RB25DET Head gasket Under Torqued, repeat sequence or new bolts

[Pattey21]

Good morning all,

 

I am in the last stages of putting my car back together and was reading something that made me realize I hadn't had my torque wrench calibrated that I used to do my head.

After doing a few weight measurements turns out it's reading low 10-20nM at 100nM.

I'm now borrowing a mates Warren and Brown Deflection Torque wrench for the job.

Stock top end rebuild OEM gaskets and OEM bolts.

 

Given the process is 

Torque to 29nM,98Nm, Back off, 25-34Nm, 92-103Nm.

And I've essentially under Torqued,

Do I 

1. just torque to final value if it's under (arbitrary 80Nm)

2. Back of and start again 

Given I have reach the final torque I am hoping that they haven't TTY get and I can still use the new bolts.

 

Thanks In Advance

 

 

 

[GTSBoy]

I think you should be fine to just back them off, do the last two stages again. You haven't hit the "right" torque values on the way up last time, and if you are as low as you think you are, you probably haven't started to yield the bolts. if you have started to yield the bolts, they should be only "just" started, and I can't imagine that backing them off and bringing them all the way to their proper torque would be worse than just doing it right the first time.

[Duncan]

Good choice to check the calibration, just tighten them to the correct torque

[Pattey21]

59 minutes ago, GTSBoy said:

I think you should be fine to just back them off, do the last two stages again. You haven't hit the "right" torque values on the way up last time, and if you are as low as you think you are, you probably haven't started to yield the bolts. if you have started to yield the bolts, they should be only "just" started, and I can't imagine that backing them off and bringing them all the way to their proper torque would be worse than just doing it right the first time.

If re-doing the head, besides releasing tension from timing belt, and aux bolt, do the intake and exhaust need to come off.

Currently turbo and intake plenum are bolted on

[GTSBoy]

I think you can lift the head off with both sides still attached. But you're not contemplating taking the head back off, are you?

[Duncan]

Only remove what you need to, to remove the cam covers and get at the bolts. everything else will be fine

[Pattey21]

16 minutes ago, GTSBoy said:

I think you can lift the head off with both sides still attached. But you're not contemplating taking the head back off, are you?

Sorry that was worded poorly.

If I choose re-doing the torque sequence rather than nipping them up; ie backing off all the head bolts to 0Nm, whether I would need to remove intake or exhaust manifold, due to the weight imbalance (exhaust manifold plus turbo vs intake plenum)

 

[Pattey21]

6 minutes ago, Duncan said:

Only remove what you need to, to remove the cam covers and get at the bolts. everything else will be fine

Okay no worries.

[GTSBoy]

22 minutes ago, Pattey21 said:

due to the weight imbalance

Yeah, nah. The weight is nothing compared to the forces applied through the bolts.

[Pattey21]

So I tested the torque wrench, first at 80Nm based on my torque calibration weight calculation then to 98Nm where the first point in the manuals sequence is before undoing them all to zero.

Majority did not move and a couple may have moved 1/16 or less or simply cracked (audible) when I reached the torque spec.

To compared I did both the intake cam and harmonic balancer properly (backed off then did up to 15% below ideal.

Ie 115Nm then 132Nm. The torque wrench actually turned a reasonable amount, let's say a good 1/8th or enough to confirm I was doing it up more, and compatibly a lot more than it moved on the head.

Both the intake cam, harmonic, balancer and idle Tensioner anything around 15% I could noticably torque up more.

I even tried approx 102.5-104nM on the head and same result as trying at 98

Makes me think the head is definitely above 80 and that I should leave it as I'm probably in the yield range