First of all - I’ve been a lurker on this forum for a number of years and the info is CRAZY knowledgeable! Ive managed to scare myself away from buying a “modern” mini for all this time - reading the horror stories and reviews made me a bit jaded toward Mini’s.

So several weeks ago I walked into a deal buying an ‘09 Clubman S with a “problem” engine for $1500. Its clean and dry and loaded with features. It’s got 105k on it and I’m the 3rd owner. The P.O. installed a bigger inner cooler, silicone hoses, a tune, a catless custom exhaust and various other little bits. He also installed a bigger turbo and herein lies the problem. He said he drove it with the big turbo for a number of days until coming home from work it “let go” losing some power and blowing smoke. He suspected a piston issue: busted skirt and/or rings. He gave up and re-installed the original turbo and I bought it.

The little dude is clean as hell and not a dent or scratch on it. I performed a leak down on it and found cylinder 3 hissing out of the exhaust manifold. I have a shop with a lift and went ahead and removed the head. The valves and cam appear clean and straight. (He had the c chambers and valves walnut-blasted) The cylinder bores “look” fine. No scratches or gouges and the crank turns smooth and easy. I poured some carb cleaner in each bore and every bore EXCEPT no 3 held. No 3 bore leaked down like a sieve! So - I’m gonna replace rings I think. I wanna do this without removing the engine. I’ve worked on and built old BMWs and early Porsches and a ‘72 Mini Cooper but never a new Mini. Any advise would be hugely appreciated!!! Or if there’s anything I’m missing....

Thanks!

 

An update - Piston #3 lost part of its ring land on one side. I retrieved the bits when I pulled the pan. All others looked fine. The bores from top to bottom look good. I may have lucked out! I don’t see so much as a nick. The previous owner said it only ran 2 miles once it busted and smoked. I’m hoping to install new pistons and rings and hone the block without removing the engine. I’d like to keep her somewhat stock but with the tune installed I’d feel better with a forged piston. Anyone have a recommendation for a decent set of pistons?

I removed the cams and noticed a couple of cam journals have some slight scratches.... the respective head journal surfaces have slight scratches as well. The previous owner had the combustion chambers walnut blasted and there are bits of walnut media EVERYWHERE!! They’re in all sorts of nooks and crannies!!! Wondering if they used too much media and too much air pressure when they blasted it?

 

Congrats on your new project. $1500 sounds like a great buy! I paid $3500 for my 2010 R56S with 124k miles last summer. It was also clean and ran OK when I bought it, but my piston #3 suffered a failure worse than yours.

So, I went through the whole N14 rebuild process this winter. I'm 100% satisfied with the results. The car is running great, oil consumption is near zero. I however, had no choice but to pull the engine and get it bored .50mm over (and #3 cylinder sleeved due to gouges). I went with CP Carillo pistons in stock 10.5:1 CR and have no complaints.

My advice would be to measure the wear of your bores before dropping $700 or so on new pistons (not to mention TTY bolts, gaskets, etc. $$$). You mention your bores are smooth with no obvious damage, but I would be shocked if the bores are still round and straight. Piston to wall clearance will very likely not be correct. I have no personal experience with "just a rehone" and new pistons, but the piston to wall clearances are spec'd for a reason. It's really not a huge amount of additional labor to pull the engine and send it off to a machine shop for proper evaluation.

Also, for the record, my cam journals looked exactly like yours. I reinstalled them as is and haven't had any issues.

Curious, when you said you found walnut shells 'everywhere', I'm assuming you mean in the engine compartment. Not the engine itself, I hope.

Good luck!

 

Thanks for the advice!!

I am going to measure for taper and oval on the bores and keep my fingers crossed that they’re in spec.

So the shell remnants were from the PO’s carbon blast. They are about the size of black pepper grounds.

Im excited to get the little dude running - l’ve really always like the Mini!!

 

I'm really curious, was there walnut shell residue inside the engine?

What are your expectations for life expectancy after the rebuild? (the motor's, not yours!) Is your goal to drive for another 120K? Or just get another 30K - 40K out of it? If it is the latter, I suggest you avoid spending new piston money and get one used piston and "hone" the bores with a flex tool of some sort. If it is the former, then bite the big one and pull the engine. I would also wonder if the #3 injector is partially plugged.....

At the level of bore reconditioning there is no difference I can think of that distinguishes a BMW from a Mini, etc. By that I mean restoration techniques, not specs....

Was just the #1 pair of cam journals grooved? Cam journals are usually very lightly loaded so it takes a lot of miles for wear like that to show up, and then you would expect more than just the #1 to show damage. Seems like some of the busted piston made its way past the filter. I would be inclined to knock off the high spots with some 400 grit paper. Inspect the journals in the head for embedded particles and remove.

Was there any similar damage to the big end bearings of the rods? If there is, then suspect main damage as well. If not, buy Powerball tickets!

 

So a first inspection - I didn't see any wear beyond what a 105k-mile car would have on the big-end bearings. The cams aren't in front of me right now but I believe the wear shows on the #1 and maybe #3 journal and cam surface. (Not tremendous wear but noticeable as the other surfaces are pretty dam good.) I thought about piston "bits" sneaking past the filter and pick-up screen and working their way around but I'm not sure how a piece would find its way between a journal and a cam surface....

You can see in the above pic the little bit of wear on the thrust-side of the piston skirt on 3.... They all have slight wear marks on that side which is kinda expected BUT it could be the bores are ovalized a little too much which I'm hoping a measurement will prove or disprove.

I wouldn't be surprised if there is one or two injector nozzles are partially clogged! The residue was ON the engine and some in it! I'm not sure how the carbon blast was done but it looks like they shot 100lbs of shells all over the place!

I hate doing stuff half-assed (I know not WANTING to remove the engine seems "half-assed".....) so I'd like to replace the piston set. I've built carb'd M10 BMW engines and M20 engines but nothing "modern" from BMW which is why I'm stepping carefully here. As far as life expectancy goes I'd like it to be ABLE to go another 100k or so but who knows - I might get it running, hate it, and sell it.