Torque question

[jhg41977]

I am preparing to reassemble my engine tomorrow. I am reading through the shop manual assembly steps and want to be sure I have this correct. Tightening sequence for the connecting rods is noted as

First tightening sequence: 30Nm
Final tightening sequence: 1x90 degrees +/-2degrees tightening angle.

So I tighten both connecting rod nuts to 30Nm then I turn each nut an additional 90degrees+/-2degreees. Correct?

[fred cook]

Originally Posted by jhg41977

I am preparing to reassemble my engine tomorrow. I am reading through the shop manual assembly steps and want to be sure I have this correct. Tightening sequence for the connecting rods is noted as

First tightening sequence: 30Nm
Final tightening sequence: 1x90 degrees +/-2degrees tightening angle.

So I tighten both connecting rod nuts to 30Nm then I turn each nut an additional 90degrees+/-2degreees. Correct?

Correct. If you bolt the crank to the flywheel (2 bolts are enough) and set the assembly on end, it is easier to install the rods. Getting 90 degrees is more difficult than you might be anticipating! Be sure to lube the rod bearings with assembly lube before installing. Good luck!

[KTL]

Just remember you only get one shot at it. The factory style rod bolts are stretch bolts. Once you tighten them, they're permanently deformed/stretched. If you have to take a rod off again for some reason, you need to use new bolts. This is one reason why people choose to use aftermarket bolts like ARP

[jhg41977]

Kevin, the 993 factory rod bolts are reuseable provided they are within tolerance for stretch according to the shop manual. I measured mine and they are well within. However the nuts still need to be replaced.

[KTL]

Well that changes things entirely. 3 ring or 4 ring knurled bolts? 3 rings requires rod replacement should the bolts not be in spec. 4 is OK to replace just the bolts

Also don't forget to do the 60Nm/44 lb-ft check test. After you do the 90 deg. tighten to each bolt, set the wrench to 44 lb-ft and mark the bolt heads relative to the rod body. If the bolt turns in the rod, or you can't get to 44 lb-ft "click", the rod has to be replaced.

[jhg41977]

They are three ring but within stretch tolerance right now. The shop manual did not mention the 60Nm test, Ill rwview again when I get home. I assume the play would bw the result of the bolt stretch from tightening and necking down, correct?

[KTL]

Just so it doesn't look like i'm making things up as I go......

[hightuned]

Originally Posted by KTL

Just remember you only get one shot at it. The factory style rod bolts are stretch bolts. Once you tighten them, they're permanently deformed/stretched. If you have to take a rod off again for some reason, you need to use new bolts. This is one reason why people choose to use aftermarket bolts like ARP

I bought arp's but was wondering how ppl check the bearing clearence with plastiguage using std bolts, you must be able to use the old bolts for it as discarding $110 worth of bolts just to check the clearnce sounds ridiculous?

[KTL]

Yep you use the old bolts for clearance check with the plastigauge. It's also commonly recommended to include old bolts with the rods when having the reconditioned. Apparently the clearances check out OK but the bolt strength is insufficient with used bolts? Not sure on that.

I do know that pros have advised with ARP bolts that the rods should be resized with the new ARP bolts.

1) using the bolts burnishes/wears them in and makes torquing them more consisent. That said, the burnishing technically is not an issue when you use their special lube (how convenient..... )

2) since ARP bolts are torqued to a higher specified amount, the additional load distorts the shape of the big end slightly and therefore the rod should be re-sized accordingly. There's one more reason not to switch to ARP rod bolts w/out disassembling the case.

[jhg41977]

I didnt think you were making anything up. I read the check section quickly and i was so far beow the spec for bolt stretch I assume it wont be a problem. Interesting to note, the shop manual usually notes parts which need to be replaced in their diagrams but there is no note for this in the diagram for connecting rods.

[cmcfaul]

Did mine recently and it was easy to lay the crank horizontally in front of me, position the wrench at the 12:00 position then tighten to the additional 90 degrees.

Chris
73 911 E

[hightuned]

Originally Posted by KTL

Yep you use the old bolts for clearance check with the plastigauge. It's also commonly recommended to include old bolts with the rods when having the reconditioned. Apparently the clearances check out OK but the bolt strength is insufficient with used bolts? Not sure on that.

I do know that pros have advised with ARP bolts that the rods should be resized with the new ARP bolts.

I think so the shop that did my rods didnt want to resize them with the old bolts, he said to come back with the arp's i was going to use.

[irobertson]

Originally Posted by hightuned

I think so the shop that did my rods didnt want to resize them with the old bolts, he said to come back with the arp's i was going to use.

Same here, my rods were resized with the new ARPs installed.
I also measured the bolt stretch when doing my final assembly as opposed to relying on torque values.

[911pcars]

Originally Posted by KTL

Yep you use the old bolts for clearance check with the plastigauge. It's also commonly recommended to include old bolts with the rods when having the reconditioned. Apparently the clearances check out OK but the bolt strength is insufficient with used bolts? Not sure on that.

I do know that pros have advised with ARP bolts that the rods should be resized with the new ARP bolts.

1) using the bolts burnishes/wears them in and makes torquing them more consisent. That said, the burnishing technically is not an issue when you use their special lube (how convenient..... )

2) since ARP bolts are torqued to a higher specified amount, the additional load distorts the shape of the big end slightly and therefore the rod should be re-sized accordingly. There's one more reason not to switch to ARP rod bolts w/out disassembling the case.

Somewhere, there's an ARP flyer that suggests resizing the big ends when using their product due to their increased torque spec.


FWIW. It's also possible to R&R rods (and thus rod bolts) w/o splitting the case.

In another ARP doc., they recommend a pattern of tightening/loosening 4-5 times with their moly thread lube to increase the accuracy of applied torque. Download
Sherwood

[KTL]

Yep good correction of me. The rods can indeed be removed and resized w/out splitting the case. Checking the stretch of the bolts and also clearances of the rod bearings is what I had in mind when saying it's advisable to split the case.

[jhg41977]

Reading through again and I noticed there is no lock tite which surprised me. Shop manual says to install, lightly oiling the threads and contact surface of the nut.

Is this because the strain within the bolt and nut is sufficient to hold it from loosening?

[911pcars]

Originally Posted by jhg41977

Reading through again and I noticed there is no lock tite which surprised me. Shop manual says to install, lightly oiling the threads and contact surface of the nut.

Is this because the strain within the bolt and nut is sufficient to hold it from loosening?

In this application, Loktite or equivalent isn't necessary if quality fasteners are used (factory or better). In addition, thread lockers don't provide the same friction-reducing qualities as anti-seize or other recommended thread lubes needed to ensure accurate torque settings.

Sherwood

[Walt Fricke]

Plus, per Carroll Smith, what keeps fasteners from loosening in most applications is adequate stretch (or, if you will, torque to produce stretch) to exceed the stretching loads imposed. If the bolt has sufficient clamping force to do the job, it won't loosen.

There are exceptions - 6 bolt flywheels on 70.4mm cranks being one, due to some unfortunate harmonics at 8,000 or so RPM. Even then, enough stretch seems to solve the issue, although we all use a little carefully applied red stuff just in case.

I don't think rod bolts come loose. Oiling is the main problem, and there is the odd rod which breaks, or the odd bolt which missed out on quality control, or which wasn't actually fastened to the right torque. Or which is stressed beyond what it was designed to do (like money shifts, for instance).