I am asking about the manufacturer specific torque specs for a given year, make, model, component/part and bolt/stud (not asking about bolt grade and size standard specs).

Random Example: 2003, Ford Powerstroke (6.0 liter PSD), Injector Hold Down Bolts are 24 foot lbs in the service manual.

Maybe the question could be more simply stated as: Where do service manual publishers get their info? In the example, does Ford specifically make public the original torque spec used for each and every part? Does this information have a centralized source?

This question is somewhat related to data source ownership and legality of republishing said torque specs found in a given service manual. However, legal consequences are NOT the question itself. I'm simply looking for an explanation of the flow of information from the manufacturing line to the service manuals.

  • 1
    I'm quite sure the aftermarket manual publishers are reporting actual manufacturer values. How that works legally is probably a topic for a different forum, but note they also lift drawings and such from the oem manuals.
    – agentp
    Oct 17, 2017 at 11:32
  • @agentp As mentioned... while legality may be the reason for my question it is NOT the question. Why are you "quite sure" about that? Where is this flow of information and how do aftermarket manual publishers get it? That is my question.So if they "lift drawings" and "Such" from the OEM manuals, how are they doing this and what specific manuals are you referring to?
    – maplemale
    Oct 17, 2017 at 22:10

3 Answers 3


Reputable sources (e.g. Haynes, Chilton's, Alldata, etc) are paying a licensing fee to republish OEM information, or at the very least asking permission.

Haynes is probably the only "paper" DIY repair manual source left, and typically they only publish information on older popular vehicles, where the income stream from the OEM manual is little or no interest to the OEM publisher.

While proprietary, the information is not that closely protected, especially on vehilces that are no longer produced by the OEM.

About 99% of automotive fasteners are NOT critically torqued, so any discussion about bolt grade is moot - as you suggested in your question.

The "original" information is derived from a collaboration between the OEM engineers, and the OE component manufacturers. So an injector hold-down torque is determined by the application, the materials, and the ultiate goal. Maybe that bolt could be a lot tighter, but not without cracking or distortion of the injector flange, crushing a seal, etc.

(For instance, Subaru knock sensor uses an M8 bolt, but is ultra-sensitive to the distortion created by overtightening. Final torque is a small fraction of what seems appropriate.)

The engineering information is addded to the OEM "repair manual" to aid technicians in replacing components. Often there are general torque rules, which apply when no torque is specifically mentioned. Specialized torque values are provided when the general rules don't apply (knock sensor, oil pan, transmission pan, timing cover, water pump, valve cover) and the desired torque is typically much lower than a blind assumption based on the general OEM rules or bolt size.

The information flows from the OEM design engineers TO the manufacturing line AND the "repair manual" ... "electronic database". In fact, part of the "design" of the new production vehicle would be developing the tooling to tighten injector hold-down bolts to the correct values. I can't speculate on the exact timing of the information flow, but I am certain the information is not "centralized" with the possible exception of OEM manufacturing enginnering oversight.

  • I think this is the best answer. Honestly, I had no idea there was an official "OEM Repair" or Shop Manual aside from the obvious - something internal the dealerships use which is surrounded with mystery. The only manuals I've ever heard of where Haynes and Chilton which as you and others pointed out, often cover a wide range of years/models and aren't the original. I also wasn't aware until your answer prompted me to search, that manufacturers ever published an OEM "Repair Manual" to the public. I've only ever been aware of my vehicle "user manual" with limited maintenance info.
    – maplemale
    Oct 20, 2017 at 18:08
  • I think there is some sort of law that dictates (at least in the US) that OEMs must make available repair information to the public, along with specialied tools. There is, however, no limit on what a "dealer" can charge for such things, as long as the price is set evenly. The general theory is that an OEM cannot create a monopoly impediment to the business of third-party or DIY repair efforts. Besides, it represents a significant income stream to the OEM, and it would probably be a poor business practice to keep the information "secret".
    – SteveRacer
    Oct 21, 2017 at 5:38

There are many methods of tightening threaded fasteners. The most common being torque control tightening.

Torque specifications are determined by the fastener being used. After engineers determine the size and strength for the application, whether the fastener is dry or lubricated, they can calculate the torque specification.

T = K x U x D x P

T = torque
K = standard representing 1.33
U = coefficient of friction
D = diameter of the fastener
P = necessary preload

This does not apply to special fasteners, like stretch bolts which have special instructions to achieve proper torque.

How to Determine Torque Specs
Fastener and Screw Torque Calculator
Methods of Tightening Threaded Fasteners

  • Thanks... but none of this is news. "not asking about bolt grade and size standard specs" I get that engineers at various manufacturers figure this out. They then record the individual specs and use them to assemble each vehicle? Does the information stop there? Do manufacturers release/publish this information somewhere? Or, are reference manuals 100% re-derived information from breaking down all of the information above in a given application?
    – maplemale
    Oct 17, 2017 at 22:08
  • All the torque info is "re-derived" from the design engineer / team that gave the injector hold down bolt a value of 24 ftlbs to prevent it being blown out in service. So the true source is the design engineer / team : all else is copy from original....
    – Solar Mike
    Oct 17, 2017 at 22:33

If there are doubts about the aftermarket publishers recycling figures, here is a late 70s Datsun factory service manual:

enter image description here

and Haynes..

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You can pretty much find every drawing in the Haynes book in the FSM.

Re torque specs Haynes took the liberty of rounding ranges to a single number, eg 93-107 ft-lb in the FSM is 100 in the Haynes book.

I did at a quick look find one significant torque discrepancy (almost a factor of 2). I'd guess that's because Haynes covers a span of near 10 years while the FSM I have is for a specific year. You can see if the specs get changed over the years that's hard for the condensed book to capture. (It could also be a typo of course)

  • The rounding is interesting... I did not know that! I tend to get most of my torque specs online from a forum consensus and sometimes there is debate about which it is. That explains some of the discrepancies.
    – maplemale
    Oct 20, 2017 at 17:57

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