Bolt Tightening Torque + Degrees for Rear Chassis to Monocoque

1113 Views 10 Replies 6 Participants Last post by JSandov8, 2 mo ago

JSandov8

Discussion Starter · 2 mo ago

I know bolt tightening is a well trodden path at this point, but I think there may be some value-add in confirming the difference below.

Following the Fastener Checklist file, I noticed the rear chassis checklist includes a +45 angle measure for reference 3-5. The figure, does not.

Checklist mentions angle:

Figure does not have angle:

Line Font Parallel Automotive exterior Slope

I would ignore this difference and tighten to torque + angle anyway, but then I noticed the mechanical component checklist caries the +angle over to the figure.

Checklist mentions angle:

Rectangle Font Parallel Number Screenshot

Figure has angle:

Product Font Line Automotive tire Auto part

Can anyone confirm which is correct for the rear? I'd hate to have to dig out a broken bolt. The other difference here, and why I don't feel confident assuming, is that the rear requires tightening a bolt into an embedded insert, whereas the front is tightening a nut onto a stud.

Any help would be appreciated!

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Alfanut

· #2 · 2 mo ago

Ask Harri @AlfaNY . He’ll know.

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GMS

· #3 · 2 mo ago

We suggest using torque value + angle where specified. We use middle value of what's specified (4.1 to 5.1 daNm), which would be 46Nm + 45°. It's important that the fasteners are loosened first.

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JSandov8

Discussion Starter · #4 · 2 mo ago

GMS said:
We suggest using torque value + angle where specified. We use middle value of what's specified (4.1 to 5.1 daNm), which would be 46Nm + 45°. It's important that the fasteners are loosened first.

Awesome, thank you!

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advantagedent

· #5 · 2 mo ago

The only thing I did not like about this was when I did my car I marked all the bolts first. Then loosened as per, but when the first torque was applied they ALL match the original spot. So then was adding additional degree to the bolt Which made me feel uncomfortable...did anyone else notice this

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flyt100

· #6 · 2 mo ago

advantagedent said:
The only thing I did not like about this was when I did my car I marked all the bolts first. Then loosened as per, but when the first torque was applied they ALL match the original spot. So then was adding additional degree to the bolt Which made me feel uncomfortable...did anyone else notice this

It was exactly the same for me. The Nm torque brought it back to the original mark for most, and the angle added to that...

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JSandov8

Discussion Starter · #7 · 2 mo ago

advantagedent said:
The only thing I did not like about this was when I did my car I marked all the bolts first. Then loosened as per, but when the first torque was applied they ALL match the original spot. So then was adding additional degree to the bolt Which made me feel uncomfortable...did anyone else notice this

I think I’ll be setting the torque to just slightly above the lowest setting, cranking the torque wrench up to the upper bound, then going the +45*. That way, if it clicks over before I hit the full angle, I’ll know to proceed with caution.

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advantagedent

· #8 · 2 mo ago

All I can think is that this is. A way to make sure the cars bolt together well, I think we agreed on this and possibly a way to keep work coming in the door .Iam a mechanic so I see how a low production car would have little to no breakdown. So you need a way to keep you technician ( in which every shop needs and pays for training and if they stand around they will walk , getting paid or not) so let's assume the bolts are toque to yield and they just don't do the final step. Make work project...I just got a McLaren 540c so Iam going to look into if this is a thing for them.but a lot of the low volume cars have super short intervals on things like belts and fluid...i.e if your ford has 10k on it you don't go swap out all the fluid and switch the water pump... Yes peace of mind is true Bliss, but from what I see on my car in this matter I will do the bolts and probably never really worry about it again. If others could see if there car came like this we might know .and mark them afterwards.....

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HeavyFoot

· #9 · 2 mo ago

The beauty of this forum is that having a 2018, I can wait and see the results from those who perform a second tightening to see if it is truly needed.

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JSandov8

Discussion Starter · #10 · 2 mo ago (Edited)

About 3/4 of the way through both services, 5 hours down, will pick up tomorrow and put my results together… in the meantime, here’s my current tool list, per tightening guide’s numbering.

The obvious, breaker bar, 20->100Nm torque wrench, angle dial

Vehicle Fastening Check
1. 2x 22mm socket, 12” extension and a friend to hold the bolt from inside the cabin
2. Not done yet

(Remove mid-rear felt cover)
10mm socket, Philips head, T30

3. 16mm socket, 16mm crows foot, 6” extension
4. 16mm socket, 6” extension
5. 16mm socket, 6” extension
6. E18 socket, 12” extension, 6” extension, 18” extension (for lower bolts, top only done on one side, will need to pull battery tomorrow)
7. 17mm socket, 12” extension
8. Not done yet
9. Not done yet
10. 17mm socket, 6” extension

Mechanical Components Check
1. 17mm crows foot, 12” extension
2. 17mm socket, 17mm crows foot for inner bolts, 12” extension
3. 17mm socket, 17mm crows foot for inner bolts, 12” extension
4. 13mm socket, 18” extension

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JSandov8

Discussion Starter · #11 · 2 mo ago (Edited)

Saving this spot, and adding

Other than the fuel tank straps, which had shifted(paint was chipped off where bolt originally sat), none of the bolts encountered have been alarmingly loose. Out of spec, for sure, but not loose. I checked them by setting torque wrench to minimum spec and seeing if they’d spin, before loosening and torquing to spec. Most had about 10-30* of play before the wrench clicked over.

Fender liners were not removed, only two panels removed so far, mid-rear felt cover, just before aluminum engine cover, and the front diffuser covering radiator fan shroud.

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Bolt Tightening Torque + Degrees for Rear Chassis to Monocoque

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