| Author |
Message |
Mitch Alsup (Mitch_alsup)
Member
Username: Mitch_alsup
Post Number: 822
Registered: 4-2002
| | Posted on Tuesday, July 01, 2003 - 10:15 am: | |
I always shudder at the TV shows that show a guy torquing a bolt with a 'click' style TQ wrench. Goes to a bolt, moves rather rapidly, then click, and on to the next bolt. No feel at all; I actually wonder if they don't TQ the bolts off camera, and then just check the bolts on camera.....
When I used to build engines, and when TQing the critical bolts/nuts, I would creep up on the TQ feeling for any binding or non-linear increase in force until the bending-bar style TQ wrench pointed to the desired value. I never lost a bolt, or had one come apart later in application. |
Dave Helms (Davehelms)
Junior Member
Username: Davehelms
Post Number: 74
Registered: 5-2003
| | Posted on Tuesday, July 01, 2003 - 7:19 am: | |
All true. I did a test awhile back on a Ferrari Ti. connecting rod using different lubricants, checking for bolt stretch vs indicated torque. I used the $6000 Ferrari torque wrench and a beam torque wrench. The manual states to use moly grease on the threads, so we gathered up about 8 brands of moly grease and antiseizes and set about torqueing the rod to destruction. This showed you can add another 20+% variation just by the lubricant used. Some of the moly greases yeilded the same results as a dry assembly. "Hands on feel" is a major factor. If it binds, stop. |
Craig Dewey (Craigfl)
Member
Username: Craigfl
Post Number: 632
Registered: 1-2001
| | Posted on Tuesday, July 01, 2003 - 6:49 am: | |
As Jim stated, using a torque to tighten a nut(or bolt) is only an approximate method since the result is to end up with a specified clampling force which can only be accurately determined by the bolt/stud stretch. There can be a significant difference between torquing unlubricated threads and lubricated -- about 20%. There can also be a significant difference between indicated torque and desired clamping force -- the "turn of the nut" method is the most accurate but not always the most practical. Another influence is static and dynamic friction- are you seeing the indicated torque while the nut is turning or when it is stopped? Dynamic friction is usually lower than the static(breakaway) friction.
So my method is to lubricate the threads, indicate the final torque while the nut is turning and shoot for the middle range.
There are only a few applications where overtorquing could cause a serious problem. This would only occur in a case where an extremely high strength stud/bolt were used stretching it very close to the yield point - where permanent stretch does not allow the proper clamping force. |
DGS (Dgs)
Junior Member
Username: Dgs
Post Number: 119
Registered: 5-2003
| | Posted on Tuesday, July 01, 2003 - 3:25 am: | |
For head bolts on a 3.2 engine, see Service Bulletin 10-14. The procedure calls for the use of graphite grease, a torque wrench, and an angle gauge (or the computerized SPS SENSOR 1 wrench used by the factory). |
David Feinberg (Fastradio2)
Junior Member
Username: Fastradio2
Post Number: 233
Registered: 4-2002
| | Posted on Monday, June 30, 2003 - 7:39 pm: | |
Jim,
Your definition makes perfect sense...as well as your assumption. I guess what prompted my question was that some manufacturers specifically specify a "wet" and/or a "dry" torque specification. Perhaps they were taking into consideration the fastener to fastener friction issue.
Appreciate your input...as I never really gave much though to the fastener friction factor.
David |
James Selevan (Jselevan)
Member
Username: Jselevan
Post Number: 622
Registered: 6-2002
| | Posted on Monday, June 30, 2003 - 6:23 pm: | |
David - interesting question. I have always assumed that when a torque specification is provided, it applies to a "lightly oiled" thread. The reason is that the torque specification defines the compression (bolt stretching) force on the parts being held together. This is defined by the pitch of the thread and the number of turns of the thread. Thus, friction between bolt and nut (or stud hole) should not contribute to the torque required. Hope this makes sense.
Jim S. |
David Feinberg (Fastradio2)
Junior Member
Username: Fastradio2
Post Number: 230
Registered: 4-2002
| | Posted on Monday, June 30, 2003 - 6:44 am: | |
Mitchell,
Interesting...your presumption, that is. I've made that same assumption, without any problems thus far. Still seems odd that Ferrari does specify...Posibly just "standard" engineering practice that I'm not aware of?? |
Mitchell Le (Yelcab1)
Member
Username: Yelcab1
Post Number: 570
Registered: 11-2001
| | Posted on Sunday, June 29, 2003 - 9:32 am: | |
For critical high torque components like main bearing caps, and head nuts, I torqued them lubricated for an even torque. For other low torque non-critical stuff like valve covers, I just leave it dry but clean.
Unless the factory specifically specifies it dry (like Porsche), I presume it wet. If they don't care enough to make it clear, then ... I figure ... they don't know enough anyway. |
David Feinberg (Fastradio2)
Junior Member
Username: Fastradio2
Post Number: 227
Registered: 4-2002
| | Posted on Sunday, June 29, 2003 - 6:31 am: | |
For all you Ferrari engine builders out there...
When Ferrari specifies a torque figure in their WSMs, is it "presumed" to be with the fastener lightly oiled, or dry? In other engine/workshop manuals I've worked with, that information (oiled/dry) is often specified. Comments appreciated...
David |