Hi guys-

Bought a 2008 MCS a year ago with a blown head gasket and 128k on the clock. Never worked on a Mini or done a head gasket but bought the Bentley manual and have done a ton of research online. Did the tear down and sent the head off for a haircut and valve work and put it on ice for 11 months. Fast forward and I just got everything back together. Replaced the injectors, all of the gaskets (inlcuding +.3 on the had gasket), and the TTY bolts. Definitely took my time along the way and made sure everything was super clean. Assembly and timing seemed to go smoothly, and it actually fired up in about the time I would have expected to get fuel to the injectors. Was super happy for a second.

But it ran rough. Throws codes but they all seem to be related to the K-Can bus, which I assume is unrelated and not going to distract me for the moment. Ran a compression test and got 108-110 for cylinders 1-3, and 30 for cylinder 4. The low numbers for the "good" ones don't bother me as I have a sort of cobbled run to the tester, a thicker head gasket and at least they're consistent. Obviously #4 is a concern.

My POS Harbor Freight leak down tester broke on me, but if I apply compressed air to #4 with plugs in the other 3, I get a whistle from the breather hose from the intake to the valve cover. If I plug that, I get it at the oil fill. If I run the same test against cylinder 1 (just because it also is at TDC) I only get leakage at the oil fill.

So...what does this mean? The history of the original head gasket was a leak between cylinders 3 and 4. Material was missing in that spot in the head and to a much lesser degree on the block. I had the machine shop fill it on the head and left it on the block as the sleeves are both intact--it's just a little material between the sleeves missing. Gasket was replaced with a thicker one (I think +.3mm but not looking at the invoice). I'm thinking the issue is not related to this as there's still good compression on #3.

So with the leak to the breather would that indicate intake valve? Could it have just gotten that jacked up from the shop? The guy's been doing it for 30 years so I'd think that was unlikely but of course anything is possible.

Any other ideas? Sorry for the long post, but figured it's better to put in all the info the first time around. Pics available if they're of any use.

 

Updating my thread with a little more info in the hopes someone can weigh in.

I took the car out for the first time since I've owned it. It's running really well...except for the rough idling and hesitation. It's so frustrating because I think everything went together well and I was dreaming of a purring car at this point.

So I ran another compression test on #4 with the engine warm. it was about 40. It had been about 30 cold. I dumped a little oil in it and it brought it to about 50. So in a nutshell, super low, slightly higher warm, and slightly higher than that wet. I don't know if warm and/or wet would be expected to increase substantially if it was rings. Not sure if that indicates compression is an issue or if that could still be explained by an intake valve. Any ideas?

 

If you had valves or seats replaced, it could be the shop didn't check for excess valve stem length, and the valve isn't closing tight. Guy on Facebook had a similar issue recently and had to strip it all down to measure and grind stems --- common problem with hydraulic lifters. Check with the machinist and find out what measurements were taken.

 

Usually minis don't blow head gaskets or let's say it rarely happens. Assuming the shop new what they were doing, the question is, did you inspect the cylinder walls or pistons. Every now and then, we see a piston either chipped or with a broken skirt.
Also, take the valve cover off and check everything including the timing (maybe spot on but checking it again wont hurt)

 

Thanks @MiniToBe and @OldBrokenWind. Was going through receipts looking for the machine shop and ran across the invoice for the breather hose. Turns out it's "Engine crankcase breather hose" (p/n 11157605186). Since it went into the intake I had assumed it was intake-related but this makes me more suspicious that it's rings and not intake valves. Or could it be escaping from the intake side, going into the manifold, and then out the crankcase breather hose?

whistling at the side labeled #1.


According to carfax, the head gasket was done at ~63k the first time. It was definitely shot with a hole between #3 and #4. So maybe there's some fundamental issue with this engine? It's gone almost exactly the same amount of time before needing this service again. CarFax doesn't go into detail of course, but the head looked like original surfaces so they may have just replaced the gasket and not machined it.

Piston was clean as was the cylinder wall. No visible damage. I'll see if I can find relevant photos.

 

Here are some pics at teardown and re-install. Sorry about the size of the first one.

#4 (the one with compression issues) is cleaner than the others at teardown, presumably because the ground electrode was missing. So that cylinder was getting a gas bath without spark, don't know for how long. Never did find the spark plug piece but the cylinder wall isn't scored and the turbo looked fine too.


head gasket at removal.


head at re-installation. valves look seated well.


corresponding lack of material on block. The block wasn't repaired. It didn't appear that this would be an issue and I don't think this is what's causing the lack of compression. Cylinder walls are clean and the piston appears to be fine as well.

 

OK, so the answer to the question in the title (how screwed am I?)is: totally. I stopped in and chatted with an indy mechanic about a few things related to this, and he basically said to pull the valve cover and re-run the compression and leakdown tests. I did that and could hear hissing but couldn't really tell where it was coming from. but not the exhaust and not the intake. Put everything back together and introduced compressed air...and it all came out through the oil fill hole. So I'm assuming rings on #4 at this point.

Researching options, it seems like it's not that difficult to replace the rings. Doing the head gasket in the first place was so much more that I've ever done before but since I cleaned everything along the way and have now done it once, doing it a second time to get to the pistons should be fun! Well not fun, but do-able.

I'm going to start another thread with a few questions about this next venture. Thanks for the assist on this one guys.

 

Came back to research a new project and found my old thread. I like to close things up when I figure out what it was for future travelers.

This was in fact rings, sort of. One of the oil control rings was in the oil pan. But the piston skirt was in there too, keeping it company. The piston on #4 just gave up the ghost. The top was fine so I didn't think that anything was wrong and I had clearly found the issue with the damaged head gasket. Well, turns out there were two issues, one probably causing the other. Long story short, I took off the head again, removed the oil pan, pulled out all 4 pistons, replaced #4 and the rings on all the others, and the car ran absolutely t!ts after that. For about 3 weeks until someone ran a red and broadsided my daughter....

:(