25K miles ago I've rebuilt W11 on my R53. You can find info about it on my instagram (@mini_bmw_mechanic). Shortly, what was done engine-wise:
1. The original engine had a hole and damaged crankshaft. Bought another block, another crankshaft. Measured everything possible, including cylinders, journals, tolerances (plasti-guage), etc. Everything was within the spec.
1a. I've re-honed cylinders a bit, but I did not use the machine shop for that (probably, a mistake).
2. I reused original pistons and piston rods, new Hastings rings
3. Rod and main bearings are King.
4. Rebuilt / resurfaced head, new lifters, new valves, new valve seals. Again - measured the camshaft tolerances (plasti-guage), all in spec. Even polished / ported the intake and exhaust ports.
5. New timing kit with sprockets, chain, guides
6. New injectors, new fuel pressure regulator, new fuel pump, all OEM.
7. New ignition coil
8. All new gaskets all around, of course.
9. New thermostat as well.
10. New PCV.
Originally, right after assembly, the compression was 150 psi in all cylinders (cold and dry).

So, now to the problem(s). It consumes oil, initially it was about 1qt per 1500 miles of Mobile 1 5w-30. However, recently I saw it was down 1 qt after 600 miles, but I've changed oil to Valvoline European 5w-40 (it supposed to consume less oil, not more!). Checked the PCV and the hose - it is fine and the hose is dry inside. No leaks. Doesn't puff with blue smoke, not at the start not later. Here are the spark plugs (25 k miles on them):



And another problem - sometimes it started to misfire, cylinder 2 and 3 (however, afaik, it is not very reliable in figuring out which cylinder exactly is misfiring).
Misfiring is happening on the go, like it drives well but then it can start misfiring. Turning engine off, waiting a bit, restarting it - and it goes fine again till next time. Approx once in like 300 miles this happens.
A couple of times I saw DSC error 5E18 / 5E19- can data fault from DME/DDE and the car wasn't drivable. Again, had to turn it off, wait a bit and restart - it goes well again. But this is probably a different issue, might be battery or alternator (however, alternator has new voltage regulator).

Recently, measured compression. It was 150, 140, 150, 150 (engine was warmed up). 2 cyl is degraded. Adding oil into the 2nd cyl brought compression up to 165.

Checked for the blow-by with the rubber glove over the oil cap. It is weird. It is not just vacuum, like I can observe on my E46's M54. It is back and forth - vacuum - blow, vacuum - blow. I made a video:

You Tube

It seems like some cylinders are fine, some (or that 2nd one) are not.

On the same video you can also hear that idle is fluctuating, according to the scanner - between 600 and 800 rpm. And it is a new issue, didn't notice it 600 miles ago. Short fuel trim also shows fluctuations between -5 and 5 %. Can be seen here:

You Tube

Interestingly, if I remove a hose from PCV and plug it, the fluctuation stops, but short fuel trim gets into stable +8-10 % (that indicates lean condition, but like I said - I've plugged both PCV and the hose). Pressing on gas brings short fuel trim to 0.

Sooo.... Here are my current problems. I am planning to do a leak down test, but I am pretty much know what I am going to see. Valves should be fine, leaking most likely will be through rings, most likely in the 2nd cyl. Will have a look into the cylinders with a scope.
I am also thinking on doing the following test: on the running engine, open the oil cap, put the rubber glove over it and disconnect one ignition wire and see if there is any change with the glove's behavior. In my understanding, if I disconnect the cylinder which causes the blow-by, the glove will stop going back and forth.

But probably will need to rebuild the engine once again, this time with new +.5 pistons and boring cylinders. But before that, I want to understand the issue and what did I do wrong the first time. Any thoughts are welcome!

 

Sorry to hear about the issues on such a freshly built engine.

I am no expert but what does not make sense to me is; if you burn 1qt oil per 600 miles you should see blue smoke because that's a lot of oil consumption.

If not then where does the oil go? Assuming there are no external leaks, it could only end up in the coolant right? Did you replace the oil cooler gaskets?

 

No oil in coolant or coolant in oil. And my car doesn't have the oil cooler, btw. Mine is 6 spd auto, and if I am not mistaken the oil cooler is on 6MT only. But either way - replaced ALL gaskets. O2 sensors new as well, btw.

As to the blue smoke.... I know that engines may burn oil relatively smokelessly. I have another oil consumer - old M54 (200K miles), no smoke, but 1 qt per 1000 miles is its normal consumption for the last 5 years (at least).

 

When you had the engine apart what was the clearance between the cylinder and the piston? I recently completed a complete rebuild of my N12 engine, and my machinist said I was right at the limit; he recommended going to the +.020" pistons, so we did; he bored and honed the block; the final result was a clearance of .001". I got new + .020" Mahle pistons from and Ebay vendor out of China. Mahle is the OEM supplier for the N12 pistons, and it looks like all Mahle pistons are made in China now. Ring gaps had to be increased; I found a nice manual ring grinder on Amazon.

I'm pretty pleased with the results; and I pulled oil samples at 500, 1500, and 3000 miles (oil changes at each point.). Analysis shows nice decreases in all wear metals as the engine was breaking in. She doesn't use a drop of oil. Too bad the transmission just went out.

 

This could be a faulty coil. Yes, yours is new, but new doesn't mean good. Try swapping the old one in if you still have it.

This is normal for the W11 and doesn't indicate an issue. The M54 is a very different engine.

This is also normal. Nothing to worry about

Also seems normal - the blow by gases coming through the PCV are loaded with exhaust gases and have very little oxygen in them thereby thinning out the supply of oxygen in the intake. Cutting off the supply will increase the oxygen levels in the intake and make the engine run slightly leaner.

I don't believe this is true. Most of the vac/blow behavior you're seeing is air getting pushed around by the movement of the pistons causing pressure fluctuations in the crank case. Blow by is only a very small contributor.

I'm interested in the leak down test results. Also might be worthwhile borescoping the cylinders.
The biggest head scratcher to me is how you're "burning" so much oil but don't see any smoke in the exhaust. It has to be going somewhere.

 

@mrbean - thanks a lot for your replies! It is a good point about the coil, especially, considering that it is the same coils for cylinders 2-3 and 1-4 (if I am not mistaken) (so, each cylinder has an extra spark per cycle; or, is it firing ALL the cylinders ALL the time? Then it could be wires (also new, but...) rather than ignition coil). I'll find the old one and will swap it.

I'll do the leak down test and will report back. I'll record bore scope of the cyls as well!

 

I don't remember the numbers, tbh. But I measured cylinders and they were in spec (as long as I measured correctly, but I also tried to check if there is any barrel-like wear, and couldn't find any). The pistons were fine too, stock..... I'll do borescoping and will see if I find any cyl wall damage.

 

Not much of the update just yet: the weather in NW isn't cooperating, plus overall pretty busy before the Xmas.
In order to eliminate maximum potential causes for the misfire (reminding - it was misfiring in Cyl 2 and 3), I've ordered a new ignition coil ($50 from ECSTuning), new NGK wires ($30 on Amazon) and new NGK BKR7EQUP (even tho my current BKR6EQUP are still not bad), $32 from Amazon for the set of 4.
I am also going to try different oil. Up to now, I used Mobil1 5W-30 and Valvoline European 5W-40. When I used Mobil1 the oil consumption was 1qt per 1500 miles. My latest measurement with the Valvoline 5W-40 was like 600 miles per 1 qt. It still has the Valvoline in it, will re-check again in 600 miles. But I already have prepared Castrol Euro 5W-40.
Depending on the results above, I will decide whether I am rebuilding the motor again or not. Either way I got prepared: I got Wiseco 77.5 pistons ($520 from Greene Performance) and Sneed piston rods ($390 from ECSTuning with $25 discount). Those prices were Black Friday deals, doesn't seem those prices are available now from these vendors.

 

Ok, I finally got results of leakdown tests and got footage of cylinders bore scoping. They are interesting.
First, the leakdown results:
Cyl 1: 50 psi / 45 psi, i.e. 10%
Cyl 2: 45 psi / 38 psi, i.e. 16%
Cyl 3: 50 psi / 42 psi, i.e. 16%
Cyl 4: 50 psi / 48 psi, i.e. 4%

Not great, but could be worse. The only noise of exiting air I heard from the oil dip stick tube. No bubbling in coolant (I also pressure tested it anyway), no intake or exhaust air.

Bore scoping results are interesting too, will post videos once youtube finishes them.

 

Bore scoping.
Cyl 1

Cyl 2

Cyl 3

Cyl 4

The most concerning cylinder is cylinder #3. As you can see, there is a washed out area on the top of the piston, it seems even wet on that spot. Cyl #2 has that washed out area too, but smaller. Also, there is gunk build up on the bottom of the head. Reminding that coolant is fine, fuel injectors are new and tested, valve stem caps were replaced as well. This leaves us to what? Oil leaking through head gasket? I don't remember the config of oil channels in W11 engine block, is it even possible?

 

Is this marked channel an oil one? (the image is just from the Internet, it is not my engine)

 

Yea, you need to get that block to a qualified machine shop. I don't see any crosshatch in cylinders. In your initial post you said you reused the pistons, but you didn't say anything about the rings; did you replace them? Those are some nice new pistons and rods; don't waste your money; get that block fixed. Make sure you take one of the new pistons to the machine shop. The machinist will need it to match things up. Oh! Always better to buy the pistons after the machinist tells you what you need.

 

That one of three I believe. Picture I took some months ago where the oil channels are stuffed with blue paper towels:


What would concern me is the cylinder wall of cylinder 3. It also shows some sort of wash out which looks to be coming from the top of the block. Could be head gasket or warped head. It doesn't look good to be honest.

 

Yes, rings are new, of course.

77.5 is pretty much maximum size for these engines, so I got that. If even that is too small, then I will need a new block.

 

Yeah. The issue is that I don't understand what is that. Coolant is fine, no suspension in the oil, no oil in the coolant.
Injectors are all new and tested 25K miles ago.
Valve stem seals are also new (25K miles).

The head was resurfaced and checked for flatness, as well as the engine block was checked to be fully flat at its top.

Can leaking oil cause this kind of wash out?

 

A bit of update on the misfiring issue: after I replaced the ignition coil, spark plugs (I changed NGK BKR6EQUP to BKR7EQUP) and ignition wires - the misfire seems to be gone (even, though, previous components had just 25 Kmiles on them).

I still don't get why pistons #2 and #3 have washout areas, though.

 

Today news:



30K miles with brand new valves (not OEM, though, I used ENGINETECH IM4480 and EM4481. Maybe, that was a mistake)

And yeah, this is the cylinder 3.

 

Hope you can determine the cause of this

 

Surprisingly, the only known issue with this motor was oil consumption. No vacuum leak, no codes, no lean mixture. Used only premium fuel (91). Injectors, valves, rings - all was brand new. The compression and leak down tests result can be found in this thread too. If you look at the videos of cylinders inspection I made several months ago, you'll see that Cyl 2 and 3 had washed out areas, which I can't explain (usually, it looks like that than coolant is leaking into the cylinder, but it wasn't the case; like I said, the only issue - oil consumption).

But, yeah, will see what I will find out during the motor disassembly.
I'll be documenting the process on my instagram below.

 

The head is off



So far, I am still not sure why the valve was burnt. And why cyl2 and 3 have washed out areas (the washed out area is on the exhaust side, btw). One thing I noticed when disassembling: it was kinda too easy to unbolt the head. Maybe that is why the leakdown test for cylinders 2 and 3 was 16% (vs 4 % for cylinder 1 and 4).
Now I need to decide what to do next. I think I will go ahead and remove the block from the car to bore the cylinders to 77.5 mm and replace pistons.
Will remove the exhaust valves for cyl 3 for inspection of valve sits as well.

More photos can be seen here:

 

 

Pistons are out. The rod bearing looks super bad for just 30K. Probably, due to oil starvation and pollution.


More photos:

 

 

Some updates. The engine was bored to 77.5 mm, new Wiseco pistons and rings, Sneed4Speed piston rods, King bearings, new oil pump, another head and camshaft, 0.95mm Cometic HG - all is installed. Leakdown test shows almost 0 losses in each cylinder, compression test - 150 psi in each cylinder. I am pretty close to give it a first start.
More detailed updates with images is on my Insta

 

First start was successful yesterday.

The only issue is tapping lifters. I might replace the rocker arms with lifters, I afraid, those can get contaminated and stuck. But will see. Those rocker arms are not cheap, even third party brands (like AJUSA) cost ~550 USD to replace all of them.

Next step: install radiator, put coolant in, run the engine a bit longer, observing the tapping sound. Clear all of the codes too to see if any remaining codes are still there after the engine runs for a bit.