Has anyone done this procedure on a 740IL? Please let me know if there is a post somewhere. Thanks.

this isnt a simple diy. this requires completely disassembling the engine.

this isnt a simple diy. this requires completely disassembling the engine.

+1

Definitely not a job for the faint of heart or mechanically uninclined.

not to mention youll need machining work done

Is there something special about the 740 engine preventing you from changing the rod bearings by just dropping the pan?

didnt know u can change pistons from removing the oilpan. but perhaps im confused to even what the OP is saying.

I assumed he meant piston-rod bearings rather then pistons and rod bearings.

On the BMW 6's you can change the rod bearings from below by just dropping the oil pan.

oh than it doesnt seem that bad of a job

well, it is complicated, because you have a crossmember that is located directly below the oil pan and the positive battery cable would have to be removed too, then depending on what piston was affected you might need to remove the oilpump.

I would pull out the engine and:
A- completely re-build it
B- buy a salvage engine

I am in the middle of a similar project and I am considering on getting a salvage engine.

Yeah, just drop the pan, drop the oil pump, rotate the crank, and change the piston rod bearings, but how difficult is it to pull out the piston rod bolts? Please let me know.

You can still rotate the engine by hand to get to the "big end" bolts

Thanks for the reply. Yeah, but I don't think they'll just pop out. I am just worried that I need to press them out with a special tool. I wonder if you can use a rubber hammer to pop out the old bolts.

I was looking at Bentley, and I couldn't find any references to the piston-rod bearings. Is it just me, or did Bentley neglect to include this?

Commonly termed "big end" bearings, these are on the bottom end of the connecting rod (conrod) on the crankshaft. The upper end of the conrod connects to the piston through gudgeon pin bearings. The big end bearing caps are removed by undoing two nuts - the bolts are captive in the conrod and they will come out when you remove the conrod, there's no need to try to knock them out. If you have had a bearing failure (hence the desire to change the bearings, I assume) you may need to have the crankshaft journals machined to restore the bearing surfaces, and then install undersize bearings to suit the new journal diameter. If this is the case, then you'll need to remove the engine anyway because there's a lot of stuff which has to be pulled apart to allow removal of the crankshaft!

First, thank you so much for the reply.

I am not having problems with the bearings at all, but these bearings should be changed every 100,000 miles. I think the dealer recommends 50,000 miles.

I've been under there before, and I have changed piston-rod engine bearings twice on different cars.

Bentley doesn't make a reference to them, and I can't find a diagram anywhere.

I am just wondering if the bolts used in BMWs are stretch bolts or on the alternative more like ARP bolts that do not need to be changed at all.

I also need torque specs for the nuts that will go onto these bolts.

I don't like soft piston-rod bearings, although they are better for the piston rods. What are the brands of piston-rod bearings do you recommend?

If you look at the wonderful phots provided, he has the entire front suspension out. WHY???

All you have to do is drop the oil pan, remove the oil pump, and you're right there. What's up? What am I not seeing?

Please let me know.

I am not having problems with the bearings at all, but these bearings should be changed every 100,000 miles. I think the dealer recommends 50,000 miles.

Where did you get your information from? Rod bearings are not a typical maintenance item. I've never seen them done here except on an E46 M3 (rod bearing recall), and once on a E39 M5 that spun a bearing.

Most engines go their entire life and never have to rod bearings replaced. And dealers do not recommend changing them at 50k, that's absurd.

To echo White94RX, This is a colossal waste of time. If you have knocking noises from the crank, then investigate. Bearings are not a maintenance item. Their lifespan is essentially infinite given sufficient oil pressure. Soft bearings is a curious comment. All journal bearings are made with a "soft" layer of babbitt to prevent scoring the crank in the event of a minor rub.

Replacing them without cause is likely to cause more problems than it could solve. Cleanliness is paramount, assembly must be dead on to prevent a rub & destruction of the bearing. Clearances must be checked with specialized tools, etc. If you have a damaged rod bearing, you'll know it. The knock is unmistakable.

By your info, my wife's 300,000 mile Honda should have had three bearing changes by now.

I'm not sure why he took the whole suspension out. On the 3, you only have to lower the front sub-frame.

I wouldn't replace the rod bearings unless you have an issue. I'm considering replacing them because I have a problem with low oil pressure at hot idle.

If there is a knocking noise, it is highly probable that the crank has suffered some damage.

Changing the piston-rod bearings isn't a big deal. You don't need sophisticated instruments to measure tolerance levels. "sigh"

If you have a hard driving style like I do, or if you drive your car with a heavy load (car pool of 5 people weighing 200lbs each on average) on a constant basis, it is a good idea to change out the piston-rod bearing every 100,000 miles.

If you are a hardcore grease monkey like me, piston-rod bearings are a maintenance item. :buttrock

Now I'm confused by your last post, BMMERFEST. Your OP asked for advice on changing conrod bearings, now you seem to be saying changing them is no big deal. Was there a knocking noise, and this is why you are driven to change your bearings?? Are you agreeing that there is likely to be crank damage? Are you ignoring the advice of others here who say big end bearings are not a "maintenance" item? Driving style and load has hugely less effect on big end bearing wear than poor maintenance, infrequent oil changes, or low oil pressure or oil level. Taxis commonly carry 5 heavy passengers, have frantic stop and go driving all their lives, yet do half a million km or more without ever having the engine pulled down for big end bearing "maintenance". BUT - your fun if you want to do it .....

Now I'm confused by your last post, BMMERFEST. Your OP asked for advice on changing conrod bearings, now you seem to be saying changing them is no big deal. Was there a knocking noise, and this is why you are driven to change your bearings?? Are you agreeing that there is likely to be crank damage? Are you ignoring the advice of others here who say big end bearings are not a "maintenance" item? Driving style and load has hugely less effect on big end bearing wear than poor maintenance, infrequent oil changes, or low oil pressure or oil level. Taxis commonly carry 5 heavy passengers, have frantic stop and go driving all their lives, yet do half a million km or more without ever having the engine pulled down for big end bearing "maintenance". BUT - your fun if you want to do it .....

I think you're confusing the main bearings with piston-connecting-rod bearings. Even if you need to change the main bearings that are on the crankshaft, you do not need to take out the engine. All you need to do is drop the oil pan, remove the oil pump, remove the lower part of the piston-connecting-rods, then loosen the lower part of the main bearing fasteners on the crankshaft, lower the crankshaft, then replace the main bearings. While you are reassembling, you can replace the bearings, conrod bolts and nuts of the piston-connecting-rods.

Changing the piston-connecting-rod bearings is preventive. I am saying that by the time the engine is making this notorious knocking sound, it may be too late to salvage the crankshaft; in which case, you are looking at more labor and "machine" work than otherwise necessary.

Any serious grease monkey can change the piston-connecting-rod bearings, bolts and nuts on a lazy Saturday afternoon. I am just saying this. Don't wait until the crankshaft is ruined because of one piston-connecting-rod bearing at the #1 position. The other seven may be fine, but you may have to do an engine swap because of one bad bearing.

I am just saying that it could be a maintenance item for some of us and not all of us. For those who have done it, the change is considered easy.

No, my M60 is not knocking, and I hope none of your engines will knock. :buttrock

Uhuh, I am pretty familiar with the difference between main bearings and conrod bearings ..... I'd love to see you drop the crankshaft out without removing the engine. What about the big lump of flywheel hanging off the back of the crankshaft which is still connected to the gearbox? And the timing chains hanging off the front end ... and the accessory drive belts ....
So your M60 is not knocking, your oil pressure is fine, but you still want to spend a lazy Saturday afternoon replacing conrod bearings ..... good luck.

If your oil pressure is normal changing either the main or rod bearings is a colossal waste of time, because they are not worn. I have been driving an 87 325i with bad main and rod bearing from coolant contamination that was knocking horribly for thousands of miles. I just took the crank out and it looks almost perfect, only the bearings were beat up.

Good on ya, Hustler! nothing like running for thousands of miles with a bearing knock! What was YOUR oil pressure like? And do you have a calibrated eyeball - coz I reckon if your bearings are beat up, you might have a thou or two out of round on your conrod bearing journals too, despite the fact that they might LOOK almost perfect.......
Incidentally, did you manage to get the crankshaft out without pulling the engine, like the OP was proposing?? LOL.

My oil pressure was about 0-5psi at hot idle w/ 20w50. That engine took quite a thrashing with no complaints even with the low oil pressure (redline shifts, rev limiter). I have yet to measure the journals, but from eyeballing them there is no major wear or scratches. And yes, I def had to remove the engine to pull the crankshaft.

Forgot to mention the bottom end has 282,000 miles on it

Is this the 87 325i in your sig you are talking about?

I'm having low oil press at hot idle. I'm thinking maybe rod bearings but likely oil squirter's.

What did you replace and did it fix it?

Im in the process of putting the engine back together right now. I'll be putting in new rod and main bearings, which I believe should fix the low oil pressure problem.

I'm not sure why he took the whole suspension out. On the 3, you only have to lower the front sub-frame.

I wouldn't replace the rod bearings unless you have an issue. I'm considering replacing them because I have a problem with low oil pressure at hot idle.
Pardon my apparent ignorance, but isn't oil pressure created by the crank main bearings?

Both, oil is fed to the rod bearings through holes drilled in the throw:

http://www.maritime.org/fleetsub/diesel/chap3.htm#fig3-01

Pardon my apparent ignorance, but isn't oil pressure created by the crank main bearings?

The pressure is created by the pump. The max pressure is limited by a relief valve in the pump. The running pressure is determined by clearances where oil escapes the pressurized system: mains, rods, pistons, cams, oil squirters. Of course pressure varies by viscosity and RPM.