Help in assessing compression and leakdown test results
 

Hi All-
Warning: book ahead. I figured it would be better to put all the data in. if you're not an engine guy you might want to skip this one....

So I picked up a 2008 MCS with a suspected head gasket leak. Ran, but horribly with a small amount of oil in the coolant. I pulled the plugs and they were not surprisingly fouled but one was actually missing the side electrode, the little L bracket the center electrode sparks against. Thinking I had discovered a cheap and easy fix to my project, I replaced all 4 plugs and fired it up. It ran better but still was nowhere near maintaining idle. So I ran a compression test to see how bad it was:
Cyl 1: 160
2: 140
3: 80
4: 30
So not great. I read it was a good idea to do a leakdown test before tearing into the head to get an idea of the issue and I am now the embarassed owner of a Harbor Freight Leakdown Test kit. It is absolute junk. But I think I got the basic data:
Cyl 1: 42% loss, leaking through HPFP hole (HPFP is currently removed in prep for teardown, but I assume this would have leaked out the PCV in the valve cover)
2: 54% loss, leaking to cylinder 3
3: 65% loss, leaking to cylinder 4
4: 76% loss, leaking to cylinder 3
So all in all, a steaming pile. I have no history from the PO, it was sort of a sketchy deal. But a carfax did indicate the had gasket was replaced at 70k. Car now has 120k.

Next step in my plan is to get the head off and do a visual inspection and send it to a machine shop. I had a couple questions though if anyone has an opinion.
1.) My amateur opinion would be that #1 has an intake valve issue, and all others have a gasket issue. At the very least. With numbers this bad there can really be no assessment of the bottom end. Is there any way to determine condition of the rings with the head on or off? Or do I roll the dice and repair the top end and see how it goes? Budget is an issue.
2.) Considering the head gasket has been replaced in the past, can I have it milled again? I actually don't know if it was milled or not in the past but I assume that the machinist could tell be based on tolerances. Do I need to get a higher profile gasket? 2?
3.) is there any way to tell if it overheated? I guess I'm concerned because of failures in 3 cylinders. that seems pretty unlikely that a head gasket would fail in multiple places.
4.) I;ve never seen a spark plug missing the electrode bracket. Could that have melted off? And where would it have gone? <gulp> through the turbo? The turbo blades looks pretty clean from what I can see of it with the hose off. the PO did say it was replaced at some point in the past.
5.) any other guidance/advice? I'm going to tear into the exhaust side and timing chain next. Everything else is off the engine at this point. Carbon in the intake is pretty bad for a mini I think, but nowhere near where an e90 was with 120k....

Thanks for reading this far!

Squirt a little motor oil in the cylinders and do another compression test. If there is no or little change in the reading from a dry compression test, then your rings are probably alright.

What was your oil pressure reading? If it was around 50 to 60 psi cold, your bottom end bearings are fine.

I've seen the electrode broken on three cars so far. When that happen, the piston will most likely be chipped hence the 30psi (should be even lower). Also, most likely, the new plug you put in the cyl was soaked in oil. if you look through the hole, you will see a mirror like surface.
the head should be removed either way and you'll see what the issue is.
Personally, I dont think you need to mill the head. I've done a handful of HG and not once i needed a machine shop.

where you located?>

San Rafael CA, about 20 minutes north of San Francisco.
Piston chipped? Does that guarantee I'd need to pull the entire engine and go through the bottom end? That would suck and I'd probably end up trying to source the whole thing elsewhere. I'll try to get through the turbo and exhaust manifold plus the timing cassette this weekend. Then I can get to the head. What specifically would determine if the head needs to go to the machine shop?

Thanks for the input.

I think it depends on the damage...with piston chipping, often times the cyl wall would be grooved. So, you can buy a block and transfer good parts or pick another engine.

Take is one step at a time, take the head off and assess the damage and make a plan.

Don't take the head off yet. Get an inspection camera from Harbor Freight and have a look down the spark plug holes for damage on the cylinder walls.

I feel like no matter what it is, rings, pistons, valves or head gasket, the head needs to come off. If it's cylinder scoring, it'll just make the block that much lighter to take out and drive to the dump. if it's anything else, I'd need the head off anyway.

Could you see the results changing that? I mean I'm all for a good reason to own one of those cams--those are cool.

OK, head off. Gasket hosed with breaks between 3&4 and 2&3. 1 looks like it was leaking as well, so all of the compression and leakdown tests are explained. the rest looks pretty good. Valves and pistons intact, no scoring on the cylinder walls.
Couple questions for you guys:
1.) Cyl 4 looks pretty clean (it was the one with a broken plug, so not sure if this means it was just washed with gas). But the other 3 look like there's a bunch of carbon buildup. I'll clean it up before putting it back to together, but is that anything to worry about?
2.)Machining. Assuming the surfaces look pretty good, do I need to have it decked? If so, can the shop tell if it was done before? According to carfax, the gasket was replaced at 65k, 70k miles ago. If it was (or even if it wasn't) do I need to get a thicker head gasket?

More pictures at https://imgur.com/a/n07Ry

https://i.imgur.com/v1fpU0Y.jpg

I see few issues right off the bat! That might explain low/no pressure.


https://cimg8.ibsrv.net/gimg/www.nor...2120000c81.jpg

@MiniToBe: the shiny part I think I hit with a rag. It's OK. The gasket definitely explains the issues. I've cleaned up both the head and block a bit and run a flat bar across. Pics below. The head is .006 and the block .002 off flat, at both of the spots where the gasket failed between the cylinders. So I know I need to get the head machined at this point.

Anyone know if I need to do something to the block to address the .002? I absolutely do not want to take it out, but I've heard about using a flat block and some 100 and then fine sandpaper to flatten it a bit. Seems scary...

https://i.imgur.com/tFb4dCj.jpghttps://i.imgur.com/k0HuCbn.jpg

This is a tricky one man...you can always ask the machine shop about it an what they recommend.

or: https://www.ebay.com/itm/07-12-Mini-...xaDwxy&vxp=mtr

Hi Guys-

OP here. I got the head back from the machine shop. Everything looks pretty good. He took .006 off and welded the spot between cylinders 3 and 4 that had gapped a bit with the blow.

I had always assumed that I'd get the 1.2MM gasket instead of the typical .9MM gasket due to the machine work. The shop said I could go either way. Any reason to go one vs. the other? .006" is .15MM according to the google, so it's literally half the difference between stock and the .3MM thicker head gasket they make. Apparently it would lower the compression a bit (not a horrible idea as far as I'm concerned) and be slightly more likely to leak in the future which I don't want. I assume the timing chain tensioner would take up any difference and the head bolts would be OK either way.

So...any pros or cons one way or the other? If I should get the 1.2MM gasket, which is recommended? I don't see a lot of options for those.

Regarding head work --- were the valve guides checked for tolerances? And did the shop install new seals for the valve guides? If valve guides are original and worn, there could be "wobble" in the valve travel --- a thicker head gasket will minimize valve / piston interference.

I've lost spark plug electrodes a couple times --- never caused any obvious damage. I'm told they commonly "disappear" due to heat. Valves are also subject to heat damage --- I hope your shop inspected them all closely while it was apart

Yes, guides checked and surprisingly were good. Seals replaced. the bores are clean, no indication it scraped the cylinder walls. Still no idea about the rings or anything else on the bottom end but hopefully I can catch a break.