[n00b0rKa]

Hey guys!

Long story short, my '05 E90 325i with 170k km on clock was consuming oil since I bought it. I replaced the PCV and valve stem seals since, but the oil consumption reached 1l/3-500km. There is no blue smoke on startup and slight blue smoke can be seen on acceleration.

Cold compression after 6 cycles was 14+- 0.5 bar on all 6 cylinders. I blocked the PCV and found normal amount of blow-by. Since it is an early E90, I suspect the oil control rings are worn and they cause the issue. I plan on replacing piston rings myself.

Is anyone out there who has re-ringed their N52 and has any experience? I'm concerned about the honing process as the cylinders are coated with ALUSIL. Some say that re-ringing is not even possible, as the alusil coating wears off, others suggest re-ringing without honing, but I'm afraid that the new rings won't seat properly. I've found people suggesting a light honing with scotchbrite pads and silicone paste at 150 RPM for 1 and a half minutes per cylinder. These oppinios all come from different ALUSIL coated engines (Audi, Porsche), but I haven't found anything specific for this engine. The newtis service manual does not mention anything about honing.

I would be really thankful if anyone could share their experience/thoughts on this!
Have a nice day, nbK

[gbalthrop]

Originally Posted by n00b0rKa

...'05 E90 325i with 170k km [106,000 miles] on clock was consuming oil since I bought it. I replaced the PCV and valve stem seals since, but the oil consumption reached 1l/3-500km. There is no blue smoke on startup and slight blue smoke can be seen on acceleration.
Cold compression after 6 cycles was 14+- 0.5 bar [200 PSIG] on all 6 cylinders...

At that mileage, that engine should just be getting "broken in", and equal compression on all cylinders @ 200 PSIG does NOT suggest a ring problem. UNLESS it smokes MUCH more severely on "over-run" when you let off gas after accelerating, I don't see any indication of worn rings causing oil smoke or consumption.

Doesn't your 325i have the EXTERNAL Oil Separator under rear of intake? Have you checked for oil in the hose that goes from separator to Intake Manifold? It appears more likely to me that you are sucking oil from the separator into the intake. Oil film on rear bumper, etc. above tailpipe I presume?

George

[tlow98]

Originally Posted by gbalthrop

At that mileage, that engine should just be getting "broken in", and equal compression on all cylinders @ 200 PSIG does NOT suggest a ring problem. UNLESS it smokes MUCH more severely on "over-run" when you let off gas after accelerating, I don't see any indication of worn rings causing oil smoke or consumption.

Doesn't your 325i have the EXTERNAL Oil Separator under rear of intake? Have you checked for oil in the hose that goes from separator to Intake Manifold? It appears more likely to me that you are sucking oil from the separator into the intake. Oil film on rear bumper, etc. above tailpipe I presume?

George

Worn oil control rings on the b25 engine are very well documented.

[mxchris727]

Originally Posted by tlow98

Worn oil control rings on the b25 engine are very well documented.

I assumed all years of N52s were the same regardless of model, unless there's a superseded part number for the piston rings.

I'm curious because I used to own an 06 325i back in the day... wish I had kept it as a daily.

[hassmaschine]

Originally Posted by mxchris727

I assumed all years of N52s were the same regardless of model, unless there's a superseded part number for the piston rings.

I'm curious because I used to own an 06 325i back in the day... wish I had kept it as a daily.

They're not. The N52B25 only came in europe and yes, it has issues with the piston rings that the N52B30 doesn't.

Also the US 325i and 328i still use the N52B30, not the B25. I think only Canada got the B25 (poverty spec 323i).

I would really consider swapping in another motor, possibly a B30 if you can find one (and get away with it).

You can re-hone the alusil block but it's a bit different. You don't use a honing stone like a steel block, and it ends up with a much different finish. I recommend researching Porsche engine rebuilds because they have used alusil for decades.

The "coating" doesn't wear off because it's not a coating, the (inner) block is alusil itself. What honing actually does is remove the softer aluminum material, and leaves the harder silicone material (it's actually harder than steel).

Theoretically once the rings are broken in, the cylinder walls never wear because they are much harder than the steel rings. Probably on the B25, the oil control rings were faulty or too soft which is why they burn oil when the B30 doesn't.

[n00b0rKa]

Originally Posted by gbalthrop

At that mileage, that engine should just be getting "broken in", and equal compression on all cylinders @ 200 PSIG does NOT suggest a ring problem. UNLESS it smokes MUCH more severely on "over-run" when you let off gas after accelerating, I don't see any indication of worn rings causing oil smoke or consumption.

Doesn't your 325i have the EXTERNAL Oil Separator under rear of intake? Have you checked for oil in the hose that goes from separator to Intake Manifold? It appears more likely to me that you are sucking oil from the separator into the intake. Oil film on rear bumper, etc. above tailpipe I presume?

George

Dear George!

You are right, it has an external oil separator to which I referred as PCV and I already replaced it. I tried completely blocking it in order to exclude any issue related to it but it did not yield anything. There is no oil film on the rear bumper but the tailpipes are all black. The slight blue smoke can be observed when accelerating rather than decelerating so this is why I suspect the oil control rings to be worn.

Originally Posted by hassmaschine

They're not. The N52B25 only came in europe and yes, it has issues with the piston rings that the N52B30 doesn't.

Also the US 325i and 328i still use the N52B30, not the B25. I think only Canada got the B25 (poverty spec 323i).

I would really consider swapping in another motor, possibly a B30 if you can find one (and get away with it).

You can re-hone the alusil block but it's a bit different. You don't use a honing stone like a steel block, and it ends up with a much different finish. I recommend researching Porsche engine rebuilds because they have used alusil for decades.

The "coating" doesn't wear off because it's not a coating, the (inner) block is alusil itself. What honing actually does is remove the softer aluminum material, and leaves the harder silicone material (it's actually harder than steel).

Theoretically once the rings are broken in, the cylinder walls never wear because they are much harder than the steel rings. Probably on the B25, the oil control rings were faulty or too soft which is why they burn oil when the B30 doesn't.

An engine swap is what most of the people suggest, however there are a few problems: N52B25 engines are rare and I have no warranty that the one I'd get does not have the same problem. The B30 would be an option, however either I'd do it illegally, or I'd have to pay a lot of fees and extremely high taxes afterwards for the 3 litre engine which I can't afford. This is why I got the "poverty" 2.5l in the first place.

So theoretically as my compression is good, (and maybe if a leakdown test comes out good as well), I could leave the compression rings in place and just replace the oil control rings? Do you have any experience with this?

[tlow98]

Originally Posted by n00b0rKa

Dear George!

You are right, it has an external oil separator to which I referred as PCV and I already replaced it. I tried completely blocking it in order to exclude any issue related to it but it did not yield anything. There is no oil film on the rear bumper but the tailpipes are all black. The slight blue smoke can be observed when accelerating rather than decelerating so this is why I suspect the oil control rings to be worn.



An engine swap is what most of the people suggest, however there are a few problems: N52B25 engines are rare and I have no warranty that the one I'd get does not have the same problem. The B30 would be an option, however either I'd do it illegally, or I'd have to pay a lot of fees and extremely high taxes afterwards for the 3 litre engine which I can't afford. This is why I got the "poverty" 2.5l in the first place.

So theoretically as my compression is good, (and maybe if a leakdown test comes out good as well), I could leave the compression rings in place and just replace the oil control rings? Do you have any experience with this?

is there an MOT test that verifies the engine block numbers or the DME coding that would give you away?

I believe the b25 is known to develop oil burning issues in as little as 40k miles. Given you have to remove the motor anyway, I'd just replace it with something that works, aka, the b30. replacing the block as opposed to tearing it down would be easier too.

I don't know how strict your emissions are tho...

[hassmaschine]

They should look the same on the outside. I figured you could be somewhere that a swap wasn't possible, but I thought it was at least worth suggesting. It's possible to spoof the CVN, checksum and software id.. FYI.

You could probably get away with just replacing the oil rings, but if you've torn it apart far enough to remove the Pistons, I can't imagine putting it back together without at least a basic refresh.

[richievn]

I'm pretty much in the same boat, just different continent :-)

My E60 with N52B25 engine just hits 140k kms (90k miles) and still runs acceptably. However it started eating oils 2 years ago and I've since replace all the possible parts including PCV, hoses, all the gaskets and valve stem seals. Still it eats oil though at much lesser extent, around 1litre per 3000 km, mostly when I hit the pedal hard together with oil burning smell into the cabin.

Last week I went for compression test and ironically 2 of the cylinders failed terribly while only 1 cylinder got to the 14 bar mark. The remaining 3 are in the range of 11. Given all the work done on the engine, piston rings are the only thing left for maintenance. However, similar to OP, i am quite concern on the alusil wall and the honing work in my country is sub par. Its not easy to find a N52B30 in my country to swap though.

Any advice would be appreciated. Also which parts do I need to buy for re-ring?

[n00b0rKa]

Originally Posted by tlow98

is there an MOT test that verifies the engine block numbers or the DME coding that would give you away?

I believe the b25 is known to develop oil burning issues in as little as 40k miles. Given you have to remove the motor anyway, I'd just replace it with something that works, aka, the b30. replacing the block as opposed to tearing it down would be easier too.

I don't know how strict your emissions are tho...

Originally Posted by hassmaschine

They should look the same on the outside. I figured you could be somewhere that a swap wasn't possible, but I thought it was at least worth suggesting. It's possible to spoof the CVN, checksum and software id.. FYI.

You could probably get away with just replacing the oil rings, but if you've torn it apart far enough to remove the Pistons, I can't imagine putting it back together without at least a basic refresh.

Nobody really checks your engine during MOTs so I could get away with a B30 swap, but it would be illegal. Probably nobody would ever find it out...

I'm more concerned about the state in which I'd get the replacement engine. These cars are old and I could not verifiy the service history of one. Moreover, a complete B30 engine would cost me around 1500€. The cost of a complete engine rebuild done by myself wouldn't come even near this. Another point for keeping the engine is that I've changed almost anything on this one: water pump and thermostat, PCV, a lot of gaskets and the valve stem seals. I've invested a lot of money and work in it, and I would not like to let it go just like that.

I thought about replacing only the oil control rings because the compression is good, and I'm not sure that the new compression rings would seal without honing. I see the honing as the critical point of the engine rebuild, because nobody seems to have ever done it..of course, I'd love to replace as many things as I could, but I don't want to do any harm either.

Originally Posted by richievn

I'm pretty much in the same boat, just different continent :-)

My E60 with N52B25 engine just hits 140k kms (90k miles) and still runs acceptably. However it started eating oils 2 years ago and I've since replace all the possible parts including PCV, hoses, all the gaskets and valve stem seals. Still it eats oil though at much lesser extent, around 1litre per 3000 km, mostly when I hit the pedal hard together with oil burning smell into the cabin.

Last week I went for compression test and ironically 2 of the cylinders failed terribly while only 1 cylinder got to the 14 bar mark. The remaining 3 are in the range of 11. Given all the work done on the engine, piston rings are the only thing left for maintenance. However, similar to OP, i am quite concern on the alusil wall and the honing work in my country is sub par. Its not easy to find a N52B30 in my country to swap though.

Any advice would be appreciated. Also which parts do I need to buy for re-ring?

I know the struggle, you can't find these engines on every corner in my country either, and I've replaced so many stuff on mine that I would rather not take the risk of installing an unknown one.
You will need a rocker cover gasket, a set of new screws for the rocker cover, a head gasket and a set of new screws for that, the oil pan gasket and probably a set of new screws for that as well (don't know if they must be replaced or not), and the piston rings. I would think of replacing the conrod bearings, depending on your budget a bunch of gaskets (I found my oil filter housing gasket to be leaking for instance, but the valvetronic motor gasket and the rear main seal are also a good bet. Basicly any gasket you see or touch). If you are not feint hearted, I'd recommend changing the steel rings on the end of both camshafts (2X2) which seal for the VANOS. These were updated to some kind of plastic because the metal ones would cut into the cylinder head, and once this happens, you have to replace it all. For this, you'd need new screws for the camshafts as well.
Don't consider this as a complete list, I'm just trying to give some ideas.

[richievn]

Thanks. Im thinking since the engine will be taken out the would it be better to hone the cylinder to 85mm and grab a set of used n52b30 piston and replace all the bearing with new set? Should I go down this path or just stick with N52B25

[hassmaschine]

Like I said, re-ringing and honing on alusil blocks have been done before, many many times. Look to the Porsche community for how it works.

you're not going to hone the cylinder to 85mm though. Honing only takes a tiny amount of material off the cylinder walls. I'm not sure how easy it will be to find somebody to bore it out although I imagine it must be possible - but the alusil material will definitely dull cutting tools pretty quickly. I'd look for a Porsche engine builder and talk to them about it.

[tlow98]

The water pump and all the ancillaries you have replaced would carry over just fine - no sunk costs there.

All the gaskets need to be redone if you're building an engine anyway - those repair dollars are all down the drain.

Have you ever rebuilt a motor? If you're not a pro at this then there is a high likelihood that you will mess it up. I'm not trying to be negative, but you should know the % chnace that all of this work will be a waste of time and money will be very high.

[n00b0rKa]

Originally Posted by richievn

Thanks. Im thinking since the engine will be taken out the would it be better to hone the cylinder to 85mm and grab a set of used n52b30 piston and replace all the bearing with new set? Should I go down this path or just stick with N52B25

I would personally not invest in such a big job. I'm no expert, but boring an engine block requires very high precision work and I think it's more expensive than a new engine, put aside the risk that something will go wrong and you will need a new engine anyway.

Originally Posted by hassmaschine

Like I said, re-ringing and honing on alusil blocks have been done before, many many times. Look to the Porsche community for how it works.

you're not going to hone the cylinder to 85mm though. Honing only takes a tiny amount of material off the cylinder walls. I'm not sure how easy it will be to find somebody to bore it out although I imagine it must be possible - but the alusil material will definitely dull cutting tools pretty quickly. I'd look for a Porsche engine builder and talk to them about it.

I've spent a few days reading these forums but altogether, there is nothing really concludent... Some do it without honing, some do it with honing. Some turn out to be working, some not really. Nobody can tell why.

Originally Posted by tlow98

The water pump and all the ancillaries you have replaced would carry over just fine - no sunk costs there.

All the gaskets need to be redone if you're building an engine anyway - those repair dollars are all down the drain.

Have you ever rebuilt a motor? If you're not a pro at this then there is a high likelihood that you will mess it up. I'm not trying to be negative, but you should know the % chnace that all of this work will be a waste of time and money will be very high.

you are right, but the brand new PCV, for example, would go down the drain. I don't know what material the VANOS seals on the end of the B30's camshafts are made, but I've just replaced the metal ones on mine. Valve stem seals are also done just now. These smaller or larger jobs would all go...
Yes, I've rebuilt a cast iron engine before, and it is running ever since (and is through another 40k km, totalling 370k). I'm starting to see how much of a gamble it is to re-ring it, however if I could rebuild mine and have acceptable odds for it to work, it would still be a lot cheaper, and I would remain within the law.

This is why I thought I'll try to find at least someone, who has done it and has some experience on these blocks.

Thanks a lot for your inputs guys, nbK

[richievn]

I have a good pal running a engine shop here and his skill is top-notch. The only drawback is he never did the job on magnesium block and alusil cylinder wall but he assured it can be done with proper paste.

Also I looked at the ring and bearing for N52b25 and wonder jf I should get the original spec or +0.25", including the new head cover gasket with abestos +0.3". If we open the engine and recondition the cylinder without boring the wall then would it be better option still? I dont need excessive power, just need the car to run smoothly and durably. But if honing is a must then my thought on the boring while I'm at it came up :-)

[hassmaschine]

the magnesium is inconsequential - except for maybe hot tanking it (you probably have to be careful there), the inner block is not magnesium so it doesn't matter for honing.

Probably it's best to measure the cylinders first to see if they've worn at all.

[n00b0rKa]

Back with some updates: I performed a leakdown test today. The leakdown tester was home-made, with a 1mm hole used as restrictor, but the results seemed really consistent so I have no reason to not trust them. I used 5 bar as starting pressure, and the readouts were the following:

1. cyl 1 - 4.65/5 = 7%
2. cyl 2 - 4.6/5 = 8%
3. cyl 3 - 4.25/5 =15%
4. cyl 4 - 4.65/5 = 7%
5. cyl 5 - 4.55/5 = 9%
6. cyl 6 - 4.6/5 = 8%

Cylinder 3 was also consuming the most oil based on spark plugs.
The cylinders are in pretty good shape, the rings, esp. the oil control rings are failing, am I right?

[tlow98]

Originally Posted by n00b0rKa

Back with some updates: I performed a leakdown test today. The leakdown tester was home-made, with a 1mm hole used as restrictor, but the results seemed really consistent so I have no reason to not trust them. I used 5 bar as starting pressure, and the readouts were the following:

1. cyl 1 - 4.65/5 = 7%
2. cyl 2 - 4.6/5 = 8%
3. cyl 3 - 4.25/5 =15%
4. cyl 4 - 4.65/5 = 7%
5. cyl 5 - 4.55/5 = 9%
6. cyl 6 - 4.6/5 = 8%

Cylinder 3 was also consuming the most oil based on spark plugs.
The cylinders are in pretty good shape, the rings, esp. the oil control rings are failing, am I right?

Glad to hear you've rebuilt a motor. I'd say you could likely just re-ring without anything else if you aren't worried about the possibility of losing your sweat equity.

[hassmaschine]

I suppose you could scuff it up real good with green scotchbrite pads (don't use honing pads for a steel engine, they will ruin it), replace the rings, and call it a day. it can't really get much worse than it already is right?

[n00b0rKa]

Originally Posted by tlow98

Glad to hear you've rebuilt a motor. I'd say you could likely just re-ring without anything else if you aren't worried about the possibility of losing your sweat equity.

These are the values before I even touched the bottom end.

Originally Posted by hassmaschine

I suppose you could scuff it up real good with green scotchbrite pads (don't use honing pads for a steel engine, they will ruin it), replace the rings, and call it a day. it can't really get much worse than it already is right?

Yes, basically. I would not rate this engine usable right now... I'm thinking about getting my hands on the Sunnen AN-30 paste and polish it after a good cleaning with scotchbrite, but that stuff is more expensive and harder to get than cocaine... I think first I'll take the head off and take a look/measure it, and will see where are we heading from there...

[hassmaschine]

this is about the best (specific) instructions I can find to rehone the cylinders:
https://cdn.shopify.com/s/files/1/14...structions.pdf

I think whether you use the stones they list or not depends on how bad your cylinder walls are. If they are just lightly scratched/scuffed, just the honing paste will probably be enough.

This is also informative on the whole process of alusil blocks (and similar alloys):
https://www.sunnen.com/NewsDetails.aspx?NewsID=11

[n00b0rKa]

I haven't posted an update in a while as I've been busy with a lot of things.

In the past few weeks I managed to source AN-30 paste from Goodson and have a friend bring it over to Europe. What is more important, I finally pulled the head and made a few observations (pictures at the end):

1. The head looked just as good as before my valve stem seal job, clean and nice.
2. As I tried to release the head bolts, I found 3 of them snapped. All 3 were the same, 2 in front of the timing chain: 1 was already missing its head, and the other one's was in place, but snapped off, so I removed it with my hand. The 3rd one was at the back of the oil filter housing, outside the engine. I think I can call myself extremely lucky that nothing got caught between the timing elements.
3. The head bolts, especially the T60 ones were extremely tight. I used an extension on top of a breaker bar, and it was still hard to break them loose. Each and every one of them felt like I'm snapping the head off or pulling some threads out, but in the end, everything went well.
4. The head gasket and the sealing surfaces looked healthy and clean, so did the cylinder wall. It is shiny as used alusils should be, but I did not see any scoring. I'm yet to measure it, as I was unable to find someone to borrow me the tooling needed.
5. There was some carbon buildup on the pistons but nothing extreme. In exchange, the valves look so bad, that I don't understand how I wasn't experiencing any issue besides the oil consumption. Maybe some more experienced user can help me out here: how much carbon deposit is normal on the valves?

I think the next step will be to pull the engine and tear down the bottom end as well, pull the pistons and see what's down there. In the meanwhile I had to return to university, so I will be working on weekends, and expect to finish the project no sooner than Christmas.

And now, the pictures:

1. Snapped bolt outside the engine
2. Snapped bolt in front of timing chain
3. The bolts
4. Overview of the head
5. Valves on Cyl2
6. Valves on Cyl6
7. Overview of the block
8. Cyl3 (Shiny wall, no scoring. I was somewhat relieved, as this one was consuming the most oil based on spark plugs)
9. Cyl6