Oil Consumption After Rebuild (Re-ring)?

[MichaelCT]

Hi All,

Got a strange issue with oil consumption here with my N52 BMW here.

Recently, I had to replace my short block due to a small crack on its outer casing; the engine had no mechanical problems and did not burn oil before this.

Upon tear down, everything looked okay as expected, pistons measured ~ 84.95mm (down from 84.99) and the replacement block was ~ +0.05mm from 85mm. Ring gap was on the upper limit of 0.3mm and they were replaced.

According to BMW technical manual, total wear tolerance (piston and cylinder combined) needs to be below 0.15mm, which I was well under.

Engine was put back together with just new rings and "consumables" like AL screws and various seals gaskets, filled with Shell Helix Ultra 0W40 and 5W40.

Oil level went down 1/4 (down one full bar would mean 1L) after ~30KM, didn't read much into it figured it might be slightly underfilled or some creavices were getting filled.

But now after 330KM (fairly varied city and highway driving, load is relatively light), oil went down another 1/4.

A little concerned, I pull plugs on cylinders 1-3, and they look just fine - dry with light white-brownish deposits like I have seen before; the tops of the pistons are all golden brown with no carbon deposits. Also did a compression test which came out to be ~12bar/150psi, consistent with before the rebuild.

I have had the car for a long time and am familiar with all the usual oil consumption culprits (piston rings, CCV, oil filter housing gaskets, valve stem seals, etc.), the car didn't have this issue before and I did check basic things like crankcase pressure and gasket leaks, valve stem seals weren't needed but had them replaced anyway.

I am a little confused, the most obvious variable here is the rebuild (or more accurately, just a re-ring?) itself. But at this rate of oil consumption, plugs would be pretty fouled (I have seen it before on the same engine type) if the oil was being burnt in the cylinders. And the fact compression is good doesn't sound like a ring installation/seating issue.

Any thoughts?

 

[KrisZ]

The rings likely need to break in. I would give it a few thousand kilometers before drawing any conclusions.

 

[wpod]

Run it hard and see what happens with the oil consumption, Did you hone the cylinders?

 

[MichaelCT]

The rings likely need to break in. I would give it a few thousand kilometers before drawing any conclusions.

I thought about this as one of the possibilities and sure hope so.

What is a bit confusing for me is the difference between a good ring seal and ring seat, I obviously have good seal from the compression results.

Ring seat, from what I read, can refer to both the proper expansion of the ring (into good contact with the cylinder), and establishing a matching wear pattern between the cylinder walls and rings. The former concept, seemed a little redundant to ring seal, and I feel like the latter is a more microscopic process that takes longer to happen, thus will take more milage to actually see a difference?

 

[MichaelCT]

Run it hard and see what happens with the oil consumption, Did you hone the cylinders?

I did not, the cylinders were pretty clean (looks just like my original cylinder walls) and they were Alusil which is hard to hone properly.

I sure would run it harder when I drive it again.

 

[wpod]

I did not, the cylinders were pretty clean (looks just like my original cylinder walls) and they were Alusil which is hard to hone properly.

I sure would run it harder when I drive it again.

BMW... I am such a fool !

 

[jetman]

The harder you run it the better to seat the rings.

 

[Audiman]

You may never achieve the oil consumption position that you had with the original block, as you say the block was not honed due to the nature of Alusil so new rings won’t have the same bed in ability as the factory block/ engine. You can try running with higher rpm to achieve higher dynamic compression to “force” the rings into the cylinder wall but this may prove futile.

When I used to do the 2.0 TFSI EA 888 gen 2 engine piston and rod replacements all we could do in the workshop was remove the glaze build up from the cylinder and give it a good “Italian tuneup” road test afterwards in order to seat the new rings.

Let us know how you get on.

 

[Nessism1]

That Alusil block reminds me of the Chevy Vega! Internet suggests many owners have iron sleeves installed. Not looking good to resolve this issue easily. I agree with the recommendation to drive hard. You already have good compression, though, it's the oil rings you are having issues with.

 

[MichaelCT]

You may never achieve the oil consumption position that you had with the original block, as you say the block was not honed due to the nature of Alusil so new rings won’t have the same bed in ability as the factory block/ engine. You can try running with higher rpm to achieve higher dynamic compression to “force” the rings into the cylinder wall but this may prove futile.

When I used to do the 2.0 TFSI EA 888 gen 2 engine piston and rod replacements all we could do in the workshop was remove the glaze build up from the cylinder and give it a good “Italian tuneup” road test afterwards in order to seat the new rings.

Let us know how you get on.

The EA888 also has some coating instead of sleeves right?

How did your past piston replacements on them come out in terms of long-term oil consumption?

Both the VAG EA888 and BMW N series are very popular in my area, and there seem to be many cases of successful piston/ring replacements to address oil consumption issues.

For BMW, there is even an official service bulletin that calls for straight piston/ring replacement in case of high oil consumption, for earlier production cars that came with inferior ring designs.


Anyhow, I am not naively hoping to have zero oil consumption (although my original block is close to that), the replacement block does have wear after all. I do hope the oil consumption keeps tapering off, especially with harder driving. I'd be happy if I don't have to add oil for every few thousand KMs.

Will report back.

 

[kschachn]

You may never achieve the oil consumption position that you had with the original block, as you say the block was not honed due to the nature of Alusil so new rings won’t have the same bed in ability as the factory block/ engine. You can try running with higher rpm to achieve higher dynamic compression to “force” the rings into the cylinder wall but this may prove futile.

When I used to do the 2.0 TFSI EA 888 gen 2 engine piston and rod replacements all we could do in the workshop was remove the glaze build up from the cylinder and give it a good “Italian tuneup” road test afterwards in order to seat the new rings.

Let us know how you get on.

Unlike a Nikasil coating, Alusil is an alloy and it is possible to re-machine the bores. But it has to be done in a shop that can then properly etch the surface.

 

[kschachn]

The EA888 also has some coating instead of sleeves right?

No, it is an iron block to start with.

 

[Audiman]

Unlike a Nikasil coating, Alusil is an alloy and it is possible to re-machine the bores. But it has to be done in a shop that can then properly etch the surface.

I said due to the nature, not that it cannot be done. You need a shop that has the correct tooling and knowledge of the process.

 

[MichaelCT]

Unlike a Nikasil coating, Alusil is an alloy and it is possible to re-machine the bores. But it has to be done in a shop that can then properly etch the surface.

I said due to the nature, not that it cannot be done. You need a shop that has the correct tooling and knowledge of the process.

That's exactly why I decided not to re-hone it, given the condition of the cylinders was relatively good, didn't want to make things worse with a subpar hone job.

BTW, did you get any long-term feedback on your past EA888 piston/ring replacements, in terms of oil consumption?

 

[Cujet]

Rings will often eventually seat in re-used plated bores. When new they are rough enough to accomplish the job.

As crazy as it sounds, maximum pressure is required.

 

[Audiman]

That's exactly why I decided not to re-hone it, given the condition of the cylinders was relatively good, didn't want to make things worse with a subpar hone job.

BTW, did you get any long-term feedback on your past EA888 piston/ring replacements, in terms of oil consumption?

Most customers were happy that they had gone from topping up 1 litre every 200 miles to 1 litre every 2-3000 miles.

 

[AdmiralYoda]

Drive it like you stole it for a while. Take a long trip and get it nice and hot on the highway...then drive it hard some more. Change the oil and see how it goes. Might take a few times. After a thousand miles or so it is probably going to be as good as it gets.

 

[MParr]

Take it out and get on it. Intermittent high speed pulls are what’s needed.

 

[MichaelCT]

Drive it like you stole it for a while. Take a long trip and get it nice and hot on the highway...then drive it hard some more. Change the oil and see how it goes. Might take a few times. After a thousand miles or so it is probably going to be as good as it gets.

Take it out and get on it. Intermittent high speed pulls are what’s needed.

This seems to be the consensus here and I believe you guys are right.

I took the car out for some harder pulls and monitored the raw readings form oil level sensor, so far so good.

Rings will often eventually seat in re-used plated bores. When new they are rough enough to accomplish the job.

As crazy as it sounds, maximum pressure is required.

That make sense, I took a scope camera into the cylinder walls today and there are some new surface marks along the path of piston skirts, so there is break in happening after all I guess.


Well, I will continue to drive it at higher loads and hope for the best, thanks everyone.

 

[cbrf3]

I was told in the past to leave the unit in a lower gear and do some hard throttles and quick decelerations when you are moving, not from a dead start. This was in a stick car or motorcycle. Might be an old school way that is not relevant today, but it has always produced strong motors that did not burn oil.