The silly mistakes which can cost you an engine

Modding cars and turning them into cool, fast pieces of stress relief can be a tumultuous experience. The joy of completing an engine swap, or bringing a long-forgotten car back from the dead, can soon be shattered by soaring temperature gauges or the dreaded rod knock. 

Having spent 25 years buying, building, driving, wrecking, and blowing up cars (good lord, I am old), here are some of the key ways to avoid blowing your engine up like a goose (ie: don't do what I did).  

Health Check

When you get a new project, or you pluck it's new heart from the clutches of a wrecking yard, It's way too easy to tear straight into trying to make it run. Many of our favourite enigines (including Barras and LS V8s) are well over 20 years old, and so you can't expect to slap one into a car, boost it up to double the horsepower, and then have it last for another 20 years. 

Before trying to get your car to make noise go right over the engine looking for simple problems like cracked vacuum hoses, wiring that is brittle (and therefore needs replacing), and fluid leaks. You should also pop the timing cover off the engine and turn it over by hand to check the condition of the timing chain or belt and the tensioner, as these are wear items and will need to be replaced at some point - it may as well be sooner rather than later.

RPM

Taking an engine to redline is a lot of fun (hello Hondabois and classic BMW M-car drivers), however this is one way you radically increase the risk of killing your engine. Paul Rosche, the noted engineer who gave us some of the greatest performance engines of the 20th Century, once said to me that the strain on an engine exponentially doubles for every 250rpm past 8000rpm.

That means you're putting four-times the strain through an engine at 8500rpm compared to 8250rpm, and that strain will do damage. The bearings in an engine are actually wear items and by spinning an engine to its redline, you're accelerating the wear on those parts. If you're doing it with a second-hand engine you don't know the intimate history of, then you're risking your entire engine.

It isn't just enough to know you've chucked in fresh oil and a new filter. Friends of mine much smarter than me took to installing oil pressure and oil temperature gauges so they could see how their 2nd hand engines behaved before they sent them to the moon. They also did compression tests to have a good understanding of how tired the engine was, before they even put the car on the road - one simple check can tell you if the engine you've just bought is a dog, or a superstar waiting to change your life.

The wrong oil

As engines wear with age they actually need to have their oils changed to suit. Hang around old-timers who play with pre-80s engines and you'll often hear them talk about how engines would "free up" over time, as they got more kilometres on them and would apparently run better. Part of this comes down to engine tolerances being looser back in the day, as well as the lack of modern ECUs/fuelling/ignition systems meant having less control over how an engine ran (when was the last time you needed to take a car in for a "tune up"?)

You can kill a high-mileage engine super-fast by using the same oil it was specced with when new. As the engine wears and tolerances grow, moving up one grade of oil to a heavier option is often one way to prolong engine life. If you're unsure what oil to put in your car, ask a trusted engine builder. You might be fine with what you have currently, but this is one quick, easy way to avoid a spun bearing (and curing that requires a new crank at least). 

It is also important to realise that a 5W-30 oil from the 60s has radically different chemical make-up to a current 5W-30. A lot of classic muscle car owners are killing camshafts and lifters because oils today miss important additives like zinc, which help lubricate mechanical parts, but are left out of modern oils as current-tech engines simply don't need those additives.  

Oil control

If you're a fan of corners (let's face it who isn't?), then you know sticky tyres and modern suspension mods allow you to rail through bends faster than we've ever been able to go before. However, chucking your car merrily though corners on a stock oil pan comes with some fairly heavy risks. 

As with running old oil or the wrong grade of oil, you need to ensure your engine has a constant, properly pressurised stream of oil being delivered to all its reciprocating components. The single biggest impediment to this is a factory oil pan and windage tray - if it has one. 

Few engines of the 90s featured complex baffling systems to stop oil slosh, and their windage trays were often designed to prioritise cost efficieny over preventing oil aeration (and that frothing does bad things for the oil). If you're going to drive your car hard consider safeguarding your motor with a gated oil pan, high-volume oil pump, an upgraded windage tray, and potentially an oil accumulator.  

Cylinder pressure

Here is a big one for everyone wanting to do a "stock bottom-end" build, or push a used factory turbo engine hard. Cylinder pressure will kill a lot of engines, and normally it takes a while before the problem shows its head. Once it does, however, then you'll be buying a new engine, or embarking on a full tear-down rebuild. 

"Cylinder pressure" is a dynamic beast, changing as the engine runs through its four stages of the combustion cycle: suck, squish, bang, and blow. Cylinder pressures are at their highest during the squish (compression) and bang (combustion) process,  when the piston is literally fighting against the compressed air and fuel miture sitting in the combustion chamber. 

In overly simple terms, think about an aluminium NA engine. These were designed with a certain cylinder pressure in mind but you, Johnny Modder, have come along and strapped a bus turbo to the side of your engine in the aim of turning tyres to smoke, and you want to push 35psi through it because you've read that's what the cool kids on the Internet do.

The more boost you jam into this engine, the more force you're pushing into the cylinder and onto the head studs. This is why so many people running high-boost set-ups upgrade their engines with stronger aftermarket studs, as the factory bolts will stretch under the increased cylinder pressure.

A lot of early adopters of turbo LS1 combos found they were turning their round cylinders oval (killing pistons) as the additional pressure from turbo boost was deforming the cylinders. The 2.5-litre Volvo "whiteblock" engines are also renowned for having weak cylinders that are perfectly reliable at the stock 300hp, but will almost certainly fail once you add boost.

How do you fix this? Simple, keep the boost sensible.