 

The answer to everyone of your questions is: YES.


> LONG WAY:
The reason why WIS has a procedure to align timing marks is to relax the chain slack... a non-issue for tensioner considering all the steps to access crank pulley.


> CHECK VALVE:
Long before your MY'20 engine was built (MY'12), Mercedes was not using check valves, so tensioners oil pressure could drain out quickly. That allowed startup tensioners rattling besides the classic VVT on low pressure...


> ACCESS ROUTE:
On your turbo, the easy way to reach pump solenoid connector is from the under side. (top side is too crowded).


> NORMAL PRESSURE :
Pistons "spray-cooling" is what you can consider to clean stuck rings that cause engine vivrations and extreme heat soaks.

This is experienced by upgrading stock oil.
Reference this thread for complete information.

 

Well, if you set the crank to 40 past TDC, you'll have a bit more slack in the chain to change the tensioner - that's what I'd do......

 

Absolutely critical to be at TDC. The tensioner is spring-loaded; if you remove it without the engine being properly locked in place, the chain can jump teeth on the sprockets. This will throw your timing off, leading to potential bent valves and catastrophic engine damage. It's not worth the risk.

Since you're already in there, replacing the tensioner as preventative maintenance is smart at your mileage. Also check the chain itself for stretch and consider replacing the guides if they show any wear. Don't skip the proper locking tools.

 

I'm conflicted here. Probably the best route would be to just do the TDC as mentioned in the WIS. Seems like there's a risk if not set and better to just do it.
All this means is that I need to now buy the upgraded intercooler (CTS) if im taking the stock one out. This project just keeps on getting larger. :O

I'm at...
Molly Flush with 2x oil change and switch out to the green stuff
Rear Diff oil
Transfer case oil
Break Fluid change
Front Disk rotors/pads
Transmission Oil change (+TC drain)
NGK spark plugs
4x Camshaft Solenoid
4x Solenoid Harness
Timing cover reseal
L/R tensioner
Wisetec Cold Air Intake
Unplug oil solenoid mod
CST Intercooler
Coolant flush both circuits

 

Good maintenance coverage.
You're missing :

• 4x cam position sensors + pigtails.
• serpentine belt kit.

Following WIS procedure is fine choice...
The hydraulic tensioners are limp enough to be compressed with one hand.

 

One last question/validation...Messing with anything timing related gets me nervous. According to the WIS

The LEFT tensioner needs markings up





and the RIGHT tensioner needs markings down





Am i mechanic-ing correctly?

 

Aren't these alignment marks for VVT work ?

You're swapping tensioners.

 

See attached
They want TDC set for both left and right

 

crank pulley alignment "+40° after TDC" specs

- That WIS alignment step is the way to guarantee neutral camshafts position for static chain skack.

- To SAVE TIME you can experiment a simple in/out swap... this works without trouble due to engines stop rotating in the neutral position.
RESTING HYDRAULIC TENSIONER DOES NOT HOLD ANY SLACK. That's how when removed: nothing happens because limp tensioner is of no use. Empty tensioners hold nothing.


> OBVIOUSLY...
-- This shortcut is strictly for tensioners only (not VVT's).

-- Do not rotate crank or VVT while secondary tensioner is out, one side after another! Else you may need to reset cam timing the usual way.

(Never rotate crank while camshafts are static: $$$$)