Factory Rod Bolts Torqued Dry or Lubed?

[eobturn2]

Doing a rod bearing swap on my '04 and wondering whether or not lubricant on the rod bolt threads is recommended when using the factory bolts. I did search the forum but could not locate an answer to this.

[karter16]

TIS/SIB 11 04 04 doesn’t mention this. I would suggest that BMW expected there to be oil in the rod threads already. TIS doesn’t mention, as far as I can see, any specific lubrication to be applied before the torquing process.

I’d suggest therefore that no additional lubrication needs to be applied.


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[eobturn2]

I noticed that the TIS didn't mention it also. I assume that if they do not specify lube then they do not expect you to use any. But I wasn't totally confident that was a reasonable assumption.
Thanks for the reply.

[D-O]

The TIS (at least the version I have) shows only the 11mm bolt for the S54 in the torque spec section. Some of the other engines (S50/S62) do list the 10mm bolt and specify that they should be replaced, cleaned, and oiled. I asked this same question when I did my bearings last year, and was advised to oil them.

[karter16]

For TTY bolts (10mm) it probably doesn’t matter enormously as it’s angle torque to stretch the bolt a defined amount, so it will stretch the same amount regardless of how lubricated it is.


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[enjoy_m3]

The threads should be cleaned with brake cleaner and lightly oiled when assembling. If you have the updated rod bolt, you have to torque it 3 times to stretch as per newTIS.

[Obioban]

Yep. Lightly oiled.

[karter16]

Yep. Lightly oiled.

Is there a BMW source that states this for the S54? I haven’t been able to find one and would be great to identify it if there is.


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[sapote]

For TTY bolts (10mm) it probably doesn’t matter enormously as it’s angle torque to stretch the bolt a defined amount, so it will stretch the same amount regardless of how lubricated it is.

But the initial torque does matter if oiled or dried, as the bolt could turn 90 deg or not after this first step. This means 90 deg more or not in the final step, which is a very big deal.

[karter16]

But the initial torque does matter if oiled or dried, as the bolt could turn 90 deg or not after this first step. This means 90 deg more or not in the final step, which is a very big deal.

True that the initial torque will be affected somewhat. Initial torque is only 30Nm though which is not much compared to the 105 degrees of rotation that follows it.

Not sure what you mean when you say “it could be 90 deg more or not in the final step”. If you’re using an angle gauge, as you should be, then the rotation will be 105 degrees as per the procedure.

I’m not trying to disagree with those saying the bolts should be lubricated. My personal view is that BMW don’t mention it because:

1: if you’re replacing them, is that there is already oil in the receiving threads.

2: it doesn’t actually matter. The initial torque is relatively low and the level of friction involved in torquing to 30Nm is not much, so lubrication doesn’t impact this much. For the final step angle-torquing is used because, by nature, it ignores the friction component that needs to be overcome and stretches the bolt a defined amount (the goal being to keep the bolt in its elastic zone).


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[sapote]

True that the initial torque will be affected somewhat. Initial torque is only 30Nm though

30Nm is like hanging 3Kg of steak at the end of a 1meter long stick (6lbs steak on 3.3ft stick) and I don't think I can hold this, so 30Nm is not a small torque.
Let's say with oiled bolt, 30Nm turned the bolt 180 deg more from where it was bottomed on the cap, and without oil it only turned 90 deg more, then the oiled bolt turned 90 deg more than the dried bolt. So with the final step of adding 105 deg turns, the oiled bolt turned a total 90 + 105 while the dried bolt turn only 105 deg. Imagine you want to add 90 deg turns more after the 105 deg turns, and this 90 deg become scary more isn't it?

[karter16]

30Nm is like hanging 3Kg of steak at the end of a 1meter long stick (6lbs steak on 3.3ft stick) and I don't think I can hold this, so 30Nm is not a small torque.
Let's say with oiled bolt, 30Nm turned the bolt 180 deg more from where it was bottomed on the cap, and without oil it only turned 90 deg more, then the oiled bolt turned 90 deg more than the dried bolt. So with the final step of adding 105 deg turns, the oiled bolt turned a total 90 + 105 while the dried bolt turn only 105 deg. Imagine you want to add 90 deg turns more after the 105 deg turns, and this 90 deg become scary more isn't it?

It seems like a lot when you're trying to hold onto it with your fingers (which aren't very good at resisting torque) but 30Nm is not much for a high tensile bolt.

I understand what you're saying in that there will be a difference between an oiled bolt and not when setting the initial torque. However the amount of rotation required to hit 30Nm for the rod bolts (lubricated or not) isn't anywhere near 90-180 degrees. It's more like 15-ish degrees total (when lubricated). So not really very scary.

The whole point of the procedure, and why torque to angle is used, is to almost completely eliminate the variability of lubrication. Think of it like this. The bolt has a target stretch zone to apply maximum clamping force. The aim is to land somewhere in this zone. The initial torque of 30Nm is chosen specifically because at that low level of torque impacts of lubrication and friction are low, and therefore the impact on the end result is minimal. The 105 degrees of angle torque that follows is a set amount of rotation (regardless of friction and lubrication) and is designed by the engineer to land the bolt in the target zone for maximum clamping force.

[sapote]

The whole point of the procedure, and why torque to angle is used, is to almost completely eliminate the variability of lubrication.

Yeah, and also the torque wrench clicking is not reliable during stop-and-go turning compared to one continuous turning motion. (keep clicking the wrench will end up with an over-torqued fastener).

But why the factory not just spec out 120 deg total angle and eliminate the initial 30Nm torque to make thing easy regardless oiled or not? I think the problem is where the starting point -- the bolt bottomed out location? But every person has their own unique bottomed out position so it's no good. This is exactly why the initial 30Nm, to have a reliable common "bottomed out" position to start with.

[karter16]

But why the factory not just spec out 120 deg total angle and eliminate the initial 30Nm torque to make thing easy regardless oiled or not? I think the problem is where the starting point -- the bolt bottomed out location? But every person has their own unique bottomed out position so it's no good. This is exactly why the initial 30Nm, to have a reliable common "bottomed out" position to start with.

Yeah I agree, I guess you’d have everyone with their own interpretation of what the starting point should be, which would definitely be problematic.

I think that’s why they specify 30Nm as a line in the sand. The idea being it’s a “close enough” starting point, regardless of environmental factors, to execute the angle torquing from.


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[enjoy_m3]

Yeah, and also the torque wrench clicking is not reliable during stop-and-go turning compared to one continuous turning motion. (keep clicking the wrench will end up with an over-torqued fastener).

But why the factory not just spec out 120 deg total angle and eliminate the initial 30Nm torque to make thing easy regardless oiled or not? I think the problem is where the starting point -- the bolt bottomed out location? But every person has their own unique bottomed out position so it's no good. This is exactly why the initial 30Nm, to have a reliable common "bottomed out" position to start with.

lol.
The purpose of the steps is to ensure the rod cap is aligned with the rod as accurately as possible. These are forged broken rods. You want to the rod cap to clamp on the rod with as much even distribution as possible. Otherwise, risk spinning the bearing on first start-up.