[yupetc]

Originally Posted by whyzee125

People say it's an oil starvation issue but I don't know that I agree. The oiling system is supposedly better on the N55 than the N54 but it's always the N55's spinning bearings with no warning. Additionally, it's not always after an OFHG change (often is, but not always).

Lastly, if they are having oil starvation issues this commonly, I doubt it's one event in the life of the car that takes it out, but multiple events and eventually they let go. IMO putting fresh bearings gives you a better buffer of protection against wear or oil starvation events.

Not quite all of the story, but your point still has merit.

And What Malteser_wfj says are still the best summarized common causes to why oil isn't properly maintaining the needed oil film for the bearings:
* Not priming the engine properly after changing OFHG, or sump gasket etc
* Lack of oil pressure from hard driving and high G braking
* Some idiot mechanic loses your oil filter cage

But I'd like to contend against saying N55's oiling system is better than that of N54, I think both N55/N54 oil systems are shit, the real superior oiling system is that of S55, and there are variants of the S55 which can be retrofitted to the N55 motor. Matter of fact, I have that entire kit sitting in my garage for two years now, and I couldn't install it because it's meant for a manual transmission based N55, and mine's an auto, so that kit is sitting with a nice dust cover on it.

While I do agree with fresh set of bearings to be the ultimate solution, I have ACL, Kings, and other B-series motor bearings all sitting in my garage, and compare any of those against the N55, I can tell you that the N55 bearings are too thin on the bearing babbit. The other variants I've mentioned all have some sort of Irox or organic layer babbit, some even have Calico coating treatment as the babbit layer gets further buffered to tolerate more debris which are the ones which causes the bearing wear to begin with. I think we do want to change out for a fresh set of bearings, but we should aim to use an aftermarket set which has at least a tri-layer setup in which the babbit layer has much better tolerance and can buy much more time before the bearing gives up.

My above statement comes with a caveat, the OEM N55 bi-layer bearings, while offering almost no tolerance room for debris on the babbit layer, it's commonly used in the industry because it's longevity is the most superior for non-racing applications. Henceforth, on pre-auto stop/start vehicles, you'll typically find engines with the bi-layer setup, it lasts the longests because the layering are made of ultra-hard alloys, and it's not the bearings which do the work, it's the oil film between the bearing and the journal that makes all this work. The tri-layer bearings are more common place when you dwelve into the race application realm, they are typically built with the typical hard metal bi-layer plus a highly sacrificial babbit which is meant to give you that allowance for debris mixing into the oil and buy more time in case the bearing's babbit layer and the inner layer starts to heat up and give. So its longevity index is comparably WORSE than the OEM bi-layer bearings, but it offers that sacrificial gapping, and thus more protection in case the bearing gap is compromised by failure. However, nowadays, there are coatings and composites which are being used to be best of both worlds, and the ACL folks are right there on the money. So consider these when any of you are going for bearing swap.

Lastly, one thing that I don't see much people talk about in the forums is the bearing clearance. BMW's OEM clearance are set between 0.011" to 0.018", that's a very thin clearance to play with. Typical engine builder's clearance for our size journal is between 0.017" to 0.023". While I am a fan of small room for oil film so that low-vis oils can be used and you can achieve better fuel economy, I'm more worried about the low tolerance to debris and likelihood of higher temperature generation which will also lead to bearing stress. So when I get to opt out of OEM bearings and go for aftermarket tri-layer stuff, I get to ease up on that bearing gap for friction control and running higher viscosity oil to have better oil integrity and temperature tolerance before degradation.

Folks, we're talking very small window of operation with these bearings and oils. So don't beat yourself up listening to my opinions. Ultimately, BMW did build these engines with a wide enough spec range. It's up to you to pick and choose your own flavor with what's available out there.

[bmw335ie90]

Originally Posted by whyzee125

People say it's an oil starvation issue but I don't know that I agree. The oiling system is supposedly better on the N55 than the N54 but it's always the N55's spinning bearings with no warning. Additionally, it's not always after an OFHG change (often is, but not always).

Lastly, if they are having oil starvation issues this commonly, I doubt it's one event in the life of the car that takes it out, but multiple events and eventually they let go. IMO putting fresh bearings gives you a better buffer of protection against wear or oil starvation events.

There are early and late N55s with seized bearings that were covered under warranty with 20k-30k miles, full engine replacement. If it's a bearing problem how do you explain that? There are tons of N54s with seized or spun bearings also, it's not un-common on that platform either. To say this is isolated to early n55 is uninformed and to say replacing the bearing protects you from a seizure is conjecture. It only takes a few seconds of no lubrication at high load to ruin a bearing, and a few minutes at idle.

[Dynamics99]

Would it be worth it to shell out almost $2k for S55 oil pump system retrofit or move oil changes from 5k to 3k mile intervals? Just found two e9x cars on FB marketplace with rod knock. Both are from 2011. One is a rare spec (e90, N55, M-Sport, iDrive, Manual).

[yupetc]

Originally Posted by Dynamics99

Would it be worth it to shell out almost $2k for S55 oil pump system retrofit or move oil changes from 5k to 3k mile intervals? Just found two e9x cars on FB marketplace with rod knock. Both are from 2011. One is a rare spec (e90, N55, M-Sport, iDrive, Manual).

I have a full kit laying around that I can't use. PM me if you would like to propose an offer. I bought mine from a 25k mile car shipped in to the States from Europe.

[Dynamics99]

Originally Posted by yupetc

I have a full kit laying around that I can't use. PM me if you would like to propose an offer. I bought mine from a 25k mile car shipped in to the States from Europe.

Sent a PM, I do see an issue with this retrofit. The S55 oil pan does not have bolts for the power steering pump.

Wondering if I can use the S55 oil system with the scavenge pump and the S55 oil deflector with the N55 oil pan. Not sure if the oil pan will have clearance issues with the scavenge pump or oil deflector. Cannot find enough information on this. FCP says it fits but that bs since E9x came with a power steering pump while S55 used EPS I think.

That would be the first option. The second option would be to buy a power steering block off the plate and remove the pump and reservoir.

[whyzee125]

Originally Posted by bmw335ie90

There are early and late N55s with seized bearings that were covered under warranty with 20k-30k miles, full engine replacement. If it's a bearing problem how do you explain that? There are tons of N54s with seized or spun bearings also, it's not un-common on that platform either. To say this is isolated to early n55 is uninformed and to say replacing the bearing protects you from a seizure is conjecture. It only takes a few seconds of no lubrication at high load to ruin a bearing, and a few minutes at idle.

Same as S54, S65, etc??

Tons of those seized early due to faulty bearings too. New OE bearings don't entirely solve it in those engines either. You can think N54 and N55 have the same number of failures all you want, but N54's were made for 7 years in the e9x platform whereas the N55 was made for 3 and there are still way more N55 failures, more often stock, and more often at low mileage. Neither you nor I know exactly what the cause is, so your opinion is just as uninformed as mine, but I stated my opinion which I'm entitled to especially given the many, many hours of research I've done, the owners and shop owners I've spoken with, the N55 cars I've owned, and the N54 cars I've owned. YMMV.

[yupetc]

Guys, save your jab trading with each other. The N54 and N55 bearings are all the similar make up, bi-layer hard alloy bearings. And as I've mentioned, rather than paying much attention to bearings, you all need to pay closer attention to the bearing gap which was originally prescribed from the OEM design to be very small. It's very tight, and therefore, the motor oil specs are on the thinner side of the fence. This is especially great for fuel economy as the oil pump also operates under two modes, along with higher target oil operating temperature deliberately preset by BMW, altogether, fuel economy and engine smoothness is ultimately achieved by this combination. The trade off is that the risk of operating with small bearing gaps is highly likely under the oil starvation or pre-mature degradation situation. I'll state the proverbial causes again, those were stated by Malteser_wfj before:

* Not priming the engine properly after changing OFHG, or sump gasket etc (avoidable)
* Lack of oil pressure from hard driving and high G braking (S55 retrofit solves the issue)
* Some idiot mechanic loses your oil filter cage (avoidable, and frequent oil change)
* Last one I'll add is you start with lower Viscosity oil as OEM stated, but each 75k miles you accumulate, you should jump the hot viscosity up by 5. So if you're starting with 0w-20, then when you get to 75k miles, either 0w-20 or 0w-30 or a mixture half/half. Then when you get to 150k miles, go for 0w-30 full. That'll help you with maintaining a good bearing gap oil film and more resistive against high-temp oil degradation/loss. Consider the highest spec fully synthetic oil once you get beyond 150k miles.

A whole lot of us looked too deep into N54 vs N55 bearings, then N55 early vs late bearings, in actuality, they are all bi-layer with a thin babbit. And with such small bearing gap, it doesn't matter what year, make, type of motor you're dealing, they are all likely to heat stress the babbit layer and let the hard alloys weld to your crankshaft in any singular event of oil starvation/degradation, period.

And I've shined a lot of info on how aftermarket bearings being tri-layer may exhibit the rightful solution to these issues in terms of longevity and time-buying if you have just a few skips in your oil. It's time to seal this topic and move on.

[bmw335ie90]

Originally Posted by whyzee125

Same as S54, S65, etc??

Tons of those seized early due to faulty bearings too. New OE bearings don't entirely solve it in those engines either. You can think N54 and N55 have the same number of failures all you want, but N54's were made for 7 years in the e9x platform whereas the N55 was made for 3 and there are still way more N55 failures, more often stock, and more often at low mileage. Neither you nor I know exactly what the cause is, so your opinion is just as uninformed as mine, but I stated my opinion which I'm entitled to especially given the many, many hours of research I've done, the owners and shop owners I've spoken with, the N55 cars I've owned, and the N54 cars I've owned. YMMV.

I never said N55s seize or experience rod knock less than N54s. N54 bros always act like that motor has no problems with bearings which is untrue is all I'm saying.

What I do feel is incorrect is telling people that changing their bearings somehow solves the problem. Almost every picture of preventively replaced bearings I've seen look completely normal with the exception of 2 examples. If that's enough to convince you they need to be replaced be my guest and replace them. It humors me when people replace their bearings, then ask the forum....how do these look? You mean to tell me you replaced the bearings, because the forum makes it seem like you have to, and you don't even know enough about engine building to gauge how worn your bearings are? I means it's totally ass backwards.

If you loose oil flow to your con rod bearings, it's toast, with new bearings or old ones. If you own an N55 you have to accept that there is a very tiny chance of a random failure causing your to loose your engine just like all other engines made. If you do 5,000-7,500 mile oil changes, clean your engine bay and remove the intake manifold when replacing the OFHG to ensure nothing falls in, prime you engine after opening the oil circuit, ensure the cage is in your oil filter cap, and never go WOT when your oil is cold; you will more than likely never have an issue.

There have been less than 100 reports of engine seizure or rod knock on early N55s, I have done extensive research. There were over 20,000 made. 100/20,000 = 0.5%. You guys are acting like an N55 is going to seize eventually when in reality less than 1% will ever experience an issue at all.

At the end of the day these cars are dirt cheap. Buy one, maintain and treat it well and you won't have problems.

And PS: going on N55 threads with owners experiencing rod knock telling people "N55 is a nightmare engine", "RIP", "Another N55 bites the dust" is extremely annoying and immature.

[yupetc]

I second the above post. Well said.

[ptpending]

there is a lot of seizures and even mutiple seizures of the N55 and similar N20 and N63 engines
and usually the owners of the 3-er is discussing this on forums, while owners of the X5 and X6 repair or swap engine and sell the car

[Malteser_wfj]

Right so I now have my car back post engine rebuild - the shop I chose are BMW engine specialists and build many high bhp forged builds, particularly S63's and AMG V8s (GND_motors on instagram)

Anyway - my engine had spun the rod bearing for cylinder 1 with no obvious inclination as to what caused the spin (but I have mentioned the history of my car previously).

These are the parts they used in mine & their other OEM spec reconditioning:

* ACL race rod bearings
* BMW crank bearings
* Same piston rings that CP/JE uses in their piston sets (can't remember which company exactly but one of the high end aftermarket piston manufacturers)
* FEBI timing chain
* OE gaskets
* Valves & valve seats recut
* Valve guides left on N55 as they're relatively long and don't suffer much wear apparently.

I then opted for an MMR low temp oil thermostat and am running 5w-40 oil. I did get a VAC Motorsport sump baffle but they couldn't do the welding themselves so I'll get this done later.

Thankfully they had a spare N55 from which they took the crankshaft and a connecting rod as both of those on mine were toast.

They've already done a couple of oil changes to get rid of the assembly lube and I have a 1000 mile break-in advised <2.5k for continuous cruising & <3.5k for shorter journeys.

They very kindly gave me all of the bearings and no1 con rod, but unfortunately altogether in a box so the pictures are not in any particular order, just for reference.

[yupetc]

Looks to be another clean build. Enjoy the new life this N55 will breathe into. Very good choice of bearings as those ACL rod bearings are tri-layer, with a lot of give on the babbit layer, so you get to have a few skips on oil before you'll toast the bearings. So if there aren't any serious cause for oil starvation, you should be fine as long as you maintain that oil cleanliness. Seeing how you've settled on 5w-40 oil from the get-go, my guess is that after they've set the bearings and dialed the piston ring gaps along with piston-to-wall clearance, you're probably on the loose side of the fit, which is GREAT for a high power setup, a whole lot less frictional drag relatively speaking against the tight-fitters. In this setup, if you haven't done so, I'd also highly recommend that you make sure to have an oil catch can installed and monitored going down the road. I've built my N55 twice and with first build landing on the loose-fit side, I did catch myself losing engine oil through the PCV system due to higher blow-by and oil evaporative smoke within the crankcase. I was using 0W-40 Castrol EDGE synthetic (black bottle). But I was seeing about a quart lost every 2500-3500 miles depending on how hard I drove it.

Anyway, a year later I took the motor out and inspected the internals for wear assessment. All looked well except this time I've dialed in my piston rings on the tighter side, (re-honed the cylinder for more precise cross-hatch), after that I'm now able to use 5w-30 (Castrol EDGE titanium synthetic, the gold bottle). I see about 1/4 quart loss in 6000-7000 miles now, and I catch about half a can of milk-shake in the oil catch from PCV breather. That's about as fully accountable as it'll get for managing oil during combustion dynamics. Bottom line is, do your homework on those numbers knowing how your gaps are set, and you can apply the right oil and right driving, your bearings will be in champ shape.

[Malteser_wfj]

I'll be honest I have no idea on the piston-to-wall clearances as I just left them to it and trusted their judgement.

I don't plan on running any more power soon (because I can't afford to lol) apart from possibly a light remap & sharpening up the throttle response.

I figured the thicker oil was due to larger clearances in the bearings and it generally offering better protective properties than the stock 5w-30 or whatever it is. They recommended I use Motul 300V for any track days or a Nurburgring trip etc with a 3000 miles change interval.

I plan on doing oil changes every 6000 miles or so and will stick with a good 5w-40. Either Motul LL-04 specific or a Millers CFS. With the low temp oil thermostat it's reaching no more than 90C with normal driving at the moment. I'll chat with the builders when I take it in for the final break in oil change and see what they think about the oil thickness with the lower than factory oil temps.


How were you able to re-hone the cylinder bores? I thought they had a coating that made it impossible to do without re-coating them?

[yupetc]

Originally Posted by Malteser_wfj

I'll be honest I have no idea on the piston-to-wall clearances as I just left them to it and trusted their judgement.

I don't plan on running any more power soon (because I can't afford to lol) apart from possibly a light remap & sharpening up the throttle response.

I figured the thicker oil was due to larger clearances in the bearings and it generally offering better protective properties than the stock 5w-30 or whatever it is. They recommended I use Motul 300V for any track days or a Nurburgring trip etc with a 3000 miles change interval.

I plan on doing oil changes every 6000 miles or so and will stick with a good 5w-40. Either Motul LL-04 specific or a Millers CFS. With the low temp oil thermostat it's reaching no more than 90C with normal driving at the moment. I'll chat with the builders when I take it in for the final break in oil change and see what they think about the oil thickness with the lower than factory oil temps.


How were you able to re-hone the cylinder bores? I thought they had a coating that made it impossible to do without re-coating them?

Honing it lightly will only scratch that coating just enough to get the cross-hatch. The coating is arc-welded, it's quite hard to totally remove it unless you sit there and hone the bejeezes out of it. And I use a sprung stone honing tool, a little more aggressive, but will keep the cylinder straighteness in control; and with each honing pass I was bore-gauging to make sure I'm not really taking much out.

The reason for honing again is because during my first build, I wasn't really paying much attention when I hone it the first time, basically went in and out a couple of times keeping that motion and angle of incidence. When I open it up to re-assess, I find all the hone patterns gone, I have some very shiny cylinder bores; so I gave it another scratch and actually paid more attention to CP's cylinder wall surface requirements.

On oil vis, do consult your builder and ask what's the acceptable range for the gaps, then ask where in that range did they gap your assembly in. You'll have 6 cylinders to work with, so I hope they gap them all closely enough to eliminate geometric variations.
* Rod bearing gap
* Crank bearing gap
* Piston-to-wall clearance
* All 2 piston ring gaps plus the oil ring gaps
With a good foundation, then you can figure out which oil vis you'll use. Basically the bigger the gap, the higher vis you'll want. Smaller the gap, you can use thinner vis. Stock BMW gap as a new motor will usually be on the tighter side, that's also why 5w-20 is their rec'd oil on a new motor. On newer B-series motor, you'll even see 0W-20 being stated on their book. The tighter gap is ideal for fuel economy and smoother rotational stability, but leaves a small oil film on the bearings and if things get squeezed in there, or if oil film is skippy, it'll heat up easily and quickly. Cooling is a big must on tighter fit motors. Our OEM bearings are bi-layer with a very thin babbit, so that's why it's so easy to toast our bearings: small gap and very hard layering on the bearing plus oil starvation. You have ACL race bearings, that's tri-layer with some specialized coating as a dry lubricant, and if they gap you on the bigger side, you can really tolerate some ponies under that horse carriage.

One last note is after the build and with everything up and running, make sure to monitor for oil loss with paranoia, seeing how oil behaves and taking note of compression ratio will help you determine how well the motor is built and define your starting line. After that, if economics permit, you'll be better situated to know what mods you can go into next.

[Will_460cs]

Originally Posted by yupetc

Looks to be another clean build. Enjoy the new life this N55 will breathe into. Very good choice of bearings as those ACL rod bearings are tri-layer, with a lot of give on the babbit layer, so you get to have a few skips on oil before you'll toast the bearings. So if there aren't any serious cause for oil starvation, you should be fine as long as you maintain that oil cleanliness. Seeing how you've settled on 5w-40 oil from the get-go, my guess is that after they've set the bearings and dialed the piston ring gaps along with piston-to-wall clearance, you're probably on the loose side of the fit, which is GREAT for a high power setup, a whole lot less frictional drag relatively speaking against the tight-fitters. In this setup, if you haven't done so, I'd also highly recommend that you make sure to have an oil catch can installed and monitored going down the road. I've built my N55 twice and with first build landing on the loose-fit side, I did catch myself losing engine oil through the PCV system due to higher blow-by and oil evaporative smoke within the crankcase. I was using 0W-40 Castrol EDGE synthetic (black bottle). But I was seeing about a quart lost every 2500-3500 miles depending on how hard I drove it.

Anyway, a year later I took the motor out and inspected the internals for wear assessment. All looked well except this time I've dialed in my piston rings on the tighter side, (re-honed the cylinder for more precise cross-hatch), after that I'm now able to use 5w-30 (Castrol EDGE titanium synthetic, the gold bottle). I see about 1/4 quart loss in 6000-7000 miles now, and I catch about half a can of milk-shake in the oil catch from PCV breather. That's about as fully accountable as it'll get for managing oil during combustion dynamics. Bottom line is, do your homework on those numbers knowing how your gaps are set, and you can apply the right oil and right driving, your bearings will be in champ shape.

Quick question when I did rod bearing on my N55, I got a clearance consistently of approx .38mm (which I thought was middle of the range), on OE replacement bearings. What oil grade would you suggest? (tune, larger intercooler, catless approx 380bhp)

[yupetc]

Originally Posted by Will_460cs

Quick question when I did rod bearing on my N55, I got a clearance consistently of approx .38mm (which I thought was middle of the range), on OE replacement bearings. What oil grade would you suggest? (tune, larger intercooler, catless approx 380bhp)

Did you also change out your crank bearings, too? And what clearance did you gap them if you did.

Also, what's your piston ring gap on first ring set and second ring set?

Lastly and most importantly, what oil are you using right now and with it, what's your oil loss rate? 1-quart per oil change, 2-quart per oil change, etc. And are you running oil catch cans to retain oil for PCV evaporative/pressure oil loss.


Gotta have the above questions cleared before I can really tell you.

The horsepower/mods you indicated are still on lower/streetable power figures. So unless you're dealing with oil loss or having to track your car much, going with the standard stuff should be fine on blind recommendation.

[Will_460cs]

Originally Posted by yupetc

Did you also change out your crank bearings, too? And what clearance did you gap them if you did.

Also, what's your piston ring gap on first ring set and second ring set?

Lastly and most importantly, what oil are you using right now and with it, what's your oil loss rate? 1-quart per oil change, 2-quart per oil change, etc. And are you running oil catch cans to retain oil for PCV evaporative/pressure oil loss.


Gotta have the above questions cleared before I can really tell you.

The horsepower/mods you indicated are still on lower/streetable power figures. So unless you're dealing with oil loss or having to track your car much, going with the standard stuff should be fine on blind recommendation.

Hi thanks for the reply, I have not changed RINGS/ main bearings etc. Just rod bearings and other maintenance.

Between 360-380, Large intercooler, remap and catless. Standard PCV no catch cans.Power is enough and I want be changing further. all maintenance done and no oil leaks.

So far It hasn't used any oil, presently running 5w-40 Miller CFS.

Let me know if anything else.

[yupetc]

Originally Posted by Will_460cs

Hi thanks for the reply, I have not changed RINGS/ main bearings etc. Just rod bearings and other maintenance.

Between 360-380, Large intercooler, remap and catless. Standard PCV no catch cans.Power is enough and I want be changing further. all maintenance done and no oil leaks.

So far It hasn't used any oil, presently running 5w-40 Miller CFS.

Let me know if anything else.

Looks like you've checked most boxes and are safe. Keep it leakless and you'll be fine. Looking at your location under your avatar, I've never been in UK, but assuming the latitude you are in the hemisphere, that's gotta be cold at times. Here's the last piece of the puzzle:

- With tune, I would assume you have the ability to change your engine cooling mode. At least through MHD you can, not sure of other can-tune options, or if you got an actual tuner, not sure what extent they can tinker with this. But if you're running any of the lowered coolant/temperature modes, you'll need to consider selecting lower viscosity oil just to get it a little more free-flowing because lower temps tend to thicken up your oil, that's resistance to flow and is bad for efficiency, and henceforth, performance and fuel economy; however, thicker oil is good for removing and carrying debris throughout the system, good for cleaning. Other benefits as I've mentioned in the forums is that thicker oil is better at smoothing out the rotating geometries, protection against low-end torque thrust on the bearing shells, and lastly, retain a better protection against oil film degradation in the gap. So that's your trade-off to consider.

- With mostly colder ambient environment conditions, engine warm up takes longer with higher viscosity oil, And with our N55's it can take extremely long on the 5w-40 oils, at least I noticed that much during the colder days here in Houston, TX. And we're nothing compared to UK in the extremities under a cold front. So I'd be more opinionated towards using lower viscosity again, something like 0w-30 would be my best bet. 0w so that upon startup, it'll lubricate your system sooner and better, also helps to warm up relatively sooner. "30" simply because if it's mostly cold out there, if your engine is fighting to stay hot, then a freer flowing oil is better than something thicker. I'm blindly and relatively suggesting out of my very personal opinion. So do your own research and see how you feel overall; ultimately you're the one dealing with it if any issues should arrive.

Lastly, referring back to how you've changed out the rod bearings only, and sounds like you have top notch maintenance done so far, though you're right dag in the middle of that OEM specification for bearing gap; believe it or not, factory N55's as they are being put together at the plant are gapped slightly on the tighter side, and henceforth the lower viscosity rating being recommended. Additionally, it's this smaller factory gap that contributes to that smoothness in engine operation; but the dagger is sharp on both sides, smaller gap provisions a more prone condition for heat generation, that's why though our rod bearings from the factory are fine the way they are, it's those intermittent or absolute absence of oil during starvation that causes the bearings to heat up very quickly and eat up the babbit layer quite soon, seizing up the rod bearing, the whole bit.

Anyway, 0.38mm probably isn't what you really meant, I work in imperial units, and by rule of thumb our rod's big end diameter is about 2.1 inch or so, and being a legacy hobbyist engine builder, something around 0.002 inch rod bearing gap is where I start, that translates to 0.05mm, I think you're referring to 0.038mm? Check my math as I've not done this in a long while since I have a baby boy on the rise and most my recent years are spent in child caring, much less in engine work. So I may be brain farting. If I recall correctly, in my experience, the tightest N55 rod bearing gap I've ever seen was 0.0012 inch, and that's measured with both mechanical gauges and confirmed using some plasti-gage. That translates to 0.028mm. Much smaller than your 0.038mm; and I'll also state this here: in my street racing days dealing in legacy American motors, I would never have dialed in at 0.001" bearing gap on a 2-inch rod end diameter. It's way too tight and not meant for racing applications. But since the N55 is a production car, I'm wanting to say that these tight clearances are why we're getting such smooth accelerating motors but at the same time, so easy to toast the rod bearings.

In summary, your gap at 0.038mm would be something I'd ideally gap my car, but since I have some forged internals in the mix, I've gapped mine in at around 0.045mm and I am using 0w-30 and 5w-30 oil on mine. With your gaps being smaller and your horse power figures are still very streetable, I'd finalize my opinion for you to set your oil on the thinner side of things, 5w-40 is too thick in my opinion unless you're tracking the car, running it at 215 deg-F constantly, or if you're just drag racing your car from every stop.

There are many schools of thought, I voiced mine, it's still your own job to do your research and fit what's right for you. Hope the best, buddy.

[Will_460cs]

Hi

Thanks for the response, as general note due to the Gulf Stream it’s allot warmer in the uk than equiverlent places on the same latitude. Unfortunately this can also mean we get allot of wet weather in winter months but snow is quite rare or fleeting particularly in my location.

I had a couple of questions and would welcome your input.

Cold starting

- my present understand is 5w viscosity is suitable for starts upto -30 or -22f, I would never use the condition below 2c or 36f

- I’ve always use the rational of 40w for superior temperature range, but given your comments perhaps 30w would offer better flow. I’ve worked on the belief that 30w and 40w are quite close together in any case / ir 30w is closer to 35w (if such a thing existed and 40w is like 39w (if such a thing existed)

What are you thoughts on mid saps vs full saps if the protection package is better with full saps?

You were quite right it was 0.038mm or approx 1.5 thou, I measure the old bearings and new with plastigauge all of them and they were all on this number a few photos attached.

[yupetc]

Originally Posted by Will_460cs

Hi

Thanks for the response, as general note due to the Gulf Stream it’s allot warmer in the uk than equiverlent places on the same latitude. Unfortunately this can also mean we get allot of wet weather in winter months but snow is quite rare or fleeting particularly in my location.

I had a couple of questions and would welcome your input.

Cold starting

- my present understand is 5w viscosity is suitable for starts upto -30 or -22f, I would never use the condition below 2c or 36f

- I’ve always use the rational of 40w for superior temperature range, but given your comments perhaps 30w would offer better flow. I’ve worked on the belief that 30w and 40w are quite close together in any case / ir 30w is closer to 35w (if such a thing existed and 40w is like 39w (if such a thing existed)

What are you thoughts on mid saps vs full saps if the protection package is better with full saps?

You were quite right it was 0.038mm or approx 1.5 thou, I measure the old bearings and new with plastigauge all of them and they were all on this number a few photos attached.

I'm surprised you'd bring up this topic regarding SAPS, nearly no one ever talks about it here since in the States SAPS weren't really point of focus. If it were me, AND if I know how well my engine blow-by performance is, I"d go full SAPS for longevity, and I"m assuming your car isn't purposed for track/race applications.

Plasti-gauge looks good.

Those pits on your bearing shells are originated from long term debris, as the debris settled into the babbit layering, over time and under thrust stroke in high load driving, the debris which "peeped their head out" above the babbit layer will gain higher temp than the bearing itself. I don't see a tremendous amount of heat stress in your bearings; but it does appear that the pitted holes are also associated with some of the wear happening on the shells. The babbit layer did its job in containing the debris and keeping it under control. That's because with little debris peppered across the bearing shell, most of the babbit layer are still in tact, if the babbit layer fails (and this will main be due to oil starvation events), you will see some scorch witness marks where the debris were; on same note, if that does happen, you won't be doing this maintenance check today, you're looking for a new build and possibly going plus 0.5 on your bearing size already. Anyway, your bearing shell pictures tell me that you've done a terrific job with maintenance, you've kept good oil film and have that oil do the work instead of letting the bearing shell babbit consume and end up with a seized/spun bearing. Great work.

And I also am in alignment with you on the 0w vs 5w and 30 vs 40. I do feel that they are only slightly differ and that difference there matters in your preference in how you select your oil. Neither of the oil in this range will get you in any sort of trouble as long as you stick with some good quality oil and consistent with maintaining the oil condition and level in the motor. Since you've established that in where you live, it does seem like your temps aren't that extreme, yeah, going higher vis may just be the right choice. I've long been using 5W-40 (Castrol EDGE), and I'm now using 5W-30 on my car for over a year already, all good, no issues stemming from the oil selection. The main reason I made this switch is because at Wal-Mart, I've been able to consistently purchase the 5w-30 at an discount, and the 5w-30 is the Castrol EDGE in their ultimate tier (the gold bottle). The 5W-40 (black bottled Castrol EDGE) didn't have too many promos throughout the year, and both kinds will end up around the same price in this mannerism. So I thought that's an upgrade for the same price and henceforth the switch. But I did notice that the gold bottle Castrol EDGE does a better job against oil degradation/evaporative loss than the black bottles (I monitor them through the oil catch can from the PCV vent pipe. So there's that. There are probably better and more exact names between the two types of oil I'm referring to, but it's late night and I don't really remember. I only know their difference due to their bottle colors, sorry about that.

I'll say though, our N55 motors do take their time to warm up in cold weather. My B58 in the 540i takes only 1/3 the time to warm up in 30 deg-F cold weather. Having noticed this difference is also why I'm leaning towards a lower vis oil if price tag allows, lol.

[Will_460cs]

Originally Posted by yupetc

I'm surprised you'd bring up this topic regarding SAPS, nearly no one ever talks about it here since in the States SAPS weren't really point of focus. If it were me, AND if I know how well my engine blow-by performance is, I"d go full SAPS for longevity, and I"m assuming your car isn't purposed for track/race applications.

Plasti-gauge looks good.

Those pits on your bearing shells are originated from long term debris, as the debris settled into the babbit layering, over time and under thrust stroke in high load driving, the debris which "peeped their head out" above the babbit layer will gain higher temp than the bearing itself. I don't see a tremendous amount of heat stress in your bearings; but it does appear that the pitted holes are also associated with some of the wear happening on the shells. The babbit layer did its job in containing the debris and keeping it under control. That's because with little debris peppered across the bearing shell, most of the babbit layer are still in tact, if the babbit layer fails (and this will main be due to oil starvation events), you will see some scorch witness marks where the debris were; on same note, if that does happen, you won't be doing this maintenance check today, you're looking for a new build and possibly going plus 0.5 on your bearing size already. Anyway, your bearing shell pictures tell me that you've done a terrific job with maintenance, you've kept good oil film and have that oil do the work instead of letting the bearing shell babbit consume and end up with a seized/spun bearing. Great work.

And I also am in alignment with you on the 0w vs 5w and 30 vs 40. I do feel that they are only slightly differ and that difference there matters in your preference in how you select your oil. Neither of the oil in this range will get you in any sort of trouble as long as you stick with some good quality oil and consistent with maintaining the oil condition and level in the motor. Since you've established that in where you live, it does seem like your temps aren't that extreme, yeah, going higher vis may just be the right choice. I've long been using 5W-40 (Castrol EDGE), and I'm now using 5W-30 on my car for over a year already, all good, no issues stemming from the oil selection. The main reason I made this switch is because at Wal-Mart, I've been able to consistently purchase the 5w-30 at an discount, and the 5w-30 is the Castrol EDGE in their ultimate tier (the gold bottle). The 5W-40 (black bottled Castrol EDGE) didn't have too many promos throughout the year, and both kinds will end up around the same price in this mannerism. So I thought that's an upgrade for the same price and henceforth the switch. But I did notice that the gold bottle Castrol EDGE does a better job against oil degradation/evaporative loss than the black bottles (I monitor them through the oil catch can from the PCV vent pipe. So there's that. There are probably better and more exact names between the two types of oil I'm referring to, but it's late night and I don't really remember. I only know their difference due to their bottle colors, sorry about that.

I'll say though, our N55 motors do take their time to warm up in cold weather. My B58 in the 540i takes only 1/3 the time to warm up in 30 deg-F cold weather. Having noticed this difference is also why I'm leaning towards a lower vis oil if price tag allows, lol.

Really interesting comments on the foreign debris. Did you notice the one shell (upper -3) that i individually photo), that was way worse than any others. My suspicion was that this was dues to misfires/knock events - is that plausible or do you think that one is also just worse affected debris?

Re Oil - I think in Europe and the Uk we perhaps have few more options, in the UK we have Millers OILs who also do oil testing. They produce allot of "boutique" products and most of the engine builders here like to use Miller CFS (which is a full saps oil and often ppl associate it a s race/trackday oil) with fantastic engine protection, but no certification and definitely not long life. In the Uk a BMW main dealer will service ON CBS so these car regularly have stupidly long oil changes and that is why my shells probably look like they do..
The arguments that I understand is that High Saps vs Mid relates has higher degradation on catalysts at cost of slight detrimental protection. I've never been able to get any data on this tho, or see anything..

[yupetc]

Originally Posted by Will_460cs

Really interesting comments on the foreign debris. Did you notice the one shell (upper -3) that i individually photo), that was way worse than any others. My suspicion was that this was dues to misfires/knock events - is that plausible or do you think that one is also just worse affected debris?

Re Oil - I think in Europe and the Uk we perhaps have few more options, in the UK we have Millers OILs who also do oil testing. They produce allot of "boutique" products and most of the engine builders here like to use Miller CFS (which is a full saps oil and often ppl associate it a s race/trackday oil) with fantastic engine protection, but no certification and definitely not long life. In the Uk a BMW main dealer will service ON CBS so these car regularly have stupidly long oil changes and that is why my shells probably look like they do..
The arguments that I understand is that High Saps vs Mid relates has higher degradation on catalysts at cost of slight detrimental protection. I've never been able to get any data on this tho, or see anything..

On SAPS you'll get degradation to the catalysts only if you're experiencing excessive oil loss through combustion into the exhaust. This can stem from worn piston rings which gets you high amount of blow-by into the PCV ducting, back to intake, into combustion, into exhaust, etc. You'll also get excessive oil loss through worn piston rings or compromised cylinder walls where oil gets lubed onto the cylinder walls, then piston rings do a bad job at scrapping the oil back down, letting that oil get through combustion then the exhaust. If I remember correctly, it's the sulfuric components after combustion of oil that gets the catalysts all gunked up, I am not a chemist, so correct me if you discovered else chemicals doing this harm. But whatever it'd be, it's the oil passing through that'll work against the catalyst; and that's why in my earlier post I refer to how a car driver need to know the health of their engine and oil loss characteristics to consider using full SAPS. Nowadays the bearing gaps and piston-cylinder wall clearances are on a much tighter tolerance for emissions and efficiency, you'll almost have no issues running full saps unless you're riding on a oil-leaky motor (internally). Our N55's when the valvecover is working well, has a good PCV oil catcher. And our factory spec'd piston-wall clearance and ring gaps are pretty tight. Like I was saying, if you're not losing oil just from operating the engine, I think you can run full SAPS without much worrying.

On your 3rd pic, it still doesn't reveal much semblance to misfire events, at least not from the way it looks to me. I see that's more of a long term wear on the thrust side is all. For knock associated wear, it has to have a very district heat-associated discoloration in mid-section or grind marks for me to say that, and I'm just not seeing it.