Thought I would post my latest project car. Nice clean low mileage vehicle, 2009 MC Base R56, N12 engine.
PO (I am the second owner) apparently did not believe in using synthetic motor oil, and ignored chain rattle for just one drive too many...




Took out an intake valve which rattled around knocking the spark plug electrode off.
Remarkably, no major scoring in the cylinder, a light hone fixed it. No ring damage.
Hone the cylinder, new piston/ring in this cylinder, (the other cylinders are measuring > 150psi) new head, and its back on the road.

Lesson: replace the tensioner every 50k miles. Use synthetic oil.

 

Wow. Thanks for sharing. Destroyed.

 

good job....never ignore what the car is trying to tell you

 

Here's the new head - good scrap yard find. Dead flat, valves in great shape, less than 60k on the clock. New seals, gaskets...
N12 Used Head

 

The head bolt washer that fell into the timing chain....

 

Strongly suggest that you replace the valve seals before going back on. doing that job in-car is a serious challenge (I have a thread on it...)

 

As a rule, when I tear any head apart, I always replace the valve stem seals - ** but ** in this one particular instance, base model, low mileage car, low mileage salvage head, clean flat and obviously ran synthetic, no damage - I decided not to pull it apart.
They are a serious PITA without the correct clamp / tool for holding spring tension on the return springs on the intake side, so I figured no big deal...
I would stress that for any engine that had some miles, or clearly was abused / dirty, icky - no question, I would replace the valve stem seals. If it was a turbo, I usually replace the valve guides anyway, and many times, at least the exhaust valves.

Probably, IMHO, if I owned the tool (Mini / BMW # 119650) I probably would have done it anyway since the seals come in most hg kits,,,

 

Just posting a few more pics of the rebuild:

Honing cylinder #4

About .002" diameter over starting, around 0.004" diameter over nominal. Still a few light scratches. Ended up at +0.0045" diameter. Most of the scratches were in the smaller dimension (horizontal) - the cylinders tend to wear oval anyway.

New cylinder in place, block cleaned up - just need to inspect rings and clean tops of pistons - make sure no shrapnel is hiding in the residue

 

Re-assembling...




Car is back together - initial start - second try (had to pressurize the fuel rail). Stumbled a little - rings need to seat.
300 miles on the odo post repair, Cyl 1 - 3 ~ 150 psi compression, cyl 4 ~ 145 psi. Consumed about 3 oz of oil in the first 60 miles - more than I would have suspected. Probably a minor leak somewhere.
Stain in the driveway - looks like the oil pan was bent and the uv indicator shows its leaking opposite the bend. Easier fix than everything else.
Car is running great! Taking it easy for ~ 500 miles, but averaging 37 mpg indicated in mixed mild driving. Car has plenty of power. One last oil leak and its good to go!

 

beautiful

 

Nice work, great read!

 

could you send me that thread? I'm doing valve stem seals without removing the head

 

He didn't do it, but here is a link that might help newtis.info you need to source a special tool to remove the springs.

 

Wow that poor piston. Glad you brought it back to life.

On the tool i think you are talking about this one. https://www.ecstuning.com/b-baum-too...rs/119570~btu/

These are what I use.

https://www.newtis.info/tisv2/a/en/

Bentley manual.
https://www.ecstuning.com/b-bentley-...nual/bm13~bty/

Schwaben Tool for afterward to make sure everything is fine and no bad sensors or connections
https://www.ecstuning.com/b-schwaben...020sch01a~scf/