Rod bearing failure. What now?

[sapote]

My nice, fresh, OE BMW (S85) crank, from when recently presented with the same dilemma:

They grind the corners at the journal meets the crank throw to a round radius to avoid stress-riser leading to crack. Don't see that on older cars.

[Obioban]

I'd inspect and, based on what is found, replace some combination of bearings, crank, and the rod that spun. Personally, I'd just buy a new OE BMW crank (in fact, I recently did, for my s85) if yours in damaged-- regrinds and used are too much of a roll of a dice for the money actually saved.

Option 3 is going to result in no meaningful gains and the car being a PITA the rest of the time you own it.

My nice, fresh, OE BMW (S85) crank, from when recently presented with the same dilemma:

[GreyM340i]

Doesn't BMW sell rebuilds for ~15k?

Edit: here ya go: https://parts.bmwnorthwest.com/p/BMW...000304349.html

Not a bad price

[Pklauser]

Doesn't BMW sell rebuilds for ~15k?

Edit: here ya go: https://parts.bmwnorthwest.com/p/BMW...000304349.html

[tlow98]

There is always this option: https://carbahn.com/product/s54-3-3l...ngine-rebuild/ Little expensive, but if I needed a new engine, would seriously consider this route. Lots of options for what kind of engine build you want.

Yeah this is kind of the ballpark. The most reasonable rebuild I found was about $10k.

[wahsm]

There is always this option: https://carbahn.com/product/s54-3-3l...ngine-rebuild/ Little expensive, but if I needed a new engine, would seriously consider this route. Lots of options for what kind of engine build you want.

[discoelk]

OP, I'd at least pull the pan/caps and see what's going on before planning out a full rebuild. The crank may be fine.

[tlow98]

Contrary to popular belief, for longevity, forged pistons are not the way to go. They have to expand more than cast and before heated up, they slap which lead to a quicker hour glass shape of the cylinder wall. It isn't going to happen for 10s of thpusands of miles and unless there's FI going into the engine, there's also no point. More performance typically does equal less reliability and that stands with forged pistons. Stock pistons will handle 600hp all day and it'll never be close NA.

yeah, I’m in board. I’m going that route. But there are no other cast options out there… only forged. Of those, the most reasonable are the ones I mentioned.

[Arith2]

Agreed. Next best from my research was the mahle forged units in stock sizes. That’s an especially good option as they come with rings for $1k all-in.

NPR rings are great for stock pistons. About $250 for those.

Contrary to popular belief, for longevity, forged pistons are not the way to go. They have to expand more than cast and before heated up, they slap which lead to a quicker hour glass shape of the cylinder wall. It isn't going to happen for 10s of thpusands of miles and unless there's FI going into the engine, there's also no point. More performance typically does equal less reliability and that stands with forged pistons. Stock pistons will handle 600hp all day and it'll never be close NA.

[tlow98]

i would use stock pistons if rebuilding for maximum longevity.

Agreed. Next best from my research was the mahle forged units in stock sizes. That’s an especially good option as they come with rings for $1k all-in.

NPR rings are great for stock pistons. About $250 for those.

[digger]

this was my thought process as well. And what I’m doing with my actual rebuild.

OP, take it all apart and measure everything. Then you’ll know where you stand. More than likely you’re cylinders and pistons/rods are fine. If that’s true, have your block honed and go from there. Rebuild the head.

if you need a new crank, source one. If not, great!

your rings are wayyyy out of spec by now. Mine were at double BMW’s biggest spec.

well, I should say I’m doing all of this myself. If you’re paying someone to do this that changes things a lot. And it will impart a lot of trust and cash on your part as well!

i would use stock pistons if rebuilding for maximum longevity.

[tlow98]

I'd need to see the time and money difference between options 2 and 3. But I'd probably try to go option 1 and if that's not available go straight to 3. Once you're changing engines, any incentive to stay close to OEM spec goes away for me. At that point, build it the way you want it, as if you only have to sell one of them to yourself (as opposed to 80 thousand of them to some marketing bell curve).

maw

this was my thought process as well. And what I’m doing with my actual rebuild.

OP, take it all apart and measure everything. Then you’ll know where you stand. More than likely you’re cylinders and pistons/rods are fine. If that’s true, have your block honed and go from there. Rebuild the head.

if you need a new crank, source one. If not, great!

your rings are wayyyy out of spec by now. Mine were at double BMW’s biggest spec.

well, I should say I’m doing all of this myself. If you’re paying someone to do this that changes things a lot. And it will impart a lot of trust and cash on your part as well!

[cornerbalanced]

Yeah that sucks but don't roll any more dice. If you want hotter cams, this would be that time. I'm in the warmup, drive it sensibly group and my car is creeping slowly up to 100k miles, which is why I'm trying to figure out the cams issue as well. And yes, the rockers price is a WTF in that discussion. That said, I only plan to have the engine open and available for that work once.

maw

Yeah, great point. I'd like for everything to be done once (correctly) and never have to think about it again...or at least for another 100-150k miles.

[maw1124]

Yeah, if it were up to me I'd replace them every 70-100k miles, although I'm a firm believer in frequent oil changes and I'm religious about warm-up procedures. Nevertheless, took a gamble, and it didn't work out in my favor.

Yeah that sucks but don't roll any more dice. If you want hotter cams, this would be that time. I'm in the warmup, drive it sensibly group and my car is creeping slowly up to 100k miles, which is why I'm trying to figure out the cams issue as well. And yes, the rockers price is a WTF in that discussion. That said, I only plan to have the engine open and available for that work once.

maw

[cornerbalanced]

Well, there you go no offense.

I'm one of the most uncautious owners, subcribing to the believe that the updated bearings (or what newer cars came with) can go 150k, but even I opted to do it before that mark, at 141k (in 2014).

Yeah, if it were up to me I'd replace them every 70-100k miles, although I'm a firm believer in frequent oil changes and I'm religious about warm-up procedures. Nevertheless, took a gamble, and it didn't work out in my favor.