Old bolts get stressed and strained.

the bolts will be fine IMO, why waste your money

so may opinions gosh!

 

haha, new bolts old bolts, well it dosnt really bother me ay i just wont rev the shit out of it!...

 

haydn.

you might not rev the shit out of it but bet's on that you'll be dropping skids everywhere! Thats what'll stress your bolts haha.

 

The reason people change out the flywheel bolts is often because they will plastically deform when you torque them up (designed that way). I dunno if a K series bolt would be in that basket though, torque setting probably isnt that high....? I'll have a read.

The reason people change out the flywheel bolts is often because they will plastically deform when you torque them up (designed that way). I dunno if a K series bolt would be in that basket though, torque setting probably isnt that high....? I'll have a read.

 

All bolts stretch to some degree when you torque them up. What matters is the tensile rating of the bolt versus how tight you've torqued them. There comes a point where the bolt becomes permanently stretched.

 

Seen as its friday and my brains not working well wikipedia can say it for me:

 

The property classes most often used are 5.8, 8.8, and 10.9. The number before the point is the tensile ultimate strength in MPa divided by 100. The number after the point is 10 times the ratio of tensile yield strength to tensile ultimate strength. For example, a property class 5.8 bolt has a nominal (minimum) tensile ultimate strength of 500 MPa, and a tensile yield strength of 0.8 times tensile ultimate strength or 0.8(500) = 400 MPa.

 

Tensile ultimate strength is the stress at which the bolt fails (breaks in half). Tensile yield strength is the stress at which the bolt will receive a permanent set (an elongation from which it will not recover when the force is removed) of 0.2 % offset strain. When elongating a fastener prior to reaching the yield point, the fastener is said to be operating in the elastic region; whereas elongation beyond the yield point is referred to as operating in the plastic region, since the fastener has suffered permanent plastic deformation.

http://en.wikipedia.org/wiki/Screw#Tensile_strength

^^^^^^^

 

Bugger me. Never knew that.

This kind of thing is becoming more and more common in automotive applications.

Especially headbolts - most headbolts I have ever worked with (them being of the opel variety) have all been 'torque to yield' variety.

It's important to make sure a small amount of lube is used on high pressure applications too; this gives the bolt the ability hold it's maximum yield and prevents friction in the threaded portion from exerting too much run-on torque.

 

Or something like that :dance:

 

So yeah, old cars tend not to need new bolts, unless you stuff them up with poor handling :blush:

You'll only be using 25-35nm on them for a clutch plate and about 35-45nm on a fly wheel ...

Edited August 15, 200818 yr by yakkmeister