whelp. Here we go. I’ve been hazed straight into the world of Mini Cooper.

Recently bought this 2009 Mini Cooper S with 134k miles on it. (For cheap)

it had lots of valve train noise. I thought it was broken timing chain guides. After inspecting the chain once I got it home, I found it to be in good shape. No broken guide rails, and chain was new and tight. Seller changed chain about 10k mikes ago.

it also ran really rough and wouldn’t idle.

it was throwing about 5 codes that led me to replace the O2 sensor Upstream_#1 on top of engine. The idling was improved and I cleared the previous error codes, no check engine light.

I also replaced the spark plugs And topped off the oil among other inspections and testing earlier, including a sea foam treatment via PCV hose.

I ran the engine in the garage for a while with no problems and decided to take it for a drive.

About 5 min in the engine light came on and it was running sluggish still.

10 min in, I heard a little bit of noise and then the engine stalled.

It wouldn’t start and it smelled like it was flooded. I could smell the sea foam that was burning off through the gas treatment.

There was a misfire in cylinder 3

I pulled the plugs to check them out and clean them.

this plug is what I pulled out of cylinder 3. 🥺

I have 2 theories.
1- a piece of the valve broke off and smashed into the plug.

2- some carbon deposits broke off and smacked into plug.

any ideas?


I am pretty sure I’m going to need to pull the head off for sure now. I was sort of leaning towards doing it anyway to solve the previous rough engine issues and do a General overall refresh of the motor with new gaskets and seals and such.




Broken cylinder 3

 

Possible when the timing chain was replaced, whoever did the work didn’t get it just right, and you got some piston-valve contact? Hopefully, that wasn’t it...

 

yeah, that’s one thing I’ve been a bit suspicious of. I know he did the job himself. Wondering if the valve train noise I’m hearing could be valves tapping cylinders. I was assuming lifter noise.

 

Did you check if engine is in time? If reusing crank bolt the crank gear can slip. The already stretched bolt will not get to the correct torque when reused.

 

I don’t know if it’s in time.

im curious though. How can the crank sprocket slip? Is it really just sandwhiched in between the crank and the hub fastener/bolt? There are no grooves or slots or keys?

 

True, the crank bolt can slip --- no keys, slots, or grooves, strictly a friction-fit. Same with both cam sprocket bolts.

To check timing, you'll find a good set of illustrated instructions in https://www.newtis.info/tisv2/a/en/ and of course, the proper tool set. Unless you have lotsa experience with Mini timing, don't even think about using the "equal length straws" method. Gasket kits and TTY bolts are available from our NAM vendors --- much better pricing than dealers. And if you need other parts, all Mini DIY'rs need to know about https://www.realoem.com/bmw/enUS/select

Before pulling the head, try inspecting piston tops and cylinder walls with a borescope. Then do a compression and/or leak-down test. Gives you a better idea of what to expect for repairs.

If timing was far enough out to cause valve / piston interference, the engine wouldn't run at all. Rough / sluggish running could've been from a damaged valve or plug. I've had a plug break from knocking.

Welcome to the world of Mini Coopers. Best of luck ---

 

did a borescope yesterday and snapped these pics of cylinder 3 where the spark plug got smacked by something.

looks like I will be pulling the head off of this engine.

im trying to figure out if it’s worth rebuilding this myself or just swapping out with another motor. I’ve been pricing out all the components and bolts and gaskets and seals and it seems like I’d be spending north of $2k just in parts to rebuild this motor.

thoughts on rebuild costs? (I’ll know more once I pull the head off and inspect the pistons)



Cylinder 3

Higher up shot of the valve opened on the left side

 

Last time I bent all my valves, it cost about $1500 total. This included $740 for Supertech valves and a few guides, then $420 for head work.

How did cyl #3 wall look? If damaged beyond rebore, it's new engine time. If damage can be bored out, then it's machine shop labor and new pistons / rings, etc. If only piston top damage, it can sometimes be smoothed out and re-used, but only on a DD, not a good idea for a built engine. You should consider all this before tearing it down and making final decision. Don't forget all the tools needed to do a Mini engine rebuild. Costs add up quick --- break-in fluids, A/C recharge, misc parts get lost / damaged, unexpected tools needed.