Hey y'all
It's me basketcasebear.. But I am more like rikerty bear now.
Silly q, how imperative is it to torque fly wheel bolts?? On a vxv6
So called mech says it don't matter!
Thanking you all
Bcbrb

Flywheel bolts in general are a very specialised fastener that operate under a lot of stress, both in tension and in shear.
Correctly torquing them serves two functions, one, obviously, to make sure they are tight, and two, and not so obvious, to make sure they are pre-stressed to the correct tension value.
Engineers spend a lot of time worrying about such things, and designing specialised fasteners for this specific function.
"Torquing" a bolt establises a stress level, or tension, in the bolt which is essential for it to operate correctly. Torque indicating tools are also called "tension wrenches", as this is their real function.
I suggest that if your mechanic doesn't see the benefit in torquing them correctly, then find a new mechanic who does.

Edited by user Thursday, 25 May 2017 10:41:46 AM(UTC)  | Reason: Not specified

When you do find someone who is prepared to use a torque/tension wrench it would be good to ask when it was last calibrated. They do change.

It isn't difficult to do yourself, all you need is a vice, a metre of pipe, a tape measure and a bucket of water.

One theory I've heard is to tighten the bolt until you hear a crack, then back it off a quarter of a turn.

To test our tesnion wrench, what we need to do is apply a known force over a known distance to the tension wrench and compare it to the scale reading. Like this:

1/ Find a length of pipe, usually around 2 feet long, that's a slip fit over the handle of your tension wrench. The lighter the tube, the better.

2/ Clamp the socket adaptor in the vice with the torque wrench horizontal, and on the left hand side of the vice.
(Pushing down on the handle should click it off - sorry to all those mollydukers who want to check left hand thread tension wrenches, you get to use the right hand side of the vice)

3/ Slip the pipe over the tension wrench handle and measure from the centre of the socket adaptor along the pipe to a point 3 feet from the socket adapter centre, and mark it. Make sure the pipe is only over the section where your hand would normally rest on the tension wrench.

4/ Set the tension wrench to the value you want to check. This setup allows you to check up to about 60 ftlbs, so let's say set it to 60 ftlbs.

5/ Hang your bucket (plastic 9 litre is about the right size for up to 60ftlb) with the handle on the mark at 3 feet.

6/ Fill the bucket slowly until your tension wrench clicks/beeps/indicates or does its thing at 60ftlb.

7/ Measure how much water is in the bucket, by volume. Bale it out with a measuring cup. You could just weigh the water, but I don't trust your bathroom scales, so volume is a better way. Lets say 8.5 litres is how much you used for this example.

8/ Multiply the number of litres by 2.2046, and then by 3. In this example, 8.5 x 2.2046 x 3 = 56.2ftlb. This means that when your tension wrench indicates 60 ftlbs, you are actually applying 56.2 ftlbs.(see the note below)

It would be good practice to check the tension wrench at a few points in the scale, say 30 and 60ftlbs for the places we usually play. If you need more than this, a bigger bucket or a longer piece of pipe are needed.

Note This method doesn't take into account the weight of the pipe, the empty bucket, or the tension wrench itself. This means the result will read slightly lower than the tension wrench setting, which is why the tube and the bucket should be as light as possible. You could correct for these slight errors in the calculation, but the maths and measurements are tedious and this was supposed to be a quick check.
You could also use an accurate spring scale in place of the bucket, should you happen to have one.

For those purists who just have to use metric, instead of 3 feet for the distance from the socket adaptor to the bucket handle, use 1 metre (and the socket adaptor will still be 1/2", so you aren't that pure after all...)

Using 1 metre the maths for the above example becomes 8.5 x 9.81 x 1 = 83.4 Nm.

Enjoy.

The old tighten the bolt right up till it just starts to become easy-er and then just the trick of backing it off just a bit.

When you tighten the bolt and hear a crack, that's it, you can't turn it back at all, because it's snapped off.

I remember torqueing up a 1975 Falcon 250 head once, it had only been weeping oil down the side of the block is why I was told to changed the head gasket, when one head bolt that was in the position of the weep went to about 55LB and started to go less pressure, so I stoped directly out of fear and left it at that, it must of started to cross thread in the block I assumed.

I have seen bubbles in the block castings before even to the size of a jelly bean and assumed maybe that was the problem and buggered if I know what to do to fix the problem if that was the case. imagine telling the owner, oh we will just have to get another block ? because um well ar, oh no ! this is not going to go down well regardless.

Had a Mechanic working on a Citroen cyl head un bolting it, well the thread down one side happens to turn the other way around when you go down the other side of the block, well he ended up striping the thread in the block, and then there was the throwing of spanners and some harsh words were being yelled out, not to mention what he was going to tell the next Citroen customer where they could go. now I could of went and did my Political Correct duty and went and pat him on the back and said now now that's no way to speak of the French is it.

Rolls Royce do this crap as well with the wheel nuts, so down one side you set your socket wrench to anti clock wise to un do the wheel nuts and down the other side you have to set it for clock wise to un bolt. brilliant !

Pretty common for light trucks to have left hand threads on the wheel nuts. They do this to reduce the chance of them undoing. My chainsaw has a left hand thread on the driven sprocket for the same reason.

Yeah I check everything before I undo them. Lots of Toyotas like Dynas and forklifts are. I think my old 48 Fargo ute might even have them.

did some testing today on the torque wrenches for comparison.
I compared three against each other. the old, sidchrome free wheel type around 1970's, a newer kingchrome I bought around 1990's and my newest sidchrome which I won 5 years ago.
I used a piece of exhaust pipe and a plastic bucket for the test which I didn't weigh because it was used for all tests and it was for comparison only.
60 ft/lb old 8ltr,newer 7.8ltr,newest 7.3ltr
40 ft/lb old 4.8ltr, newer 4.75ltr, newest 4.3ltr
the totals were close enough measurements with a bit of spillage and a little to late stopping after the click.
seems my "newest" torque wrench is the most out. doesn't always pay to update?

An interesting spread, but that's the problem with having more than one instrument of any kind - which one to believe.
None of those are over tightening bolts, that's for sure.

I have a Warren and Brown Dual Signal 120 ftlb type I've had for years which I check every year or so, and comes up within a few percent of set point each time. It can be adjusted, but I haven't had to do so yet. The deflecting beam type units do change as they age, usually on the low side, but it depends on the initial quality, degree of abuse, and how much use they see. I guess the Warren and Brown uses some reasonable quality old school BHP steel for the beam, as opposed to the lovely recycled concrete reinforcement bar that comes from China, universally known as Chinesium.

Some manufacturers are claiming +/- 2% accuracy for their tension wrenches between 20 and 100% of the range of the tool. Sounds good, but how much it change as the tool ages is the real question.

What we are really trying to do is obtain a given bolt stretch when we tighten it, and there are a lot of other variables aside from the tension wrench to consider.

I saw some numbers a while ago about average accuracy for various methods, and it went something like:

1/ Tightening by "feel" +/- 35%
2/ Tightening by torque wrench +/- 20%
3/ Tightening by nut rotation distance

I think how you actually use the tension wrench has a big effect on the result also. Not being a trade trained mechanic, I am probably using it incorrectly. I have a Warren and Brown one, and I know it shows you how to hold it. I guess if you need to use an extension to reach a bolt it must change the reading. I just rebuilt a XR engine and I had to use an extension to reach the front two barrel bolts.