RIGHTY TIGHTY…

BY TIM BARTROP

This session deals with fasteners and their use in building hot rods. 

Fasteners are used to hold things together that aren’t welded and need to come apart for maintenance and assembly. They provide pivot points in suspension applications and clamp mechanical components together.

For vehicle applications the use of fasteners has a few common rules:

l  Select the right size fastener to suit the applied load. TAC Guideline books provide plenty of direction to help with choices. In vehicle building there are plenty of worked examples to get sizing from. Go to a local oval show and look at what others are doing. Suppliers also help by providing components with the right fasteners and with fixing holes to tell you what size bolts to use. 

l  Mild bolts are suited to low load applications like securing panels together. In my opinion, Grade 5 fasteners are suited to all other situations but check with specific local requirements. Grade 8 bolts are for holding the big ends in place.

Make sure that the screw or bolt is long enough to engage the full thread length of the nut or tapped hole. For nyloc nuts ensure that the fastener fully engages the nylon section.

l  Vehicles are dynamic machines that vibrate so use flat washers under bolt heads to give then a flush surface to bear on and locking nuts or spring washers the other end to keep them tight.

l  Where fasteners clamp through hollow sections, provide crush tubes to prevent side all deflection.

l  Make sure that plate thicknesses are sufficient to provide enough bearing strength to prevent elongation of holes. In a hot rod 3mm plate will perform well in most applications.

Here are some examples that we see during inspections.  

The fasteners used do not engage the full steering box thread. 
One bolt is missing from this idler bracket. 
A common problem with U bolts is obtaining full thread engagement. 
Offset bolts through seat belt plates is not good practice.
This 4 bar bolt does not engage in the nyloc sufficiently.