[yupetc]

Originally Posted by Dynamics99

Dropped the pistons off Monday at the shop. The owner said crankshaft will be ready Friday and cleareances was checked for me.

Hopefully everything comes back normal and does not need a regrind.

That's awesome.

I've some new findings on my end, don't think this will apply to you, but it's something I've overlooked on my initial forged internals build:

I've realized there are some wear on the cylinder wall this time around because the first time I had the motor put together, I was able to gap my rings (CPT-3307PVD rings). I was able to grind some off to get my final target end gaps:
Top Ring: 0.018"
Second Ring: 0.023"
Oil Scrapers: 0.025"
(The above end gaps were as of May of 2022)

Forward to July of 2023, 20k miles later:
Top Ring: 0.023"
Second Ring: 0.029"
Oil Scrapers: 0.032"


It's apparent that the ring gaps have expanded over the course of 20k miles of abuse. I drove it hard the whole time. MHD calculated at 370hp and 420tq on stage 2 and 93oct pump gas only. I've also observed a very shiny cylinder surface to where I've dial-gauged it again to have found a 0.006-0.012" of circumferential loss. This is cylinder wall wear.

I'll have to attribute the above cylinder wear to my lack of precision on cylinder honing job. On CP's piston ring installation instructions, I'm supposed to follow a honing procedure and achieve a certain pattern and surface roughness value utilizing a 2-stage hone method. I didn't do any of thise, just took a three-prong stone scraper and went to work. But on this iteration of rebuilding it, I simply re-honed it manually again and gapped in a new set of CP piston rings. I know I best bring this to a shop and have them finalize the hone for me, but I'm afraid I'll be running out of the clearance between the piston and the cylinder. And I need this car back ASAP. So current plan is to button everything back and on the side, I'll be sourcing a salvageable short block and prep it. Upon next year, I'll take it apart again and bring the whole thing to the shop for stronger cylinder sleeves and get them to hone it for me. Anyways, this motor has never settled well with me in terms of reliability. I can put all forged internals in there, but with an unforged block, they also wear quickly.

All of this may not happen to you, but just keep in mind and avoid lessons learned from others like me. May save you some headache and guesswork.

[Dynamics99]

Originally Posted by yupetc

That's awesome.

I've some new findings on my end, don't think this will apply to you, but it's something I've overlooked on my initial forged internals build:

I've realized there are some wear on the cylinder wall this time around because the first time I had the motor put together, I was able to gap my rings (CPT-3307PVD rings). I was able to grind some off to get my final target end gaps:
Top Ring: 0.018"
Second Ring: 0.023"
Oil Scrapers: 0.025"
(The above end gaps were as of May of 2022)

Forward to July of 2023, 20k miles later:
Top Ring: 0.023"
Second Ring: 0.029"
Oil Scrapers: 0.032"


It's apparent that the ring gaps have expanded over the course of 20k miles of abuse. I drove it hard the whole time. MHD calculated at 370hp and 420tq on stage 2 and 93oct pump gas only. I've also observed a very shiny cylinder surface to where I've dial-gauged it again to have found a 0.006-0.012" of circumferential loss. This is cylinder wall wear.

I'll have to attribute the above cylinder wear to my lack of precision on cylinder honing job. On CP's piston ring installation instructions, I'm supposed to follow a honing procedure and achieve a certain pattern and surface roughness value utilizing a 2-stage hone method. I didn't do any of thise, just took a three-prong stone scraper and went to work. But on this iteration of rebuilding it, I simply re-honed it manually again and gapped in a new set of CP piston rings. I know I best bring this to a shop and have them finalize the hone for me, but I'm afraid I'll be running out of the clearance between the piston and the cylinder. And I need this car back ASAP. So current plan is to button everything back and on the side, I'll be sourcing a salvageable short block and prep it. Upon next year, I'll take it apart again and bring the whole thing to the shop for stronger cylinder sleeves and get them to hone it for me. Anyways, this motor has never settled well with me in terms of reliability. I can put all forged internals in there, but with an unforged block, they also wear quickly.

All of this may not happen to you, but just keep in mind and avoid lessons learned from others like me. May save you some headache and guesswork.

Ah, thanks for that. Just called the shop. They polished the crankshaft and checked the clearance. It comes back to 2 thousand of an inch which I think is within spec. Let me know or I can check with ISTA.

[yupetc]

Ideally, no more than 2-thou. Though with wear, you're allow up to 6-thou. I'm pulling these from top of my head, so double check me if you get the chance.

[Dynamics99]

Originally Posted by yupetc

Ideally, no more than 2-thou. Though with wear, you're allow up to 6-thou. I'm pulling these from top of my head, so double check me if you get the chance.

ISTA does not show me the rod bearing clearance/play. It shows me the main bearing at 0.020 - 0.046mm.

I found a post on M3:
https://www.m3post.com/forums/showthread.php?t=892838

It shows the minimum at 0.025 mm to 0.071. Could you double-check for me? I don't see any measurements for N55 rod bearing clearance with ISTA 4.32.15.

[yupetc]

Originally Posted by Dynamics99

ISTA does not show me the rod bearing clearance/play. It shows me the main bearing at 0.020 - 0.046mm.

I found a post on M3:
https://www.m3post.com/forums/showthread.php?t=892838

It shows the minimum at 0.025 mm to 0.071. Could you double-check for me? I don't see any measurements for N55 rod bearing clearance with ISTA 4.32.15.

Rod bearing clearance on the N55 isn't readily available on ISTA, at least not from what I can find. And certainly BMW color-coded bearing shells don't help. Looking back at my own notes, I used the old-school industry rule of thumb: 0.001" per every inch of journal diameter. So that'll place you at 2-thou inch of clearance. If I'm not crazy and still remember it right, BMW's rod bearing clearances from the factory are dialed at around 0.0015"-ish. Mind the amount of zeros in 0.0015". That's on a tighter fit, so engine oil should spec at 0w-20 through 5w-30 and no more.

You also will need to look into this from the oil angle, and this is where it's more of an art of guessing how well you can get that oil film in the bearing clearances. And be forewarned, do not take my opinion as your policy, only use it as a reference from someone who's done quite a few BMW engine builds. So here it goes:

If you have that rod bearing clearance below 0.002", you best go with some 0w-20, 5w20, or 0w-30 and 5w-30 viscosity engine oils. 0w for winter and 5w for summer.

If your clearance is dialed in between 0.002"-0.0035", you can use the 30 to 40 viscosity oils, and same thing, 0w for winter and 5w for summer.

From the above, the correlation you should pick up in your head is that the smaller the clearance, the less viscous your oil should be, that's for you to allow oil to better get through the gap and maintain the oil film you need to prevent wear. And if the gap is too big, then a thicker oil is preferred to fill the void. Then you're also looking at more parasitic power loss due to thicker oil and its resistance properties. On smaller gaps, you're looking at less resistive oil used and thus will better your fuel economy; however, the smaller this gap is, the easier it is to overheat in the event of oil film loss. For me, this is why I believe the N55 motors are so easy to have spun bearings because of the modernized rod bearing clearances being so thin, and there are plenty of instances for oil starvation with this engine. Once again, in our olden days, rod bearing clearances are generally about 0.001" per inch of journal diameter. On racing applications, you can go 0.0015" per inch, and extreme applications, you can go 0.002" per inch, and each time you open up that clearance, you'll have to be creative to fit the more viscous engine oil in it.

So, back to discussing the N55's OEM bearing clearance at 0.0015" when the motor is new and fresh, 20 and 30 viscosities are good; but once the motor is being banged around and oil sloshes in the pan, rod bearings will likely experience loss of oil film in the clearance; that's when wear happens most; and at same time it's getting heated up. When oil gets fed back in, it'll enable lubricity and also cool down again. One other commonality for the N55 motor is that there are plenty of PCV regulation and lack of oil baffling effect to prevent oil loss. When thinner engine oil is being used, it tends to vaporize more. That's when it's easier to lose oil through the PCV system and lessen the amount of oil in the oil pan, too. It takes a coincidence of many things at play to cause oil starvation, then rod bearing can seize up on the crank journal or get a spun bearing.

Hope all of the above will help you make your own assessment and decision.

[Dynamics99]

Thanks for the information. My FCP Euro parts are coming in today. Likely on the weekend I will be checking rod bearing clearance and let you know for each journal and type (main and rod).

[yupetc]

Originally Posted by Dynamics99

Thanks for the information. My FCP Euro parts are coming in today. Likely on the weekend I will be checking rod bearing clearance and let you know for each journal and type (main and rod).

Fingers crossed, hope all will go your way. And be very patient with it while you're at the phase of clearancing the rod bearing. This can be time consuming and redundancy is never a bad thing. The bore and dial gauges I use aren't the most expensive types. To get good confidence in measurement, on each rod and journal I measured 5 times and took an average or a good "feel" reading as my final number then subtract to get that clearance. I then use the plasti-gauge 3 times on each set to verify my measurement. I figured, once we assemble everything, it's a big pain in the ass to go back, so I didn't mind the repetition just so I can sleep well at night with those numbers.

[Dynamics99]

I got a used block where the walls are nice. My only concern is the front crankshaft seal has some marks on it.

I have attached pictures. Let me know what you think.

[fastboatster]

Somebody butchered it when replacing the front crank seal. No idea if this will hold the oil. I’d probably get another block but that’s just me

[Dynamics99]

Originally Posted by fastboatster

Somebody butchered it when replacing the front crank seal. No idea if this will hold the oil. I’d probably get another block but that’s just me

Decided to save my original block. It's at the shop to clean up the mess and get a honel

[bbnks2]

Originally Posted by yupetc

That's awesome.

I've some new findings on my end, don't think this will apply to you, but it's something I've overlooked on my initial forged internals build:

I've realized there are some wear on the cylinder wall this time around because the first time I had the motor put together, I was able to gap my rings (CPT-3307PVD rings). I was able to grind some off to get my final target end gaps:
Top Ring: 0.018"
Second Ring: 0.023"
Oil Scrapers: 0.025"
(The above end gaps were as of May of 2022)

Forward to July of 2023, 20k miles later:
Top Ring: 0.023"
Second Ring: 0.029"
Oil Scrapers: 0.032"


It's apparent that the ring gaps have expanded over the course of 20k miles of abuse. I drove it hard the whole time. MHD calculated at 370hp and 420tq on stage 2 and 93oct pump gas only. I've also observed a very shiny cylinder surface to where I've dial-gauged it again to have found a 0.006-0.012" of circumferential loss. This is cylinder wall wear.

I'll have to attribute the above cylinder wear to my lack of precision on cylinder honing job. On CP's piston ring installation instructions, I'm supposed to follow a honing procedure and achieve a certain pattern and surface roughness value utilizing a 2-stage hone method. I didn't do any of thise, just took a three-prong stone scraper and went to work. But on this iteration of rebuilding it, I simply re-honed it manually again and gapped in a new set of CP piston rings. I know I best bring this to a shop and have them finalize the hone for me, but I'm afraid I'll be running out of the clearance between the piston and the cylinder. And I need this car back ASAP. So current plan is to button everything back and on the side, I'll be sourcing a salvageable short block and prep it. Upon next year, I'll take it apart again and bring the whole thing to the shop for stronger cylinder sleeves and get them to hone it for me. Anyways, this motor has never settled well with me in terms of reliability. I can put all forged internals in there, but with an unforged block, they also wear quickly.

All of this may not happen to you, but just keep in mind and avoid lessons learned from others like me. May save you some headache and guesswork.

Forged pistons generally aren't very friendly to daily driving. The PTC clearance is greater to allow for more expansion. Stock cast hyper pistons call for <.001" PTC and forged pistons generally call for closer to .0025." This results is piston slap until the forged piston warms up.

If this engine is torn down I would ensure you CP pistons are coated. That may be the cause of your "shiny" cylinder walls. OR the cylinders walls are out of round. You used stock head bolts, right? No machine work just a hand hone or did you have the block bored out for bigger pistons? I find it hard to believe you used a hand sanding stone to bore out the block enough to fit an aftermarket forged piston. You may not have enough PTC clearance causing cylinder wear as the aftermarket forged pistons expand from heat. What was your final PTC?

I also wouldn't assume a change in .005" in ring end gap is due only to wear on the cylinder wall. Piston rings wear down as well and the ring end gap opens up a little as the rings conform to the cylinder walls.

[Dynamics99]

Okay,

I have a question. Is it possible to bore out an N55 0.50 over for an 84.50mm bore? I dropped the block off at the machine shop originally for a hone and clean. Just talked to the owner and he said if I'm getting forged pistons I would need to bore it out to 84.50mm which is also what the AMP44 site mentions. The AMP44 has a piston coating on the thrust side.

https://www.amp44.com/index.php?rout...&product_id=96

Here is the link to the piston. The PTC is 0.035-0.040mm. What are your thoughts? Should I just get a hone and use the original pistons or go with the AMP44 pistons since it's within budget?

[bbnks2]

Originally Posted by Dynamics99

Okay,

I have a question. Is it possible to bore out an N55 0.50 over for an 84.50mm bore? I dropped the block off at the machine shop originally for a hone and clean. Just talked to the owner and he said if I'm getting forged pistons I would need to bore it out to 84.50mm which is also what the AMP44 site mentions. The AMP44 has a piston coating on the thrust side.

https://www.amp44.com/index.php?rout...&product_id=96

Here is the link to the piston. The PTC is 0.035-0.040mm. What are your thoughts? Should I just get a hone and use the original pistons or go with the AMP44 pistons since it's within budget?

Yes, the block can safely be bored for larger pistons. Why though? Get stock sized pistons... You'll still need to bore and hone the cylinders walls for forged pistons because like I said above the piston to cylinder wall clearance needs to be 3-4x more than the stock hyper pistons.

[mym3isslow]

Originally Posted by Dynamics99

Update:

I did the rod bearings and I primed the engine 4 times. After running for about 1 minute and 15 seconds I started hearing loud knocking. It seems to be coming from the top but I'm sure that I spun a bearing or two. I drained the oil and there are no big-size chunks but a small amount of tiny flakes. I lubed the top and bottom bearings on the side that touches the crank.

When I put my hand on the fuel injector tubing I can feel it vibrate.

Also, my oil pressure during the knocking was around 41-44psi at idle.

Here is the MHD Log:
https://datazap.me/u/dynamics99/rod-...og=0&data=4-16



Should I check for bent valves, and lifters, or go straight for the rod bearings? I pray my crank is salvageable. Was priming the engine with lubed bearings, not the right choice? Could I have blocked the crankshaft galley from providing oil to the bearings?

Originally Posted by Dynamics99

Well,

Cylinder 1 Rod cap shot through the oil pan. Pulling the motor out and rebuilding it.

Do you know why this happened immediately after replacing the rod bearings? What are you going to do differently the second time around so that this doesn't happen again?

[Dynamics99]

Originally Posted by bbnks2

Yes, the block can safely be bored for larger pistons. Why though? Get stock sized pistons... You'll still need to bore and hone the cylinders walls for forged pistons because like I said above the piston to cylinder wall clearance needs to be 3-4x more than the stock hyper pistons.

Hi yes,

The cylinder will be bored and honed to accommodate 84.5mm pistons. The PTC will be also checked.

[Dynamics99]

Originally Posted by mym3isslow

Do you know why this happened immediately after replacing the rod bearings? What are you going to do differently the second time around so that this doesn't happen again?

It's completely my fault for under-torquing rod cap one. It gets upgraded rods with ARP bolts so the torquing procedure is much more simpler.

When I was under the car I couldn't get a good enough grip and the e torx would slip.

[whyzee125]

Originally Posted by bmw335ie90

What exactly are we calling 'bearing wear'? That pic on the second post shows mint condition bearings. All of the bearings from OP also look decent given the mileage.

N55s seem to seize from complete oil starvation not 'wear'. Go look at pictures of S54 and S65 if you want to see true bearing wear. Preventatively replacing bearings wont stop a seizure from total oil starvation.

Yes and no. While most suspect that they spin due to oil starvation (I think I agree btw), it's usually not an ongoing and sudden loss of oil. Something about the N55 seems to be a prime target for a lack of oiling but it usually happens over many low oiling events.

For example, whether it's OFHG changes, cold starts, hard right turns, whatever, it's usually not a mint set of bearings suddenly getting toasted but rather every set of bearings has enough in it to withstand x amount of these events and finally, usually around 80k miles, they give in and spin.

Having a fresh set of bearings gives you that buffer back for when you inevitably have an event where not enough oil is being fed to them.

[bmw335ie90]

Originally Posted by whyzee125

Yes and no. While most suspect that they spin due to oil starvation (I think I agree btw), it's usually not an ongoing and sudden loss of oil. Something about the N55 seems to be a prime target for a lack of oiling but it usually happens over many low oiling events.

For example, whether it's OFHG changes, cold starts, hard right turns, whatever, it's usually not a mint set of bearings suddenly getting toasted but rather every set of bearings has enough in it to withstand x amount of these events and finally, usually around 80k miles, they give in and spin.

Having a fresh set of bearings gives you that buffer back for when you inevitably have an event where not enough oil is being fed to them.

I would agree with you if the bearings people pulled out actually showed advanced wear at 60k-100k miles. All I see are normal bearing wear from people that pulled them preventatively, or total bearing failure with no in between.

[Dynamics99]

Originally Posted by bmw335ie90

I would agree with you if the bearings people pulled out actually showed advanced wear at 60k-100k miles. All I see are normal bearing wear from people that pulled them preventatively, or total bearing failure with no in between.

Prove me wrong but I have not seen many of the later N55 spin bearings. I know the models that received the upgraded baffle system and dual pickup seem robust.

[whyzee125]

Originally Posted by Dynamics99

Prove me wrong but I have not seen many of the later N55 spin bearings. I know the models that received the upgraded baffle system and dual pickup seem robust.

F chassis not as much, but a TON of the E chassis do, mostly 2011 but I think that's because the 12-13 models were only coupes and most opted for the 335is in that case.

[wheela]

Originally Posted by Dynamics99

Prove me wrong but I have not seen many of the later N55 spin bearings. I know the models that received the upgraded baffle system and dual pickup seem robust.

Interesting, I have not heard of this. Is the baffle system integrated into the oil pan or a seperate part? Do you have any p/n references for baffle or the dual pickup? I'm e-chassis, but my car is a 2015 model n55 (it's an e84 X1), I'm wondering how I can see if my engine has these upgrades?

[Dynamics99]

Originally Posted by wheela

Interesting, I have not heard of this. Is the baffle system integrated into the oil pan or a seperate part? Do you have any p/n references for baffle or the dual pickup? I'm e-chassis, but my car is a 2015 model n55 (it's an e84 X1), I'm wondering how I can see if my engine has these upgrades?

https://www.bimmerworld.com/Engine/B...-435i-N55.html

The baffle system is integrated into the oil pan. There is a secondary oil suction pump.

I doubt yours will have it. The N55 in the F87 M2 received this upgrade as well as the F26 X4 M40i.