ACL rod bearings?

[Green-Eggs]

Originally Posted by jimmtman

I would like to understand how you did the calculations to come up with the nominal clearances for H and HX. Can you give an example?

Here's a few other points that I missed the first time.

In my simple view of things the bearing thickness should be key for the clearance. ACL H from their website has a thickness of 1.998 mm. From the wiki the 702/703 have thicknesses of 1.9977 mm top and 1.9939 bottom. For ACL H the total thickness for 2 bearnings is 2*1.998 = 3.996 mm and for 702/703 it is 1.9977+1.9939 = 3.9916. So ACL H is thicker in total than 702/703 so I would think this means lower clearance. 088/089 is shown as 2.0028 mm top and 1.9977 mm btm so 4.0005 mm total. If this is right than 702/703 have more clearance than 088/089. H is slightly more clearance than the original 088/089 bearings which I think I have in my 2008 E93.

The HX thickness is given as 1.985 mm which is similar to BE's 1.9876 mm - smaller by 0.0026 mm. If did a mix of mixed set of H and HX the average thickness would be (1.998/2+1.985/2)=1.9915 mm - larger by 0.0039 mm than BE. From this HX looks closer to BE clearance than a mixed set.

It's time for that weekly reminder that the BE page only measured one set of shells. You shouldn't try to draw statistically meaningful conclusions from measuring a single set (e.g. 088/089's are thicker than 702/703's, and therefore have less clearance). Another factoid: when Bert measured those shells, he was using a ball-anvil micrometer. Today, he uses a much more accurate data-logging drop-indicator. Wouldn't it be great if Bert remeasured the shells with the drop indicator? Answer: yes, but don't hold your breath for it.

Hoping to understand how these clearances are calculated as I am confused as to how it is done. It sounds like ACL calculates the clearance some other way and often doesn't show that calcuation in their datasheets.

Thanks!

Jim

If ACL really does measure theoretical clearances differently, then they would be wrong. It's kind of like the guy on m4post who insisted that two different car accelerometer devices (VBox and Draggy) calculated slope differently.

[Helmsman]

Originally Posted by Green-Eggs

If ACL really does measure theoretical clearances differently, then they would be wrong. It's kind of like the guy on m4post who insisted that two different car accelerometer devices (VBox and Draggy) calculated slope differently.

I'd say according to attached spec they estimate clearance the same way as BE and everybody else i.e. (obviously) theoretical clearance based on their own known shell spec and assumes BMW crank spec. Although the later slightly different numbers vs BE's assumption.

Cheers

Ps. Attached spec is from ACL.

[Green-Eggs]

Originally Posted by Helmsman

I'd say according to attached spec they estimate clearance the same way as BE and everybody else i.e. (obviously) theoretical clearance based on their own known shell spec and assumes BMW crank spec. Although the later slightly different numbers vs BE's assumption.

Cheers

Ps. Attached spec is from ACL.

Yes, that's the point I was trying to make. BTW, King also has their own version of shaft diameter spec, which difference slightly from BE and ACL.

[jimmtman]

Originally Posted by Helmsman

Hi Jim!

As I probably mentioned earlier in this thread I went with extended clearance (HX) and ARP 625 bolts in July 2018, done abour 15.5k miles on them. FWIW, so far all good! (continue with 10W60, or course)

I see quite a few go with H/HX mixed sets today and to honest I'd probably do the same should I redo them. They still increase clearance a bit vs OEM, and to be fair majority of the OEM shells still run out there even with wear. So again, a tad more open I believe goes a long way while still maintain the essential even oil film pressure (which is jeopardized with increased clearance).

HOWEVER, mixing these shells must be done correctly. From what I understand some shops simply cut a H and a HX pack in half and sell off. You can read in threads from guys like Deansbimmer that the shells need to be measured in order to get the proper pair mixed and achieve targeted clearance. If you can't confirm this to be done I'd say just go with a H or HX set.

Regarding OEM bolts they are assumingly doing as good of a job as for instance ARP. The reason poeple are using them - and shops prefer them - is that OEM takes much more time due to its torque procedure. If thats fine with selected shop, go OEM (new bolts cause stretch) and save a few buck.

Good luck!

Thanks! With the HX bearings did you notice any change in engine performance? Did it feel like it had less power?

[jimmtman]

Hi folks - thanks for all of your replies!
Thanks Helmsman for the spec sheet on ACL that shows oil clearances.

I spoke to Robert at ACL Nashville again today about this. He said that PDF if the build sheet for the bearings - i.e. what range of oil clearances the bearning can withstand. It isn't necessarily the expected clearance. He said to calculate the expected oil clearance take the min and max of the shaft size and tunnel size and subtract off 2 bearing thicknesses to get the oil clearances. For H shells and taking all the permutations:

Min case 56-51.991-2x1.998 = 0.013 mm = matches PDF
56.013-51.991-2x1.998= 0.026 mm
56-51.975-2x1.998 = 0.029 mm
Max case 56.013-51.975-2x1.998 = 0.042 mm - PDF said 0.058
Ave case 56.0065-51.983-2x1.998 = 0.0275 mm

Using this simple method matches on the min reported but is a little low on the max reported. The average or median values are 0.026-0.029 mm. A little over 0.001".

Robert advised for this engine that 0.0015-0.002 inch oil clearance would be a good value - would be about 0.00075-0.001 inch per rod journal inch.

He also advised that in order to determine the oil clearance with good accuracy the crankshaft diameter and tunnel (rod bearing end that connects to shaft) be measured for the diameter and if they are circular. Was this done when you folks installed your bearings? Does Dean measure these parts? He said if the shaft or tunnel is out of the spec range given above then the bearings may not work and the engine might be in trouble. He said these parts have to be measured before can know whether to get H, HX, or a mixed set or if the shaft or tunnel are damaged they may have to be machined or replaced.

If the same calcs are done on the HX the min is 0.039 mm (matches PDF) and the max is 0.068 mm (reported is 0.084 mm). The average and median values are 0.052 mm to 0.055 mm. A bit over 0.002" the upper end of the range Robert gave.

A mixed set of H and HX would give about 0.0015" oil clearance - the lower end of the range Robert gave.

He also said that 90% of the orders he fills is for a mixed set of H and HX. The other 10% is either H or HX or a 0.25 mm oversize with a shaft that has to be machined down.

He said he would expect an installer to have a machine shop measure the shaft and tunnels before installing so very curious if y'all do this. He said without that it is just a guess if the right parts are going in. Truly if there is a problem with specs or damage then even well measured H/HX sets by Dean may not be the right size.

It sounds like mixed H/HX or HX would be ok from ACL's perspective. Curious what others think of that?

Another question. What is the downside of too big a clearance? I believe something with oil supply. A post said the oil pump is a variable rate pump and output increases if pressure is raised. What kind of pump is this - centrifugal or positive displacement? And is this oil pump a single speed? What is it driven by? if the clearance is larger then less resistence so the oil pressure would tend to fall if the pressure is not controlled in some way. If centifugal the oil flow would increase. If positive displacement the oil flow is constant but the pump would give whatever pressure the system was asking for. I am curious how the oil pump responds. Several folks have gone to HX and not have any issues with oil pump so probably fine.

Thanks!

Jim

[Green-Eggs]

Originally Posted by jimmtman

Hi folks - thanks for all of your replies!
Thanks Helmsman for the spec sheet on ACL that shows oil clearances.

I spoke to Robert at ACL Nashville again today about this. He said that PDF if the build sheet for the bearings - i.e. what range of oil clearances the bearning can withstand. It isn't necessarily the expected clearance. He said to calculate the expected oil clearance take the min and max of the shaft size and tunnel size and subtract off 2 bearing thicknesses to get the oil clearances. For H shells and taking all the permutations:

Min case 56-51.991-2x1.998 = 0.013 mm = matches PDF
56.013-51.991-2x1.998= 0.026 mm
56-51.975-2x1.998 = 0.029 mm
Max case 56.013-51.975-2x1.998 = 0.042 mm - PDF said 0.058
Ave case 56.0065-51.983-2x1.998 = 0.0275 mm

Using this simple method matches on the min reported but is a little low on the max reported. The average or median values are 0.026-0.029 mm. A little over 0.001".

Robert advised for this engine that 0.0015-0.002 inch oil clearance would be a good value - would be about 0.00075-0.001 inch per rod journal inch.

He also advised that in order to determine the oil clearance with good accuracy the crankshaft diameter and tunnel (rod bearing end that connects to shaft) be measured for the diameter and if they are circular. Was this done when you folks installed your bearings? Does Dean measure these parts? He said if the shaft or tunnel is out of the spec range given above then the bearings may not work and the engine might be in trouble. He said these parts have to be measured before can know whether to get H, HX, or a mixed set or if the shaft or tunnel are damaged they may have to be machined or replaced.

If the same calcs are done on the HX the min is 0.039 mm (matches PDF) and the max is 0.068 mm (reported is 0.084 mm). The average and median values are 0.052 mm to 0.055 mm. A bit over 0.002" the upper end of the range Robert gave.

A mixed set of H and HX would give about 0.0015" oil clearance - the lower end of the range Robert gave.

He also said that 90% of the orders he fills is for a mixed set of H and HX. The other 10% is either H or HX or a 0.25 mm oversize with a shaft that has to be machined down.

He said he would expect an installer to have a machine shop measure the shaft and tunnels before installing so very curious if y'all do this. He said without that it is just a guess if the right parts are going in. Truly if there is a problem with specs or damage then even well measured H/HX sets by Dean may not be the right size.

It sounds like mixed H/HX or HX would be ok from ACL's perspective. Curious what others think of that?

Another question. What is the downside of too big a clearance? I believe something with oil supply. A post said the oil pump is a variable rate pump and output increases if pressure is raised. What kind of pump is this - centrifugal or positive displacement? And is this oil pump a single speed? What is it driven by? if the clearance is larger then less resistence so the oil pressure would tend to fall if the pressure is not controlled in some way. If centifugal the oil flow would increase. If positive displacement the oil flow is constant but the pump would give whatever pressure the system was asking for. I am curious how the oil pump responds. Several folks have gone to HX and not have any issues with oil pump so probably fine.

Thanks!

Jim

The clearance range on the specs are the expected clearances that you will receive if every part is within tolerance. The ACL spec gave the tolerance ranges, so of course the actual clearances should fall within that same range; but there are some caveats that go along with that. The previous comment depends on having rod bolts without bore distortion and bearing shells that don't cause too much crush. Both of those will influence actual clearance and may cause them to deviate from the expected clearance range on the specs.

Most of your questions can be answered in the bearing wiki link I gave you. Everything from the math behind the clearance calculations, to the type of oil pump and how it works. I know that thread is hundreds of pages long and it may be hard to find the info...but it should all be in there. The guys who know this information no longer come to the forums. So you might find it hard to get this information from anybody here today and you might have to wade through that monster thread for the answers.

Until now, you're asking about theoretical clearances, not how to calculate actual clearances. The two are different. Calculating actual clearances is very simple but requires the engine to be disassembled. Unless you have the engine almost entirely disassembled, you can't measure the rod big-end bore -- which is what you need for this calculation. Therefore, you must remove the connecting rod, install the shells, torque them to specification. Using a highly accurate bore gauge, measure the bore at 90-degrees from the parting line. Measure the rod journal with a highly accurate micrometer. Subtract the rod journal diameter from the bore size. The difference is your actual clearance. This is how every race shop does it.

The downside of too much clearance is a blown motor. If there's too much clearance, then you will increase flow, but lose pressure. Even though you have a variable rate oil pump, it might not keep up. If that happens, you'll get metal-to-metal contact with the bearing and rod journal. Eventually, the metal-on-metal contact will cause enough damage to either the bearing or the journal that you'll blow the motor. This isn't unique to the S65, it can happen on any motor.

I can see exactly where your calculations went wrong. You assumed that the bearing shell thickness doesn't have a variance -- when it does. The spec only gave you the MAX shell thickness. Use that same formula using the max clearance to solve for MIN shell thickness. Then use that min shell thickness in your calculation to confirm that you will now equal the MAX clearance spec on their PDF. Even though this shell doesn't have a coating, bearings with coatings should be accounted for in these calculations as well -- as should bearings with different upper and lower shell thicknesses.

When the ACL guy recommends anything from OEM clearances and up -- that's a clear sign that you should seek advice elsewhere because recommending OEM clearances isn't good advice when you've already said that you believe this engine has a clearance problem.

Good luck.

[Green-Eggs]

Originally Posted by jimmtman

Several folks have gone to HX and not have any issues with oil pump so probably fine.

Thanks!

Jim

A few weeks ago, a guy reported a blown motor with pure HX shells. I believe that he had tens of thousands of miles on the engine, which would imply that the failure wasn't related to installation error. However, as of when it was reported a few weeks ago, he hadn't root caused the failure, so it's too soon to know exactly what caused it.

[Helmsman]

Originally Posted by Green-Eggs

A few weeks ago, a guy reported a blown motor with pure HX shells. I believe that he had tens of thousands of miles on the engine, which would imply that the failure wasn't related to installation error. However, as of when it was reported a few weeks ago, he hadn't root caused the failure, so it's too soon to know exactly what caused it.

Interesting, was this reported on M3post or somewhere else?

[Helmsman]

Originally Posted by jimmtman

Min case 56-51.991-2x1.998 = 0.013 mm = matches PDF
56.013-51.991-2x1.998= 0.026 mm
56-51.975-2x1.998 = 0.029 mm
Max case 56.013-51.975-2x1.998 = 0.042 mm - PDF said 0.058
Ave case 56.0065-51.983-2x1.998 = 0.0275 mm

Jim

As Green Egg says you've left out the actuall shell variance, which ACL quote to be 0.008mm iirc.

[Helmsman]

Originally Posted by jimmtman

Thanks! With the HX bearings did you notice any change in engine performance? Did it feel like it had less power?

No, there are no changes in the perfromance after RB replacement.

[Green-Eggs]

Originally Posted by Helmsman

Interesting, was this reported on M3post or somewhere else?

Reported on FB.

[Helmsman]

Originally Posted by Green-Eggs

Reported on FB.

You have a link?

[Green-Eggs]

Originally Posted by Helmsman

You have a link?

No link. But I can say that it was either the E9x V8 group, or the S65 & S85 rod bearing group because those are the only two that I read.

[Helmsman]

Originally Posted by Green-Eggs

No link. But I can say that it was either the E9x V8 group, or the S65 & S85 rod bearing group because those are the only two that I read.

Thanks mate. Not a FB user but will try to track it down.

[jimmtman]

Hi folks - I made a couple calls today.

First one was to Dean at mporium in Tx. We talked about their mixed ACL H/HX solution that also includes WPC treatment. Their target oil clearance is 0.0024 inch with tolerance of +/- 0.0001 when all said and done. This is pretty much the same clearance as BE. They have been doing this mixed solution since 2017-2018 and have installed over 500 of these in their shop there. He said this should be a one and done solution to where other engine parts (like main bearings) would likely go first.

Second call was to the performance shop in PA that my indi mechanic knows. They have done 70-75 rod bearing jobs on S65 and S85 over the last 2 years. They have been using ACL H size. Their engine builder said that there isn't much hard data out there that BE or ACL H/HX is a one and done solution and never have to do again. He says the bearing is very narrow compared to others (including previous BMW engines) and that may be a factor in keeping it with a good oil layer. He is advising his customers to consider the rod bearing as a wear item similar to say a timing belt and to replace it every 60-80k miles. I believe BMW now says to replace RB every 70k miles. He sees ACL H as superior to the OEM bearing and cheaper so he uses that but for it to be changed in 60-80k miles.

He may make a good point here....how much hard data is there that BE and ACL H/HX are a lifetime solution? I sent an email to BE to ask them this question.

Robert the ACL tech guy said he has seen ACL rod bearings inspected after 10-12 years of hard racing and looking pretty much like new. He thinks this is a lifetime fix.

In general I don't hear of RB bearing a wear item in other engines....perhaps because the clearance is larger.....perhaps the RB are wider (if this is a real thing)....perhaps something else?

[Assimilator1]

That's the whole rod bearing rabbit hole you're about to disappear down there!
Some other high revving engines are known to have narrow bearings too, but I forget what car.

I believe BMW now says to replace RB every 70k miles.
Where did you see that?

[jimmtman]

Originally Posted by Assimilator1

That's the whole rod bearing rabbit hole you're about to disappear down there!
Some other high revving engines are known to have narrow bearings too, but I forget what car.

I believe BMW now says to replace RB every 70k miles.
Where did you see that?

My indi mechanic who worked at BMW said that. I did not try to verify that by searching for it. He sent me RB pictures of a M6 with 60k miles and the aluminum/tin bearings showed alot of wear. I could try to post them if anyone is interested.

[pbonsalb]

I would base the 2nd replacement on how the originals looked at the mileage they were replaced, regardless of clearance or extra clearance. Clearance is certainly the leading theory on premature bearing wear on these motors but until about 100 replaced sets of extra clearance bearings have been pulled to inspect at 50-100k miles, the jury is still out and I would plan for a 2nd replacement. Were I replacing bearings in one of these motors today, I would specify extra clearance bearings — I think it makes sense to use them given that factory clearance is at the narrow extreme end of the range and BMW specifies just about the thickest mass production car engine oil available.

[Assimilator1]

Originally Posted by jimmtman

My indi mechanic who worked at BMW said that. I did not try to verify that by searching for it. He sent me RB pictures of a M6 with 60k miles and the aluminum/tin bearings showed alot of wear. I could try to post them if anyone is interested.

We've got a thread here where people post rod bearing photos from e9x M3s, their might be a separate thread for M6s?
Anyway, I can imagine they don't look good!

AFAIK their is no official bearing change interval for the M3 e9x (but I think their might be for M3 e46??), when newTIS was available I saw nothing about rod bearing changer intervals there and I've never come across anyone else showing that either from BMW.
Many indie garages recommend changing them at varying intervals beyond 50k miles due to the same line of thought as pbonsalb mentions above, which is understandable, if possibly a little over cautious.

I changed mine at 75k miles and they were in a rough state (I posted pics), the upper shells were showing a lot of copper and 2 had blue/purple streaks where they had got very hot!
So if I decided 50k was a safe mileage to inspect the new ones at, at an expected mileage of 3k/yr (it's not my DD) that would be 16yrs into the future! , so as you can see I can happily sit back and wait to see how other peoples fare!

[jimmtman]

Originally Posted by pbonsalb

I would base the 2nd replacement on how the originals looked at the mileage they were replaced, regardless of clearance or extra clearance. Clearance is certainly the leading theory on premature bearing wear on these motors but until about 100 replaced sets of extra clearance bearings have been pulled to inspect at 50-100k miles, the jury is still out and I would plan for a 2nd replacement. Were I replacing bearings in one of these motors today, I would specify extra clearance bearings — I think it makes sense to use them given that factory clearance is at the narrow extreme end of the range and BMW specifies just about the thickest mass production car engine oil available.

Very wise advice.....I think this is best approach....put in extra clearance and look for picture updates on how they fair to determine if this is truly a forever fix or not. If I don't own the car 50k miles in the future I suspect the next owner would have more peace of mind if the RB were replaced with extra clearance quality parts such as ACL mixed or BE.

[jimmtman]

Originally Posted by Assimilator1

We've got a thread here where people post rod bearing photos from e9x M3s, their might be a separate thread for M6s?
Anyway, I can imagine they don't look good!

AFAIK their is no official bearing change interval for the M3 e9x (but I think their might be for M3 e46??), when newTIS was available I saw nothing about rod bearing changer intervals there and I've never come across anyone else showing that either from BMW.
Many indie garages recommend changing them at varying intervals beyond 50k miles due to the same line of thought as pbonsalb mentions above, which is understandable, if possibly a little over cautious.

I changed mine at 75k miles and they were in a rough state (I posted pics), the upper shells were showing a lot of copper and 2 had blue/purple streaks where they had got very hot!
So if I decided 50k was a safe mileage to inspect the new ones at, at an expected mileage of 3k/yr (it's not my DD) that would be 16yrs into the future! , so as you can see I can happily sit back and wait to see how other peoples fare!

Thanks - I will certainly take photos of the bearings as they come out.

[jvictormp]

I'll be the next to use ACL bearings.

I've used BE Bearings in my last engine. Zero problems with them, they looked flawless when the rod broke due to hydrolock, after 6000km.

But now I spent all the money buying a new engine and won't have for the bearings

Just bought the H-STD.