Over tightened end caps

[John Mason]

What I cannot understand is :- If you are using nylock nuts which by nature are stiff to wind on the thread due to the nylon locking ring. What effect does this have on the tightness of the nut. I would think that the nylon would give a false reading of the tightness of the nut. In other words if a nylock nut and a plain nut were both tightened to the same torque then the nylon ring was cut from the nut would they be at the same tightness. What I am trying to say is a does a stiff tightening nut reach the set torque before an easy running nut.

John Mason.

[Zetomagneto]

Use of a stretch gauge is more accurate which is why ARP bolts should be done with a stretch gauge if
possible

[Alan]

John, when you tighten a bolt there are three things to consider. Firstly some of the torque must overcome thread friction. Then some more is taken up by friction between the nut and the adjacent surface. The remainder stretches the bolt as it runs up the thread. In a typical, un-oiled fastener they are roughly thirds, but to stretch the bolt and provide the clamping force you must first overcome thread friction and under head friction. So, with less thread friction, oiled perhaps , the bolt stress is increased. With a stiff nut it’s reduced. This is important. It’s very easy to put an oiled fastener into yield if the quoted torque figure is for a dry joint. Likewise a rusty nut will be stiff and will absorb a lot more torque, reducing the clamping load. If you deduce from this that torque tightening isn’t reliable then you would be right. Partly. It’s better than nothing, though. Some tests we once did showed that experienced operators working by feel only were a lot less consistent than untrained ones with a torque wrench. But, I agree with Zeto. What you really want to be doing is measuring stretch.

[Bob Culver]

A feature of the Forum is that it caters for ordinary Sevens which in their lifetime will never attain valve bounce revs, and extreme racers running to 7,000 rpm, with triple the big end loading. The requirements are poles apart.

Has anyone ever encountered a Seven engine with original Austin big end bolts not visibly stretched by over tightening?? The original bolts have the merit of very close fit, hard to duplicate except by fitting down 8mm.

The incredibly tight dry fasteners on moderns, presumably made of something very tough, do distort sense of feel.

[John Mason]

Thank you Alan and Bob for your explanations. In my life time I don’t expect to have to mess with the big ends on my seven again. (Fingers crossed). If I do I will lighten without the aid of a torque wrench as I have always done. But then again my engine is not a competition engine and it is set up more or less as it left the factory.
To add something a little more humerus I am more confident tightening big end bolts than wheel nuts. Some years ago I lost a wheel and my family will never let me forget. This tends to result in over tightening of said nuts.

John Mason.

[Ray White]

Try two men on an 8' spanner to give 1.0 mm stretch on the bolt, torque wrenches were banned.

That sounds rather like like a Loco engine.  That's big!

[Zetomagneto]

Ship engine more like!

[Dave Mann]

Quite right Zetomagneto

[JonE]

Q - Revisiting overhauling what looks like a newly overhauled standard 1 5/16" engine with its original rods and crank.
Advice from the thread seems to be new big end bolts and nylocs. Is there any point in assessing the bolts I have (and if so, how)? And are there any pluses whatsover for staying with standard nuts and split pin?

Likewise, gudgeons look new. Replace little end bolts and washer as matter of course? loctite?

[Robert Leigh]

I have assessed old bigend bolts by cleaning them and checking whether full depth old type castellated nut will run easily along the whole thread length. Frequently the nut goes tight before it reaches the top of the thread, because that is the part which stretches when overtightened since it does not have the bracing of the nut around it. Often the stretch is visible and those go straight in my scrap box. Generally I no longer use bigend bolts with an unknown history, but I will reuse bolts which I know to have been fitted new by me at the last rebuild (they have not been overtightened).