Flywheel bolts
 

Just need to buy a clutch kit and then i can fit my engine into my rolling chassis permanently :)

Whilst working on the engine i took the flywheel off and now its time to bolt it back on.

The Haynes manual states to use new flywheel bolts as a must, is this gospel or will a good glug of loctite suffice on each bolt?


I dont have a problem with getting new bolts if required i just wondered what some of the old school mechanics opinions are first.

Thanks

Mark

Replace and torque as per manual.Its very close to your feet as it comes through the bell housing like some psycho chainsaw !

I think you will understand what I mean.

I thought that might be the reply i would get!

Replace them it is as i like the lower part of my legs :eek:

I do intend to replace my flywheel bolts as ive had them off. But why is it they need to be done?
Cheers Jas Gray

The changing of the bolts is a safety issue on a critical application.

Basic theory is : When a bolt is tightened to the max, it will stretch a fraction.
When the bolt is removed it will stay stretched ;) If the old bolt is then re-used it is likely to stretch again.
This in theory may result in a weaker bolt that is just within its yeild zone & in theory is more likely to fail ( Shear ) :eek:

More science than that involved but that is the basic theory :)

I see exactly what you mean there, and if I was to unbolt a flywheel I would definitely replace the bolts with new, but my question is that if the bolt stretches, and stays stretched (in other words it's plastic) then where is the clamping force coming from? Wouldn't it want to spring back (elastic) in order for the correct amount of grip to be applied?

When I say stretch a fraction, I am only talking microns.

With the bolt under tension when cold the bolt would retain any elasticity it has.
Once the bolt has been subjected to many hours, within a relatively high tempature enviroment, the material of the bolt will become " Normalised " thus the original few microns of stretch will be lost.

The bolt will allways maintain a good mechanical grip as all things are taken into account when the optimum torque setting is calculated.

Re-using the same bolt, in theory, would be like using a bolt that is a bit of an unknown quality. Different engines will have been subjected to different levels of heat during their lifetime.

This may explain why such bolts should be changed as a matter of routine.

Cylinder head bolts also work in a very similar enviroment & very few are re-useable for similar reasons. ;)

Simply,all bolts have a Tensile strength ie 8.8 8.9 or higher,stamped on the hex end. Tensile = tension or stretch,if you think of pulling the bolt north and south from each end, sooner or later it will exceed its tensile strength and fail/break/fracture. The stretching of a bolt under torque imparts a load on it and stops it from coming loose without any use of Loctite etc.
The other end of the scale is overheating bolts like the ones used to secure cylinder heads and when this happens they lose their tension and at extremes may even break causing failure of the gasket.
You beat me to it Ronne.
Hope this makes a little sense.

umm i was always told that the ford flywheel bolts with the fancy pattern in the bolthead are self locking and once used loose the selflocking ability
and so should be replaced
cheers les g

Some bolts do come coated with a coating of a locking fluid,usually activated by the heat caused by tightening them up. And as stated previously they should be replaced as per manufacturers instructions.