M275 AMG Low Compression #1 cyl
 

M275 Low compression #1 2005 CL65 AMG 225,000 miles
So the intake took in some plastic pieces when the Charge Y Pipe which i repaired blew apart. I did a compression test all around and got 150-155 all around except #1 which had 60 psi,( tested it 3 times ) add a little oil and it went up just a little (10psi). I pulled the engine and removed the cylinder heads . I blew air ( leaf blower ) into the head ports and got some really small bubbles using thin oil / trans fluid. I thought that was enough to drop the compression. I tested other cylinders using air and got similar results some small bubbles but not much. I always thought the valves would seal water / oil tight but these didn't.?? (#1 - 2 cylinders ) ? I filled the cylinder (block side) with wd40 and it stayed full, didn't leak out a bit. Funny thing I was getting a PO300 and PO307 nothing about #1. That came up doing a compression test. The head gaskets looked fine ? I removed the piston and everything looked good ? I did hear a slightly different pop in the exhaust note coming from that bank after the Y pipe came apart for sure. I know what my engine sounds like and something was different. Another odd thing is # 1 cylinder was not misfiring at idle, you would think at 60 psi there would be no fire at all in that hole.
summarizing,
Once the compression test showed 60psi I expected to see a definitive issue, Valve issues being first on my list. Now I am second-guessing myself. Did I do something to skew the compression test ? Anyway looking for someone to put some fresh thoughts on this ???

How did the cam lobes and valvetrain look on that cylinder? I'd be more inclined to believe you had a piece go in and hold a valve open and slightly bend it or cause some other sort of damage.

I was thinking along those lines as well!
The engine ran long enough to melt off any plastic, the cam looks good. but clearly I haven't measured anything dealing with the cam. I plastic-gauged
the #1 rod bearing and it came to 1.5 thousandth, at 225,000 miles !!?? What you said makes sense, but I need to
​​​​​​​keep looking for the problem.

A slightly bent or burnt valve will give you 60psi, i'd start there. You could have a ringland broken on the piston, did you remove it?
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I did remove the piston and the rings and lands are good. The rings have good tension as well.
Im going to have the heads 're freshest , and start looking into the rest of the engine.

So after the plastic fell in did you start the engine or just do the compression test? I'd like to here the order that things were done in. Because if it was not run it could have just been the plastic holding valve and letting it leak. And if it ran after that was another test done? Maybe all got blown out and all was good, causing tons of work for nothing.

The Y pipe was cracked and I melted some plastic and patched the lower 1/2 inch. The engine was running smooth at idle and under light load but did misfire at
higher rpm and loads. I replaced the coils and plugs and took the car out and ran it hard, the engine made full boost and pulled hard. It however fell flat on the next run. I didn't feel any boost at all. I drove the car the next day about 30 miles and hit it again hard with nothing but misfires. I took a look under the hood and saw the Y pipe was shattered. The engine ran smooth but did have a slight popping sound which was surely a new occurrence. The sound was coming from the passenger side same side as the #1 cylinder. At that point I did some testing and that lead me to the low compression at #1 cylinder (60 psi).

I want to freshen up the engine, so sourcing the parts, main and rod bearings, timing chain and tensioner, oil pump ?? Is there a place folks use besides the dealers. ???:y

I think there are a few, here is one I can think of.
https://www.pelicanparts.com/Mercedes-Benz/index-SC.htm

https://www.autohausaz.com/mercedes-...placement.html

Better Yet, You google engine bearings for a M275, V12 bla bla bla. I bet you wont find anything !!!!!
I've searched and found only one listing and I couldn't confirm the figment.
I'm not being lazy here there's just no listings anywhere. Maybe because its an AMG, I'll try the 600 type V12 engines

https://cimg4.ibsrv.net/gimg/www.mbw...1c237eebef.jpg