THIS issue we welcome ‘Doctor’ Tim Bartrop to the Street Machine fold. An experienced automotive engineer, Tim will pen a series of yarns talking us through the dos and don’ts of car modification – starting this issue with the don’ts. This feature deals with the most common mistakes Tim has encountered in the course of his automotive engineering work.


MOST state registration jurisdictions do not allow steering components to be welded, even with X-ray and other non-destructive test methods to prove their soundness. I have not seen an application yet where the welded part could not have been made in one piece of material to eliminate the weld. Exceptions are welded components made by vehicle manufacturers where they take responsibility for performance. Welded steering components are common in privately imported vehicles, so beware. Likewise, brake parts – such as pushrods and brake pedals, for example – should not be welded, due to their critical nature. Brake pedals can have pivot bosses welded into their levers, but not onto them; we don’ want to see brake pedals break off during operation. Any fabricated brackets also need to be carefully thought through. Engineers do not like the risk involved in welded brake elements.


I SEE so much bad welding on modified cars. The owners don’ seem to realise that, highway speeds, a weld failure can be fatal. Vehicle welds are subject to cyclic loads fatigue stresses, so all welding should be carried out by qualified welders. In the modern age, quality assurance and workplace health and safety are part of our everyday lives, it must extend into our garages and apply to the quality of our welding.


I NEVER stand in front of or behind newly finished cars at start-up, due to the number of times I have seen the vehicle immediately jump backwards or forwards. That’ why it’ important to fit a neutral start switch so the car can only be started in neutral or park. These days I know to check this before starting a car up!


GROUND clearance under a vehicle is generally accepted as being 100mm minimum. What about other clearances? For safety, steering shafts should have at least 10mm or finger’ clearance to moving parts such as the engine and exhaust system. Clearance to fixed components can be minimal, of course. The exhaust system is a source of heat and vibration, and so must be clear of the floor and allow full movement of the differential without contact. Allowing enough tailshaft clearance might seem to be obvious, but see so many tailshaft rub marks that I know it’ not obvious to everyone!

Paging Dr Tim

TIM Bartrop completed his Bachelor of Mechanical Engineering in Adelaide in 1982, but was accredited with the SA Department of Transport as an automotive engineer prior to that. He’s also a proper car guy, pioneering the fitment and certification of rack-and-pinion steering to Holden front ends, and commencing his first hot rod build – a ’34 Chev – at age 18. He has also built a ’36 Ford, a ’40 Ford, a ’48 Anglia, a ’28 Model A roadster and a ’32 five-window, and his most ambitious project – an HQ Monaro which he built with his son – made the Elite Top 20 at Summernats three times, and scored a feature in Street Machine. Tim moved to Queensland in 1990 and also became accredited there, and has now been certifying modified cars for over 35 years. His business, Dr Tim’s Auto Engineering, is something of a retirement project, and he proudly approaches certifications with a can-do attitude.

“When I talk to people, they soon realise I’m a car person, and I want to see their cars on the road just like I do my own projects,” Tim says. “I take an encouraging approach to it; I’m there to help them, and I’ll push the limits as far as I can while remaining legal and sensible. It helps that I’ve come from a practical background of doing the actual work.”