Aftermarket Parts Selection and Fitting
Rod Bearings
- ACL Standard size bearings. Part # 6B1569H-STD
- They have a solid reputation and are coated in the standard size. Can be purchased most anywhere from $100-200.
In the stock rod big end and stock crank, I achieved the following fitment:
Cyl #1 = .045mm
Cyl #2 = .051mm
Cyl #3 = .051mm
Cyl #4 = .045mm
Cyl #5 = .055mm
Cyl #6 = .051mm
The stock spec is 0.03 - 0.070mm. So, right in the middle. Happy with that.
Main Bearings
- ACL Standard size bearings. Part # 7M1532H-STD
- A lot of people sell them for ~$250. I bought them at Hack Engineering. Good people over there.
On the stock crank with stock main bearing bolts, I achieved the following fitment:
#1 = .051mm or slightly greater, depending on the day that I measured
#2 = .045mm
#3 = .045mm
#4 = .042mm
#5 = .051mm or slightly greater, depending on the day that I measured
#6 = .040mm
#7 = .040mm
The stock spec is .019 - .051mm. These numbers were all on the larger side and I'd say bearings #1 and #5 were slightly larger than spec. I've heard from several sources that this is common for #1. And it's well within the commonly held main bearing philosophy, especially with a performance engine.
Piston Rings
- NPR STD size 87mm. Part #120007004700.
- Bought these at Hack Engineering, as well. You should probably buy these from a reputable reseller. Highly critical part.
- These are generally believe to be the best, highest quality OE-like ring you will find, they are 1/10th the cost of BMW OE rings. The BMW OE rings are believed to be Mahle, but I could only find those being sold from the People's Republic of China with no reviews from reputable posters... anywhere. Nothing against China, but Japanese manufacturers are KNOWN for fantastic rings and there are a lot of reviews on the NPR rings from all over. NPR seems like the safest bet for stock-sized rings at the current time.
Ring #1 fitment:
- 0.35mm across every cylinder, out of the box.
- On the larger side, but stock spec is 0.02 - 0.35mm, so here we go!
- The stock, used rings #1 were at ~ 0.07mm - a lot of wear there!
Ring #2 fitment:
- 0.45 to 0.48mm across the board, out of the box. They were so tight across the board that depending on the time of measurement they were basically the same. So, I haven't filed any of them.
- Stock spec is 0.35 - 0.60mm, so well within stick spec.
- They are larger than ring #1 by > 0.05mm which is what you want for releasing gas pressure.
- The stock, used rings were > 0.8mm which is huge.
Ring #3 fitment:
- 0.30mm across the board, out of the box.
- stock spec is 0.25 - 0.50mm. They were on the lower side, but filing them is a huge pain and risky due to the "H" design.
- I phoned Hack Engineering about this fitment. They said they leave them and that they are within BMW's "conservative" specs, so send it. No problem, they said.
Other Ring Observations:
- Ring #1 is slightly narrower than the stock ring. See the image below. Hack Engineering noted this is known and presents no issues. By my calcs you have about 11% less surface area of the ring touching the ring land. How important that is, well, maybe only Mahle and NPR know?
- Ring #2 is exactly like the stock OE ring as far as I can tell.
- Ring #3 - the oil control ring - is very slightly different. There are more oil relief holes and they are slightly smaller. This seems like a good idea given the state of my OE oil control rings. They were clogged and caked in sludge. Though the motor appeared to burn no oil, so maybe it's not incredibly critical.
Fasteners:
Rod Bearings
- ARP M11-sized bolts. I have the early motor, so the M11 bolts come standard. Technically, they are reusable, if they go back into the exact hole they came out of. After passing them back and forth from the machinist there is no way I could guarantee this would happen. The machinist suggested I get the ARP bolts. I bought them and fitting them to the crank at the recommended 70 ft-lbs has yielded the clearances above. Pretty happy with that and I won't complicate the situation further.
- Reusable
Main Bearing Bolts
- Stock. I don't have a machined crank and the recommendation from several sources (including the machinist) was that stock bolts will cause the least possible issues. The main issue with aftermarket bolts is the clamping force will be different causing an out-of-round situation. This seems sound, but the downside is you only get one shot, so make sure everything is perfect a bunch of times with your old stock bolts and when you've crossed all your t's and dotted all of your i's go ahead and send it to 25NM + 50 degrees.
- One time use
Head Bolts
- ARP Studs. The name of the game is clamping force here. More is better, up to a point. Plus they're reusable. I see no downsides or risks here.
Head Gasket
- Cometic 0.040". $200. The stock head gasket is 0.027", but they round it up and call it 0.030". As I described above I removed 0.01" total between the head and the black surfacing. I don't really want to increase the compression from 11.5 to ~11.7 on Cali 91 pisswater, so likely I will lower it ever so slightly with the 0.040" Cometic gasket.
- Cool fact about Cometic - they'll make you basically whatever thickness you want, and won't charge you anymore for it. I toy'd with the idea of buying a .037" gasket from them, but that seemed like a risk I don't want to take. As I wouldn't want to test the first one they've ever made on this motor. So, off the shelf 0.040" it is!
Rod Bearings
- ACL Standard size bearings. Part # 6B1569H-STD
- They have a solid reputation and are coated in the standard size. Can be purchased most anywhere from $100-200.
In the stock rod big end and stock crank, I achieved the following fitment:
Cyl #1 = .045mm
Cyl #2 = .051mm
Cyl #3 = .051mm
Cyl #4 = .045mm
Cyl #5 = .055mm
Cyl #6 = .051mm
The stock spec is 0.03 - 0.070mm. So, right in the middle. Happy with that.
Main Bearings
- ACL Standard size bearings. Part # 7M1532H-STD
- A lot of people sell them for ~$250. I bought them at Hack Engineering. Good people over there.
On the stock crank with stock main bearing bolts, I achieved the following fitment:
#1 = .051mm or slightly greater, depending on the day that I measured
#2 = .045mm
#3 = .045mm
#4 = .042mm
#5 = .051mm or slightly greater, depending on the day that I measured
#6 = .040mm
#7 = .040mm
The stock spec is .019 - .051mm. These numbers were all on the larger side and I'd say bearings #1 and #5 were slightly larger than spec. I've heard from several sources that this is common for #1. And it's well within the commonly held main bearing philosophy, especially with a performance engine.
Piston Rings
- NPR STD size 87mm. Part #120007004700.
- Bought these at Hack Engineering, as well. You should probably buy these from a reputable reseller. Highly critical part.
- These are generally believe to be the best, highest quality OE-like ring you will find, they are 1/10th the cost of BMW OE rings. The BMW OE rings are believed to be Mahle, but I could only find those being sold from the People's Republic of China with no reviews from reputable posters... anywhere. Nothing against China, but Japanese manufacturers are KNOWN for fantastic rings and there are a lot of reviews on the NPR rings from all over. NPR seems like the safest bet for stock-sized rings at the current time.
Ring #1 fitment:
- 0.35mm across every cylinder, out of the box.
- On the larger side, but stock spec is 0.02 - 0.35mm, so here we go!
- The stock, used rings #1 were at ~ 0.07mm - a lot of wear there!
Ring #2 fitment:
- 0.45 to 0.48mm across the board, out of the box. They were so tight across the board that depending on the time of measurement they were basically the same. So, I haven't filed any of them.
- Stock spec is 0.35 - 0.60mm, so well within stick spec.
- They are larger than ring #1 by > 0.05mm which is what you want for releasing gas pressure.
- The stock, used rings were > 0.8mm which is huge.
Ring #3 fitment:
- 0.30mm across the board, out of the box.
- stock spec is 0.25 - 0.50mm. They were on the lower side, but filing them is a huge pain and risky due to the "H" design.
- I phoned Hack Engineering about this fitment. They said they leave them and that they are within BMW's "conservative" specs, so send it. No problem, they said.
Other Ring Observations:
- Ring #1 is slightly narrower than the stock ring. See the image below. Hack Engineering noted this is known and presents no issues. By my calcs you have about 11% less surface area of the ring touching the ring land. How important that is, well, maybe only Mahle and NPR know?
- Ring #2 is exactly like the stock OE ring as far as I can tell.
- Ring #3 - the oil control ring - is very slightly different. There are more oil relief holes and they are slightly smaller. This seems like a good idea given the state of my OE oil control rings. They were clogged and caked in sludge. Though the motor appeared to burn no oil, so maybe it's not incredibly critical.
Fasteners:
Rod Bearings
- ARP M11-sized bolts. I have the early motor, so the M11 bolts come standard. Technically, they are reusable, if they go back into the exact hole they came out of. After passing them back and forth from the machinist there is no way I could guarantee this would happen. The machinist suggested I get the ARP bolts. I bought them and fitting them to the crank at the recommended 70 ft-lbs has yielded the clearances above. Pretty happy with that and I won't complicate the situation further.
- Reusable
Main Bearing Bolts
- Stock. I don't have a machined crank and the recommendation from several sources (including the machinist) was that stock bolts will cause the least possible issues. The main issue with aftermarket bolts is the clamping force will be different causing an out-of-round situation. This seems sound, but the downside is you only get one shot, so make sure everything is perfect a bunch of times with your old stock bolts and when you've crossed all your t's and dotted all of your i's go ahead and send it to 25NM + 50 degrees.
- One time use
Head Bolts
- ARP Studs. The name of the game is clamping force here. More is better, up to a point. Plus they're reusable. I see no downsides or risks here.
Head Gasket
- Cometic 0.040". $200. The stock head gasket is 0.027", but they round it up and call it 0.030". As I described above I removed 0.01" total between the head and the black surfacing. I don't really want to increase the compression from 11.5 to ~11.7 on Cali 91 pisswater, so likely I will lower it ever so slightly with the 0.040" Cometic gasket.
- Cool fact about Cometic - they'll make you basically whatever thickness you want, and won't charge you anymore for it. I toy'd with the idea of buying a .037" gasket from them, but that seemed like a risk I don't want to take. As I wouldn't want to test the first one they've ever made on this motor. So, off the shelf 0.040" it is!
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