Oops

[chris.richard]

Did I overtorque it?

New bolts please! :(

[Sando]

That'll be F.F.FT then? :D :D

At least you got it out........

My run on the rolling road was abandoned today after my overtightening of a cam cover caused the oil to go on it's holidays all over the exhaust. :o Very smokey very slow drive home I can tell you.
The good news was though that on the one run it had confirmed that I am massively missing power .............
makes my Grin at abingdon re-appear when I think back to the fun I had chasing the rest of you (peaked at only 112 at the wheels!)
Robbie :)

[SUSIT]

That'll be F.F.FT then? :D :D

At least you got it out........

My run on the rolling road was abandoned today after my overtightening of a cam cover caused the oil to go on it's holidays all over the exhaust. :o Very smokey very slow drive home I can tell you.
The good news was though that on the one run it had confirmed that I am massively missing power .............
makes my Grin at abingdon re-appear when I think back to the fun I had chasing the rest of you (peaked at only 112 at the wheels!)
Robbie :)
Hi Rob
It Just proves you dont need massive grunt to have fun Rob makes your results at Abingdon look even better. At least you had 2 hp more at the wheels than mine did at the flywheel. Keep at it and save the pennies for a nice V6 of some sort.

Stephen
ps Chris where did the bolt come out of?

[chris.richard]

I was bolting the caliper mount to the hub carrier. 3 bolts clicked, and one just kept on going... I don't know if it's a duff bolt, or whether I overdid the torque wrench setting. I'm sure my tables said 58Nm for an 8.8 10 X 1.5 bolt, but it is higher than other tables I've found on the web just now. The molyslip probably didn't help - the lower friction means I should have reduced the torque. I'm sure Arthur or John Rutter will have some technical comment.

[Arthur]

Chris,

I've got my tables in front of me.
These are based on 65% Yield strength (some tables are based on UTS, and are then usually quoted at 90% UTS) and say 44 NM for an 8.8 M10 fastener.
These tables use a "Friction Factor" of 0.20.
This means - Teflon and Anti Sieze together - Friction factor 0.08
Anti-seize alone - Friction Factor 0.11
Dry - (like degreased dry) - depends on materials. That's why the 0.2 in the tables above, but can be as high as 0.3.

Conversions and sums - FtLb to NM - multiply FtLbs by 1.356
Friction factor 0.3, torque 300 LbFt is the same as Friction Factor 0.1 and torque 100 LbFt.

Out of interest, these tables give relative accuracies of torque settings.
By feel - +/- 35%
Torque wrench - +/- 25%
Angular turn of nut - +/- 15%
Load indicating washer - +/- 10%
Measured elongation of bolt - +/- 3 to 5 %
Strain Gauging - +/- 1%

Bit of an eye-opener for me too. The biggest thing with the torque wrench is static friction. The idea is to pull the fastener up to the click (or the indicator) in one clean pull, of not less than half the quoted torque. So ideally do them zero to tight in one pull, or for heads, zero to half torque sequentially, then half to full torque sequentially. Don't let the bugger stop on the way. Use about 0.15 for friction, and use assembly paste or anti-seize. (at sea, big diesel engines, torques are still quoted based on tallow and graphite...........)
(Oh yes, and forget all of that with those silly stretch bolt thingies, and use whatever the manual says)

Have fun.
Arthur.

[chris.richard]

That'll be F.F.FT then? )

I rate it as 2FT :D

[chris.richard]

Thanks, Arthur.

The lube you use makes a huge difference, doesn't it? I hadn't fully appreciated how much.
From nothing to torque in one smooth motion is a bit impractical in restricted areas where you need the ratchet in operation.

[Sando]

I rate it as 2FT :D
:D :D :D

[Arthur]

Chris,

Yep, the lube does indeed make a huge difference. For guidance, once again forgetting stretch bolts, most car manuals state torques based on engine oil as a lubricant.
And very true - restricted room makes a smooth pull-up a right bugger.

I recall (anecdote time) doing fuel pump suction valves on a big marine engine. 1,400 NM was the torque. We broke the supplied wrench, bought a new Britool one, at only £1100 quid, plus a £150-quid extension bar and calibration table (cos the original 6-foot bar only went to 850 NM) and ended up with 3 guys at about 9 feet from the job, for which we had to construct a huge, solid jig, walking through an arc of about 30 degrees on the bar, and finishing with the end guy almost pushed over the handrails into a 30-foot drop.

But I have to confess most serious fasteners these days are tightened using axial hydraulic jacks and special nuts, which are as accurate as your pressure gauge. (900 Bar before you ask. We don't p**s about).

Best of luck, lads - there is no magic.

[chris.richard]

I've got my tables in front of me.
These are based on 65% Yield strength (some tables are based on UTS, and are then usually quoted at 90% UTS) and say 44 NM for an 8.8 M10 fastener.
These tables use a "Friction Factor" of 0.20.


So I torqued it to 58, when it should have been 24! That explains it, and confirms that i need to replace all 8, not just the buggered one. CarrolSmith says in his book that over-torqued bolts are stronger than under-torqued ones, but I'll not take the chance! Hey Ho, you live and learn! :rolleyes:

[Arthur]

Chris,

Depends who you believe for that one.
Where ultimate failure is a broken (overloaded) bolt, then I agree with Mr Smith - overtorque is better than undertorque. Theory then goes that overtorque will at worst go into the plastic range of the fastener, which will give a little, then settle just under the plastic range, at less tension, but still tight-ish. (Almost into stretch-bolt territory here).
Undertorqued bolts can move under stress, and what you get is a fatigue failure (intercrystalline cracking) at a weak point or stress-raiser in the bolt.
This would be fine for bolts mounted in shear, either single or preferably double.

For bolts in pure tension, though, there is another possibility, which is that overtorque can crush the component (ally heads case in point), leaving the resulting assembly deformed AND loose, leading to gasket failure, permanently goosed component, and probably bolt failure as well.
In this case, undertorque is safer, but you'd still likely blow the gasket.
Remember that, in pure tension, the load on the bolt is the static (torque) plus the dynamic. Think con-rod bolt here. The total is the algebraic sum of the parts, and can be a lot higher that the initial pull-up. If you torque the con-rod bolt to 95% Ultimate Tensile, then it's a pound to a pinch that when the accelerating mass of the rod a piston hit it, it will overload. Now they are Very, Very good bolts.
Last one is that most recorded failures, and these will be in aircraft, marine diesels, and tractors, state overtightening as a prime cause of failure, rather than the other way round. And being a practical lad, I'd go with the recorded failure history over the theory any time.
Speaking of tractors, if you buy bolts from people like Burgess, they'll be good stuff. Having read the good Mr Smith, you'll be aware of the dangers of SAE bolts, which is what you have in an "ordinary 8.8" bolt. Meself, I'd go for Allen head bolts and washers if they go in the space available, or equivalent quality hex head bolt - Holo-Krome spring to mind as a very good fastener. Then go to say 10.9 quality, for very little more money, and what you have is a gem of a bolt with about twice the strength, and a LOAD more fatigue life, than the original. (I think the highest rating is 14.10).
Allen-headed fasteners (with a maker's name you recognise - stick to Unbrako or Holo-Krome, with Allen a trailing third, unless you know better) are automatically better bolts. Hex heads are the worry.

Arthur.

[chris.richard]

Tell me about stretch bolts please, daddy?

[Arthur]

Lord, don't you get to deal with some sarky sods on this Forum!!!!!!!!

OK, Son, now sit down and stop fidgeting.
Stretch bolts are designed to be one-time usage only, and are so designed that they have a reduced shank diameter that will go - just - into the plastic mode when you pull them up. They then give a tad and settle to the correct designer-calculated tension. There is usually a very complex method to pull them up correctly, and if they ever come out, you chuck them in the bin and fit new.
You can tell if you got it wrong, cos they just stretch for ever and then break - similar to your caliper bolt.

I don't like them at all, but car manufacturers do, especially on ally heads, cos you can't deform the head, and the final tension is more accurate than torque-wrench.

So there you go.
Arthur.

[chris.richard]

Alfa use them to attach the calipers to the caliper cradles for some reason. I'd planned on just using normal bolts - doesn't seem any reason not to from what you say.

[Arthur]

Chris,
I can't think of a reason why not.

Arthur.