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  • SoCalE30M3
    started a topic Replacing rod (and possibly main?) bearings

    Replacing rod (and possibly main?) bearings

    Hi all,
    I have the S14 out of the car and on a stand for a mild refresh.
    The engine has around 120K miles on it and has been well cared for.
    In the last 8,000 miles, the previous owner had around $3,000 of work done to it. Head gasket, timing chain rails, chain tensioner, water pump and some other things.
    I've searched the various threads on rod bearing replacement but a few things are still unclear, or I'd like to confirm.

    1. What is the torque spec for the OEM rod bolts?
    2. Assembly lube on both sides of the bearings, or only the side facing the crank?
    3. What is the clearance range for the bearings?

    This seems fairly straightforward:
    1. Remove end cap.
    2. Push piston up a bit to allow rod side bearing to be removed.
    3. Install new rod bearings.
    4. Using the old rod bolts, torque to spec with Plastigauge to confirm sizing.
    5. If sizing is ok, lube bearings with assembly lube (both sides?), reassemble and torque with new rod bolts.

    The mains seems a little more controversial. With the engine out of the car, it does seem like it would be easy to simply tap the old bearing shells out from under the crank, and tap new ones in. There's many videos on Youtube of people doing that on various cars, and it seems to go smoothly.

    The issues I see with that are:

    1. It seems like there were many different sized bearing shells used in the assembly of each engine, presumably to "fine tune" the gap to a very narrow range. Yet, places like FCP sell main bearing kits that are just "standard" size. So that seems inconsistent. Will the bearings in the car have color codes that I can still see? If that's the case, should I check those and order that same color scheme? Not sure on that.

    2. Can the main bearing bolts be reused? (I know the rods can't, but the answer on the mains seems unclear).

    3. Is tapping the mains out from under the crank really as easy as it looks??

    Thanks very much!

  • Ironhead
    replied
    Originally posted by proctor750 View Post

    Yes I remember seeing you post that somewhere else now Thank You.

    "Connecting rod bearing clearance
    Standard classification: 0.0012-0.0027 in. 0.03-0.07 mm
    Double classification: 0.0008-0.0022 in. 0.020-0.055 mm"

    ^^ What's the double classification for? I know they did 3 colors for main bearings and 2 for rod bearings so which is which? Either way I fall into both but just curious which applies to me.


    Also: Doesn't that seem like a pretty large range? No saying it's wrong but it seems like a lot of slop for something like a rod bearing but I'm no machinist.

    Did anyone cringe torquing those poor caps to 70 ft lbs as ARP calls for? ouch
    I DO NOT understand the "Standard Classification-Double Classification" crap BMW uses....but you are well within either spec range. If it makes you feel better...I have done the bottom end assembly on two engines...and each time wound up with right around .0015" rod bearing clearance.

    And those are the BMW specs....I don't really think the range is "pretty large". Keep in mind the difference between the low and high range is just a bit more than a thousandth of an inch....well less than the thickness of a human hair.

    I used ARP rod bolts...but with Pauter rods. I tightened them with a stretch gauge...and IIRC the correct stretch was obtained at about 55 ft lbs....but if you are using ARP bolts with standard rods I have no doubt the values are different. Bottom line....do what ARP says....and make sure you use the exact lube they specify....and make sure the threads are clean. They made the bolts and know what they are talking about.
    Last edited by Ironhead; 03-30-2018, 11:41 AM.

    Leave a comment:


  • proctor750
    replied
    Originally posted by Ironhead View Post

    Con rod bearing clearances are here:


    http://m3guru.bmwe30m3.net/s14-rebuild-specs

    If you are at .0015"....you are good...right in the middle of the specs.
    Yes I remember seeing you post that somewhere else now Thank You.

    "Connecting rod bearing clearance
    Standard classification: 0.0012-0.0027 in. 0.03-0.07 mm
    Double classification: 0.0008-0.0022 in. 0.020-0.055 mm"

    ^^ What's the double classification for? I know they did 3 colors for main bearings and 2 for rod bearings so which is which? Either way I fall into both but just curious which applies to me.


    Also: Doesn't that seem like a pretty large range? No saying it's wrong but it seems like a lot of slop for something like a rod bearing but I'm no machinist.

    Did anyone cringe torquing those poor caps to 70 ft lbs as ARP calls for? ouch

    Leave a comment:


  • Ironhead
    replied
    Originally posted by proctor750 View Post
    "IIRC for rod bearings you want around .0015" give or take a few ten thou.."


    Can anyone confirm these numbers?

    I'm using the plastigage as a Go-NoGo gage so just need to be within spec. I'm a touch under .0015 on cyl 1


    Also- 70t lbs for the ARP seems nuts but I suppose a single torque method must be higher than a multiple torque method to avoid re-torque later. That and ARP's counsel probably suggested the highest allowable number for liability reasons...
    Con rod bearing clearances are here:


    http://m3guru.bmwe30m3.net/s14-rebuild-specs

    If you are at .0015"....you are good...right in the middle of the specs.

    Leave a comment:


  • proctor750
    replied
    "IIRC for rod bearings you want around .0015" give or take a few ten thou.."


    Can anyone confirm these numbers?

    I'm using the plastigage as a Go-NoGo gauge so just need to be within spec. I'm a touch under .0015 on cyl 1

    Click image for larger version  Name:	0015.png Views:	1 Size:	258.2 KB ID:	1269293Click image for larger version  Name:	0015 2.png Views:	1 Size:	409.5 KB ID:	1269294


    Also- 70t lbs for the ARP seems nuts but I suppose a single torque method must be higher than a multiple torque method to avoid re-torque later. That and ARP's counsel probably suggested the highest allowable number for liability reasons...

    Leave a comment:


  • JS154
    replied
    Originally posted by Ironhead View Post

    It is possible to replace the rod bearings with the engine in the car..on a race weekend in the rain in the paddock between qualifying and the race..but you will still have to do a lot of work on your back under the car while oil drips on your face (once you pull the oil pan, oil will drip for days), and trying to do precision/critical work like replacing rod bearings and checking clearances under these circumstances.....I dunno. Sounds like a bad idea to me.

    HTH
    Fixed it for you. :-/ Yep.

    To add to what others have said

    just replace the rod bolts with ARP
    use coated bearings
    you can do it in with the car on a lift if you know what you are doing
    drill an extra hole in the center of the bearings for better oil flow

    Leave a comment:


  • SoCalE30M3
    replied
    Hi Don,
    Small world, you were kind enough to take some of your time to speak with me on the phone a few weeks ago regarding the torque issues.
    I'm done, the engine is back in the car and runs beautifully. Thanks for your help, and thanks everyone else for your help too!

    Leave a comment:


  • MrMCar
    replied
    Late to the party here. There are 2 different posted specifications for the connecting rod bolt torque. There is the later version listed in BMW TIS, which is graciously hosted by bmw guru here: http://m3guru.bmwe30m3.net/s14-rebuild-specs

    If you click the torque specs on the right side of the page, then scroll down to 11-24 connecting rods and bearings. The newer spec given is 55Nm. Curiously the spec for the S38 connecting rod bolts are the older of: 5Nm, then 30 Nm and a 60° stretch. Both connecting rods are identical, as long as the weight class is the same.

    I still have the old spiral notebook, which lists the older specification of the three step method for the S38 (above) for BOTH connecting rod variants. We have been doing them this way since 1988. My thinking is thus: The older method is better as the final torque (of the newer method) can vary dependent on what lubricant is used on the threads. WD-40 to ARP rod bolt lube as an example. The ARP lube is very slippery and will result in a higher torque value applied to the bolt vs: that of a thin oil like the WD-40.

    Angle is more consistent and you end up with a better loading of the fastener. W/O the variables of which lubricant was chosen for the newer method.

    Rod bolts are a ONE TIME use.

    MrMCar

    Leave a comment:


  • SoCalE30M3
    replied
    Thanks for the offer, but I already have a set of ($400, ouch!) factory BMW standard shells to use.

    Leave a comment:


  • christsay
    replied
    I've got a full set of Blue Evo bearing shells that I didn't use for my rebuild, WPC coated if you were interested. I bought both red and blue and ended up only needing the red.

    -chris

    Leave a comment:


  • Ironhead
    replied
    Originally posted by SoCalE30M3 View Post
    As far as tapping in the bearings, see this video (you can start at 2:30)

    https://youtu.be/jHeO1h3U4GE?t=2m30s
    The only reason I can see to do that would be if you did not want to remove the crank....why not just remove the crank....?

    You will need the crank out to check clearances anyway....although I did not watch the entire video....short attention span again...

    Leave a comment:


  • Dave @nz
    replied
    Hi I would just like to add to Ironhead's good advice, with regards to bearing colours do yourself a favour as the best starting point buy BMW genuine set of Red big end bearing shells
    install them and palsti-gauge to target 0.0015-0.002” may have to buy and use some Blue shells as well.

    If you are going to do the main bearings I can not see any issue with following the tube video but would remove all the main caps at once that way the crank is only resting on the shells in the block and they can be monovered out and replaced one at a time with the aid of a credit card cut in strips to push the shell out bearing in mind that the crank won’t rotate due the timing chain is attached.

    Red main shells in the block and buy and try Blue in the main caps I think that would suit a used engine


    Leave a comment:


  • SoCalE30M3
    replied
    As far as tapping in the bearings, see this video (you can start at 2:30)

    https://youtu.be/jHeO1h3U4GE?t=2m30s

    Leave a comment:


  • Ironhead
    replied
    Here is a link with a bunch of stats that you will find useful. I have found them all to be correct:

    http://m3guru.bmwe30m3.net/s14-rebuild-specs

    Just ignore the "triple bearing classification" part.

    Sorry...for some reason I thought you were trying to do this with the engine in the car...apologies for not reading closely....my short attention span at work.

    I don't understand then the part about "tapping" the main bearings out. Once you remove the crank you should be able to pull out the main bearings with your fingers. The are kind of wedged in, but not very tightly. Same with the rod bearings.

    Regarding the discrepancy in rod bolt torque figures....I think you are right....it would make sense that the two methods would result in about the same preload.

    Leave a comment:


  • SoCalE30M3
    replied
    Thanks!

    Sorry for my long first post, stuff gets lost in it.

    But as I said, the engine is out of the car and on the stand. Stripped to the long block at this point.

    As far as torque for the rod bolts, I found conflicting info. In my Post 2 above, it says do it in stages - 7 ft lbs, then 22 ft lbs, then 60 degrees.

    In my Post 3 above (which also appears to be from a manual), it says torque to 55 nm (40 ft lbs). Not in stages, just straight to 55 nm.

    My guess is they end up being close to the same torque, but I'm not sure.

    As oil clearance for the rod bearings, what I've seen is - Big end oil clearance = 0.0009” – 0.0025” (0.0024mm – 0.064mm). I'd like to confirm that.

    Leave a comment:

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