Re Dial Guage

[Mike Whitworth]

Hi Folks
I am going to show my ignorance now .
What is the purpose of a dial guage e.g when torqueing down the cylinder heads you first do it to 20nm then with a dial guage turn the nut a further 180 degrees. Why
Why not just specify a higher torque setting in the first place

 

[Steptoe]

Because it doesn't matter what the stiction of the threads are (i.e. if any grease or lube on them) they'll all be the same

 

[(RIP) Bin Ridin]

Name like Whitworth and your asking us?

 

[(RIP) Bin Ridin]

It's called torque-turn, gives a precise tension as Steptoe said.

 

[(RIP) Bin Ridin]

Here ya go!

Q: Why can't your bolts be torqued?
A: Any bolt can be torqued. The question is: will using the torque method of tightening a bolt give you good, repeatable results? This is important because at top dead center of the exhaust stroke, the piston wants to continue right up through the cylinder head and the crankshaft wants to pull the piston back down the cylinder walls. At high RPM this load can exceed 18,000 pounds of pull on the cap. It is the job of the bolt(s) to provide enough clamping force to keep the cap from separating from the tower of the rod. The problem is a torque wrench only measures friction not clamp load and every time you tighten the bolts you change the mating surfaces of the threads and where the head of the bolt contacts the rod. This changes the amount of friction that must be overcome to correctly tighten the bolt. What this means is if you tighten the bolts to the same torque level, you will have a different clamp load on the bolts each time. Because of the large potential variations in the actual clamp loads achieved by using torque, we strongly recommend against using torque.

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Q: Why use torque and angle?
A: We didn't invent this. It has been used by automobile and diesel manufacturers and in the aerospace industry for many years because it is much more accurate than using torque to tighten bolts. Torque and Angle uses the pitch of the threads as a good, repeatable reference for properly tightening the bolts. For example, if the bolt has a 7/16" 20 threads per inch pitch, then one full (360 degree) turn of the bolt will move the bolt exactly .050" (fifty thousandths of an inch), or 36 degrees of turn will move the bolt exactly .005" (5 thousandths of an inch). We have a specification for Torque and Angle for all of our bolts, no matter their size (5/16", 3/8", 7/16" etc.) and our specs are all derived from the pitch of the specific thread on each size of bolt.

From Oliver Racing (whoever they are?)

 

[pomm001]

like Bin Ridin said torque measures the effort required to turn the stud/ bolt/nut and is not linear to clamp load.
Torque plus angle is used on 'strech' bolts, after intial torque is applied the angle has been calculated and tested to give the correct amount of strech to the bolt.
At the pre determined angle the bolt goes into its elastic state and its clamp load increases.
As you can imagine the graph of the strech rises rapidly, then flattens off and drops very rapidly corresponding to the amount of angle applied.
Its at the top of this cure where the most clamp load is generated, the torque plus angle is calculated to put you in this area.
Overstep this slightly and the load will drop rapidly.
Sometimes the manufactures will recommened that new 'strech' bolts are fitted to some areas to ensure maximum clamp load

I am sure we have all experienced tighten a bolt up, it get harder and the.....goes loose just before it snaps
Thats a prime example of taking the material out of its 'elastic' state

 

[Mike Whitworth]

Thanks for the information guys
I am going to treat myself to a dial guage asap
Regards to all

Mike.
Heavon does'nt want me
and Hell is afraid I'll take over.

 

[Greg Masters]

Name like Whitworth and your asking us?

Greg

 

[cookie]

Thanks for the information guys
I am going to treat myself to a dial guage asap
Regards to all

Mike.
Heavon does'nt want me
and Hell is afraid I'll take over.

a dial guage is something else altogether. you want an angular torque guage (i think)

 

[Greg Masters]

I think what is required is a protractor!

Greg

 

[(RIP) Bin Ridin]

One article I read described how most bolts are tightenedto under the yield point, still elastic, and can be reused. However, some bolts, including those for aluminium components where there is thermal expansion to take care of, are tightened past the yield point, apparently better for clamping in such case. Might be these that have to be replace every timed.

 

[pomm001]

One article I read described how most bolts are tightenedto under the yield point, still elastic, and can be reused. However, some bolts, including those for aluminium components where there is thermal expansion to take care of, are tightened past the yield point, apparently better for clamping in such case. Might be these that have to be replace every timed.

If you tighten any bolt past its yeild point, then its knacked and looses all load.
Most manufactures have a 'free' length' and diameter' check to see if strech bolts can be used again.
But its good commercial practice for them to insist on replacement.

I think someone is pulling your leg about the use with Aluminium.

Back to the plot, all you need is a torque wrench and a stick of chalk, mark the socket, and a point on the head, most angles are multiples of 90 deg.
If you have plenty of dosh, or do it for a living buy a fancy socket protractor thingy

 

[northengit]

Hi Folks
I am going to show my ignorance now .
What is the purpose of a dial guage e.g when torqueing down the cylinder heads you first do it to 20nm then with a dial guage turn the nut a further 180 degrees. Why
Why not just specify a higher torque setting in the first place

I would'nt go asking for a dial gauge when you go shopping cause you will only confuse the man.... just get yourself a degree disc if you really need to, ? but as some have already said most are nuts /bolts are done up in incriments of 90 deg or so...

 

[Frank Warner]

I would'nt go asking for a dial gauge when you go shopping cause you will only confuse the man...

Dial gauge ...

Not what you are after... you can make do with a protractor ...

 

[cookie]

angular torque guage

i have one & it's a PITA to use. as previous poster has pointed out, most specs call for multiples of 90º so i do it by eye.

 

[northengit]

angular torque guage

i have one & it's a PITA to use. as previous poster has pointed out, most specs call for multiples of 90º so i do it by eye.

Exactly.... mine went to the back of the shed years ago....still use my dial gauges for run outs etc.. but for degrees no no. 12 oclock, quarter past, half past, quarter to, easiest for me.

 

[(RIP) Bin Ridin]

TTY - Tightening Torque to Yield (one of many references which can be found on t'internet - I know it sounds odd but it is practiced, honest...)

Tightening torque-to-yield bolts is done in several stages using a combination of torque and turning angle. First, the bolts are tightened to a low torque specification so that even clamping load is placed on the parts being assembled. Often, the bolts are tightened again to a slightly higher torque as a second stage. This is still a low enough torque that friction and stiction on the bolt threads affect tightening torque very little. Then each bolt is turned a specified number of degrees usually in two or three steps. For example, each bolt might be turned 90 degrees, then another 90 degrees and the tightening completed by turning a final 70 degrees. The clamping force exerted by the bolts is accurate and even.

There are special tools available that measure the degrees a bolt or wrench is turned. Some tools are low cost protractors with a moveable pointer, while other tools use electronics to measure the turning angle and cost several hundred dollars. Both types of tool work well but the electronic ones make the job go faster.

Why do we need these torque-to-yield bolts now? We didn't need them in the 1960's or 70's! The simple answer is engine materials are different. Aluminum cylinder heads expand at a different rate than cast iron blocks. As an engine warms up, bolted together parts have to move against each other or slide on their gaskets. The elastic properties of the torque to yield bolts allow movement between parts yet maintain even clamping loads and sealing.

Engine parts are also lighter than they were a few decades ago. Heavy cast iron parts could withstand some variations in torque without failures. Thin wall castings and aluminum alloys used today require extremely accurate torque or warping and leaks occur.

Even the way engines are designed is changing because of the need for even clamping forces. For example, Ford has prototype engines where the bolts that hold the cylinder head on pass all the way through the engine block and thread into the bottom casting that holds the crankshaft. Imagine only a few bolts holding the complete engine together. That would certainly change the way we assemble and disassemble engines of the future.


Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist's Association of Canada (AJAC).