Advice: How to re-power an older truck

Back in the 1950s and ’60s, re-powering trucks was all the rage. Pommy trucks were never designed for long-distance haulage on Australian roads and their asthmatic diesels soon packed it in when pressed hard for hours on end in hot weather.

Yank trucks of that time were predominantly big-bore petrol-powered beasts that drank fuel like it was free. Swapping out the original powerplants was pretty much par for the course.

Those of us with grey hair can remember Commer ‘Knockers’ with their original three-cylinder, six-piston donks replaced by GM 4-71 or Nissan Diesel Uniflow-scavenging Diesel (UD) two-strokes. They screamed and needed to be driven like you stole 'em, but mostly got where they intended. Cummins NHs and Gardner LXs were also popular for engine swaps.

As proper linehaul diesels dominated the heavy truck market from the late 1970s the process changed. Typically, these mostly North-American-origin trucks would outlast their engines, so the 'tired' engines were given an in-frame overhaul and the truck was downgraded to shorter-haul and local cartage.

Then, as fuel costs and traffic density increased, shorter hauls were done more economically and efficiently by purpose-designed trucks, so weary US- and European-origin linehaul trucks were moved on. Many of these vehicles were well-maintained, but had outrun their extended powertrain warranties, so fleets no longer wanted them.

By century's end, emissions reduction was the dominant factor in truck engine design and vehicles became very complex. Many operators who had traditionally done their own maintenance couldn't continue to do that, so the golden age for the DIY truck operator was the 1990s, before emissions targets radically changed engine design.

Back then, any diesel mechanic worth his or her salt could diagnose and fix engine problems, without the need for a computer. Pulling out engines, rebuilding them and putting them back were all part of a day's work, and that's the mindset necessary for operating an older vehicle.

Related reading:
Caterpillar C15 Repower: Review
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Another very important factor is the suitability of a repowered truck for its intended workload. Long-distance running isn't out of the question for an older truck, but it'll need a more leisurely travel time frame than many linehaul contracts specify. Some freight forwarders insist that sub-contractors have late-model trucks.

An older vehicle requires more frequent maintenance than a new one and the replacement parts bills are inevitably higher. Balancing that is the absence of monthly lease payments that pile up, whether the truck is working or not.

Operators with a DIY mentality feel much more comfortable with pre-emissions machinery and for many rural truckies, who don't have easy access to diagnostic equipment, it's essential that they can do their own running repairs and servicing.

However, there comes a time when an old girl’s ticker needs more than regular CPR or bursts from a defibrillator: it's re-building or re-powering time.

We're assuming in this article that you own the truck you intend to re-power, but if you're buying a truck that you expect will need a re-power, please check out our Buying Used guide.

If the engine can be brought back to good health by an in-frame overhaul it's probably fine to keep it, but if oil sampling shows significant bearing wear or serious contamination it could be a more reliable, long-term solution to opt for a replacement engine.

Emissions laws aren't retrospective, so as a general rule you can replace your 'dead' engine with one with similar emissions compliance, or newer. In other words, if your existing engine had Euro I emissions compliance when new, the replacement engine needs to have only that level of compliance, or it can be Euro II and beyond.

Of course, there's a catch. If you install an engine that was built to comply with a particular emissions law, it must retain all the emissions control equipment originally fitted to it when you install it in your truck. You cannot take off, say, Euro 5 emissions kit that may include exhaust gas recirculation, intercooler, diesel particulate filter and selective catalytic reduction unit, and claim that the engine, by default, meets Euro I.

To avoid this trap it's best to look for a replacement engine that has the same degree of emissions compliance as your 'dead' engine, or one without a radically different emissions level.

Tied to this issue is the question of compatible electronics. When engine development progressed beyond mechanical injection, things got more complicated – especially electronically. The first electronically injected engines were mechanical-injection engines, with in-line pumps, such as the Cummins PT system, or unit injectors that Detroit Diesel employed, with add-on electronics. The wiring harness and electronic control 'black boxes' were unsophisticated.

That's not how it is with modern Euro V and Euro VI engines that bristle with ECUs and sensors. Today's engine wiring bundle can be as thick as your arm, so putting a modern engine in an old truck will require considerable re-wiring effort. Even worse, some of the ECUs need input from electronically connected transmissions to function properly.

Fortunately, most engine-swappers are in pursuit of installation and maintenance simplicity and don't attempt that late-model re-power route.

It's always tempting to upgrade power and torque when you opt for an engine swap, but care is needed. If the proposed engine was originally offered as an option on your truck, with no additional specification changes, then you may not have an issue.

However, if the engine outputs are beyond those offered with your truck's ex-factory specification you may need to modify other components before it can be approved for registration.

In the case of passenger car 'hot rodding', a more powerful engine almost always requires the owner to upgrade brakes and suspension. Truck brakes and suspension are normally not much different between, say, 350hp and 550hp engine options, because legal axle weights are the same, but turbochargers, radiators, transmissions, propshafts and drive axles are almost always different.

A more powerful engine may have a larger, or slightly relocated, turbocharger and, sometimes, that will foul your truck's steering shaft. (It's a particular problem with engines that have right-hand-side turbos, because in Europe and the USA the steering column is on the left hand side of the engine bay – check out a LHD-market engine bay and one of ours.)

Cooling capacity is absolutely critical, to the point where some popular new truck models have needed a redesign to accommodate larger radiators – check out the original Kenworth SAR and today's model, for example. If you put a more powerful engine in your truck, you may not be able to squeeze in the correct radiator for its required cooling package.

The typical entry-level, older-truck transmission, designed for single-trailer fleet drivers, was an Eaton 10-speed, rated for 1800Nm input torque, where the same truck with B-Double capability came with an 18-speed and 2500Nm torque capacity. Ditto the final drive tandem's combination mass capacity: 45 tonnes GCM vs 90 tonnes GCM.

By far the simplest engine swap is 'like for like': a new engine of the same emissions-compliance level with the same or only a modest increase in power and torque. That may seem very constraining, but in the same engine family there were quite different power and torque characteristics available.

For example, one of the universally hated, rev-limited Cummins 'Formula' engine range was the Formula 290 – a gutless, torque-less horror of an engine – but that 1900rpm-limited 14-litre could easily be swapped out for a 2100rpm 350hp variant that was much more pleasant to operate.

Modern American-brand trucks have pretty tight engine options – Freightliner uses Daimler engines; Mack fits Volvo engines; Kenworth uses only Cummins and Paccar engines, and Caterpillar doesn't make new-model truck engines any more – but in the 1990s most of them offered a wide choice of Caterpillar, Cummins and Detroit Diesel powerplants.

All major engine makers, including Caterpillar, still produce 'crate' engines or remanufactured ones, with varying degrees of emissions compliance and there are mounts and brackets for a choice of engines available from wreckers and the aftermarket.

If you're getting serious about an engine swap, check out the legalities spelled out in Vehicle Standards Bulletin (VSB) 6. For more information click here.