Stripped threads.

[Forumadmin]

The Jowett engine is made from low strength aluminium and often the studs pull out. This should not be a problem as threaded inserts are available and after reading this I came to realise the repair is actually better than the original.

Due to their flexibility, wire thread inserts create internal
threads which have a much improved distribution
of residual stress loading when compared with
conventional tapped holes, where up to 70% of the
shearing forces are carried by the first three threads
in the tapped hole. The flexibility of wire thread inserts
helps to compensate for pitch and flank angle errors,
inherent in normal tapped holes, and significantly
enhances the load bearing capacity by deflecting
the residual forces into a helical hoop stress which is
dispersed into the wall of the tapped hole. This enables
the design to be confidently based on the bolt strength
utilising smaller and shorter threads even when used in
low strength materials.

Source: http://www.wti-fasteners.co.uk/largenewdatabook0606.pdf

[ian Howell]

Just so!

I used to sell Helicoils and about 45 years ago I repaired a thread for Ed Nankivell in one of his Jupiters.

Whren I meet him now I use that as a reminder. He reports no problems.

I still have taps and a few inserts for 5/16 BSF. Available on request at postage costs.