Well Spaced Out

Clearances are basic yet most important things to sort out before you start hacking away at your pride and joy. If they’re not great enough the problems you can come across will not only damage your car but could also see you in your local hospital ward.
OK, you’ve got that 426ci Hemi that’s been lying around for a while and have finally decided to put it in your latest project a Ford Pop. Where do you begin? That’s your problem. But follow the guidelines laid out here and your ride will wind up safer and hopefully free of annoying knocks and rattles. Unless you are using a solid motor mount (not recommended for the street) your engine will move both from side to side with torque and forward and backwards with acceleration and braking. There must he a minimum clearance between the fan (or the front of the engine if you have a fixed electric fan) and the radiator of 20mm for a four cylinder lump. With progressively larger engines this gap should he increased: a Rover V8 needs a minimum of 25mm; a small block Chevy, Ford or Mopar 30mm; most big blocks need at least 40mm. From the engine to any fixed part - chassis, crossmembers, and steering box - there should be at least 15mm clearance. A block of wood cut to size can be used as a ‘feeler gauge’ to tell you if there’s enough room. If it slides in the gap, great: if not back to the drawing board.
Allowance must be made for forward movement of the engine under braking or you’ll wind up with a chewed radiator; the bigger the engine the more clearance you need. 30mm is recommended for small block Chevy’s. so we’re well within limits here.
Allow 15mm for side-to-side rocking of the engine under torque. Wooden block makes good feeler gauge.
For those who’ve heard it all before and can do all this standing on their respective heads, don’t forget the ancillaries. Alternators, power steering and air conditioning pumps should be adjusted out to their maximum travel -belts do stretch and they also have to be fitted - and the 15mm measurement taken at that outer limit.
for the gearbox allow the same gap as the engine to fixed parts-like the transmission tunnel - of 15mm. Simple cardboard profiles can be made to ensure a minimum propshaft clearance of 20mm is maintained throughout its length. This should avoid those terrible scraping sounds which can be heard under heavy load or cornering.

Even though the radiator is fixed to the body, a top clearance of 15mm is a good idea; otherwise a heavy slam of the bonnet could leave a perfect imprint of the radiator cap in your fresh paintwork. Similarly, it’s best to allow 20mm above the air filter. Depending on they type of filter used this could also aid breathing. To check the gap place a large chunk of plasticine on the filter and close the bonnet (carefully!). If on inspection the plasticine looks like it would be at home in a sesame seed bun you have a bit of rethinking to do. Don’t forget flexible hoses; they may have some give but they still need a small clearance, about 8mm.

All flexible brake hoses should have slack in them any position. In the event of a suspension collapse you don’t want to lose your brakes as well. Check and re-check those hose positions at both extremes of suspension travel. At the back, get the axle sitting on its bump stops, even if it means temporarily removing the springs. Then jack the body up until the axle is hanging down as far as it will go. Carry out the same test at the front, also moving the wheels from lock to lock and ensuring there is still free travel on the hoses.
The exhaust pipes should clear all components by a minimum of 16mm and extra care should be taken not to run them near brake lines, wiring looms or other items that could be affected by the heat, including fibreglass or wooden floors.

Don’t be caught out by engine ancillaries.
Check there is still sufficient clearance with them at the outer limits of their adjustment -belts have a nasty habit of stretching.
With a full load on the suspension, or preferably with the spring removed, turn the front wheels from lock to lock and check there remains at least 15mm all round and 35mm above the tyres
Don’t just plonk the battery in any old out-of-sight-out-of-mind corner. As well as providing for easy access for times of trouble, leave at least 20mm between any part of the exposed live terminal and a potential earth. Think about if the battery were to start leaking and ensure the acid cannot reach anywhere it might cause serious damage, jeopardise your safety or just plain make a mess - think brakes, electrics, hoses and paintwork.

You don’t want to shred your Mickey Thompsons first time out, so make sure you leave enough space between tyres and surrounding body and chassis. In use tyres distort in all directions so allow a minimum of 15mm all round (the taller the sidewall the more you should allow) and 35mm above the tyre with the suspension on its bump stops.

With the rear suspension on its bump stops the propshaft should still be 20mm clear of everything.
Remember, this is only a guide and there will always be exceptions to the rule. Use your common sense and if you are baffled look at standard cars, produced with millions of pounds worth of research and development - they may have found a way round a similar problem to yours. If you are still in doubt seek the advice of an expert. Most of the specialists advertising in rodding magazines will be happy to share a little wisdom.